Reference
HVAC glossary
Plain-language definitions for the heating and cooling terms you'll see on estimates and equipment spec sheets — so you can compare options with confidence.
How to use this glossary
Use these definitions to decode estimates, compare equipment, and understand what actually matters for your home before you book. Each term links to related Learning Center guides and the services they apply to.
A–Z
Every term, defined
17 heating and cooling terms in plain English.
- Heating AFUE How efficiently a furnace turns fuel into heat, as a percentage. Define →
- Heating Boiler A system that heats water for radiators or in-floor heat. Define →
- General BTU The basic unit of heating and cooling capacity. Define →
- Cooling Ductless mini-split A heat pump that heats and cools without ductwork. Define →
- Cooling Evaporator & condenser coils The two coils where an AC or heat pump moves heat. Define →
- Heating Furnace A central heater that warms and blows air through ducts. Define →
- Heating Heat exchanger The furnace part that separates combustion gases from your air. Define →
- Heating Heat pump Equipment that moves heat to both heat and cool your home. Define →
- Heating HSPF2 The seasonal heating-efficiency rating for a heat pump. Define →
- General Manual J load calculation The industry method for sizing equipment to your home. Define →
- Air Quality MERV rating How much an air filter captures — higher catches more. Define →
- Cooling Refrigerant The fluid that carries heat through an AC or heat pump. Define →
- Cooling SEER2 The seasonal efficiency rating for air conditioners and cooling. Define →
- General Short cycling When a system turns on and off in rapid, short bursts. Define →
- General Smart thermostat A programmable, connected control for your HVAC system. Define →
- Cooling Tonnage Air conditioner / heat pump capacity, measured in tons. Define →
- Efficiency Variable-speed / two-stage Equipment that adjusts output instead of just on/off. Define →