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AIR CONDITIONING & HEAT PUMP SYSTEMS
A/C - HEAT PUMP CONTROLS & SWITCHES
AIR CONDITIONER COMPONENT PARTS
AIR CONDITIONER TYPES, ENERGY SOURCES
AIR FILTER EFFICIENCY
AIR FILTERS, FIBERGLASS PARTICLES
AIR FLOW MEASUREMENT CFM
APPLIANCE EFFICIENCY RATINGS
BLOWER DOORS & AIR INFILTRATION
BLOWER FAN CONTINUOUS OPERATION
BLOWER FAN OPERATION & TESTING
BOOKSTORE - Air Conditioning "How To" Books
CAPACITORS for HARD STARTING MOTORS
CLEANING & Legionella BACTERIA
CHINESE DRYWALL HAZARDS
CONDENSATION or SWEATING PIPES, TANKS
DEFINITION of Heating & Cooling Terms
DEW POINT CALCULATION for WALLS
DEW POINT TABLE - CONDENSATION POINT GUIDE
DIAGNOSTIC GUIDES A/C / HEAT PUMP
DIAGNOSE & FIX HEATING PROBLEMS-BOILER
DIAGNOSE & FIX HEATING PROBLEMS-FURNACE
DUCTS - Asbestos
DUCT INSULATION, Asbestos Paper
DUCT INSULATION for SOUNDPROOFING
DUCT SYSTEM & DUCT DEFECTS
DUCT SYSTEM NOISES
DUCTS, Asbestos Transite Pipe
DUST, HVAC CONTAMINATION STUDY
ELECTRIC MOTOR OVERLOAD RESET SWITCH
EVAPORATIVE COOLING SYSTEMS
FAN LIMIT SWITCH
GAS EXPOSURE EFFECTS, TOXIC
GAS DETECTION INSTRUMENTS
HEAT LOSS (or GAIN) in buildings
HEAT LOSS (or GAIN) INDICATORS
HEAT LOSS R U & K VALUE CALCULATION
HEATING SMALL LOADS
INSPECTION CHECKLIST - OUTDOOR UNIT
INSPECTION LIMITATIONS, A/C SYSTEMS
LEED GREEN BUILDING CERTIFICATION
LOST COOLING CAPACITY
LOW VOLTAGE TRANSFORMER TEST
MOTOR OVERLOAD RESET SWITCH
MOLD in AIR HANDLERS & DUCT WORK
OPERATING COST, AIR CONDITIONER
OPERATING DEFECTS, AIR CONDITIONING
REPAIR GUIDES A/C / HEAT PUMP
REPAIR & DIAGNOSTIC FAQs for A/C
THERMOSTATS, HEATING / COOLING
THERMOSTATIC EXPANSION VALVES
WATER COOLED AIR CONDITIONERS
WINDOW / WALL AIR CONDITIONERS
WINDOW / WALL A/C SUPPORTS
Air Conditioner & Heat Pump Efficiency Ratings: this article explains air conditioning SEER energy efficiency ratings for air conditioners and heat pumps along with related terms like BTUs, Watts and hourly operating cost, in easy to understand language. Latent heat, superheat, latent heat of vaporization, latent heat of condensation, sensible heat & specific heat and joules are defined separatelyh at
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Also see AIR CONDITIONING HEAT PUMP SAVINGS for suggestions on cutting A/C or heat pump operating cost. For a history of the US Government's use of energy efficiency ratings for air conditioners, also see SEER RATING HISTORY. More definitions of electrical terms can be found at DEFINITIONS of ELECTRICAL TERMS and other heating and cooling terms are at DEFINITION of Heating & Cooling Terms. This article series answers most questions about air conditioning systems. We continue to add to and update this text as new details are provided. Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution.
Definition of SEER - Seasonal Energy Efficiency Ratio
SEER stands for "Seasonal Energy Efficiency Ratio. This is a measure of the energy efficiency of the air conditioning system. SEER ratings permit consumers to compare operating costs of various cooling systems and products.
SEER = [Total Cooling Output Over the Cooling Season] / [Total Electrical Energy Input Over the Cooling Season]
Higher air conditioning SEER rating means more efficient, or in other words lower energy cost to cool the building. Older air conditioning systems are likely to have a lower SEER (perhaps 5 or 6) than a newer more efficient system (perhaps SEER=10). But beyond comparing SEER ratings, a look at the building insulation, air leakage, and the layout, insulation, and adequacy of the air conditioning duct system are likely to have a very large, usually determining effect, on the operating cost of air conditioning systems in buildings.
Here are the U.S. Government's Energy Star Program definitions of SEER and EER: 
At Questions & Answers about the Energy Star Program's SEER and EER definitions and equipment ratings you'll see discussion about some confusion around just what the SEER rating means for individual air conditioner components versus the SEER or EER for the whole A/C system.
The Energy Star program also provides a performance rating factor for heat pumps since those units, unlike straight air conditioning systems, operate through both heating and cooling seasons:
We note that because electrical energy costs vary widely in different areas of North America, and because in some areas the electric utility may give preferential rates (reduced rates) for people using electric heat, the HSPF number may need adjustment for your area.
At Other Heating & Air Conditioning System Performance Measurements & Standards we define other heating and cooling terms such as AFUE and HSPF. Also see ENERGY STAR PROGRAM and for tips on how to cut air conditioning or heat pump operating costs, see AIR CONDITIONING HEAT PUMP SAVINGS.
Standard Required Air Conditioner or Heat Pump SEER Ratings
Currently (2012) in the U.S. new HVAC products are required to have a SEER rating of 13 or better. Equipment is readily available with a SEER of "up to" SEER 16, possibly higher from some manufacturers.
How Much Energy Does an Air Conditioning System Use?
How to Calculate Energy Usage using an Air Conditioner's SEER rating
A concise way to translate SEER number directly into energy cost is SEER 10 = 10 BTUs/WattHour. In other words, an air conditioner that has a SEER rating of 10 will provide 10 BTUs of cooling per WattHour (Wh) of operation.
So if our air conditioner has a SEER of 9, it is less efficient than an A/C unit with a SEER of 10 because our SEER 9 air conditioner produces 9 BTUs of cooling for the same Wh of operation. That is, we've kept the energy consumption (one Wh) the same, but we got less cooling output.
Let's define Watts and BTUs so we can better understand these air conditioner figures of SEER efficiency, BTUs, Watts, and air conditioning operating cost calculations.
What is the SEER for Older Air Conditioners?
Older air conditioning systems are likely to have a lower SEER (perhaps 5 or 6) than a newer more efficient system (perhaps SEER=10). But beyond comparing SEER ratings, a look at the building insulation, air leakage, and the layout, insulation, and adequacy of the air conditioning duct system are likely to have a very large, usually determining effect, on the operating cost of air conditioning systems in buildings.
Testing Requirements for SEER Ratings for Air Conditioners & Heat Pumps
According to the ENERGY STAR program requirements,
How do we calculate watts, volts, and amperage for an electrical device like an air conditioner?
Watt hours (Wh), sometimes written W.h, can measure either electrical energy produced, say by a power station, or Watts can measure the amount of electrical energy consumed (say at a light bulb or an air conditioner in our home). For air conditioners, the A/C units' total Wh is the energy used in running the air conditioning system for an hour. Details are at Definition of WATTS and at Definition of WATT HOUR. Also see DEFINITIONS of ELECTRICAL TERMS for details about volts, watts, amps, and power factor.
Watts (W) as used in a simplified manner here and by electricians, is a measure of electrical power and is expressed by any of the formulas shown below. [All forms of power are measured in units of Watts, W, but this unit is generally reserved for real power (see definitions further below.]
DC circuits: W = V x I (this is a simplified formula and is technically exactly correct for DC circuits. For AC circuits,
AC circuits: Watts W=V*I*PF where PF = power factor
See DEFINITIONS of ELECTRICAL TERMS for details about volts, watts, amps, and power factor. Also see AMPS & VOLTS DETERMINATION "How to estimate the electrical service ampacity and voltage entering a building".
Reader Daniel Mann adds that "Watts is correctly shown as Watts-Voltage times Current times power factor. Since power factor varies all over the place,..." [W = V x I] "perpetuates misinformation". We include additional more technical explanation of power factor, real power, apparent power, complex power, and reactive power as we elaborate at DEFINITIONS of ELECTRICAL TERMS.
Lots of electrical appliances include a label providing the appliance's wattage, and in the case of heating and air conditioning equipment, lots of other details are provided too. See A/C DATA TAGS for details.
A BTU is a measure of heat energy, or the amount of heat given off when a unit of fuel is consumed. One BTU is the amount of heat energy we need to raise the temperature of one pound of water by one degree Fahrenheit. One BTU also is defined as 252 heat calories (this is not the same as food calories).
When talking about air conditioners or heaters, we talk about the A/C unit's BTUh capacity - the number of BTUs of cooling (lowering rather than raising temperature) it can produce in an hour of running.
When we are heating a building BTUs describe heat given off by consuming fuel or energy from some source (electricity, natural gas, LP gas, oil, etc.) of which some portion is delivered to the building occupied space (see AFUE and HSPF).
When we are cooling a building, or when we are describing an air conditioner or heat pump's rated capacity (in BTUs), we are desribing the removal of a quantity of heat from the building - or really from the building's air.
Also see DEFINITION of Heating & Cooling Terms where we further discuss and define BTUs, Calories, and other energy measures.
At Definition of BTUs you can see a table of BTUs translated into other measurements:
Based on the definition of BTUs above, BTUH describes the number of BTUs of energy produced (as heat) or removed (by air conditioning) in one hour.
One ton of air conditioning capacity produces the same cooling ability as melting one ton of ice in 24 hours. Sketch courtesy of Carson Dunlop Associates.
288,000 BTUs / 24 hours = 1 Ton of cooling
12,000 BTUs / hour = a 1-ton air conditioning system
A one-ton air conditioner claims to remove 12,000 BTUs of heat from the building air per hour of operation.
Or if we know the total number of BTUs at which an air conditioning system is rated, since this number is usually given in BTUH or BTUs / hour, we just divide that number by 12,000 to get the number of tons of cooling capacity.
A 36,000 BTUh air conditioner is providing 36,000 / 12,000 or 3 Tons of cooling capability per hour.
If we know the number of tons of cooling capacity that an air conditioning system is rated for, we just multiply the number of air conditioning capacity in Tons by 12,000 to get the number of BTUs of cooling capacity of the system.
To assist in choosing the right sized air conditioner, we provide a typical air conditioner chart at AIR CONDITIONER BTU CHART.
Watch out: more is not always better. Don't buy an air conditioner that is too big: if you install a system that is too powerful (too many tons of cooling capacity) the building will be less comfortable than if you install a properly-sized air conditioner. Too many tons of air conditioning mean the system will shut off on short cycles and won't run long enough to reduce the indoor humidity to a comfortable level. Details are at DEHUMIDIFICATION PROBLEMS
How much electricity our air conditioner uses
per hour is easy to calculate.
Let's assume that the data tag on our air conditioner
says that the unit is a 5000 BTUh device with a SEER rating of 10. This means our A/C unit will produce
5000 BTUs of cooling in an hour of running. Since SEER=10 means that 10 BTUs used per Wh, then
How Much Electricity Does An Air Conditioner Use in one Cooling Season?
A common example we use (because the math is easy) is to assume we have 125 days of cooling season during which we run the air conditioner for eight hours per day.
8 x 125 = 1000 hours of cooling operation over a season
So we are using 500,000 Watt Hours of energy (electricity) per cooling season. We divide this by 1000 to convert to Kilowatts since that's how our electrical bill will express our electricity usage.
500,000 Wh / 1000 = 500 kWh or kilowatt hours per season of use
At OPERATING COST we determine the actual dollar cost of running an air conditioner either by the hour of by the season of use. It's easy to get from that data to actual air conditioning operating costs in dollars.
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Frequently Asked Questions (FAQs)
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Question: I purchased a 16 SEER system. The unit outside has an energy rating of 14 SEER. Did my contractor install the wrong unit?
I purchased a 16 SEER system. The unit outside has an energy rating of 14 SEER. The company tried to tell me that the coils add 2 SEER to the overall system. I think that they are lying, and that they installed the wrong unit. What is the correct answer? - Michelle
Reply: Maybe. Rely on the product labels and check with the manufacturer about the combined SEER of your compressor/condenser unit and air handler unit
Michelle, the US EPA / Energy Star program's definition of SEER given at the top of this page describes the "... total cooling of a central air conditioner or heat pump (in Btu) during the normal cooling season as compared to the total electric energy input (in watt-hours) consumed during the same period..."
For purposes of the ENERGY STAR program, Central Air Conditioner is defined as the combination of both indoor and outdoor components and you should have received an ENERGY STAR SEER number for that whole system.
But unless your central air conditioning system is a "Matched Assembly" [defined below], it is likely that the SEER definition for your central air conditioner does not address the confusion that can arise when your inside unit air handler (which includes the evaporator or cooling coil you mention) and compressor/condenser (the outside unit) may have separate individual SEER ratings. Each of those two major system components will be on or off (running or not) at different times during a cooling cycle, depending on a variety of factors.
If your installer did not install a Matched Assembly central air conditioning system, and if the installer did not provide you with documentation [not just an oral statement or claim] of the overall SEER rating for your central air conditioner, to obtain a SEER rating for the combined system you'd need to consult the manufacturer and make some assumptions about the on-off time of each of these components.
For combinations of air handlers and compressor/condenser units intended to be sold as a complete, installed, system, the manufacturer may be able to give you an overall SEER rating for that system.
Or maybe not not. Given the Energy Star definition of Central Air Conditioners and SEER (see SEER RATINGS & OTHER DEFINITIONS), it it would not be accurate to simply add a few SEER points to the compressor/condenser unit's SEER based on an opinion about other system components. Nor are component SEER ratings additive - you don't just add them together to get an overall system SEER. Not without the manufacturer's agreement.
We can save some potential embarrassment - don't assume your installing company has been dishonest (as you put it) without first asking the manufacturer for clarification.
The U.S. Government's Energy Star Program's discussions and documents about the SEER rating program (and SEER targets for newly installed equipment) suggests that folks in both government and industry are aware that the lack of clarity or of technical details in SEER rating definitions is a source of potential misunderstandings between consumers and their installing contractors. 
Notice that for a split system air conditioning system, the ENERGY STAR definition is more clear about the necessity to combine the major components in arriving at a SEER rating, as it refers explicitly to the ... actual condenser-evaporator coil combination of the split system.
Questions & answers or comments about the Energy Star Program's SEER and EER definitions and other HVAC equipment energy efficiency ratings
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Technical Reviewers & References
Related Topics, found near the top of this page suggest articles closely related to this one.