Aquastat
A temperature-sensitive controller that commands a hot water boiler's burner to a setpoint, with a high-limit function for safety.
Technical Glossary
Definitions of common terms in combustion, boilers, HVAC, ventilation and mechanical plumbing.
The technical vocabulary of heating, combustion and HVAC systems can be complex. This glossary gathers the essential terms you will encounter during diagnostics, quotes or intervention reports on your mechanical equipment.
Each definition is written for building managers, maintenance directors and technical decision-makers who want to understand the issues without necessarily mastering the specialized jargon. Terms cover natural gas combustion, hot water and steam boilers, commercial air conditioning, ventilation and mechanical plumbing.
BACnet
An open communication protocol that lets HVAC equipment and building controls from different manufacturers exchange data and commands over a shared network.
Carbon Monoxide
A toxic, colorless and odorless gas produced by incomplete combustion of gas, dangerous to occupants of a poorly ventilated or poorly maintained building.
Chiller
A machine that cools a secondary fluid (typically chilled water) to air-condition large spaces via coils or heat exchangers.
Combustion
An oxidizing chemical reaction of fuel that releases heat; its tuning determines safety, efficiency and emissions quality.
Combustion Analysis
Measurement of flue gases and flame-related parameters to evaluate burner tuning and combustion quality in operation.
Compressor
The component that compresses gaseous refrigerant to sustain the refrigeration cycle — the main mechanical part, and the most expensive one, in an air-conditioning system.
Condensing Boiler
A boiler that recovers the latent heat held in flue gas water vapour by condensing it, raising efficiency compared with a conventional appliance.
Control Valve
A motorized valve that continuously meters the flow of water or steam to a coil or heat exchanger, following a controller signal.
Draft
The pressure difference that draws in combustion air and vents flue gases from a gas appliance to the outside, a condition for safe and efficient combustion.
Economizer
A heat exchanger placed in a boiler's flue gas path to recover part of their heat and preheat water, which raises overall efficiency.
ÉcoPerformance
A Québec program for evaluating and labeling energy performance in commercial and institutional buildings, following published rules.
Excess Air
The amount of air supplied to a burner beyond what is strictly required for complete combustion of the gas.
Expansion Tank
A vessel connected to a closed hydronic loop that absorbs the increase in water volume as it heats, so system pressure stays within its working range.
Flame Detector
The device that continuously proves a burner's flame is present and causes the gas supply to be shut off as soon as that proof is lost.
Gas Burner
A device that mixes combustible gas with air to produce a controlled flame feeding a generator or boiler.
Gas Train
The ordered set of valves, regulators and safety devices that feeds gas to a burner and shuts that supply off on demand.
Glycol
An antifreeze blended into the water of a hydronic loop to lower its freezing point and protect circuits exposed to cold.
Heat Exchanger
A device that transfers heat from one fluid to another without mixing them, at the core of boilers, recovery units and many HVAC components.
Heat Pump
Equipment that moves heat between an external source and the building to provide heating and cooling based on cycle and regulation.
Hot Water Boiler
A generator that heats water for a heating network or domestic hot water needs, often configured in cascade on demanding sites.
HRV
A device that transfers part of the energy from exhaust air to incoming fresh air to reduce heating or cooling loads.
HVAC
An umbrella term for the heating, ventilation and air conditioning systems of a building, treated as one interacting system rather than separate pieces of equipment.
Low Water Cutoff
A safety device that monitors boiler water level and shuts off the burner as soon as that level falls below the point considered safe.
Modulation
The ability of a burner or boiler to continuously adjust its output to the heating demand, instead of running in a simple on/off manner.
NOx (Nitrogen Oxides)
Nitrogen oxides (NO and NO₂) formed during high-temperature gas combustion, a monitored pollutant that low-NOx burners are designed to limit.
Pressure Switch
A device that monitors a pressure (gas, air or water) and opens or closes a control circuit when it crosses a set threshold, one link in a gas appliance's safety chain.
Preventive Maintenance
A structured program of inspections, cleaning and planned replacements to reduce failures and drift before they impact operations.
Refrigerant
The fluid that absorbs heat from the building by evaporating, then rejects it outdoors by condensing — the thermal carrier of the refrigeration cycle.
Rooftop (RTU)
A rooftop air handling unit that typically combines heating, cooling and ventilation for commercial or institutional zones.
Safety Relief Valve
A mechanical device that opens by itself to release boiler pressure once it reaches the set pressure, so the appliance never exceeds the pressure it was built to withstand.
Steam Boiler
A unit that generates pressurized steam for heating, sterilizing or driving industrial and institutional equipment.
Steam Trap
An automatic device that discharges condensate and non-condensable gases from a steam system without letting live steam escape.
Water Treatment
A set of chemical and mechanical methods to control hardness, corrosion and biological growth in the hydraulic circuits of thermal equipment.
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