2,400+ Definitions
HVAC GLOSSARY
Every HVAC term, acronym, and industry phrase — defined in plain English.
Orifice
An orifice is a precisely sized opening or aperture within…
OSHA Refrigerant Safety
OSHA Refrigerant Safety regulations establish workplace protection standards for technicians…
Outdoor Air Fraction
The proportion of the total supply airflow delivered to a…
Outdoor Reset Control
A control strategy that automatically adjusts the boiler or system…
Outdoor Unit Piping Header
The manifold assembly on a multi-port VRF outdoor unit where…
Outlet Velocity Profile
The spatial distribution of air velocity across the face of…
Outside Air Damper
An outside air damper is a motorized or gravity-operated device…
Overall U-Factor
The area-weighted average thermal transmittance of an entire fenestration unit…
Overcharge
An overcharge occurs when excess refrigerant is added to a…
Oxy-Acetylene Torch
A high-temperature cutting and welding torch that burns a mixture…
Oxygen Barrier Tubing
PEX or other flexible tubing with an added layer, typically…
Ozone Generator
Ozone generators produce ozone gas (O₃) that oxidizes odors, VOCs,…
P H Diagram
The P-H diagram is a graphical representation of thermodynamic properties…
PACE Financing
PACE (Property Assessed Clean Energy) financing allows property owners to…
Package Unit
A package unit is a self-contained HVAC system in which…
Packaged Heat Pump
A packaged heat pump is a self-contained HVAC system that…
Packaged Rooftop Unit
A Packaged Rooftop Unit (RTU) is a self-contained HVAC system…
Packaged Unit
A packaged unit (also called a packaged system or rooftop…
Packaged Unit Installation
Packaged unit installation involves mounting a single heating and cooling…
Panel Filter
Panel filters are flat, rectangular air filters constructed from woven…
Panel Radiator
A factory-assembled steel heating panel consisting of one or more…
Parabolic Trough
A parabolic trough is a concentrating solar collector with a…
Parallel Fan Powered Box
A parallel fan powered box is a type of variable…
Parallel Rack
A parallel rack is a refrigeration system configuration where multiple…
Parking Garage Ventilation
Parking garage ventilation systems remove vehicle exhaust, carbon monoxide, and…
Part Load Value
Part Load Value (PLV) is a single-number efficiency metric that…
Part-Load COP
The coefficient of performance measured at less than full rated…
Particulate Matter
Particulate matter (PM) consists of tiny solid particles and liquid…
Particulate Monitor
A particulate monitor measures airborne dust and fine particle concentrations,…
Pascal
A pascal (Pa) is the metric unit of pressure measurement…
Passive Chilled Beam
A passive chilled beam is a ceiling-mounted or ceiling-suspended heat…
Passive Cooling
Passive cooling uses natural ventilation, shading, thermal mass, and evaporative…
Passive Design
Passive design uses building orientation, envelope properties, and thermal mass…
Passive Heating
Passive heating captures and retains solar energy and internal heat…
Passive House Standard
The Passive House Standard is a rigorous, voluntary building energy…
Passive House Ventilation Standard
A rigorous energy-efficiency building standard that mandates mechanical balanced ventilation…
Passive Solar System
A passive solar system operates without mechanical pumps or electrical…
PCM Wallboard
PCM Wallboard is a building material embedded with phase-change materials…
Peak Demand
Peak demand refers to the highest amount of electrical power…
Peak Demand Charge
A peak demand charge is a utility billing component that…
Peak Sun Hours
Peak sun hours are the equivalent number of hours per…
Peak Watt
A peak watt (Wp) is the unit of measurement for…
Peltier Effect
The Peltier effect is a thermoelectric phenomenon where direct electrical…
Performance Rating Method
The Performance Rating Method is the primary energy compliance approach…
Performance Testing
Performance testing measures an HVAC system’s ability to meet design…
Perimeter Heating
Perimeter heating is a heating strategy that places heat sources…
Permanent Split Capacitor Motor
A single-phase induction motor that uses a run capacitor in…
PEX Pipe
PEX (cross-linked polyethylene) pipe is a flexible plastic tubing used…