HVAC Glossary
HVAC Terms, in Plain English
50 heating, cooling and air-quality terms you'll hear from a technician, on a quote or on a rebate form — each with what it means and why it matters in a Fraser Valley home.
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- Heating & Furnaces AFUE AFUE (Annual Fuel Utilization Efficiency) is the percentage of a furnace's or boiler's yearly fuel energy that becomes usable heat in the home. A 96% AFUE gas furnace turns 96 cents of every gas dollar into heat and loses about 4% up the vent. Older furnaces often rated near 60%; modern condensing models reach roughly 95–98%. What it means for you →
- Water Heating & Hydronics Anode Rod An anode rod is a metal rod, typically magnesium or aluminum, threaded into the top of a storage tank water heater. It corrodes sacrificially, drawing corrosive action away from the tank's steel shell and glass lining. Once the rod is consumed, the tank itself begins to rust, which ends in leaks and replacement. What it means for you →
- Heat Pumps & Cooling Auxiliary (Backup) Heat Auxiliary heat is the supplemental heat source that helps a heat pump when it cannot meet demand alone, typically electric resistance heat strips in the air handler or a gas furnace in a dual-fuel system. It engages during very cold weather, defrost cycles, or large thermostat setbacks. Emergency heat runs the backup alone, without the heat pump. What it means for you →
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- Heating & Furnaces Carbon Monoxide (CO) Carbon monoxide (CO) is a colourless, odourless, toxic gas produced when fuels such as natural gas, propane, oil, or wood burn incompletely. In homes it can come from a cracked furnace heat exchanger, a blocked vent or chimney, a malfunctioning fireplace or water heater, or an idling vehicle. Early exposure symptoms resemble the flu. What it means for you →
- Heat Pumps & Cooling Cold-Climate Heat Pump A cold-climate heat pump is an air-source heat pump engineered to keep delivering substantial heating capacity and efficiency at low outdoor temperatures, commonly verified at -15°C (5°F). It typically uses a variable-speed inverter compressor and enhanced refrigerant controls, so it relies far less on backup heat than standard models during freezing weather. What it means for you →
- Ductwork & Sheet Metal Custom Sheet Metal Ductwork Custom sheet metal ductwork is rigid galvanized steel duct, trunks, transitions, and fittings fabricated to the exact dimensions of a home and its equipment, rather than assembled only from stock catalogue parts. Made-to-fit metal reduces turbulence, pressure loss, and leakage at joints, helping the furnace, air conditioner, or heat pump deliver its rated airflow. What it means for you →
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- Heat Pumps & Cooling Defrost Cycle A defrost cycle is a heat pump's automatic routine for clearing frost from its outdoor coil during heating. When sensors detect frost build-up, the system briefly reverses to send warm refrigerant through the outdoor coil, stops the outdoor fan, melts the frost, then returns to heating. Rising steam from the outdoor unit during defrost is normal. What it means for you →
- Heat Pumps & Cooling Dual-Fuel (Hybrid) System A dual-fuel system pairs an electric heat pump with a gas furnace in one ducted system. The heat pump handles cooling and most heating, and the controls switch to the furnace below a set outdoor temperature, called the balance or changeover point, or when the heat pump cannot meet demand. Only one heat source runs at a time. What it means for you →
- Ductwork & Sheet Metal Duct Sealing Duct sealing closes leaks at duct joints, seams, connections, and register boots using mastic, approved foil tape, or aerosol sealant, so conditioned air reaches the rooms instead of escaping into crawlspaces, attics, or wall cavities. Sealing return ducts also keeps dusty or damp air from unconditioned spaces being drawn into the system. What it means for you →
- Ductless & Zoning Ductless Mini-Split A ductless mini-split is a heat pump that links an outdoor unit to one or more wall, ceiling, or floor-mounted indoor heads through a small refrigerant line set, with no ductwork. Each indoor head has its own control, so rooms are heated or cooled independently, usually by an inverter-driven, variable-speed compressor that adjusts output to the load. What it means for you →
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- Heating & Furnaces Flame Sensor A flame sensor is a thin metal rod positioned in a gas furnace's burner flame that confirms combustion is actually happening. It carries a tiny electrical current through the flame to the control board; if no current is detected within seconds of ignition, the board shuts off the gas valve to prevent unburned gas from building up. What it means for you →
- Heating & Furnaces Furnace Tune-Up A furnace tune-up is an annual professional service visit combining a safety inspection with a performance check. The safety half covers combustion, the heat exchanger, venting, gas pressure, and safety controls; the performance half cleans burners and blower and measures temperature rise, static pressure, and motor amperage against the manufacturer's specifications. What it means for you →
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- Fireplaces & Gas Gas Fireplace Insert A gas fireplace insert is a sealed, direct-vent gas firebox installed inside an existing masonry or factory-built wood fireplace. It draws combustion air from outside and exhausts through liners run up the old chimney, turning a drafty, inefficient open hearth into a controllable zone heater with a glass front and thermostat or remote control. What it means for you →
- Fireplaces & Gas Gas Fitter (Class A / Class B) A gas fitter is a tradesperson certified to install, alter, and service natural gas and propane piping and appliances. In British Columbia, gas fitters are certified through Technical Safety BC: Class B covers appliances up to a set input limit, typical of homes and light commercial buildings, while Class A has no input limit. What it means for you →
- Rebates, Code & Costs Gas Permit (Technical Safety BC) A gas permit is the authorization required in British Columbia before installing or replacing gas equipment such as a furnace, boiler, gas water heater, fireplace, or new gas line. It is administered under Technical Safety BC, pulled by the licensed gas contractor rather than the homeowner, and the completed work is subject to inspection. What it means for you →
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- Water Heating & Hydronics Hard Water & Scale Hard water is water carrying dissolved minerals, mainly calcium and magnesium, that drop out as scale when the water is heated. In a tank water heater, scale settles on the bottom between burner and water, so the burner runs longer. In a tankless unit, it coats heat exchanger passages and restricts flow, costing efficiency first and lifespan second. What it means for you →
- Heating & Furnaces Heat Exchanger A heat exchanger is the sealed metal chamber or set of tubes inside a gas furnace where burner flames heat the metal and household air blown across the outside picks up that heat. It keeps combustion gases, including carbon monoxide, separate from the air you breathe. Cracks or corrosion can let those gases escape. What it means for you →
- Heat Pumps & Cooling Heat Pump A heat pump is an electric heating and cooling system that moves heat instead of generating it. In winter it extracts heat from outdoor air and pumps it indoors; in summer it reverses and removes heat from the home. Because it transfers heat with a refrigerant circuit, it typically delivers two to three units of heat per unit of electricity. What it means for you →
- Rebates, Code & Costs Heat Pump Rebate (CleanBC / BC Hydro) A heat pump rebate is a payment from a provincial or utility program, such as CleanBC or BC Hydro, toward installing a qualifying heat pump. In BC, eligibility generally depends on the heating system being replaced, equipment efficiency thresholds, installation by a registered contractor, sometimes household income, and an application filed within the program deadline. What it means for you →
- Air Quality & Ventilation HEPA Filtration HEPA (high-efficiency particulate air) filtration uses dense media that captures at least 99.97% of particles 0.3 microns in size, the size hardest to trap. In homes it is usually delivered through a whole-home bypass unit connected to the ductwork or a portable air cleaner, because most furnace blowers cannot push air through a HEPA filter directly. What it means for you →
- Heating & Furnaces High-Efficiency (Condensing) Furnace A high-efficiency condensing furnace is a gas furnace with a secondary heat exchanger that cools exhaust gases until their water vapour condenses, recovering extra heat. That pushes efficiency to roughly 90–98% AFUE. Because the exhaust is cool and acidic, it vents through plastic pipe and produces condensate that must drain away. What it means for you →
- Heating & Furnaces Hot Surface Igniter A hot surface igniter is a ceramic element, usually silicon carbide or silicon nitride, that glows red-hot when energized and lights the gas at a furnace's burners. It replaced the standing pilot light on most modern gas furnaces, saving gas between cycles. Igniters are brittle and wear out over thousands of heating cycles. What it means for you →
- Air Quality & Ventilation HRV (Heat Recovery Ventilator) An HRV (heat recovery ventilator) is a balanced mechanical ventilation unit that exhausts stale indoor air and brings in fresh outdoor air in equal amounts, passing both streams through a heat-exchange core. The core transfers heat from the outgoing air to the incoming air without mixing them, so the home gets fresh air with much less heating loss. What it means for you →
- Heat Pumps & Cooling HSPF2 HSPF2 (Heating Seasonal Performance Factor 2) rates a heat pump's heating efficiency: total seasonal heat delivered in BTUs divided by the watt-hours of electricity used, including defrost and backup heat. It replaced the older HSPF test in 2023 with tougher conditions, so it reads lower for identical equipment. Higher HSPF2 means less electricity per unit of heat. What it means for you →
- Water Heating & Hydronics Hydronic Air Handler A hydronic air handler is a blower cabinet containing a hot-water coil that heats a home's air using water from a boiler or high-output water heater instead of a gas burner. A pump circulates hot water through the coil, and the blower pushes air across it and through the ductwork, delivering forced-air heat without combustion in the cabinet. What it means for you →
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- Heating & Furnaces Limit Switch A limit switch is a temperature safety control on a furnace that shuts off the burners when the heat exchanger or cabinet gets too hot. The high-limit switch most often trips because of restricted airflow — a clogged filter, closed vents, or undersized ducts. Rollout switches are related controls that detect flames escaping the burner area. What it means for you →
- Ductless & Zoning Line Set A line set is the pair of copper refrigerant tubes connecting an outdoor heat pump or condenser to an indoor coil or mini-split head. The larger, insulated suction line returns refrigerant vapour to the compressor; the smaller liquid line carries refrigerant indoors. Correct diameter, length, insulation, and leak-tight connections are essential for rated capacity and efficiency. What it means for you →
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- Ductwork & Sheet Metal Manual J (Heat Loss / Heat Gain) Calculation A Manual J calculation is a room-by-room heat loss and heat gain estimate that determines how much heating and cooling a home needs, based on insulation, windows, air leakage, orientation, and local design temperatures. Developed by ACCA, it is the basis for correctly sizing furnaces, heat pumps, and air conditioners, instead of guessing from square footage. What it means for you →
- Air Quality & Ventilation MERV Rating MERV (Minimum Efficiency Reporting Value) is a filter rating from the ASHRAE 52.2 test standard that measures how well an air filter captures particles between 0.3 and 10 microns. Ratings run from 1 to 16; higher numbers capture smaller particles, but denser filters also add airflow resistance that the blower and ductwork must overcome. What it means for you →
- Ductless & Zoning Multi-Zone System A multi-zone system is a ductless heat pump in which one outdoor unit serves two or more indoor heads, each with its own line set and control. Every head conditions its own room or zone at its own set temperature, while the shared outdoor compressor varies its output to match the combined demand of the heads that are running. What it means for you →
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- Heat Pumps & Cooling Refrigerant (R-410A / R-454B) Refrigerant is the working fluid that carries heat through an air conditioner or heat pump, evaporating to absorb heat and condensing to release it. R-410A has been the standard residential refrigerant for years; newer equipment is moving to lower-global-warming-potential refrigerants such as R-454B, a mildly flammable (A2L) blend, under the international HFC phase-down. What it means for you →
- Air Quality & Ventilation Relative Humidity Relative humidity (RH) is the amount of water vapour in the air expressed as a percentage of the maximum the air can hold at its current temperature. Because cooler air holds less moisture, RH rises as air cools, and when it reaches 100% at a cold surface such as a window, the vapour condenses into water. What it means for you →
- Rebates, Code & Costs Repair vs. Replace Repair vs. replace is the decision of whether to fix failing heating or cooling equipment or install a new system. It weighs system age against expected life, repair cost against replacement cost, repair history, refrigerant type, and how long you will stay. A common starting point is the 50% rule on repair cost. What it means for you →
- Heat Pumps & Cooling Reversing Valve A reversing valve is the four-way valve in a heat pump's outdoor unit that changes the direction of refrigerant flow, switching the system between heating and cooling. A solenoid shifts the valve on a signal from the thermostat or control board. The same valve reverses the system briefly during each defrost cycle in winter. What it means for you →
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- Heat Pumps & Cooling SEER2 SEER2 (Seasonal Energy Efficiency Ratio 2) rates the cooling efficiency of an air conditioner or heat pump: total seasonal cooling output in BTUs divided by the watt-hours of electricity used. It replaced the older SEER test in 2023 using higher, more realistic duct static pressure, so it reads lower for the same equipment. Higher SEER2 means cheaper cooling. What it means for you →
- Rebates, Code & Costs Service Call Fee A service call fee is the flat charge an HVAC company bills to send a technician to your home and diagnose a problem. It typically covers travel and the diagnostic inspection, sometimes for a set number of appliances, while the repair itself is quoted separately for your approval. Rates commonly vary by distance and equipment type. What it means for you →
- Heating & Furnaces Short-Cycling Short-cycling is when a furnace, heat pump, or air conditioner turns on and off far more often than normal, running brief cycles that never fully heat or cool the home. Common causes are an oversized system, a dirty flame sensor, a tripping limit switch, restricted airflow, a plugged condensate drain, or a poorly placed thermostat. What it means for you →
- Ductless & Zoning Smart Thermostat A smart thermostat is a Wi-Fi-connected thermostat that controls heating and cooling equipment through a phone app, schedules, and automation such as occupancy sensing or learning routines. Many models report runtime and filter reminders, and most need a steady power supply, usually a common wire (C-wire), plus correct wiring for the furnace, heat pump, or dual-fuel system. What it means for you →
- Ductwork & Sheet Metal Static Pressure Static pressure is the resistance to airflow that a furnace or air handler blower works against, measured in inches of water column. Filters, coils, undersized ducts, tight fittings, and closed registers all add to it. When total external static pressure exceeds the equipment's rating, airflow drops, rooms go short of air, and efficiency suffers. What it means for you →
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- Water Heating & Hydronics Tankless Water Heater A tankless water heater is a wall-mounted appliance that heats water only as it flows. Opening a hot tap trips a flow sensor, which fires a gas burner that heats water passing through a heat exchanger. With no stored water there is no standby heat loss and no tank to run out, but output is limited by flow rate. What it means for you →
- Heat Pumps & Cooling Tonnage (BTU Capacity) Tonnage is the nominal capacity of an air conditioner or heat pump. One ton equals 12,000 BTUs of heat moved per hour, the cooling effect of melting one ton of ice over a day. Residential systems typically range from about 1.5 to 5 tons, and the correct size comes from a room-by-room heat-loss and heat-gain calculation. What it means for you →
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- Air Quality & Ventilation Whole-Home Humidifier & Dehumidifier A whole-home humidifier or dehumidifier is equipment connected to the HVAC system that adds or removes moisture for the entire house, controlled by a humidistat. Humidifiers use a water panel or steam generator in the ductwork; dehumidifiers pull air across a cold coil to condense moisture and drain it away, then return drier air. What it means for you →
- Air Quality & Ventilation Wildfire Smoke & PM2.5 PM2.5 is fine particulate matter 2.5 microns or smaller, the main health concern in wildfire smoke. These particles stay airborne for long periods, travel hundreds of kilometres, and pass easily through windows, doors, and basic furnace filters. Reducing indoor PM2.5 requires a closed-up home plus effective filtration, such as MERV 13 or HEPA. What it means for you →
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