HVAC Glossary

Furnace

A heating appliance that warms air using natural gas, propane, oil, or electricity and distributes it through your home's ductwork.

Heat Pump

An energy-efficient HVAC system that transfers heat between indoors and outdoors to both heat and cool your home using electricity.

Heat Exchanger

The metal component inside your furnace that transfers heat from combustion gases to the air flowing through your home.

Boiler

A heating system that uses hot water or steam distributed through pipes and radiators to heat your home.

Radiant Heating

A heating method that delivers warmth directly through floors, walls, or ceilings using hot water tubes or electric elements.

Thermostat

The control device that monitors your home's temperature and tells your HVAC system when to turn on and off.

Smart Thermostat

A Wi-Fi connected thermostat that learns your schedule, adjusts temperatures automatically, and can be controlled remotely.

Pilot Light

A small, continuously burning flame in older gas furnaces that ignites the main burner when the thermostat calls for heat.

Ductless Heat Pump

A heat pump that provides heating and cooling without ductwork, using a wall-mounted indoor unit connected to an outdoor compressor.

Hydronic Heating

A heating system that uses hot water circulated through pipes to deliver heat via radiators, baseboard heaters, or radiant floor systems.

Air Conditioner

A cooling system that removes heat and humidity from indoor air and transfers it outside, keeping your home comfortable.

Condenser

The outdoor unit of your AC or heat pump system that releases absorbed heat from your home into the outside air.

Evaporator Coil

The indoor coil where refrigerant absorbs heat from your home's air, cooling it before it's distributed through ductwork.

Compressor

The pump in your outdoor unit that pressurizes refrigerant and circulates it between indoor and outdoor components.

Refrigerant

The chemical compound that circulates through your AC or heat pump, absorbing and releasing heat to cool or heat your home.

Mini-Split

A ductless system with an outdoor compressor connected to wall-mounted indoor units, providing zone-specific comfort.

Tonnage

The unit of measurement for AC cooling capacity, where one ton equals the ability to remove 12,000 BTUs of heat per hour.

R-410A

The standard refrigerant in modern residential AC and heat pump systems, replacing the older ozone-depleting R-22.

Air Filter

A replaceable screen that traps dust, allergens, and debris to protect your equipment and improve indoor air quality.

MERV Rating

A scale from 1 to 20 that rates how effectively an air filter captures airborne particles.

Indoor Air Quality (IAQ)

The overall quality of air inside your home, including pollutants, allergens, humidity, and ventilation levels.

Humidity

The amount of moisture in the air, which directly affects your comfort, health, and HVAC system performance.

HEPA Filter

A specialized filter that captures 99.97% of particles as small as 0.3 microns, including allergens and bacteria.

Carbon Monoxide (CO)

A colorless, odorless, toxic gas produced by incomplete combustion that can be lethal in enclosed spaces.

UV Light (Gemicidal)

An ultraviolet light installed in your HVAC system that kills mold, bacteria, and viruses as air passes through.

Ventilation

The process of exchanging stale indoor air with fresh outdoor air to maintain healthy oxygen levels and control moisture.

Dehumidifier

A device that removes excess moisture from indoor air, working alongside your HVAC system to prevent mold growth.

SEER Rating

Seasonal Energy Efficiency Ratio — a measure of your AC or heat pump's cooling efficiency over an entire season.

AFUE

Annual Fuel Utilization Efficiency — the percentage of fuel your furnace converts into usable heat.

HSPF

Heating Seasonal Performance Factor — a measure of your heat pump's heating efficiency over the entire heating season.

Energy Efficiency

Using less energy to achieve the same level of comfort through equipment, installation, insulation, and system management.

Energy Star

A government-backed certification identifying HVAC equipment meeting strict energy efficiency guidelines.

BTU

British Thermal Unit — the standard measurement of heat energy, used to rate heating and cooling capacity.

Manual J Load Calculation

The industry-standard engineering calculation that determines exactly how much heating and cooling your home needs.

Energy Trust of Oregon

An independent nonprofit that helps Oregon utility customers save energy through cash incentives and rebates.

Air Sealing

Finding and closing gaps in your home's exterior that allow outside air to leak in and conditioned air to leak out.

Insulation

Material installed in walls, attic, and floors that slows heat transfer, keeping your home comfortable year-round.

Ductwork

The network of tubes that carry heated or cooled air from your HVAC system throughout your home.

Air Handler

The indoor unit housing the blower fan, evaporator coil, and air filter for circulating conditioned air.

Blower Motor

The electric motor that drives the fan pushing conditioned air through your home's ductwork.

Capacitor

An electrical component that stores and releases energy to start your compressor and fan motors.

Contactor

An electrically controlled switch that connects power to the compressor and fan motor when cooling is needed.

Expansion Valve (TXV)

A precision device controlling the flow of liquid refrigerant into the evaportor coil based on cooling demand.

Ignitor

The component in modern gas furnaces that electrically heats up to ignite the gas burner.

Gas Valve

The safety device controlling natural gas flow to your furnace burner, opening only when conditions are safe.

Return Air

The air drawn back from your rooms through return vents to be filtered, reconditioned, and recirculated.

Static Pressure

The resistance to airflow within your HVAC ductwork — similar to blood pressure for your air distribution system.

Condensate Drain

The pipe that carries water away from your AC — water that forms when moisture condenses on the cold evaporator coil.

Pressure Switch

A safety device verifying the exhaust vent is clear before allowing the gas valve to open in your furnace.

ECM Motor

An energy-efficient variable-speed blower motor that adjusts speed to match your home's airflow needs.

Draft Inducer

A motor and fan that pulls combustion gases through the heat exchanger and up the flue for safe venting.

HVAC

Heating, Ventilation, and Air Conditioning — the complete system controlling your indoor temperature, air quality, and humidity.

Zoning System

A setup dividing your home into separate temperature zones, each with its own thermostat for customized comfort.

Short Cycling

When your system turns on and off too frequently in short bursts, wasting energy and causing excessive wear.

Load Calculation

The engineering process of determining exactly how much heating and cooling capacity your specific home requires.

Preventive Maintenance

Regular scheduled service designed to keep your system running efficiently and catch small problems early.

Refrigerant Charge

The precise amount of refrigerant in your system — too much or too little reduces efficiency and can cause damage.

Superheat

A critical diagnostic measurement indicating how much refrigerant temperature rises above its boiling point.

Subcooling

A diagnostic measurement showing how much liquid refrigerant cools below its condensing temperature in the outdoor unit.

Combustion Analysis

A diagnostic test measuring the efficiency and safety of your gas furnace by analyzing exhaust gas composition.

Refrigerant Leak

An unintended escape of refrigerant through cracks, corrosion, or failed connections — simply adding more isn't the fix.

Two-Stage System

A furnace or AC that operates at two capacity levels for better comfort and efficiency on most days.

Variable Speed System

The most advanced HVAC equipment that continuously adjusts output for the most precise temperature control.

Warranty

The manufacturer's and contractor's guarantees covering parts, labor, and workmanship on your HVAC system — with specific conditions that must be met to remain valid.