Glossary

HVAC terms, explained in plain English

Efficiency ratings, equipment types, and the Ontario regulations behind them — defined once, so every guide on this site can point back here instead of re-explaining.

16 of 16 terms

A

AFUE (Annual Fuel Utilization Efficiency): AFUE measures the percentage of fuel a furnace converts into usable heat over a full year, with the rest lost up the vent. A furnace rated 96% AFUE turns 96 cents of every fuel dollar into heat inside your home; the remaining 4 cents escapes as exhaust.
AFUE vs. SEER2: Common Efficiency Rating Myths: AFUE and SEER2 are frequently confused or conflated in sales conversations, but they measure completely different things on different equipment: AFUE rates a furnace's fuel-to-heat conversion, while SEER2 rates a cooling (or heat pump) system's electrical efficiency. A high-AFUE furnace says nothing about your air conditioner's efficiency, and vice versa.

B

BTU & Tonnage: A BTU (British Thermal Unit) is the standard unit for heating and cooling output; one 'ton' of air conditioning capacity equals 12,000 BTU per hour. Tonnage and BTU ratings describe how much heating or cooling a system can produce, not how efficiently it does it.

C

Cold-Climate Heat Pump: A cold-climate heat pump is an air-source heat pump specifically engineered to keep producing meaningful heat output well below freezing, unlike standard heat pumps that lose most of their heating capacity in cold weather. It uses enhanced compressor and refrigerant technology to stay effective through an Ontario winter.

D

Ductless Mini-Split: A ductless mini-split is a heating and cooling system that connects an outdoor unit to one or more indoor wall- or ceiling-mounted units through small refrigerant lines, with no ductwork required. Each indoor unit can be controlled independently, so different rooms can run at different temperatures.

E

ECM Motor (Electronically Commutated Motor): An ECM motor is a variable-speed, electronically controlled blower motor used in furnaces and air handlers, replacing older single-speed PSC motors. It can run at low, efficient speeds for continuous airflow and ramp up only when needed, rather than only ever running at one fixed speed.
ESA (Electrical Safety Authority): ESA is Ontario's electrical safety regulator, responsible for permits and inspections on electrical work across the province — separate from TSSA, which covers gas and fuel-fired equipment. Any new circuit, panel upgrade, or electrical connection for HVAC equipment (like a heat pump) falls under ESA's jurisdiction.

H

Heat-Pump Water Heater: A heat-pump water heater draws heat from the surrounding air and transfers it into stored water, rather than generating heat directly through a gas burner or electric element the way conventional water heaters do. It typically uses less electricity than a standard electric tank for the same amount of hot water.
HRV/ERV (Heat/Energy Recovery Ventilator): An HRV or ERV brings continuous fresh outdoor air into a home while capturing most of the heat (HRV) or heat and humidity (ERV) from the stale air being exhausted, so ventilation doesn't mean losing all the energy already paid to heat or cool the house.
Hydronic Loop (Boiler Heating): A hydronic system heats water in a boiler and circulates it through a closed loop of pipes to radiators, baseboard units, or in-floor tubing to warm a home, rather than heating and moving air the way a furnace does. The water loop is sealed and reused continuously.

M

MERV Rating: MERV (Minimum Efficiency Reporting Value) is a 1-to-16 scale, set by ASHRAE, rating how effectively an air filter captures particles of different sizes. A higher MERV number means the filter traps smaller particles, but it can also restrict airflow more if your system isn't designed to handle it.

R

R-454B Refrigerant: R-454B is a newer refrigerant with a substantially lower global warming potential than the R-410A refrigerant it's replacing in new residential air conditioners and heat pumps sold across North America. It requires different handling, tools, and safety procedures than older refrigerants.

S

SEER2 & HSPF2: SEER2 and HSPF2 are the current lab-tested efficiency ratings for central air conditioners, heat pumps, and ductless systems — SEER2 measures cooling efficiency over a season, HSPF2 measures heating efficiency for heat pumps. Higher numbers mean more cooling or heating output per unit of electricity used.

T

Tankless Water Heater: A tankless water heater heats water directly as it flows through the unit, on demand, instead of storing and continuously reheating a tank of hot water. It takes up less space than a tank and can supply hot water continuously, but its output is limited by flow rate rather than tank size.
TSSA (Technical Standards and Safety Authority): TSSA is the Ontario regulator responsible for licensing and inspecting gas-fired heating equipment, fuel-burning appliances, and related trades across the province. Any furnace, boiler, or gas-fired water heater installation in Ontario falls under TSSA's licensing and code requirements.
Two-Stage & Modulating Systems: A single-stage furnace or air conditioner runs at full output or not at all. A two-stage system can run at a lower output level for milder conditions; a modulating (variable-capacity) system can fine-tune its output across a wide range, matching heating or cooling to what the home actually needs at that moment.

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