HVAC Glossary

Understanding HVAC terminology is essential for homeowners making informed decisions about heating and cooling systems. This comprehensive glossary explains common HVAC terms, acronyms, and concepts used in the industry.

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Efficiency Ratings

Measurements of system energy performance.

AFUE (Annual Fuel Utilization Efficiency)

Percentage of fuel converted to heat by a furnace over a heating season. Higher percentages indicate more efficient operation.

SEER (Seasonal Energy Efficiency Ratio)

Measure of air conditioner or heat pump cooling efficiency. Higher SEER ratings indicate lower operating costs.

HSPF (Heating Seasonal Performance Factor)

Measure of heat pump heating efficiency. Higher HSPF ratings indicate better performance in cold weather.

EER (Energy Efficiency Ratio)

Ratio of cooling capacity to electrical input at specific conditions. Used for peak efficiency comparisons.

System Components

Key parts of HVAC systems.

Air Handler

Indoor unit containing blower, coils, and controls. Circulates conditioned air through ductwork.

Blower Motor

Electric motor that moves air through the system. Available in single-speed, multi-speed, and variable-speed types.

Condenser

Outdoor unit where refrigerant releases heat. Contains compressor, condenser coil, and fan.

Compressor

Heart of the refrigeration system. Compresses refrigerant vapor to increase pressure and temperature.

Evaporator Coil

Indoor coil where refrigerant absorbs heat from indoor air. Allows refrigerant to evaporate at low pressure.

Heat Exchanger

Component that transfers heat between two fluids without mixing. Critical safety component in furnaces.

Air Quality Terms

Measurements and concepts related to indoor air quality.

CFM (Cubic Feet per Minute)

Measure of airflow volume. Indicates how much air a system moves in one minute.

MERV (Minimum Efficiency Reporting Value)

Rating system for air filter efficiency. Higher MERV ratings indicate better filtration of smaller particles.

HEPA (High-Efficiency Particulate Air)

Filter standard that removes 99.97% of particles 0.3 microns and larger. Used in medical and clean room applications.

VOC (Volatile Organic Compounds)

Chemicals that evaporate at room temperature. Common sources include paints, cleaners, and building materials.

Refrigeration Cycle

The process by which refrigeration systems cool air.

Refrigerant

Specialized chemical that changes from liquid to gas and back. Carries heat from indoor to outdoor environments.

Superheat

Temperature of refrigerant vapor above its boiling point. Measured at compressor inlet to verify proper charge.

Subcooling

Temperature of refrigerant liquid below its condensing point. Measured at condenser outlet to verify charge.

Reversing Valve

Valve in heat pumps that reverses refrigerant flow direction. Allows system to switch between heating and cooling.

Ductwork Terminology

Terms related to air distribution systems.

Return Air

Air drawn back into the HVAC system for conditioning. Usually from living spaces.

Supply Air

Conditioned air delivered to living spaces through supply vents.

Duct Damper

Adjustable plate in ductwork that controls airflow to specific areas. Used for zoning and balancing.

Plenum

Large box-like chamber connected to ductwork. Distributes air from air handler to branch ducts.

Control Systems

Components that regulate system operation.

Thermostat

Device that senses room temperature and signals HVAC system to maintain desired conditions.

Contactor

Electrically controlled switch that connects power to compressor and condenser fan motor.

Capacitor

Electrical component that provides starting torque for motors. Available as run or start capacitors.

Pressure Switch

Safety device that monitors system pressure. Shuts down system if pressure falls outside safe range.

Maintenance Terms

Common maintenance and service terminology.

Tune-up

Comprehensive system inspection and adjustment. Includes cleaning, testing, and minor repairs.

Load Calculation

Mathematical determination of heating and cooling requirements. Uses Manual J methodology.

Air Balancing

Process of adjusting dampers to ensure even air distribution throughout the home.

Refrigerant Charge

Correct amount of refrigerant in the system. Too much or too little affects performance.

Fuel Types

Different energy sources for heating systems.

Natural Gas

Clean-burning fossil fuel delivered through pipelines. Most common fuel for residential furnaces.

Propane (LP)

Liquid petroleum gas stored in tanks. Used in areas without natural gas service.

Fuel Oil

Heating oil burned in oil furnaces. Requires storage tank and regular delivery.

Electricity

Direct electric resistance heating or used to power heat pumps and air conditioners.

System Types

Different categories of HVAC equipment.

Split System

HVAC system with separate indoor and outdoor units connected by refrigerant lines.

Packaged System

Self-contained unit with all components in one cabinet. Can be installed outdoors or on roof.

Ductless System

Mini-split system without ductwork. Individual indoor units connect to outdoor compressor.

Zoned System

System divided into separate comfort zones with individual temperature control.

Installation Terms

Terms related to system installation and modification.

Manual J

Industry standard method for calculating heating and cooling loads. Considers building characteristics.

Manual D

Standard for residential ductwork design. Ensures proper airflow and system efficiency.

Manual S

Standard for selecting proper equipment size based on load calculations.

Line Set

Copper tubing and wiring connecting indoor and outdoor units in split systems.

Safety Terms

Important safety-related terminology.

Carbon Monoxide

Colorless, odorless gas produced by incomplete combustion. Deadly in high concentrations.

High Limit Switch

Safety device that shuts down system if temperature exceeds safe limits.

Flame Rollout Switch

Safety device that detects flame escaping from burner area. Indicates blocked heat exchanger.

Ground Fault Circuit Interrupter (GFCI)

Electrical safety device that protects against shock by detecting ground faults.

Environmental Terms

Concepts related to environmental impact and regulations.

Ozone Depletion

Destruction of stratospheric ozone layer by certain refrigerants. Led to phase-out of R-22.

Global Warming Potential (GWP)

Measure of refrigerant contribution to climate change. Lower GWP preferred for environmental reasons.

Energy Star

US EPA program certifying energy-efficient products. Higher standards than federal minimums.

Performance Terms

Measurements of system operation and capacity.

BTU (British Thermal Unit)

Measure of heat energy. One BTU raises one pound of water one degree Fahrenheit.

Ton

Measure of cooling capacity. One ton equals 12,000 BTU per hour of cooling.

Static Pressure

Resistance to airflow in duct system. Measured in inches of water column.

Delta T

Temperature difference between supply and return air. Indicates system performance.