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Heating, Cooling and Air Purification Terminology Explained

If you're shopping for heating, cooling or air purification products, you're probably running into terms you haven't heard before or at least in a while. We've listed the terms we use to rate our products and offer you a brief explanation.

The terms are listed in alphabetical order. If we've left one out, or there's one you'd like to know more about, give us a call!


Annual Fuel Utilization Efficiency

The annual fuel utilization efficiency is a thermal efficiency measure of combustion equipment like furnaces, boilers, and water heaters. AFUE attempts to represent the actual, season-long, average efficiency of that piece of equipment.

It is a ratio of useful energy output to energy input, expressed as a percentage. For example, a 90% AFUE for a gas furnace means it outputs 90 BTUs of useful heating for every 100 BTUs of Natural Gas input (where the rest may be wasted heat in the exhaust). A higher AFUE means higher efficiency.


Coefficient of Performance

The COP ratio is the ratio of the heating or cooling provided by a heat pump for the electrical energy consumed.

These ratings are usually expressed for heat pumps and geothermal products. A geothermal heat pump operating at a COP of 3.5 provides 3.5 units of heat for each unit of energy consumed (i.e. 1 kWh consumed would provide 3.5 kWh of output heat).

Given the same energy source and operating conditions, a higher COP heat pump will consume less purchased energy than one with a lower COP.


A decibel is one tenth of a bel, a seldom-used unit named in honor of Alexander Graham Bell.

The decibel (abbreviated dB) is the unit used to measure the intensity of a sound. The decibel scale, is said to be logarithmic.

The smallest audible sound (near total silence) is 0 dB. A sound 10 times more powerful is 10 dB. A sound 100 times more powerful than near total silence is 20 dB. A sound 1,000 times more powerful than near total silence is 30 dB.

Here are some common sounds and their decibel ratings:

  • Near total silence - 0 dB
  • A whisper - 15 dB
  • Normal conversation - 60 dB
  • A lawnmower - 90 dB
  • A car horn - 110 dB
  • A rock concert or a jet engine - 120 dB
  • A gunshot or firecracker - 140 dB


Energy Efficiency Ratio

The Energy Efficiency Ratio (EER) of a particular cooling device is the ratio of output cooling (in BTU/h) to input electrical power (in watts) at a given operating point. EER is generally calculated using a 95 °F outside temp and an inside (actually return air) temp of 80 °F and 50% relative humidity. The EER is a more realistic measurement of energy efficiency in warmer climates due to the high demand and higher cost of peak hour electricity.

EER is related to SEER but is always expressed as a lower number A typical EER rating for residential central cooling units = 0.875 × SEER.

As with the SEER rating, a higher number is more efficient.


Heating Seasonal Performance Factor

HSPF is specifically used to measure the efficiency of air source heat pumps. The efficiency of air conditioners are often rated by the Heating Seasonal Performance Factor.

The higher the HSPF rating of a unit, the more energy efficient it is. HSPF is a ratio of BTU heat output over the season to watt-hours of electricity used. It is expressed in units of BTU/watt-hour.

Depending on the system, an HSPF of greater than or equal to 8 can be considered high efficiency and worthy of a US Energy Tax Credit.


Minimum Efficiency Reporting Value

Minimum efficiency reporting value, commonly known as MERV rating is a measurement scale designed in 1987 to rate the effectiveness of air filters. Experiments indicate that less obstructive, medium-efficiency filters of MERV 7 to 13 are almost as effective as true HEPA filters at removing allergens, with much lower associated system and operating costs.

Below is a table grouping MERV ratings and what that rating should control:

MERV Rating Typical Contaminant Controlled Typical Application
17–20 Virus, carbon dust, sea salt, smoke Electronics & pharmaceutical manufacturing cleanroom
13–16 Bacteria, droplet nuclei (sneeze), cooking oil, most smoke and insecticide dust, most face powder, most paint pigments hospital & general surgery
9–12 Legionella, Humidifier dust, Lead dust, Milled flour, Auto emission particulates, Nebulizer droplets Superior residential, better commercial, hospital laboratories
5–8 Mold, spores, dust mite debris, cat and dog dander, hair spray, fabric protector, dusting aids, pudding mix Better residential, general commercial, industrial workspaces
1–4 Pollen, dust mites, cockroach debris, sanding dust, spray paint dust, textile fibers, carpet fibers Residential window AC units


Seasonal Energy Efficient Ratio

The SEER rating of a unit is the cooling output during a typical cooling-season divided by the total electric energy input during the same period. The higher the unit's SEER rating the more energy efficient it is.

SEER rating more accurately reflects overall system efficiency on a seasonal basis and EER reflects the system’s energy efficiency at one specific operating condition. Both ratings are useful when choosing products, but the same rating must be used for comparisons.

Note: All information obtained and presented here came from either or

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