2,400+ Definitions
HVAC GLOSSARY
Every HVAC term, acronym, and industry phrase — defined in plain English.
Mixing Damper
A mixing damper is an HVAC component consisting of multiple…
Mixing Ratio
The ratio of the mass of water vapor to the…
Mixing Valve
A mixing valve combines hot boiler water with cooler return…
Mixing Valve Controls
Mixing valve controls regulate the temperature of water or air…
Modbus
Modbus is an open industrial communication protocol that allows HVAC…
Modbus Interface
A serial communication gateway that allows VRF system controllers to…
Modbus RTU
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
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
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…
Monoflo Tee
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
Morning Warmup is a scheduled preconditioning operation that activates heating…
Morning Warmup Mode
A pre-occupancy BAS operating mode in which a zone is…
Motion Sensor HVAC
Motion sensor HVAC systems use motion detection technology to automatically…
Motor Efficiency
Motor efficiency is the ratio of mechanical power output to…
Motor Enclosure
Motor Enclosure is the physical housing that protects motor windings…
Motor Insulation Class
Motor Insulation Class designates the maximum temperature rating for motor…
Motor Lubrication
Motor lubrication is the preventive maintenance process of lubricating motor…
Motor Nameplate
The motor nameplate is the permanent label affixed to electric…
Motor Nameplate Service Factor
A multiplier applied to the nameplate horsepower rating indicating the…
Motor Overload
Motor Overload occurs when a motor draws sustained current exceeding…
Motor Protection Module
An integrated solid-state device that combines overload, phase loss, phase…
Motor Run Capacitor
A motor run capacitor continuously supplies voltage to single-phase motors…
Motor Service Factor
Motor Service Factor (SF) is a multiplier that indicates how…
Motor Start Capacitor
A motor start capacitor is a high-capacity electrical component that…
Motor Starting Current
Motor Starting Current is the high inrush current flowing when…
Motor Test
Motor testing encompasses multiple diagnostic procedures including current draw measurement,…
Motorized Damper
A motorized damper is an electronically controlled device that regulates…
MPPT
MPPT (Maximum Power Point Tracking) is a technology that continuously…
Multi Stage Furnace
A multi-stage furnace is a gas-fired heating appliance designed to…
Multi-Zone Mini-Split
A ductless system in which a single outdoor unit connects…
Multizone Airflow Network
A building simulation approach that models each room as a…