NATE Heat Pump Install key terms

A ratio of heating or cooling output to electrical energy input, expressed in the same units. Higher values indicate greater efficiency; used to compare heat pump performance at a given operating condition.

A measure of a heat pump's seasonal heating efficiency, calculated as total heating output in Btu divided by total electrical energy input in watt-hours over a defined season. Higher is better.

The outdoor temperature at which a heat pump's heating capacity equals the building's heat loss. Below this point, supplemental heating is needed to maintain indoor temperature.

Supplemental heating, often electric resistance, that activates when the heat pump cannot meet the load, such as below the balance point or during defrost. Also called emergency or backup heat.

The repeating process in which refrigerant absorbs heat at low pressure and releases it at high pressure through evaporation, compression, condensation, and expansion, moving heat between indoor and outdoor spaces.

The pump that raises refrigerant pressure and temperature, driving the refrigerant cycle. Common types include reciprocating, scroll, and rotary; it is the primary energy consumer in the system.

A metering device that reduces refrigerant pressure and regulates flow into the evaporator, controlling superheat. Types include thermostatic (TXV), electronic (EEV), and fixed orifice.

The temperature of refrigerant vapor above its saturation temperature at a given pressure. Measured at the evaporator outlet, it verifies proper expansion valve operation and protects the compressor from liquid slugging.

The temperature of liquid refrigerant below its saturation temperature at a given pressure. Measured at the condenser outlet, it indicates charge level and ensures solid liquid reaches the expansion valve.

A four-way valve that changes refrigerant flow direction, switching the system between heating and cooling modes by swapping the roles of indoor and outdoor coils.

An industry-standard method for sizing heating and cooling equipment by calculating room-by-room heat loss and gain based on construction, insulation, windows, infiltration, and local design conditions.

The outdoor winter and summer temperatures used for sizing HVAC equipment, typically the 99% winter and 1% summer design conditions for the location. These values drive load calculations.

A pre-installation inspection of the building and site to verify dimensions, access, structural support, electrical capacity, clearances, and routing for refrigerant lines, drains, and ductwork.

The pair of copper tubes connecting indoor and outdoor units, carrying liquid and suction refrigerant. Sizing, insulation, and routing affect system performance and must follow manufacturer specifications.

The process of removing air and moisture from refrigerant lines using a vacuum pump, measured with a micron gauge. Proper evacuation prevents non-condensables and moisture from damaging the system.

An instrument that measures very low absolute pressure during evacuation. A reading of 500 microns or below, holding steady, indicates a dry, leak-free system ready for charging.

Displacing air in refrigerant piping with dry nitrogen during brazing to prevent oxidation and scale formation inside the tubing. Also used for pressure testing for leaks.

A joining process for copper refrigerant lines using filler metal melted at high temperature, typically with a torch. Proper heat control and nitrogen flow prevent leaks and internal contamination.

The amount of refrigerant in a system. It may be factory-charged, weighed in, or adjusted based on superheat or subcooling measurements to match the system's requirements.

The resistance to airflow in a duct system, measured in inches of water column. High static pressure reduces airflow and efficiency; it must be checked against the equipment's rated capacity.

The volume of air moved by the blower, typically measured in cubic feet per minute (CFM). Correct airflow is essential for capacity, efficiency, and reliable heat pump operation.

Selecting duct dimensions to deliver required airflow within acceptable friction loss and velocity, using methods such as equal friction or static regain. Proper sizing minimizes noise and energy use.

A timed or demand-initiated sequence in heating mode that temporarily reverses refrigerant flow or stops the outdoor fan to melt frost from the outdoor coil, then returns to normal heating.

The minimum distance required between the outdoor unit and walls, obstructions, or other units to ensure adequate airflow and service access, as specified by the manufacturer and local codes.

The location and orientation of the condensing unit, considering clearances, sun exposure, prevailing winds, snow and flood levels, noise, and structural support to optimize performance and durability.

The systematic process of verifying that a newly installed system operates safely, efficiently, and according to design intent, including checks of airflow, charge, controls, and electrical values.

The initial activation of a newly installed heat pump, including electrical checks, system evacuation verification, charging, and operational testing before handover to the owner.

Measuring and documenting system operating parameters such as temperature split, superheat, subcooling, static pressure, and amperage to confirm the installation meets specifications.

The difference between return air and supply air temperatures across the indoor coil. It indicates system capacity and airflow; abnormal splits signal charge, airflow, or mechanical issues.

A control state that prevents compressor or auxiliary heat operation under unsafe conditions, such as low outdoor temperature or high discharge pressure, protecting the equipment from damage.

A control device that senses indoor temperature and signals the heat pump to heat, cool, or provide auxiliary heat. Proper configuration and wiring are critical for efficient operation.

The low-voltage control circuit (typically 24V) connecting the thermostat, indoor unit, and outdoor unit. Correct color coding and terminal identification ensure proper communication and operation.

A manually operable switch or breaker installed near the outdoor unit to isolate electrical power for service. Required by code and must be rated for the circuit's voltage and amperage.

Practices that prevent shock, arc flash, and fire, including lockout/tagout, proper grounding, circuit protection, and verifying power is off before servicing equipment.

The process of removing refrigerant from a system into a recovery cylinder for reuse, recycling, or disposal. Required by EPA regulations before opening a refrigerant circuit.

The federal regulation governing refrigerant handling, including certification requirements, leak repair, recovery, and safe disposal. Technicians must be certified to purchase and handle regulated refrigerants.