# HVAC terms homeowners should know

Summary: Decode common heating and air-conditioning words before you compare an estimate or agree to a replacement scope.  
Publisher: HomeFAQ  
Published: 2026-09-29  
Canonical: https://homefaq.com/hvac/hvac-terms-homeowners-should-know/  
Tags: HVAC terms, furnace, air conditioner

HVAC means heating, ventilation, and air conditioning. You do not need to master the terminology to ask for a clear scope, but these words help you compare whether two proposals describe the same system and work.

## Common estimate terms

**Furnace:** Equipment that heats air and sends it through ducts. It is different from an air conditioner, even when both share the same ductwork.

**Air conditioner:** Equipment that removes heat from indoor air and releases it outside. It provides cooling, not heat.

**Heat pump:** Equipment that can provide cooling and heating by moving heat. It may use backup heat in some designs or conditions.

**Condenser:** The outdoor portion of a typical air conditioner or heat pump. Replacing it alone may not be a complete system solution.

**Air handler or indoor coil:** Indoor equipment that moves air and exchanges heat. Its compatibility with outdoor equipment matters.

**Ductwork:** The passages that deliver conditioned air. New equipment cannot by itself correct every airflow or comfort issue caused by ducts.

**Thermostat and controls:** The devices that tell the system when and how to operate. A proposed replacement should say whether controls are included and compatible.

**Capacity or sizing:** The amount of heating or cooling a system is designed to provide. A contractor should explain how they selected it for your home rather than relying only on the old equipment size.

**Refrigerant:** The fluid that carries heat in an air conditioner or heat pump. It is handled by qualified technicians.

**Commissioning:** Startup checks used to confirm the installed system operates as intended. Ask what will be tested and documented.

## Use the terms to compare scope

Ask whether a proposal includes indoor and outdoor equipment, ducts, electrical work, drainage, controls, permits, startup testing, and removal of old equipment. Then use [How to compare furnace and air conditioner replacement estimates](https://homefaq.com/hvac/how-to-compare-hvac-replacement-estimates/).

## Sources

- [U.S. Department of Energy: Heating and Cooling](https://www.energy.gov/energysaver/heating-and-cooling)