HVAC Glossary

This number represents how efficiently a furnace converts fuel to energy. The ratio of annual output of useful energy or heat to the annual energy input to the furnace. The higher the AFUE, the more efficient the furnace -- higher efficiency translates to more savings on fuel bills. This will range from 80% to 95%. Percentage of fuel used for heating. A measure of heating efficiency, in consistent units, determined by applying the federal test method for furnaces. This value is intended to represent the ratio of heat transferred to the conditioned space by the fuel energy supplied over one year.

Device used for removal of airborne impurities. A device that actively removes impurities from the air, including forced air filtration systems and electronic air cleaners. Air cleaners may be added to HVAC systems or stand-alone room units.

Fan-blower, filter, heat transfer coil, and housing parts of a system. Also known as the blower section and part of the split system, this unit is commonly in your home or attic and blows the air through your house. This has to be matched with the condenser properly to assure maximum efficiency. This will contain your heating and evaporator coil.

The distribution or movement of air.

The process of adjusting the flow of air in duct systems, or water flow in hot-water heating systems. Proper balancing is performed using accurate instrumentation to deliver the right amount of heating or cooling to each area or room of the home.

A device used to start a motor or compressor (or to keep it running after start up.)

The output or producing ability of a piece of cooling or heating equipment. Cooling and heating capacity are normally referred to in BTUs. The capacity of an air conditioner is measured by the amount of cooling it can do when running continuously. The total capacity is the sum of the latent capacity (ability to remove moisture from the air) and sensible capacity (ability to reduce the dry-bulb temperature). Each of these capacities is rated in BTUS per hour (BTU/H). The capacity depends on the outside and inside conditions. As it gets hotter outside (or cooler inside) the capacity drops. The capacity at a standard set of conditions is often referred to as "tons of cooling."

Part of a refrigerating mechanism which pumps vaporized refrigerant from the evaporator, compresses it, liquefies it in the condenser and returns it to the refrigerant control. The outdoor portion of a split system air conditioner contains the compressor and outdoor coil ignoring the reverse cycle operation, also the outdoor in a heat pump system.

A device that is located in ductwork to adjust air flow. This movable plate opens and closes to control airflow. Dampers are used effectively in zoning to regulate airflow to certain rooms. There are basically two types of dampers: Manual and motorized. A manual damper generally consists of a sheet metal (or similar material) flap, shaped to fit the inside of a round or rectangular duct. By rotating a handle located outside of the duct a technician can adjust (see balancing) air flow to match the needs of a particular area or room. A motorized damper is generally used in a zoned system (see Zoning) to automatically deliver conditioned air to specific rooms or zones. In particular, the following types, can be distinguished: Multiple leaf dampers, comprising of a number of blades (or shutters) of opposed or parallel leaf type. Single leaf dampers (the flap being mounted at one end), commonly called splitter dampers. Hit-and-miss dampers, having two or more slotted slide mechanism. Butterfly dampers, with two flaps in "V" arrangement.

The process of removing ice or frost buildup from the outdoor coil during the heating season.

The reduction of water vapor in air by cooling the air below the dew point; removal of water vapor from air by chemical means, refrigeration, etc.

A pipe or closed conduit made of sheet metal, fiberglass board, or other suitable material used for conducting air to and from an air handling unit. Hollow pipes or channels that carry/transfer air from the Air Handler to the air vents throughout your home. The delivery system through which warm air from the furnace is brought to where it's needed. Ductwork is made of sheet metal, fiberglass, or flexible plastic, and can be round or rectangular in shape. Ductwork is one of the most important components of a home heating and cooling system.

The backup electric heat built into a heat pump system. The same as an auxiliary heater, except it is used exclusively as the heat source when the heat pump needs repair.

[Also see Indoor Coil] The evaporator coil is located inside your house in a split system in the air handler, or above the gas furnace. This will produce cooling in the air conditioning mode and heating in a Heat Pump mode. This coil section in the evaporator is where refrigerant evaporates and absorbs heat from air passed over the coil. This is also very important in removing humidity from your home.

A device for removing dust particles from air or unwanted elements from liquids.

Usually installed in a single, continuous piece between the register and plenum box, a flexible duct usually has an inner lining and an insulated coating on the outside.

That part of an environmental system which converts gas, oil, electricity or other fuel into heat for distribution within a structure.

This is a device that enables furnaces to transfer heat from combustion safely into breathable air. The primary heat exchanger transfers heat from combustion gases to the air blowing through the ductwork. It's vital that none of the combustion gas itself gets into the airstream. The primary heat exchanger handles the hottest gases. This device transfers heat from outgoing stale air to incoming cold air. In warm climates, this process can be reversed. In high efficiency furnaces, secondary heat exchangers recover heat that used to be vented up the chimney with the exhaust gases. By recovering this heat, the furnace becomes more efficient. Part of the heat recovered here causes the water and acid to condense out of the exhaust gas. Because this liquid is corrosive, secondary heat exchangers must be designed to prevent deterioration. Usually this means they are made of stainless steel or some derivative of it.

A heating and air conditioning unit that heats or cools by moving heat. A Heat Pump is a reverse cycle air conditioner. The Heat Pump uses a compression cycle system to supply heat or remove heat remove a temperature-controlled space. An air-conditioning unit which is capable of heating by refrigeration, transferring heat from one (often cooler) medium to another (often warmer) medium, and which may or may not include a capability for cooling. This reverse-cycle air conditioner usually provides cooling in summer and heating in winter. When you run your air conditioner, your outdoor unit will be blowing hot air, (in other words, removing the heat from your home and sending it outside). When you run your heat pump, you reverse the flow of refrigerant and remove the heat from the atmosphere outside and blow it inside. When the temperature dips below 40 degrees outside, the Heat Pump labors in producing heat so they install a backup or auxiliary electric heat strip to supplement the Heat Pump. Electric Heat strips are very expensive to operate. In southern climates where it rarely dips below 40 degrees the heat pump is very efficient. A 3 to 1 savings in heating compared to electric heat strips.

In the cooling cycle of a Heat Pump, you are removing hot air from inside the house and sending it outside. You can feel the hot air outside, over the condenser fan motor.

In the heating mode of a Heat Pump the refrigerant cycle is reversed and you are now removing the heat from the outside and sending it inside the house. You can feel the cool air outside, over the condenser fan motor. When temperatures go below 40 degrees Heat Pumps labor in producing heat and must use back up electric heat strips. Heat strips cost 3 times as much to operate as a Heat Pump when producing heat.

A device that adds moisture to warm air being circulated or directed into a space. This adds necessary moisture to protect your furnishings and reduce static electricity.

Refers to the systems and technologies used to regulate environmental comfort in settings such as homes, offices, and vehicles.

Particles and dust, fibers, mists, bioaerosols, and gases or vapors.

Air movement into an enclosed space through cracks and openings. Unintentional movement of outdoor air into a house. Air flow inward into a space through walls, leaks around doors and windows or through the building materials used in the structure. It results from the forces of wind, temperature difference, and HVAC operation.

The cooling load caused by moisture in the air. The net amount of moisture added to the inside air by plants, people, cooking, infiltration, and any other moisture source. The amount of moisture in the air can be calculated from a combination of drybulb and wet-bulb temperature measurements.

A self-contained unit or system that has the Air Handler & Condenser in same unit. Normally placed outside the home and connected to a duct system by a penetration through the homes foundation. Except for geothermal which is a self-contained indoor unit that is place in a closet, attached garage, basement, or mechanical room.

A program of building maintenance implemented to reduce the possibility of problems, usually through periodic inspection, cleaning, adjustment, calibration, and replacement of functioning, parts of the HVAC system, as well as housekeeping practices to reduce the buildup of potential contaminants. Primarily done on a building's mechanical systems, this involves a regular and systematic inspection, cleaning, and replacement of worn parts, materials, and systems. Preventive maintenance helps to prevent parts, material, and systems failure by ensuring that parts, materials and systems are in good working order.

A measure, in BTU/ (ft2 F), of the resistance to transmission of heat by an insulating material. The higher the R-value of a material, the greater is its insulating properties and the slower the heat flow through it. The specific value needed to insulate a home depends on climate, type of heating system and other factors.

Substance used in refrigerating mechanism. A substance that produces a refrigerating effect while expanding or vaporizing. Air conditioning systems use Refrigerant in the Evaporator Coil to cool air as it passes by. Refrigerants absorb heat in evaporator by change of state from a liquid to a gas and releases its heat in a condenser as the substance returns from the gaseous state back to a liquid state.

The amount of refrigerant contained within the air conditioning equipment and required for proper operation.

Air drawn into a heating unit after having been circulated from the heater's output supply to a room. The air removed from an occupied space and returned to the air handler to be exhausted or recirculated.

An efficiency measurement that is similar to Miles Per Gallon for cars. The higher this number, the more energy efficient they system is. The amount of cooling your equipment delivers per every dollar spent on electricity. The higher the number the lower the operating cost (not more cooling.) SEER applies to air conditioners and heat pumps. In the past, a unit with a SEER of 8.00 was considered standard efficiency, and a unit with a 10.00 SEER was considered high efficiency. After January 1, 1992, the minimum SEER required by the DOE is 10.00 and 15.00+ SEER is considered high efficiency. EER & SEER cannot be compared equally. Air source equipment is rated by SEER and geothermal equipment is rated by EER. New units have SEER ratings from 10 to 17 BTUs per watt. The total cooling of a central unitary air conditioner or unitary heat pump in Btu's during its normal annual usage period for cooling divided by the total electric energy input in watt-hours during the same period. The Seasonal Energy Efficiency Ratio is a standard method of rating air conditioners based on three tests. All three tests are run at 80 degrees Fahrenheit inside and 82 degrees Fahrenheit outside. The first test is run with humid indoor conditions, the second with dry indoor conditions, and the third with dry conditions cycling the air conditioner on for 6 minutes and off for 24 minutes. The published SEER may not represent the actual seasonal energy efficiency of an air conditioner in your climate. The total cooling output of a central air conditioning unit in BTUS during its normal usage period for cooling divided by the total electrical energy input in watt-hours during the same period, as determined using specified federal test procedures. [Title 20, Section 2-1602(c)(11)].

The heat gain of the home due to conduction, solar radiation, infiltration, appliances, people, and pets. Burning a light bulb, for example, adds only sensible load to the house. This sensible load raises the dry-bulb temperature.

A system in which living areas or groups of rooms are divided into separate spaces and each space's heating/air conditioning is controlled independently. This can be accomplished by using either multiple independent systems, or a single system using electronic controls and motorized dampers (see Damper). For example, you might prefer to have the kitchen area of your home be slightly cool, while at the same time keeping the temperature in the bedrooms warmer.