2,400+ Definitions

HVAC GLOSSARY

Every HVAC term, acronym, and industry phrase — defined in plain English.

All A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

MERV 16 (Minimum Efficiency Reporting Value 16) is a high-efficiency…

MERV 8 (Minimum Efficiency Reporting Value) is a standard air…

MERV (Minimum Efficiency Reporting Value) is the standard rating system…

Metabolic rate is the rate at which the human body…

Metering Device

A metering device is a flow-restricting component in a refrigeration…

Microbubble Reabsorber

A high-efficiency air removal device that uses a coalescing medium…

Microgrid Controller

A microgrid controller is specialized software and hardware that manages…

Microgrids are localized electrical systems that can operate independently or…

A microinverter is a small inverter installed directly on or…

A micron gauge is a precision vacuum measurement instrument used…

A micron reading measures absolute pressure in a refrigeration system…

Mineral wool is a fibrous insulation material manufactured from molten…

A mini-split (also called a ductless mini-split or ductless heat…

Mini Split Installation

Mini split installation is the complete process of placing a…

Minimum Activation Flow

Minimum activation flow is the minimum water volume, typically 0.5-0.6…

Minimum Pipe Velocity

The lowest refrigerant gas velocity in a suction or discharge…

Minor losses are pressure drops occurring at fittings, valves, bends,…

Mixed Mode Ventilation

Mixed Mode Ventilation integrates natural and mechanical ventilation within the…

Mixed-Mode Ventilation

A ventilation strategy that combines mechanical systems with operable windows…

A mixing damper is an HVAC component consisting of multiple…

The ratio of the mass of water vapor to the…

A mixing valve combines hot boiler water with cooler return…

Mixing Valve Controls

Mixing valve controls regulate the temperature of water or air…

Modbus is an open industrial communication protocol that allows HVAC…

Modbus Interface

A serial communication gateway that allows VRF system controllers to…

A serial communication protocol widely used in HVAC and building…

Modern Air Conditioning History

Modern air conditioning history spans from Willis Carrier’s 1902 invention…

Modular Chiller

A modular chiller is a cooling system composed of multiple…

Modulating Boiler

A modulating boiler automatically adjusts its firing rate between 20…

Modulating Burner

A burner capable of continuously varying its firing rate between…

Modulating Control

A control approach in which an actuator or device is…

Modulating Furnace

A modulating furnace is a type of gas furnace that…

Moist Air Enthalpy

The total heat content of moist air per pound of…

Moisture Burnout

Moisture burnout occurs when water vapor inside the refrigeration system…

Moisture Indicator

A sight glass element or inline device containing a hygroscopic…

Moisture Infiltration Load

The latent heat added to a conditioned space by water…

Mold is a type of fungus that grows in damp…

Mold Assessment

Mold assessment is a comprehensive visual and environmental evaluation of…

Mold Remediation

Mold remediation involves the complete removal of mold contamination from…

Mold testing involves laboratory analysis of environmental samples to identify…

Mollier Diagram

The Mollier diagram is a thermodynamic chart plotting enthalpy against…

Monitoring Based Commissioning

Monitoring Based Commissioning (MBCx) uses continuous sensor data and performance…

Monocrystalline Solar Panel

A monocrystalline solar panel is made from single-crystal silicon, offering…

A special fitting used in series-loop hydronic systems that creates…

Montreal Protocol

The Montreal Protocol, signed in 1987, is an international treaty…

Montreal Protocol History

The Montreal Protocol, signed in 1987 and strengthened by amendments…

Morning Warmup is a scheduled preconditioning operation that activates heating…

Morning Warmup Mode

A pre-occupancy BAS operating mode in which a zone is…