Energy Efficiency

How much energy does my dishwasher use? What do internal heat gain and convection mean? How do I determine how much insulation I need in my home? What does the ENERGY STAR® label mean?

You'll get answers to these and many other questions on this page, where we discuss topics like: appliance energy use, efficiency ratings, and the national ENERGY STAR® program.

Efficiency Terms Read More

AFUE (Annual Fuel Utilization Efficiency): a rating that measures the efficiency with which natural gas and other fossil-fuel-burning furnaces and boilers use their primary fuel source over an entire heating season. It does not take into account the efficiency with which any component of the system, such as a furnace fan motor, uses electricity. AFUE is expressed as a percentage that indicates the average number of Btu worth of heating comfort provided by each Btu of natural gas (or other fossil fuel) consumed by the system. For instance, a gas furnace with an AFUE of 80% will provide 0.8 Btu of heat for every 1.0 Btu of natural gas it burns.
Air Infiltration: the introduction, usually unintentional, of unconditioned outdoor air into a mechanically heated and/or cooled building. Air infiltration can occur through any opening in the home's structure, including: seams where walls meet other walls, window or door frames, or chimneys; holes where wires or pipes penetrate walls, floors or ceilings/roofs; and the space between loose-fitting meeting-rails of a double-hung window or between the bottom of a door and the door's threshold. Along with internal heat gain and solar heat gain, air infiltration can play a significant role in the load that is placed on your building's heating and cooling equipment, as well as the comfort of the building's occupants.
BTU (British Thermal Unit): a measurement of the energy contained in heat. It takes one Btu of heat to warm one pound of water by 1° Fahrenheit. Btu can be used either to define an air conditioner's cooling capacity (i.e., the number of Btu of heat that can be removed by the system) or a furnace's heating capacity (i.e., the number of Btu of heat that can be supplied by the system.
Caulk: a substance used to seal air infiltration points between two immovable objects, such as where exterior or interior wall surfaces meet window or door frames and at corners formed by siding. Most caulks come in tubes and are applied with the use of a caulk "gun."
CFL (Compact Fluorescent Lamp): a light "bulb" using fluorescent technology but designed to be used in many of the same fixtures traditionally used by standard incandescent "A" bulbs. CFLs incorporate a small-diameter looped or swirled tube that is attached to a screw-in base. CFLs provide light levels comparable to 20- to 150-watt incandescent bulbs for 70% to 75% less energy. They can also last up to 13 times longer than equivalent incandescent bulbs.
Conduction: the transfer of heat through solid objects, such as glass, dry wall, brick and other building materials. The greater the difference between the outdoor and indoor temperatures, the faster conduction will occur and the more heat a building can gain or lose.
Convection: the transfer of heat to or from a solid surface via a gaseous or liquid current. Where home heat loss and gain are concerned, heat convection is caused by air (gas) currents that carry heat from warm objects (such as your body, furniture, and interior walls) to cool surfaces (such as windows, floors, ceilings, and exterior walls).
COP (Coefficient of Performance): a measurement of a heat pump's efficiency (in the heating mode) at a specific outdoor temperature—usually 47°F. A COP of 1.0 indicates that for each unit of energy being used, an equal amount of energy (in the form of heat) is being provided by the system. A heat pump with a COP of 3.0 would provide three times as much energy in heat as it consumes in electricity when the outdoor temperature is 47°F. COP is also sometimes used to measure the single-temperature cooling efficiency of chillers.
Daylighting: the technique of using natural light from windows, skylights and other structural openings to supplement or replace a building's artificial lighting system. When applied properly, daylighting can reduce a facility's lighting costs. When applied improperly, however, it can not only lead to inappropriate light levels but can also raise the building's cooling costs by introducing high levels of solar heat gain into the interior of the building.
Dedicated Fixture: a lighting apparatus that is designed specifically for use with a particular type of lamp (bulb). For example: the increasing popularity of CFLs has led to the development of a growing number of fixtures—including floor torchieres, table lamps, ceiling drums, and recessed canisters—dedicated solely for use with compact fluorescent lamps.
EER (Energy Efficiency Ratio): a measurement of the energy required by a cooling system as it attempts to maintain indoor comfort when the outdoor temperature is at a specific temperature—usually 95°F. The term EER is most commonly used when referring to window air conditioners and geothermal heat pumps. EER equals the number of Btu-per-hour worth of cooling provided at the specified outdoor temperature divided by the number of watts used to provide that level of cooling.
Efficiency: the degree to which a certain action or level of work can be produced for the least expenditure of effort or fuel. For instance, a light bulb that uses 15 watts of electricity to produce 900 lumens of light would operate with much greater efficiency than one that required 60 watts to produce the same light level.
HSPF (Heating Seasonal Performance Factor): a measurement of an all-electric air-source heat pump's efficiency (in the heating mode) over an entire season. HSPF is calculated by dividing the total number of Btus of heating provided over the entire season by the total number of watt-hours required to operate the system over the season.
Insulation: a product that inhibits conductive and convective heat transfer. Some materials are naturally better insulators than others because they contain more "dead air" pockets. These pockets of trapped gas help to slow the movement of heat. However, if processed properly, virtually any product, including glass, cotton, paper, and plastic, can be used to make insulation.
Internal Heat Gain: the accumulation of heat produced by a building's energy systems, appliances and occupants. Depending on the number of occupants and the type and number of energy systems used during the day, it's not unusual for internal heat gain to account for 20% of a home's total summer cooling load. Internal heat gain can also help to reduce the need for mechanical heating in winter. Solar gain and air infiltration also contribute to overall heat gain in a building.
Kilowatt: 1000 watts.
Kilowatt-hour: 1000 watts used for one hour—or any combination of energy multiplied by time that is equivalent to that rate of electrical consumption (such as one watt used for 1000 hours, 10 watts used for 100 hours, or 50 watts used for 20 hours). For example, a 100-watt light bulb left on for five hours a day would consume one kWh of electricity in two days. Kilowatt-hour is the primary measure on which U.S. electric companies base most customer billing. Most CWLP residential customers pay an average of 11.27¢ per kWh. (This figure, which includes the average per-kWh-rate paid by our regular residential customers, plus the fuel adjustment charge and Illinois State Utility Tax that are applicable to each kWh of use, was last updated in April 2013.)
LED (Light Emitting Diode): a light "bulb" using LED technology but designed to be used in many of the same fixtures traditionally used by standard incandescent "A" bulbs. LEDs looks like incandescent but use 85% less energy as an incandescent. A 9-watt LED has the same lumen output of a 60-watt incandescent.
Low-E: (which stands for low-emissivity) refers to a material designed to reduce the amount of radiant heat that can be transferred through glass or other translucent window coverings. Low-E coatings or films have the ability to re-radiate a high percentage of heat back toward its source. In summer, low-E windows can be effective in reducing the amount of solar gain in the building. In winter they can reduce the amount of furnace-generated heat that can be lost to the outdoors.
Lumen: a unit of light given off by a light source. Lumen is the measurement used to compare the levels of illumination provided by different light sources. For instance, a 15-watt compact fluorescent lamp (CFL) will produce approximately the same number of lumens as a 60-watt incandescent bulb.
Payback Period: the amount of time it takes to achieve a full return on an investment. For instance, if a high-efficiency air conditioner would cost you $300 more to purchase than a lower-efficiency model but would save you $100 a year in operating costs, your payback period on the extra $300 investment would be three years.
Radiation: a method of heat transfer by which heat is transmitted from surface to surface via infrared waves. Radiant heat warms the surfaces it touches without increasing the temperature of the air through which it travels. All warm bodies radiate infrared energy.
Rate: the amount charged to utility customers per unit of service used. For instance, CWLP electric customers are charged a certain rate for each kilowatt-hour of electricity they consume (see Residential Electric Rates or Business Electric Rates), while water customers are charged per unit of water consumed (see Water Rates). The actual rate charged is based on the type of service provided and, in the case of water customers, whether or not the customer is located inside or outside the city limits.
Electric Rates Water Rates
ROI (Return on Investment): the annual rate at which an investment earns income. It is calculated by dividing the annual earnings by the original investment. For instance, a bank savings account paying $3 per year per $100 investment, has an ROI of 3% ($3 divided by $100). An efficiency investment's ROI comes not from money paid to you, but rather from money saved by you on your energy bills.
R-value: a measurement of a material's ability to resist heat transfer. Insulation products are rated according to their R-value. The higher the R-value, the better a product will be able to resist heat flow.
SEER (Seasonal Energy Efficiency Ratio): a measurement of the energy efficiency with which a central cooling system can operate over the course of an entire cooling season. This term is most often applied to central air-source heat pumps (in the cooling mode) and air conditioners. SEER is expressed as the dividend of the number of Btu of cooling provided over the season divided by the total number of watt-hours the system consumes. Federal law requires all central split systems now made and sold in the United States to have minimum SEERs of 13.
Settled Density: the amount (depth) of insulation remaining after the insulation has had a chance to settle. This term is most often applied to loose-fill insulations—particularly those made of cellulose. To ensure loose-fill cellulose insulation will maintain its desired insulating value (R-value) once it has settled, you will need to install it to a depth that is 20% to 25% deeper than your settled density R-value actually calls for.
Solar Gain: heat that builds up inside a structure as a result of sunlight that enters through transparent or translucent surfaces, such as windows, and is converted to heat after striking other surfaces inside the building. In summer, solar gain can cause as much as 50% of the heat gain in a home. In summer, heat gain can increase the operating load on your air conditioner. In winter, heat gain, can reduce the operating load on your heating system. Internal heat gain and air infiltration also contribute to overall heat gain in your building.
Thermostat Setback: an intentional effort to control building energy consumption by manually or automatically controlling thermostat settings according to the amount of cooling or heating that is needed at any given time of the day or night.
U-value: the measurement of how readily heat can flow through glass, brick, drywall and other building materials. U-values, which are expressed in decimals, are the opposite of R-values. The higher the U-value, the less efficient the building material will be.
Vapor Barrier: a material designed to resist the migration of moisture through a wall or other building component. As water vapor in the air moves from a warmer to a cooler part of the building it can condense on cooler building components, such as rafters, beams and walls, eventually causing those components to mildew, rust or rot. Vapor barriers, which are impermeable to water vapor migration, help to protect against this. The most common vapor barriers are made of plastic, but other materials, including oil paint, can also serve the purpose.
Watt: a unit of electric power. The amount of power required by electric appliances is expressed in watts. One watt equals 1/1000 of a kilowatt.
Watt-hour: a unit of electric energy, equal to one watt used over a period of one hour. One watt-hour equals 1/1000 of a kilowatt-hour.
Weatherstripping: a product designed to seal the cracks that exist between two moving parts or one moving and one stationary part of windows, doors and other movable building components. Weatherstripping is used to improve a building's energy efficiency by preventing air infiltration.

Energy Saving Tips Read More

Although most of the tips below are aimed especially at helping residential customers reduce energy consumption, many of them can be used by businesses too, to reduce load and save money.

Even when indoors, dress appropriately for the season. By layering clothing in winter and wearing light-colored, loose-fitting, "breathable" clothing in summer, you might be able lower (in winter) or raise (in summer) your thermostat setting by a couple of degrees or more, and still be comfortable.
Try turning your thermostat up even higher in summer and using ceiling or box fans in occupied rooms to increase air flow and the cooling effect it creates. A fan will use much less energy than the air conditioner, operating at a lower temperature, will. Just be sure you don't leave fans running in unoccupied rooms. That will waste energy and provide no added comfort.
Practice thermostat set-back. This means setting the thermostat a few degrees higher (in summer) and lower (in winter) during times you plan to be away from the house for a few hours or at night when you are sleeping. If you don't already have an electronic set-back thermostat, consider investing in one. For a relatively low cost (you don't need a fancy, expensive one), you can program in your set-back schedule and then forget about it. Hassle-free savings. (NOTE: If you have a heat pump, thermostat set-back is usually not recommended.)
Make sure all windows are tightly shut (and locked to keep them from accidentally popping open) when your air conditioner or furnace is on.
Clean or replace your HVAC system air filters regularly. How often you need to do this depends on conditions in your house. For instance if you have pets that shed or you live in a particularly dusty area, you'll need to clean/replace them more often – perhaps as often as once a month. At the very least, do it at the start of each heating and cooling season. A clogged air filter not only makes your system work harder (meaning it becomes more costly to operate), but it can also reduce the lifespan of your furnace and air conditioner.
Wherever possible, replace incandescent lights with LEDs, which use about one-sixth the energy and usually last several times longer than incandescents.
Turn off unnecessary lights (and other appliances). This can save you money all year-round, particularly in summer when reducing the use of heat-generating appliances can limit interior heat gain and the need for additional air conditioning to combat it.
In summer, save clothes washing and drying, dishwashing, cooking, vacuuming and other heat- and humidity-producing activities for the late evening hours, when outdoor temperatures are cooler and your air conditioner doesn't have to work so hard. In winter, open your dishwasher after the clean and rinse cycles and let the dishes air dry. This will add humidity to the indoor air, which can make you feel more comfortable at lower temperatures, and will save the energy you would otherwise use to power-dry the dishes.
Control your window shading/covering for maximum efficiency. In summer, keep windows shaded – particularly those facing west – especially in the afternoon, to limit solar heat gain. East-facing windows can be shaded to block morning sunlight. In winter, you want to let in all the sunlight you can to allow the warming effect of the sun to supplement your heating system. But on cloudy, blustery days or cold winter nights, pulling the curtains and shades can help reduce heat loss through windows, especially if you use insulating blinds or curtains.
Use storm windows to reduce unwanted heat loss through windows. The trapped air or inert gas between layers of glass (or between the glass pane and plastic sheeting, if you've installed temporary interior storms), adds insulating value to the window.
Storm doors serve the same purpose as storm windows, providing a layer of insulation that reduces heat loss through exterior doors.
Installing low-e films on window glass can further help reduce heat transfer through windows. Some types of film reduce both unwanted solar gain in summer and the loss of furnace-generated heat in winter.
Use caulk and weatherstripping to seal exterior doors and windows against air infiltration. Caulk is used to seal cracks around window and door frames and other non-moving parts of the window or door, while weatherstripping is used to create a tight seal between the door and its frame or the window sash and frame, or between the meeting rails of double-hung and side-sliding windows. Don't forget to caulk and weatherstrip doors or access panels that lead into unconditioned spaces, such as garages and unheated basements and attics.
Use regular or expanding foam caulk to seal holes where pipes and wires enter the building, as well as openings in the building's facade (including where masonry meets siding or where siding meets at corners) through which unwanted air can pass. Caulk can also be used to seal the gaps between baseboards and crown moldings and the walls and ceilings or floors they abut.
Landscaping can have an impact on your building's energy efficiency. In summer, trees, shrubs or other plantings can reduce the temperature of walls and roofs they shade by several degrees. That cuts the amount of heat available for transfer to the interior of your home. In winter, evergreen trees planted along the northern and western perimeters of your property and evergreen shrubs planted close to the foundation can serve as screens to protect your building from cold winds.
Make sure your building is properly insulated. The right amount of insulation installed in the right places can make a big difference both in your energy bills and your comfort.
Install insulating gaskets behind your wall outlet and light switch cover-plates. A lot of unwanted air can enter and escape your home through the holes behind these covers, and foam gaskets cut to the shape of the cover-plates can reduce a lot of that air flow.
Wrap your electric water heater tank in an insulating "blanket" and your water pipes with foam pipe insulation
Do you need to turn down your water heater thermostat? Most hot water needs can be met with a water temperature of about 120°F. If your water heater thermostat is set higher than this, turn it down to save money and energy. Doing so can also be a safety measure, especially for kids and the elderly.
Taking short showers (5 minutes or less) instead of baths will save energy as well as water.
Run dishwashers and clothes washers only when you have full loads. This also saves water as well as energy.
Unplugging TVs, radios and other electronics when they aren't in use can save energy. This is because many of these types of appliances continue to draw some electricity even when they are turned off.
If you have a fireplace, make sure the damper is tightly closed when the fireplace is not being used. If your fireplace is equipped with glass doors, keeping those closed will further help reduce the loss of conditioned air up the chimney.
If you have a whole-house fan, cover it with a sheet of rigid-board insulation (cut to size and attached with magnetic strips or tape) when it is not in use.
When cooking, use the right size pan for the stove burner. This will help ensure most of the heat from the burner will go to heat your food, not the air in your house.
Run kitchen and exhaust fans only as long as absolutely necessary to clear excess humidity caused by cooking and bathing from the room. This is especially important when your furnace and air conditioner are running. Exhaust fans not only remove excess humidity, they can also pull conditioned air from the building.
Have your major energy systems – especially your heating and cooling systems – routinely checked by a professional to make sure they are performing at peak efficiency.
If you are replacing old energy systems, appliances, windows/doors, or any other product that can impact the efficiency level of your home or business, it's usually worth it to spend a little more and buy the most efficient option you can afford. It will cost you more upfront, but if you do your preliminary research and buy wisely, you'll be paid back in energy savings over the long term. In some cases, such as for heat pumps and commercial lighting, CWLP offers rebates when you select qualifying energy-saving options.

Regional Energy Emergencies

Energy Emergency FAQs & New Advisory Status Levels
It has been in the news—the talk about Midwest energy shortages and rolling blackouts. We put together information to explain what it means and give you some tips to prepare. Visit www.CWLP.com/energyemergency to also view the current Energy Emergency Advisory Status. This is based on any Midwest Energy Emergency Declaration by the 15-state grid operator MISO, that would call for electric conservation and/or preparation for protective power outages, rolling blackouts.

About Energy Star® Read More

City Water, Light and Power is a proud partner of ENERGY STAR®, a nationwide partnership of federal, state and local governments, businesses, and consumers united in the pursuit of a common goal—to protect our environment for future generations.

Products that earn the ENERGY STAR® — including doors, windows, air conditioners, heat pumps, refrigerators, compact fluorescent lamps, and computers and their peripherals—reduce greenhouse gas emissions by meeting strict energy efficiency guidelines set by the USEPA and USDOE. These products use less energy, save money, and help protect the environment.

ENERGY STAR® Website

Appliance Energy Use Read More

Knowing how much electricity your various home appliances use can help you make adjustments in your energy use habits that will, in turn, allow you to better control your monthly energy costs. Our Appliance Energy Use Chart is designed to provide you with this knowledge.

In addition, ENERGY STAR@home is a fun and interesting interactive tool that provides tips on how to reduce energy consumption in each room of your home.

Links to more information about appliance energy use and related topics can be found in the left-hand column of this page.
Appliance Chart Energy Star Home

Efficiency Ratings Read More

The materials from which a building is constructed, as well as the systems and appliances installed there, can dramatically affect the amount of energy that the building will consume over its lifetime. Efficiency ratings for many building components and energy systems have been devised to help customers compare the potential impact of one to another.

Definitions and other information about the most common building material and appliance efficiency ratings can be found by clicking the blue expandable panels below.

Building Materials Efficiency Ratings

The materials from which a building is constructed can have a marked impact on the structure's efficiency. Materials that allow a lot of heat to pass through them lower the overall efficiency level of the building. Conversely, materials that resist a significant amount of heat transference can help ensure greater efficiency. R-value and U-value are the two most common measurements of building material efficiency.

R - Value

Definition: the measurement of how effectively a material resists the transfer of heat via conduction.

The higher the R-value, the less heat transference can take place through the material.

Some materials are more resistant to heat transfer than others, giving them higher R-values. One of the best ways to enhance the product's R-value is to increase the amount of gas (including air) inside or immediately surrounding it. For instance, the glass of a single-pane window has virtually no R-value, but the thin film of air that normally exists on either side of the glass gives the window an R-value of about 0.83. Adding a second pane of glass and sealing the space between the panes will increase the thickness of one of the insulating gas layers, thereby more than doubling the window's R-value.

Another example of how the presence of dead-air spaces affect a product's R-value can be seen with wood. Hardwoods, like oak, typically have an insulating value of R-1 per inch of thickness. However, softer woods, such as pine, might have R-values twice as high due to their greater number of air-filled pores.

Products developed especially for the purpose of impeding unwanted heat transfer are called insulation. Insulation can be made of a variety of materials, including old newspapers and wood fibers, glass fibers, and synthetic foams. It can also come in a variety of configurations, including soft blankets, rigid boards, or fluffy loose-fill. But what all of these configurations have in common is their abundance of air-filled pores or pockets.

The actual R-value of insulation products can vary greatly, depending on their composition and form. The least resistant and least common are perlite and vermiculite loose-fills, at R-2.2 to R-2.7 per inch of thickness; the most resistant are polisocyanurate rigid boards, at R-7 per inch of thickness. Fiberglass blankets and cellulose loose-fills, two of the most common residential insulations have R-values of 3.1 to 3.7 per inch.

U - Value

Definition: the measurement of how much heat can be conducted through a building component (such as a wall or window). As such, it is the opposite of R-value.

The higher the U-value, the more heat the material will allow to be transferred through it. The lower a material's U-value, the higher its R-value will be. U-values are always expressed in decimals (e.g., U-0.166).

To determine the R-value of a product for which the U-value is given, you first convert the U-value to its equivalent fraction and then invert it. For instance, the equivalent fraction of U-0.166 would be 166/1000, or 1/6. This inverts to 6/1 or 6, giving you an R-value of 6.

Appliance Efficiency Ratings

When referring to the efficiency of an appliance or energy system we are actually talking about how much energy that system must use to perform a certain amount of work. The higher its energy consumption per unit of output, the less efficient the system is. For example, an air conditioner that requires 750 watts of electricity to provide 6,000 Btu of cooling will be less efficient than one that can provide the same amount of cooling for only 500 watts. The most common ratings applied to energy systems are EER and SEER for most central cooling systems; COP for some heat pumps and chillers; HSPF for all-electric heat pumps in their heating modes; and AFUE for gas furnaces and boilers.

EER

Definition: (Energy Efficiency Ratio) is the measure of how efficiently a cooling system will operate when the outdoor temperature is at a specific level (usually 95°F). A higher EER means the system is more efficient. The term EER is most commonly used when referring to window and unitary air conditioners and heat pumps, as well as water-source and geothermal heat pumps.

The formula for calculating EER is:
EER = BTU/hr of cooling at 95° / watts used at 95°

For instance, if you have a window air conditioner that draws 1,500 watts of electricity to produce 12,000 Btu per hour of cooling when the outdoor temperature is 95°, it would have an EER of 8 (12,000 divided by 1,500). A unit drawing 1200 watts to produce the same amount of cooling would have an EER of 10 and would be more energy efficient.

Using this same example, you can see how efficiency can affect a system's operating economy. First, you'll need to determine the total amount of electricity—measured in kilowatt-hours (kWh)—the unit will consume over a period of time. (A kilowatt-hour is defined as 1,000 watts used for one hour. This is the measure by which your monthly utility bills are calculated.)

To do this, let's assume you operate your 8 EER window air conditioner—drawing 1,500 watts at any given moment—for an average of 12 hours every day during the summer (1,500 watts x 12 hours). At this rate, it will use 18,000 watt-hours or 18 kWh each day, leading to a total consumption of 540 kWh over the course of a 30-day month (18 kWh x 30 days). Let's say the average cost per kWh were 10¢, then it would cost you about $54 to operate that window air conditioner each month (540 kWh x $0.10). At the same time, the 1,200-watt, 10 EER system, consuming 14.4 kWh per day and 432 kWh per month, would cost you about $43, a 20% savings over the less efficient model.

SEER

Definition: (Seasonal Energy Efficiency Ratio) measures how efficiently a residential central cooling system (air conditioner or heat pump) will operate over an entire cooling season, as opposed to at a specific outdoor temperature. SEER is calculated based on the total amount of cooling (in Btu) the system will provide over the entire season divided by the total number of watt-hours it will consume.

The formula for calculating SEER is:
SEER = seasonal BTU of cooling / seasonal watt-hours used

As with EER, a higher SEER reflects a more efficient cooling system.

By federal law, every split cooling system manufactured in or imported into the U.S. today must have a seasonal energy efficiency ratio of at least 13.0.

COP

Definition: (Coefficient Of Performance) is the measurement of how efficiently a heating or cooling system (particularly a heat pump in its heating mode and a chiller for cooling) will operate at a single outdoor temperature condition. When applied to the heating modes of heat pumps, the temperature condition is usually 47°F.

COP can be calculated by two different methods. In the first, you divide the BTU of heat produced by the heat pump by the BTU equivalent of electricity that is required to produce the heat.

This formula is stated:
COP = BTU of heat produced at 47°F /BTU worth of electricity used at 47°F

For instance, let's assume a heat pump uses 4,000 watts of electricity to produce 42,000 BTU per hour (BTU/hr) of heat when it is 47° outside. To determine its COP, you would first convert the 4,000 watts of electrical consumption into its BTU/hr equivalent by multiplying 4,000 times 3.413 (the number of BTU in one watt-hour of electricity). Then, you would divide your answer—13,648 BTU/hr—into the 42,000 BTU/hr heat output. This would show your heat pump to have a 47°F COP of 3.08. This means that, for every BTU of electricity the system uses, it will produce a little more than three BTU of heat when the outdoor temperature is 47°F.

The second formula is most frequently used to determine chiller efficiency. Using this calculation method, you would divide 3.516 by the number of kilowatts (kW) per ton used by the system.

This formula is stated:
COP = 3.516 / kW/ton

For example, a chiller that consumes 0.8 kW per ton of capacity would have a COP of 4.4 (3.516 divided by 0.8). On the other hand, a chiller that uses 0.5 kW per ton, would have a COP of 7 (3.516 divided by 0.5). The higher the COP, the more efficient the system.

HSPF

Definition: (Heating Seasonal Performance Factor) is the measurement of how efficiently all residential and some commercial all-electric heat pumps will operate in their heating mode over an entire normal heating season. HSPF is determined by dividing the total number of BTU of heat produced over the heating season by the total number of watt-hours of electricity that is required to produce that heat.

The formula for calculating HSPF is:
HSPF = BTU of heat produced over the heating season / watt-hours of electricity used over the season

The higher the HSPF, the more efficient the system. Most all-electric heat pumps installed in Springfield today probably have HSPFs in the 7.0 to 8.0 range, meaning they operate with seasonal efficiencies of anywhere from 205% to 234%. (To convert the HSPF number into a percentage, divide the HSPF by 3.413, the number of BTU in one watt-hour of electricity.) That means that, for every BTU worth of energy they use over the entire heating season, these systems will put out anywhere from 2.05 to 2.34 BTU of heat. Compare this to electric furnaces, which have nominal efficiencies of 100% (for each BTU worth of electricity used, they put out 1.0 BTU of heat), or new gas furnaces, which have efficiency ratings of about 80% to 97% (for each BTU worth of gas used, they put out 0.8 to 0.97 BTU of heat).
(NOTE: When comparing energy systems that use different primary fuel sources with different costs per BTU, it is important that you understand that higher operating efficiency is not necessarily equivalent to better operating economy. Although an electric furnace might work with greater efficiency than a gas furnace, it might or might not be more economical to operate. That will depend on the prices of electricity and natural gas.)

AFUE

Definition: (Annual Fuel Utilization Efficiency) is the measurement of how efficiently a gas furnace or boiler will operate over an entire heating season. The AFUE is expressed as a percentage of the amount of energy consumed by the system that is actually converted to useful heat. For instance, a 90% AFUE means that for every BTU worth of gas used over the heating season, the system will provide 0.9 BTU of heat. The higher the AFUE, the more efficient the system.

When comparing efficiencies of various gas furnaces, it is important to consider the AFUE, not the steady state efficiency. Steady state refers to the efficiency of the unit when the system is running continuously, without cycling on and off. Since cycling is natural for the system over the course of the heating season, steady state doesn't give a true measurement of the system's seasonal efficiency. For instance, gas furnaces with pilot lights have steady-state efficiencies of 78% to 80%, but seasonal efficiencies—AFUEs—closer to 65%.
Virtually all gas forced-air furnaces installed in this area from the 1950s through the early 1980s had AFUEs of around 65%. Today, federal law requires most gas furnaces manufactured and sold in the U.S. to have minimum AFUEs of 78%. (Mobile home furnaces and units with capacities under 45,000 BTU are permitted somewhat lower AFUEs.) Gas furnaces and boilers now on the market have AFUEs as high as 97%.

Ask The Energy Experts Read More

If you don't find the Answer you're looking for among the FAQs email us using the button below. (Please be sure to provide your name, CWLP service address and daytime telephone number in the email.) If you prefer, you can call the Energy Experts at 217.789.2070. We're always happy to hear from you.
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Window Film

Question: Will I save a lot of energy if I cover my west-facing sliding glass doors with window film?

Answer: Sunlight shining in your home can cause a tremendous amount of internal summer heat gain. Applying a light-reflecting film to west- and east-facing windows that receive a lot of sunlight can cut your cooling costs. Actual savings will depend on the VLT (visible light transmittance) rating of the film you use. The lower the VLT, the less light the film will allow to enter your home and the greater your savings will be. You'll save year-round and improve winter comfort if you use a light-reflecting film with low-E capabilities. This type of film reflects both light and infrared energy back toward its source, thus helping prevent furnace and body heat from radiating through your windows in winter.

Attic Fan Thermostat Setting

Question: At what temperature should I set the thermostat of my temperature-controlled attic fan?

Answer: A thermostat setting of 110°F should be adequate to guard against excessive attic heat buildup while ensuring the fan doesn't run more than absolutely necessary. Heat buildup in an attic (especially one that is under-insulated) can contribute greatly to a home's summer cooling load. Ventilation systems, like your temperature-controlled fan, reduce the amount of buildup, thus lowering cooling costs and improving comfort. However, because your power vent uses electricity, its energy cost will cut into your overall savings.

A more efficient way to ventilate your attic would be to install a well-designed passive system that uses no electricity at all. A good passive system could include soffit vents, installed every 8' to 12' along the roof eaves, and a continuous ridge vent. This "low-to-high" venting arrangement would allow a cooling draft to be pulled continuously through the attic.

Whatever venting method you use to control attic heat buildup, remember that the best way to limit heat transfer from the attic to your living space is to have adequate insulation in the attic. We recommend a minimum attic insulation level of R-30. R-38 is preferred.

Building an Energy-Efficient Home

Question: How can we make sure the home we plan to build is as energy-efficient as possible?

Answer: First and foremost, make sure you select a builder with a reputation for quality energy-efficient construction. Insist on receiving detailed specifications outlining each efficiency feature to be included in the home. Among the features we strongly recommend are: 1. a passive solar design in which the house site and window positions maximize solar gain in winter and minimize it in summer. 2. construction techniques that eliminate air and heat bypasses in walls and above the dropped ceilings often found in kitchens and baths. 3. caulking at all structural joints to maximize air tightness. (Air wraps should not be used as a substitute for this.) 4. all-electric heat pumps with the highest cooling and heating efficiency levels you can afford to purchase. (ENERGY STAR® qualified heat pumps will provide the highest level of efficiency and environmental friendliness.) 5. properly located and well-sealed ductwork. (Ducts located in attics can waste tremendous amounts of energy.) 6. high-quality insulation installation. You should consider "super-insulating" your walls and attics. 7. high-efficiency, low-E windows (look for ENERGY STAR qualified windows). 8. air-tight recessed light fixtures.
Regardless of which efficiency features you choose for your new home, the more involved you are in the construction process, the greater the likelihood you will be satisfied with the results once the project is completed.

Calculating Appliance Energy Use

Question: How can I calculate the cost of energy used by my electric appliances?

Answer: For "simple" appliances—like light bulbs, irons, hair dryers, TVs and radios—you can multiply the device's wattage rating* by the number of hours you use it each month. Divide your Answer by 1000. That tells you how many kilowatt-hours (kWh) of electricity the appliance uses per month. Finally, multiply the kWh by your electric cost (which, on an annual basis, currently averages about 9.5¢ for the majority of CWLP's residential customers).

This calculation method doesn't work well for more complex systems—especially air conditioners, refrigerators, water heaters, and other appliances that cycle on and off during operation. For help estimating the energy use of these types of appliances, you can contact the Energy Services Office.

More information about calculating appliance energy usage, including a chart listing the approximate energy use of many common household appliances, can be found on our Appliance Energy Use page.

If you do not know how many watts your appliance uses, you can calculate it if you know the appliance's amperage and voltage. Most household appliances operate on 110 volts; a few, such as electric clothes dryers and stoves/ovens, require 240 volts.
Wattage = amps x volts

Thermostat Setback

Question: What is thermostat setback?

Answer: Thermostat setback refers to the practice of setting your thermostat at a higher- or lower-than-normal temperature so your air conditioner or furnace will run less during periods when you need less cooling or heating. The most appropriate times to set back your thermostat are when you are sleeping and anytime you expect to be away from the house for several hours. Thermostat setback is an excellent way to cut your energy bills. For every degree you set your thermostat up in summer and down in winter, you can reduce your heating- and cooling-related energy use by about 2% or 3%—assuming the setback period lasts for several hours (such as overnight) each day. Setback is particularly easy if you use a programmable, electronic setback thermostat.

Insulating a Brick Wall

Question: My brick wall has no insulation. How can I add some?

Answer: Insulating an existing brick wall poses problems not encountered when insulating walls covered with wood and other siding materials. In those types of structures, you would drill right into the wall surface (either going directly through the siding or lifting it and drilling into the sheathing below). With brick, however, you don't want to drill into the exterior surface and there's no way to lift the brick to expose the sheathing below.

If the walls are brick veneer over wood framing and you will be doing major indoor remodeling, you could remove the plaster or sheetrock from the interior surfaces of all your exterior walls and fill in the exposed stud cavities with blanket insulation. Or you could drill through the interior wall surface and blow in loose fill cellulose. (You would need to patch the wall surfaces when done.)

If neither of these options would work for you, your only other real choice would involve blowing insulation into the wall cavity through holes drilled into the stud wall's top and sole plates. To do this, you would work in the attic and basement or crawl space rather than outside. If your walls are solid brick, if access to wall plates is blocked by a shallow roof or a slab foundation, or if the cost of installing the insulation is higher than you want to pay, you can take other steps to reduce energy costs and discomfort. These include moving beds and chairs away from exterior walls, sealing air infiltration points, and using shades or drapes to cut heat loss through windows.

Passive Solar Energy

Question: I am building a new house. How can I make use of passive solar energy?

Answer: The first thing you should do is to try to purchase a lot that will allow you to orient your home so one of the two longest walls faces due south. Then design the house so that the majority of your windows are on this wall, with large roof overhangs shielding them from as much summer sun as possible. This will allow your home to benefit from a maximum amount of solar gain in winter, when you need it, while limiting solar gain in summer, when you don't need it.

Second, because windows are a very common source of cold air infiltration in winter, limiting the number and size of windows on both the west and north sides will also help enhance comfort and efficiency when the cold winter winds blow.

When selecting windows for your home, look for ENERGY STAR® qualified models. Windows and other appliances and building products that bear the ENERGY STAR label provide the highest level of energy efficiency.

Don't forget, when designing your passive solar home, to make sure it is well insulated. A well-insulated building will help block the sun's heat from entering the home in summer and will help keep solar gain and furnace-generated heat inside the home in winter.

The CWLP Energy Experts offer free technical assistance to our electric customers, including review of and advice regarding your building plans. To take advantage of this free service, contact the Energy Services Office.

Shutting Off Air Supply to Unused Rooms

Question: I have two bedrooms I seldom use. Can I save on my energy bills by closing the heating and cooling vents in these rooms?

Answer: Under the right circumstances, shutting off heating and cooling to unused rooms might save you some money. But the savings typically will be small. If not done correctly, this procedure could actually increase your energy costs and seasonal discomfort.

Your savings will probably be greatest if the rooms you want to close off are near the air handler/ furnace. Because of their proximity to the source of the conditioned air, these rooms would normally be warmest in winter and coolest in summer. By closing off the air supply to them, you can redirect more conditioned air to other areas of your home. This will let you improve the comfort in the spaces you use most often without the need to increase energy use.

If your duct joints aren't well sealed, pressurization caused by shutting supply vents at the end of a duct run (in the room) can cause conditioned air to leak through the duct joints. Wrapping the joints in aluminum foil duct tape will help reduce this problem. (Do NOT use regular duct tape to seal duct joints. It dries out too quickly and loses its effectiveness.)

If you have duct dampers, you should use them instead of shutting room vents. Located inside the ducts, these devices can be closed to keep air from entering the ducts they control. This eliminates the potential the for duct pressurization problems mentioned above. If you have duct dampers, you will see a small metal tab on the duct about a foot from the main trunk. If the tab is lined up with the duct, the damper is open. To close the damper, turn the tab 90 degrees.

To avoid choking off too much air flow through your system, the rooms you close off should not represent over 20% of your home's total square footage. If you have a heat pump, we do not recommend closing off air supply to any part of your home.

The R-Value of Wall Siding

Question: I plan to install vinyl siding on my exterior walls. Will this make my home more energy-efficient?

Answer: Siding alone will have almost no impact on the insulating capability (R-value) of your exterior walls. Even if the siding comes with a backing of rigid board insulation, this polystyrene beadboard is usually so thin and loose fitting that it will increase R-value only minimally.

If your walls have never been insulated, we strongly recommend you blow insulation directly into the wall cavities before installing your siding. This will bring your total wall R-value to about 13. The cost of doing this can vary from a few hundred to a few thousand dollars, depending the size of your home and who does the work.

To raise the R-value by an additional 5 points or so, you can sheath the walls with rigid board insulation before installing the siding.

Tankless Water Heaters

Question: Should I replace my old water heater with one of those tankless heaters I've heard about?

Answer: The CWLP Energy Experts don't usually recommend a tankless system as a replacement for a centrally located traditional water heater. A gas unit, with its standing pilot light, probably will provide little or no savings over a well-insulated tank heater. An electric tankless system might be a little more efficient than a conventional water heater, but the savings most likely will be too small to offset the high purchase cost.

Tankless heaters are good for some specific point-of-use applications, such as when distance from a centralized tank heater makes it hard or inconvenient to get a sufficient supply of hot water to a kitchen or bathroom. In this case, you could install a tankless heater right in that room.

Otherwise, we recommend using a traditional tank heater and taking steps—like wrapping both the tank and the water pipes with insulation and installing heat traps on the pipes where they exit the top of the tank—to ensure it will operate as efficiently as possible

Using a Compact Fluorescent in a Three-Way Lamp

Question: Can I use a compact fluorescent lamp (CFL) in my three-way lamp?

Answer: Yes. You could use either a standard (one-way) or a three-way CFL. Each would provide a different effect. The standard CFL works in a three-way lamp exactly the same way a one-way incandescent does—the light remains off for three of every four clicks of the lamp's switch and you get only one level of light.

Just like a three-way incandescent, a three-way CFL would provide you with three different light levels that would be equivalent to the light output of a 50/100/150-watt incandescent.

For more information about compact fluorescent lighting, contact the Energy Services Office.

How a Crack in a Double-Pane Window Can Affect Its Efficiency

Question: Will a small crack in one pane of a double-pane window affect the window's efficiency?

Answer: If the window was filled with an inert gas (argon or krypton), the gas will seep through the crack, causing some loss in the window's overall efficiency. However, assuming the crack is very narrow and does not allow a significant amount of air infiltration, you'll still benefit from the insulating value provided by the dual panes and space of relatively "dead" air. So your actual energy-dollar loss typically will be small—probably no more than a couple of dollars per year. From an efficiency standpoint alone, the losses resulting from the crack would probably be too small to justify the cost of repairing or replacing the window.

Energy-Efficient Windows

Question: Is it economically advisable to install new energy-efficient windows in uninsulated walls?

Answer: Whether you walls are insulated or not, installing new windows for the sole purpose of increasing your home's energy efficiency would probably not be economically advisable. The monthly savings you could realize would, in most cases, be too small to provide a reasonable payback on your upfront investment.

If you're replacing your windows to improve your home's looks and comfort, by all means, choose high-efficiency multiple-pane models with low-E film or coating and an inert gas filling. Your energy savings should quickly off-set the cost difference between these and low-efficiency single-pane units.

But, if your goal is simply to increase efficiency, there are far more cost-effective things you can do—including installing storms over your existing windows, making sure the existing windows and frames are sufficiently caulked and weatherstripped, and insulating your walls.

For more information about window efficiency, contact the Energy Services Office.

City Water, Light, and Power

A Department of the City of Springfield

Misty Buscher - Mayor ~ Doug Brown - Chief Utility Engineer

Energy Efficiency

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Building Materials Efficiency Ratings

R - Value

U - Value

Appliance Efficiency Ratings

EER

SEER

COP

HSPF

AFUE

Ask The Energy Experts Read More

Window Film

Attic Fan Thermostat Setting

Building an Energy-Efficient Home

Calculating Appliance Energy Use

Thermostat Setback

Insulating a Brick Wall

Passive Solar Energy

Shutting Off Air Supply to Unused Rooms

The R-Value of Wall Siding

Tankless Water Heaters

Using a Compact Fluorescent in a Three-Way Lamp

How a Crack in a Double-Pane Window Can Affect Its Efficiency

Energy-Efficient Windows

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Misty Buscher - Mayor ~ Doug Brown - Chief Utility Engineer

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Energy Efficiency

Efficiency Terms Read More

Energy Saving Tips Read More

Regional Energy Emergencies

About Energy Star® Read More

Appliance Energy Use Read More

Efficiency Ratings Read More

Building Materials Efficiency Ratings

R - Value

U - Value

Appliance Efficiency Ratings

EER

SEER

COP

HSPF

AFUE

Ask The Energy Experts Read More

Window Film

Attic Fan Thermostat Setting

Building an Energy-Efficient Home

Calculating Appliance Energy Use

Thermostat Setback

Insulating a Brick Wall

Passive Solar Energy

Shutting Off Air Supply to Unused Rooms

The R-Value of Wall Siding

Tankless Water Heaters

Using a Compact Fluorescent in a Three-Way Lamp

How a Crack in a Double-Pane Window Can Affect Its Efficiency

Energy-Efficient Windows

Login to myCWLP

City of Springfield

Quick Links

Stay Connected

© 2017 City Water, Light & Power, Information Systems Division