Sign up and get a coupon for $10 off today's service!

Air Conditioning - Air Conditioner Terms

What do all those Air Conditioner terms really mean?

Knowledge is Power Especially When it comes to Air Conditioners

We understand that the more you know the more comfortable you will be with your decision.

Don't be afraid to ask for more information. We are here to help you.

Call or
and speak with a technician for free

Generac Sales and Service

Air Conditioning - Air Conditioner Terms

What do all those Air Conditioner terms really mean?


Annual Fuel Utilization Efficiency. This is the efficiency rating that is applied to gas furnaces. The higher the number, the lower the fuel costs for the furnace. 80% is the minimum requirement for units produced in the U.S.


British Thermal Unit. The amount of thermal energy required to raise one pound of water 1degree F. One BTU is equal to .293 watt hours. One kWh is equal to 3412 BTU's


This is the heart of the air conditioner and the heat pump. It is the device that pumps the Freon. There are several types of compressors:

  • Piston- This is the most common type of compressor found in older units. Very reliable, there are millions of these still in use.
  • Scroll- This is Copeland’s latest effort at solving some of the problems with the  Piston compressors. A true one of a kind of compressor, it has about half the moving parts of a standard compressoCopeland Scroll two-stage compressorr. It increases the efficiency of most units  by about 10%. Commonly found in the higher efficiency units today, it is the most  popular compressor in use.
  • Inertia- This is a high performance Piston compressor that is used in medium to high efficiency range units. Its lower initial cost and competitive performance make it the popular choice in the price driven market.
  • Copeland Scroll two-stage compressor-This compressor enables a central air conditioner to operate at an energy saving two thirds capacity most of the time and at "full throttle" only on the hottest days. Air conditioners equipped with Copeland Scroll two-stage compressor maintain precise temperature levels and lower relative humidity while saving up to 60 percent on energy costs when compared with a 10 SEER systems. Two stage units may cost more initially, but they pay for themselves in the long run.
Condensate drain pan

The drain pan collects the water from the evaporator coils and drains it into the condensate drain lines which drain into the house sewer system.



The condenser is the outside part of the air conditioning system.

Condenser coils

The condenser coils are the the outside coils, used to dissipate the heat from the freon.


Coefficient of Performance. This is the heater rating of the heat pump. The higher this number, the more efficient the heat pump. An electric heater has a rating of 1. This means that a heat pump that has a rating of 3 will operate for 1/3 of the price of an electric heater.


A electrical switch that is located outside near the condenser and is used to turn the unit off and on for servicing. 

Honeywell Electronic Air CleanerElectronic Air Cleaner

This is the best air filtration system on the market today. It uses the principle of electromagnetic attraction to remove particles from the air. By charging the air with around 5,000 volts of DC current, it causes the particles to stick to the collecting plates. Very low operating costs and virtually no restriction of the airflow make it very cost effective.

Evaporator Coil
Evaporator coil

The portion of the a/c that actually gets cold, located inside the house.

Flue Pipe

This is part of a gas furnace that exhausts the products of combustion out of the home. Older units used a single wall, non-penetrating style. Safety codes now require a double wall, type “B” penetrating style flue pipe. While the new flue pipe is much more expensive than the old one, it is also much safer.


The refrigerant used to transfer the heat (usually R-22or R-410).

Freon Lines

Are the lines that connect the condensing unit to the evaporator coil. They are usually made from copper.

Freon Recovery/Reclaim

Required by the EPA, these terms refer to the capture of the old Freon and returning it to the manufacturer for processing. A time consuming and expensive process (the machines range in price from $500 to $3,000), takes pride in the fact that we did this before it became the law. Just like recycling aluminum cans, it helps save our planet for future generations.

Gas Connector

This is the fitting that is used to connect the gas heater to the home’s gas supply. The standard connector was usually made of copper. In recent years, a brass connector has become the required method. This is to keep copper sulfide flakes from forming in the line, which causes clogs.

Heat Exchanger

This is the heart of the gas furnace. It seals the products of combustion off from the air inside the home. When there are cracks or holes in this part of the furnace, carbon monoxide can enter the home. Most heat exchangers used to be made of plain steel which rusted. Newer ones have an aluminum coating over the steel to help control this problem. The latest designs feature stainless steel to eliminate the rust problem.

Heat Pump

This is a special kind of air conditioner that has a “reverse”. Its main advantage is that it will cut heating costs considerably. Contrary to popular belief, heat pumps can be cost effective in this area. While they do not require special design and installation considerations, they do operate on a very simple principle. A normal air conditioner blows cool air inside and warm air outside. What it is doing is taking heat from where it is not wanted and putting it where it does not matter. It is moving heat from the home to outside. A heat pump simply reverses this process in the winter. By doing so, it produces significant savings in the heat mode. Even in the winter there is heat available in the outdoor air to heat the home. A heat pump moves this into the home in a similar fashion to the way that an air conditioner moves heat out of the home. One of the best ways to decide if a heat pump is for you is to take a look at your winter electric bill. If it is over $200, then a heat pump may be worth considering. Heat pumps are best suited for all electric homes. Homes with gas available for heating are better off with a high efficiency air conditioners and a good quality gas heater.


This part of the air conditioning and heating system where the air is distributed into various ducts that lead into the rooms of the home.

Return on Investment

This is a gauge of how quickly that a high efficiency can pay for itself based on energy savings. Most homes with a 10 year old system in them can be retrofitted with a system that will pay for itself in about 5 years. Given that most systems have a life of 10 years or better, the potential for significant profits can be realized. Coupled with long term low interest financing, most high efficiency systems can pay their own way. One of the better investments today is the modern air conditioning system. Investment returns of 30% or better can be realized easily.


Seasonal Energy Efficiency Ratio. This is the amount of cooling that an air conditioner produces divided by the watts of power that is required to run it. It is the “mileage” rating of the unit. The higher the number, the lower the operating cost. A seer of 13 is the minimum for the units produced in the U.S.

Thermostatic expansion valve (TXV)

The expansion valve regulates the freon flow through the evaporator.

Tonnage or Tons

One ton equals 12,000 BTUS of cooling. Air conditioners are normally available in 2, 2.5, 3, 3.5, 4 and 5 ton capacities for residential applications.


A transition is a sheet metal fitting that connects the furnace to the evaporator coil.

Please call us at or . We are here to help answer all of your questions. on Facebook on Twitter