❄ Delivered Capacity
✅ Field COP
Result Breakdown
Full Calculation Table
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How to Use the System Efficiency Test Calculator
Choose heat pump in heating or cooling mode, air conditioner, or gas furnace to apply the correct efficiency calculation for that equipment.
Enter measured airflow and the temperature difference across the indoor coil or heat exchanger. For cooling, you can add the sensible heat ratio to estimate total capacity.
For electric equipment, enter measured power draw. For a gas furnace, enter the gas input rate, from the nameplate or from clocking the gas meter.
Click Calculate Efficiency to see delivered capacity and field efficiency, with a comparison against the rated efficiency if you entered one.
Understanding Field Efficiency Testing
The efficiency rating printed on an equipment label describes performance under specific standardized test conditions. What that equipment actually delivers on a particular job, on a particular day, with the actual airflow and refrigerant charge present in the field, is a different number that only field measurement can reveal. Field efficiency testing closes that gap between rated performance and real performance.
Calculating Delivered Capacity
Delivered capacity comes from measured airflow combined with the temperature split across the coil or heat exchanger, the same fundamental relationship used in the coil performance test calculator, at about 1.23 W per L/s per degree Celsius. In heating this is essentially all the heat the equipment delivers, as long as any supplemental electric heat is off during the test. In cooling, the airstream also loses moisture, so the temperature split captures only the sensible part of the capacity. Enter the coil's sensible heat ratio and the calculator divides by it to estimate total capacity, and the sensible heat ratio calculator can help you find it. Leave it blank and the result is a sensible-only COP, which understates the real figure.
Field COP for Heat Pumps and Air Conditioners
Coefficient of performance, or COP, is delivered capacity divided by electrical power input, both expressed in the same units. Measure the power of the outdoor unit and the indoor blower together, since the delivered capacity includes the air the blower moves. A field COP reflects the specific outdoor temperature and operating condition present during the test, which will differ from the seasonal average implied by a rated SEER or HSPF number on the equipment label. The swing is large: in an NRCan CanmetENERGY assessment of a cold climate air source heat pump in Ottawa, heating COP averaged 1.5 at -21.1 °C outdoors and 3.0 at +4.9 °C, and cooling COP ran from 2.4 at 20.4 °C outdoors to 3.7 at 28.3 °C. A field reading on a mild day tells a different story than one taken during extreme cold.
Field Efficiency for Gas Furnaces
Gas furnace efficiency compares delivered heat output to gas energy input, giving a steady-state efficiency figure comparable in concept to the AFUE rating on the nameplate, though measured under actual field conditions rather than the standardized AFUE test procedure. The nameplate input is the rated firing rate, so clocking the gas meter gives a more honest result. Most new residential gas furnaces sold in Canada now have to meet a 95 percent AFUE floor under NRCan's gas furnace regulations, which makes a field reading far below the nameplate on a recent unit worth chasing. This calculation complements combustion analysis, since combustion efficiency and delivered system efficiency, while related, aren't quite the same measurement.
Why Field Numbers Rarely Match the Label Exactly
Airflow below design specification, refrigerant charge deviation, duct losses in unconditioned space, and outdoor conditions that differ from the standard rating test all contribute to field efficiency running below the rated seasonal number, even on correctly functioning equipment. A field efficiency reading meaningfully below rated performance, especially combined with confirmed adequate airflow, points toward investigating refrigerant charge with the refrigerant charge verification calculator or checking for duct losses. Ratings printed as EER, SEER, or HSPF need converting before you compare them with a field COP: divide by 3.412, which the COP EER converter does for you. This calculator flags a field result below 85 percent of the rated value you enter as worth investigating, a screening guideline rather than a published standard.
Documenting Efficiency Results
Recording field efficiency at commissioning creates a useful performance baseline, particularly valuable if a warranty claim or performance dispute arises later. Include results in a commissioning report alongside supporting measurements like airflow and refrigerant charge verification for a complete performance record.
Frequently Asked Questions
COP, or coefficient of performance, is the ratio of heat delivered to electrical energy consumed at a specific operating condition. Rated efficiency numbers like SEER or HSPF are seasonal averages calculated across a range of standardized conditions, while a field COP calculation reflects performance at the specific outdoor and indoor conditions present during the test, which will differ from the seasonal average number.
Rated efficiency numbers are established under specific standardized test conditions that rarely exactly match field conditions on any given day. Low airflow, incorrect refrigerant charge, extreme outdoor temperature, and duct losses can all cause field-measured efficiency to run below the rated seasonal average, even on correctly installed equipment.
A true power measurement, in watts or kilowatts, gives the most accurate efficiency calculation. Voltage and current readings can approximate power draw if a wattmeter isn't available, but that approach loses accuracy with a poor power factor, common on some compressor and motor loads, so a direct power reading is preferred whenever possible.
Significantly. Heat pump COP drops as outdoor temperature falls in heating mode, so a field COP reading is only meaningful when compared to expected performance at that same outdoor temperature, not against a single flat rated number that represents a seasonal average across many different conditions. NRCan's tests of a cold climate heat pump measured an average heating COP of 1.5 at -21.1 °C and 3.0 at +4.9 °C.
With no sensible heat ratio entered, the calculator measures sensible capacity only, which ignores the moisture removed from the air, so it understates the total cooling COP. Enter the coil's sensible heat ratio to estimate total capacity, which you can get from the coil performance test calculator or a wet-bulb measurement.
Related HVAC Tools
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Combustion efficiency check
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