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Glossary of HVAC Terms I-P

HVAC Glossary

Indoor/Outdoor System
Refers to a comfort system consisting of components in two locations. Common examples include an outside unit, such as an air conditioner, and an indoor unit, such as a furnace with a coil.

Indoor Coil
The other, less visible half of your outdoor unit. It’s attached to your furnace or air handler. As indoor air flows across it, heat and moisture are drawn out, leaving air that is cool, comfortable and conditioned.

Load Calculation
A measure to determine heat gain and loss within a structure so that properly sized HVAC equipment can be installed.


  1. Components made of multiple smaller blades, sometimes adjustable, placed in ducts or duct entries to control the volume of air flow. When used inside of ducts, their function is similar to that of a damper, but they can be manufactured to fit larger openings than a single-piece damper.
  2. Blades in a rectangular frame placed in doors or walls to permit the movement of air.

Matched System
A heating and cooling system wherein all components are matched in capacity and efficiency. This enables your system to perform at its best, and most efficient, for longer.

Allergens like dust, smoke and bacteria are particulates that are often .3 microns or less. At that size, they can get deep into your lungs, because they aren’t filtered well by your nose and throat.

NATE Certified
NATE (North American Technician Excellence) is an independent organization that certifies installation or service technicians with a knowledge-based test.

Oil Furnace
An oil furnace is the heating component in some systems in colder climates, most commonly in the northeastern United States, that converts oil to heat.

Outside air damper
An automatic louver or damper that controls the fresh air flow into an air handler and modulates to the most energy efficient setting.

Outside air temperature
A measure of the air temperature outside a building. The temperature and humidity of air inside and outside the building are used in enthalpy calculations to determine when outside air can be used for free heating or cooling. Abbreviated OAT.

Outdoor Coil
Located in the outdoor unit, the coil dissipates heat from the refrigerant, changing the refrigerant from vapor to liquid. In American Standard units, the coil is called Spine Fin™.

Outdoor Unit
The outdoor portion of a split system, such as an air conditioner or heat pump. May also be a packaged air conditioning and/or heating system in which all components are located in one cabinet.

Packaged System
An air conditioning and/or heating system in which all components are located in one cabinet. Used in certain localities and for certain building types, the all-in-one system is installed either beside or on top of your home.

“Particulates” is a label used for particles that are really, really small. Some particulates are visible to the naked eye, but most are only visible through a microscope: mold spores, skin flakes, bacteria, household dust, pet dander, tobacco smoke, cooking smoke.

Payback Analysis
A measure of the value of your system that determines the number of months required before monthly energy cost savings offset the purchase price.

Pleated Filter
Pleated filters are part of your indoor air quality system. They filter dirt, pollutants and other particles, leaving you with cleaner air.

Having an issue with your HVAC? Contact the experts at Millian-Aire who don’t need this glossary!

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