HVAC terms every GTA homeowner runs into

AFUE

also: Annual Fuel Utilization Efficiency

Annual Fuel Utilization Efficiency — the percentage of a furnace or boiler's fuel that is converted to usable heat over a full heating season. A 96% AFUE furnace turns 96 cents of every fuel dollar into heat.

Backdrafting

When negative pressure inside a home (from range hoods, dryers, or leaky ducts) reverses the flow of a chimney or vent — pulling combustion gases (including carbon monoxide) back into the living space. A major reason atmospherically-vented gas equipment is being retired.

BTU

also: British Thermal Unit

British Thermal Unit — a unit of heat energy. HVAC equipment is typically sized in BTU/h (BTUs per hour). A typical GTA home furnace is 60,000–120,000 BTU/h; a central AC is 18,000–60,000 BTU/h (1.5 to 5 tons).

CO detector

also: Carbon monoxide alarm

A carbon monoxide alarm. Required by Ontario law on every storey with a bedroom in a home with any fuel-burning appliance (or an attached garage). Alarms have a fixed lifespan — replace every 7–10 years per the manufacturer's label.

Cold-climate heat pump

also: ccHP · CCASHP

A heat pump designed to deliver rated heating capacity down to roughly –15 °C to –25 °C, using variable-speed compressors, vapour-injection, and larger outdoor coils. Modern cold-climate models keep running well into Ontario's coldest nights.

Condensate

The mildly acidic water produced when a high-efficiency furnace, heat pump, or tankless water heater condenses moisture out of its flue gases or refrigerant coil. It drains to a floor drain, condensate pump, or dedicated plumbing tie-in — and can freeze in exposed runs.

Condensing furnace

also: High-efficiency furnace

A furnace that extracts additional heat by condensing water vapour out of the flue gases in a secondary heat exchanger — reaching 90–98% AFUE. Vents through PVC instead of a metal chimney, and produces an acidic condensate that drains to the household plumbing.

ENERGY STAR

The government-backed efficiency mark (jointly administered by NRCan in Canada and the US EPA). ENERGY STAR certified furnaces, AC, heat pumps, and water heaters meet minimum efficiency and cold-climate performance criteria.

ERV

also: Energy Recovery Ventilator

An Energy Recovery Ventilator brings in fresh outdoor air while exchanging both heat and humidity with the outgoing indoor air. Ideal for tightly built new GTA homes where infiltration alone doesn't provide adequate ventilation.

ESA

also: Electrical Safety Authority

Ontario's Electrical Safety Authority — the provincial regulator for electrical installations. Heat-pump condensers, mini-split outdoor units, and electrified backup elements typically require an ESA electrical permit and inspection when new circuits or new service is installed.

Geothermal (ground-source heat pump)

also: GSHP

A heat pump that exchanges heat with the ground (via horizontal loops or vertical boreholes) rather than the outdoor air. Extremely efficient in Ontario's climate, but the loop-field cost is high — typically justified on larger lots or new-build projects.

Heat pump balance point

The outdoor temperature at which a heat pump can no longer meet a home's heating demand on its own. Below this point a backup source (gas furnace, electric strip, or a second-stage cold-climate compressor) supplies the shortfall.

HEPA

also: High-Efficiency Particulate Air

A HEPA filter captures ≥ 99.97% of airborne particles at 0.3 microns. True HEPA is only meaningful in a purpose-built HEPA unit — most residential HVAC systems cannot draw air through a HEPA filter directly because the pressure drop is too high.

HRV

also: Heat Recovery Ventilator

A Heat Recovery Ventilator exchanges heat (but not humidity) between incoming fresh air and outgoing exhaust air. In Ontario's dry winters an HRV is often the code-compliant choice for whole-home ventilation.

HSPF

also: Heating Seasonal Performance Factor · HSPF2

Heating Seasonal Performance Factor — a seasonal efficiency rating for the heating output of a heat pump. HSPF2 is the current test standard. In Ontario's cold winters HSPF2 alone doesn't tell the whole story; balance point and cold-climate rating matter too.

Hybrid heat (dual fuel)

also: Dual-fuel heat pump

A heat pump paired with a gas furnace as backup. The heat pump handles mild-to-cold weather; the furnace takes over below the pump's economic balance point. In Ontario this is often the most cost-effective retrofit path when a working furnace already exists.

Manual D duct design

also: Manual D

The ACCA duct-design procedure used to size supply and return trunks so each room gets the airflow the Manual J calls for. Poor duct design is the most common reason a new furnace still leaves upstairs bedrooms too hot in summer.

Manual J load calculation

also: Manual J · Load calc

The industry-standard room-by-room heating and cooling load calculation from ACCA. It's the correct way to size a furnace, AC, or heat pump — 'rule of thumb per square foot' typically over-sizes equipment in Ontario homes.

MERV

also: Minimum Efficiency Reporting Value

A 1–16 rating that describes how well a filter captures airborne particles. MERV 8 is a common builder default; MERV 11–13 is a strong homeowner upgrade; MERV 16 approaches HEPA-level filtration but requires an HVAC blower that can handle the pressure drop.

Mini-split

also: Ductless mini-split · Ductless heat pump

A ductless system with one outdoor condenser paired to one or more wall-mounted (or ceiling-cassette) indoor heads. Ideal for older Toronto and Scarborough homes without ductwork, hot upstairs bedrooms, bonus rooms, and finished basements.

R-410A

The refrigerant used in most Canadian residential AC and heat-pump equipment installed roughly 2010–2024. Being phased down in favour of lower-global-warming-potential refrigerants; still legal to service existing equipment.

R-454B

A lower-GWP refrigerant that is replacing R-410A in new residential AC and heat-pump equipment across North America. Mildly flammable (A2L classification), so charging and service require A2L-rated tools and updated technician training.

Refrigerant

The working fluid that carries heat between the indoor and outdoor coils in an AC or heat pump. In Canada residential systems are transitioning from R-410A to lower-GWP refrigerants such as R-454B and R-32.

Sealed combustion

A combustion appliance (typically a condensing furnace) that draws its combustion air from a dedicated intake pipe rather than the room. Eliminates backdrafting risk and is standard on modern 90+ AFUE furnaces.

SEER2

also: Seasonal Energy Efficiency Ratio 2

SEER2 is the current US/Canada seasonal cooling efficiency rating for central AC and heat pumps (as of the 2023 test standard update). Higher SEER2 = more cooling per kWh across a typical season.

Smart thermostat

also: Wi-Fi thermostat

A Wi-Fi-connected thermostat (Ecobee, Nest, Sensi, or an OEM model like Carrier Infinity or Lennox iComfort) that supports scheduling, geofencing, remote adjustment, and — for compatible equipment — modulating heat-pump or two-stage furnace control.

Tankless water heater

also: On-demand water heater

A gas or electric water heater that heats water instantaneously as it flows through the unit — no storage tank. High peak flow, endless hot water, and long service life, but higher install cost and stricter gas-venting requirements.

Ton (of cooling)

also: Cooling ton

A cooling ton equals 12,000 BTU/h of heat removal — historically the cooling power of one ton of ice melting over 24 hours. A 3-ton AC removes 36,000 BTU/h from your home.

TSSA

also: Technical Standards and Safety Authority

Ontario's Technical Standards and Safety Authority — the provincial regulator for fuels safety, including natural gas and propane appliances. In Ontario, only a TSSA-certified gas technician (with an appropriate G1/G2/G3 or ODP ticket, per current TSSA scope) may install, alter, or service a gas furnace or gas water heater.

Whole-home humidifier

A bypass, flow-through, or steam humidifier plumbed into the ductwork that raises indoor relative humidity in dry Ontario winters — protecting hardwood floors, reducing static, and easing dry-sinus symptoms.