Glossary

Energy terms, in plain language

160 terms you'll meet on bills, quotes, labels and program forms.

Last reviewed November 2, 2026
How we review content

A

A2L refrigerant: A class of refrigerants with lower global warming potential and mild flammability, such as R-454B and R-32. New heat pumps and air conditioners sold in Canada are moving to A2L refrigerants as R-410A is phased down under federal HFC regulations. Learn more
ACH50: Air changes per hour at 50 pascals of pressure, the standard measure of how leaky a house is during a blower door test. Older Ontario homes often test at 7–15 ACH50, new homes around 2.5–3.5, and Passive House buildings at 0.6 or less. Learn more
AFUE: Annual Fuel Utilization Efficiency, the percentage of fuel energy a furnace or boiler turns into useful heat over a season. New gas furnaces sold in Canada must be at least 95% AFUE. Learn more
Air barrier: A continuous layer of materials that stops air from leaking through the building envelope, such as drywall sealed at the edges, sheathing tape or spray foam. An effective air barrier is one of the most important factors in comfort and heating cost. Learn more
Air sealing: Closing gaps and cracks in a home's envelope, such as around attic hatches, rim joists, pipes and wiring, to reduce drafts and heat loss. It is usually one of the lowest-cost, highest-value energy upgrades. Learn more
Air-source heat pump: A heat pump that moves heat between outdoor air and your home, heating in winter and cooling in summer. Cold-climate models are designed to keep heating down to roughly −25 °C to −30 °C. Learn more
Attic ventilation: Intake vents at the soffits and exhaust vents near the ridge that let outside air flow through the attic. Good ventilation, combined with air sealing below, keeps the roof deck cold in winter and helps prevent ice dams and moisture problems. Learn more
Auxiliary heat: Backup heat, usually electric resistance coils or a furnace, that helps a heat pump during defrost cycles and very cold weather. It is normal for it to run sometimes, but frequent use in mild weather can signal a sizing or settings problem. Learn more

B

Balance point: The outdoor temperature at which a heat pump's output exactly matches a home's heat loss. Below it, backup heat is needed; in a hybrid system, a separate economic changeover point decides when the furnace takes over. Learn more
Baseboard heater: An electric resistance heater mounted along a wall, usually with its own thermostat. Baseboards turn 100% of electricity into heat, which sounds efficient but costs two to three times more to run than a heat pump delivering the same heat. Learn more
Battery storage: A home battery that stores electricity, often from solar panels, for use later or during outages. In Ontario, a battery of roughly 13–16 kWh typically costs about $12,000–$20,000 installed (estimate). Learn more
Bidirectional meter: An electricity meter that measures power flowing both from the grid into your home and from your home back to the grid. It is required for net metering in Ontario and is installed by your local distribution company. Learn more
Blower door test: A test in which a powerful fan depressurizes the house to measure air leakage and help find leaks. It is part of a typical home energy assessment by a Registered Energy Advisor. Learn more
Blown-in insulation: Loose cellulose or fibreglass insulation installed with a blowing machine, most often on attic floors. It fills around wiring and framing better than batts and is the usual choice for topping up an Ontario attic to R-50 or R-60. Learn more
Boiler: A heating appliance that heats water (or makes steam) and circulates it to radiators, baseboard convectors or in-floor tubing. Modern condensing gas boilers can exceed 90% efficiency when return water is cool enough to condense. Learn more
BTU: British thermal unit, a unit of heat energy commonly used to rate furnaces, air conditioners and heat pumps. One kilowatt-hour equals about 3,412 BTU. Learn more
Building envelope: The parts of a house that separate inside from outside: foundation, walls, windows, doors and roof or attic. Improving the envelope through air sealing and insulation reduces how much heating and cooling a home needs. Learn more

C

Canada Greener Homes Grant: A former federal grant for home energy retrofits that closed to new applicants in early 2024. Its companion interest-free loan closed to new applications in fall 2025. Learn more
Canada Greener Homes Loan: A former federal interest-free loan of up to $40,000 for home energy retrofits. It closed to new applications in fall 2025; existing borrowers' agreements still apply. Learn more
Carbon monoxide (CO): A colourless, odourless and poisonous gas produced when fuel burns incompletely. Ontario law requires CO alarms in homes with a fuel-burning appliance, fireplace or attached garage. Air sealing projects should include a check that combustion appliances vent properly. Learn more
CEER: Combined Energy Efficiency Ratio, the efficiency rating used for room (window) air conditioners. A higher CEER means more cooling per unit of electricity, including standby power. Learn more
Cellulose insulation: Insulation made mostly from recycled paper treated with fire retardant. It is commonly blown into attics or dense-packed into closed wall cavities, and offers roughly R-3.5 to R-3.8 per inch. Learn more
CGHAP: The Canada Greener Homes Affordability Program, a federal program for low-to-median income households delivered through provincial partners. Availability in Ontario is limited and varies, so confirm with Natural Resources Canada. Learn more
Cold-climate air-source heat pump (ccASHP): An air-source heat pump engineered to provide useful heat in very cold weather, typically down to −25 °C to −30 °C. In southern Ontario, its seasonal COP is typically around 2.5–3.0. Learn more
Commodity charge: The part of your electricity or gas bill for the energy itself, as opposed to delivery, regulatory charges and tax. For most Ontario households, the electricity commodity price is set by the OEB under the Regulated Price Plan. Learn more
Condensing furnace: A high-efficiency gas furnace that captures extra heat by condensing water vapour from exhaust gases, reaching 95% AFUE or higher. It vents through plastic pipe and needs a condensate drain. Learn more
Connection Impact Assessment: A technical study an electricity distributor may require before a generator, such as a large solar system, connects to the grid. As reported, residential systems up to 12 kW no longer need one in Ontario as of May 2026. Learn more
Cooling-off period: A period after signing during which a consumer can cancel a contract without penalty. Under Ontario's Consumer Protection Act, many direct agreements signed at home have a 10-day cooling-off period. Confirm details on ontario.ca. Learn more
COP: Coefficient of performance, the ratio of heat delivered to electricity used at a given moment. A COP of 3 means 3 kWh of heat for every 1 kWh of electricity; COP falls as outdoor temperatures drop. Learn more
Cracked heat exchanger: A crack in the furnace part that separates flames and exhaust from house air. It is a genuine safety issue, but a claim of a cracked heat exchanger is also a common pressure tactic; ask for photos and get a second opinion from a TSSA-registered contractor. Learn more
Cubic metre (m³): The unit Enbridge Gas uses to measure natural gas on your bill. One cubic metre contains about 10.35 kWh (about 37.3 MJ) of energy, and a typical Ontario home uses roughly 2,000–2,600 m³ a year. Learn more
Cubic metre to kWh conversion: To compare gas with electricity, multiply cubic metres of natural gas by about 10.35 to get kilowatt-hours of energy. Then account for appliance efficiency, such as 95% for a condensing furnace. Learn more

D

Defrost cycle: A short period in which an air-source heat pump reverses to melt frost from its outdoor coil. Steam from the outdoor unit and a brief pause in warm air are normal during defrost. Learn more
Delivery charge: The part of your electricity or gas bill that pays for the poles, wires, pipes and meters that bring energy to your home. On electricity bills it varies by local distribution company and by rural or urban density. Learn more
Dense-pack insulation: Cellulose or fibreglass blown at high density into closed wall cavities through small holes. Packing it tightly prevents settling and also reduces air leakage through the walls. Learn more
Design temperature: The cold outdoor temperature a heating system is sized for, based on local climate data in the Ontario Building Code. Approximate values: Windsor −16 °C, Toronto −18 °C to −20 °C, Ottawa −25 °C, Sudbury −28 °C, Thunder Bay −33 °C. Learn more
Direct-vent appliance: A gas appliance that draws combustion air from outside and vents exhaust outside through sealed pipes, with no air taken from the room. Most high-efficiency furnaces, boilers and fireplaces in Ontario are direct-vent. Learn more
Drain water heat recovery (DWHR): A copper pipe section installed on a vertical drain stack that uses heat from warm wastewater, mainly showers, to preheat incoming cold water. It has no moving parts and works only while water is flowing down the drain. Learn more
Dual-fuel system: Another name for a hybrid heating system that pairs an electric heat pump with a gas (or other fuel) furnace. The system switches between them based on outdoor temperature or energy prices. Learn more
Duct sealing: Closing leaks in heating and cooling ductwork with mastic or foil tape, or with an aerosol sealant applied from inside the ducts. Sealing ducts outside the heated space has the biggest effect. Learn more
Ductless mini-split: A heat pump with an outdoor unit connected to one or more wall- or ceiling-mounted indoor heads, without ductwork. A single-zone system typically costs roughly $4,500–$8,000 installed in Ontario (estimate). Learn more

E

EAP: The Energy Affordability Program, offered by Save on Energy, which provides free energy-saving upgrades such as insulation, appliances and smart thermostats to income-eligible households. Some households receiving social assistance also qualify. Learn more
ECM motor: Electronically commutated motor, a variable-speed motor used in modern furnace blowers and fans. It uses much less electricity than older permanent split capacitor motors, especially when the fan runs at low speed. Learn more
EER2: Energy Efficiency Ratio 2, the cooling efficiency of an air conditioner or heat pump at a single hot test condition, under the testing procedures in use since 2023. SEER2 covers the whole season; EER2 shows performance on very hot days. Learn more
Electrical service capacity: The maximum current a home's electrical service and main panel can carry, usually 100 A or 200 A in Ontario homes. Heat pumps, EV chargers and electric ranges can push a 100 A service to its limit; a load calculation by an electrician shows whether an upgrade is needed. Learn more
Enbridge Gas: Ontario's main natural gas distributor, serving most gas-heated homes in the province. It co-delivers the Home Renovation Savings Program with Save on Energy; EPCOR serves some areas. Learn more
Enbridge Home Winterproofing Program: An Enbridge Gas program offering free insulation, air sealing and thermostats to income-eligible Enbridge customers. Check eligibility on the Enbridge Gas website. Learn more
EnerGuide label: The Canadian label that shows an appliance's estimated annual energy use in kWh, so you can compare models. It appears on products such as fridges, freezers, washers and dryers. Learn more
EnerGuide rating: Natural Resources Canada's home energy rating, expressed in gigajoules (GJ) per year, produced by a Registered Energy Advisor after an assessment. A lower number means the home uses less energy under standard conditions. Learn more
ENERGY STAR: A certification for products that meet strict energy-efficiency criteria, administered in Canada by Natural Resources Canada. Many Ontario rebates require ENERGY STAR or similarly qualified equipment. Learn more
Equal billing: A payment plan offered by Enbridge and many local utilities that spreads estimated annual costs into equal monthly payments, with a reconciliation later. It smooths cash flow but does not lower what you pay. Learn more
ERV: Energy recovery ventilator, a mechanical system that brings in fresh air and exhausts stale air while transferring both heat and some moisture between the two streams. It can help keep winter air from becoming too dry. Learn more
ESA: The Electrical Safety Authority, which regulates electrical safety in Ontario. Most electrical work, including solar installations, heat pump circuits and EV chargers, requires an ESA permit and inspection. Learn more
EV energy management system: A device or charger feature that monitors household electrical load and reduces or pauses EV charging when the home is near its service limit. It can sometimes avoid an electrical service upgrade. Learn more
EVSE: Electric vehicle supply equipment, the technical term for an EV charging station. It supplies power safely to the car's on-board charger. Installing a Level 2 EVSE requires an ESA permit. Learn more

F

Fan coil unit: A cabinet containing a fan and a coil supplied with hot or chilled water from a central plant. It is common in Ontario condo and apartment suites, and the filter should be cleaned or replaced regularly. Learn more
Fixed monthly charge: The part of the delivery charge on an Ontario electricity bill that is the same every month regardless of use. Residential distribution rates in Ontario moved to a fully fixed monthly charge, so cutting kWh lowers the variable parts of the bill but not this charge. Learn more
Furnace filter: The filter in the return air path of a forced-air system. One-inch filters typically need changing every one to three months; thicker media filters every six to twelve months. A clogged filter reduces airflow and efficiency. Learn more

G

G1 / G2 gas technician: TSSA-issued licences for gas technicians in Ontario. A G2 can work on most residential gas appliances; a G1 can work on larger systems as well. Learn more
Gigajoule (GJ): A unit of energy equal to one billion joules, used in EnerGuide home ratings and some gas pricing. One GJ is about 278 kWh, or roughly 27 cubic metres of natural gas. Learn more
Global adjustment: A component of Ontario's electricity costs that covers the difference between market prices and the cost of contracted and regulated generation and conservation programs. For RPP customers it is built into the TOU, ULO and Tiered prices rather than shown separately. Learn more
Green Button: A standard format that lets you download your own hourly electricity (and in some cases gas) data from your utility. Ontario utilities are required to offer it, and it is useful for comparing price plans. Learn more
Ground-source heat pump: A heat pump that exchanges heat with the ground through buried loops, also called geothermal. It is very efficient but costly, typically $30,000–$60,000 or more installed in Ontario (estimate). Learn more

H

Heat loss calculation: A room-by-room estimate of how much heat a home loses on a design cold day, used to size heating equipment correctly. It considers insulation, windows, air leakage and local climate. Learn more
Heat pump: A device that moves heat from one place to another using a refrigerant cycle. In winter it moves heat from outdoor air or the ground into the home; in summer it works in reverse as an air conditioner. Learn more
Heat pump dryer: A clothes dryer that heats and dehumidifies air in a closed loop instead of venting hot air outdoors. It uses roughly half the energy of a conventional electric dryer but usually takes longer per load. Learn more
Heat pump water heater: A water heater that uses a heat pump to move heat from surrounding air into the water, using much less electricity than a standard electric tank. The HRS assessment stream has offered $500 for one, as published in mid-2026. Learn more
Heating degree days: A measure of how cold a location is over a year, based on how far daily temperatures fall below 18 °C. Toronto has roughly 3,500–3,600, Ottawa about 4,500 and Sudbury or Thunder Bay roughly 5,000–5,700. Learn more
Heating oil: Fuel oil burned in a furnace or boiler, still used in some rural Ontario homes. Oil-heated homes typically see the largest operating-cost savings from switching to a heat pump. Learn more
HRAI: The Heating, Refrigeration and Air Conditioning Institute of Canada, an industry association that offers training and certification for HVAC contractors and designers. Learn more
HRS: The Home Renovation Savings Program, jointly delivered by Save on Energy and Enbridge Gas since January 2025. It offers rebates for heat pumps, insulation, windows, smart thermostats, appliances, and solar and batteries; confirm current terms on saveonenergy.ca. Learn more
HRV: Heat recovery ventilator, a system that exchanges stale indoor air for fresh outdoor air while recovering much of the heat from the outgoing air. It is important in tightly sealed homes. Learn more
HSPF2: Heating Seasonal Performance Factor 2, the North American heating-efficiency rating for heat pumps under test standards in place since 2023. Higher is better; the Region V (cold climate) rating is most relevant for Ontario. Learn more
HST: Harmonized Sales Tax, charged at 13% in Ontario on electricity and natural gas bills. The Ontario Electricity Rebate is calculated on the electricity bill amount before HST. Learn more
Hybrid heating: A system that combines a heat pump with a furnace, using the heat pump in mild weather and the furnace below a set changeover temperature, often around −5 °C to −10 °C depending on prices. Learn more
Hydronic heating: Heating that circulates hot water through pipes to radiators, baseboard convectors or in-floor tubing. It is quiet and comfortable but needs a separate solution for central air conditioning. Learn more

I

IC-rated fixture: A recessed light fixture rated for direct contact with insulation. Airtight IC-rated LED fixtures are the right choice for top-floor ceilings under an attic. Learn more
Ice dam: A ridge of ice at the roof edge that forms when heat leaking into the attic melts snow, which then refreezes over the cold eaves. Water backing up behind it can leak into walls and ceilings. Learn more
IESO: The Independent Electricity System Operator, which manages Ontario's power grid and electricity market. It runs the Save on Energy conservation programs. Learn more
Induction cooktop: An electric cooktop that heats pots directly with a magnetic field, making it fast and efficient. Qualifying models have been eligible for appliance rebates of up to $200 through HRS. Learn more
Insulated glass unit (IGU): The sealed set of two or three panes in a modern window, often with low-e coatings and argon gas between the panes. Fogging between panes means the seal has failed. Learn more
Inverter (solar): A device that converts the direct current (DC) from solar panels into the alternating current (AC) used in your home. String inverters typically carry 10–25 year warranties. Learn more
Inverter-driven compressor: A variable-speed compressor in a heat pump or air conditioner that adjusts output to match demand, rather than switching fully on and off. It improves comfort and efficiency, especially in cold weather. Learn more
Islanding: When a generator, battery or solar system keeps powering a home, or the grid, after a utility outage. Grid-tied inverters must shut off during outages (anti-islanding) to protect line workers; backup requires equipment designed to isolate the home safely. Learn more

K

Knob-and-tube wiring: An early electrical wiring method found in many pre-1950 Ontario homes. It is not designed to be buried in insulation, so it should be inspected, and often replaced, before insulating walls or attics. Learn more
kW DC vs kW AC: Solar system sizes are usually quoted in kW DC, the combined rating of the panels. kW AC is the inverter output, which is often lower. Compare quotes using the same measure. Learn more
kW vs kWh: A kilowatt (kW) is a rate of power, like the speed of a car; a kilowatt-hour (kWh) is an amount of energy, like distance travelled. Solar systems are sized in kW, while your bill charges you for kWh. Learn more

L

LDC: Local distribution company, the utility that delivers electricity to your home and bills you, such as Hydro One, Toronto Hydro, Alectra, Hydro Ottawa, Elexicon or London Hydro. Learn more
LEAP: The Low-income Energy Assistance Program, which provides emergency help with electricity or gas bills for households in financial hardship. Apply through local social service agencies. Learn more
Level 1 charging: EV charging from a standard 120 V household outlet. It adds roughly 7–9 km of range per hour, which can be enough for drivers who travel short distances and charge overnight. Learn more
Level 2 charging: EV charging at 240 V, typically 7–11 kW at home, adding roughly 40–60 km of range per hour depending on the car. A home installation usually costs $1,500–$3,000 and needs an ESA permit. Learn more
Load displacement: A solar arrangement in which the system only offsets electricity used in the home at the moment it is produced, with no credit for exports. Systems that take the HRS solar and battery rebate operate this way for life. Learn more
Local improvement charge (LIC): A municipal financing tool that lets a homeowner repay an energy upgrade loan through the property tax bill. Some Ontario municipalities, including Toronto and Ottawa, have used LICs for home energy loan programs; terms and availability change. Learn more
Low-e coating: A microscopically thin metallic coating on window glass that reflects heat. It reduces winter heat loss and, depending on the type, summer heat gain. Learn more

M

Manual J: A widely used North American method for calculating a home's heating and cooling loads room by room. In Canada, CSA F280 is the equivalent standard; either is far better than sizing by square footage alone. Learn more
MERV: Minimum Efficiency Reporting Value, a 1–16 scale for how well an air filter captures particles. MERV 8–11 suits most homes; very high ratings in a thin filter can restrict airflow unless the system is designed for them. Learn more
Micro-embedded generation: Ontario's category for small generators, like home solar, connected to the distribution grid. As reported, the threshold rose from 10 kW to 12 kW on 1 May 2026. Learn more
microFIT: A former Ontario feed-in tariff program that paid fixed rates for small renewable generation. It closed to new applicants in 2017. Learn more
Microinverter: A small inverter mounted behind each solar panel, converting DC to AC panel by panel. It can reduce the impact of partial shading and allows panel-level monitoring. Learn more
Mid-peak: The middle-priced period on Ontario's Time-of-Use and Ultra-Low Overnight plans, priced at 14.6¢/kWh from 1 November 2026. Learn more
Modulating furnace: A furnace whose gas valve and blower adjust output in small steps to match heat demand, instead of running only at full or half power. It gives steadier temperatures and quieter operation. Learn more

N

Net metering: An arrangement under Ontario Regulation 541/05 where exported solar electricity earns kWh credits at the retail commodity value. Credits roll forward for up to 12 months and then expire; there is no cash payout. Learn more
Net-zero home: A home designed to produce, typically with solar panels, about as much energy as it uses over a year. It relies first on a very efficient envelope and equipment. Learn more
NOSI: Notice of Security Interest, a notice registered on a property's title by some equipment rental or financing companies. Ontario legislation in 2023–24 banned NOSIs on consumer goods, with protections taking effect in phases; verify details on ontario.ca. Learn more

O

ODP certificate: Ozone Depletion Prevention certificate, required in Ontario for anyone who handles refrigerants. Ask your heat pump or air conditioning installer to confirm they hold one. Learn more
OEB: The Ontario Energy Board, the independent regulator of Ontario's electricity and natural gas sectors. It sets Regulated Price Plan electricity prices and approves utility delivery rates. Learn more
OER: The Ontario Electricity Rebate, a provincial credit applied as a percentage of most of an eligible customer's pre-tax electricity bill. It is 15.7% effective 1 November 2026, down from 23.5%. Learn more
OESP: The Ontario Electricity Support Program, which provides a monthly on-bill credit to lower-income households. It is administered through the OEB. Learn more
Off-peak: The lowest-priced period on Ontario's Time-of-Use plan, 9.1¢/kWh from 1 November 2026. It covers weekdays from 7 p.m. to 7 a.m. and all day on weekends and statutory holidays. Learn more
OHPA: Oil to Heat Pump Affordability, a program that helps income-qualified households switch from oil heat to a heat pump. The Ontario stream, delivered through Save on Energy, offers up to $25,000 plus $250 upfront; confirm current intake status. Learn more
On-peak: The highest-priced period on Ontario's Time-of-Use plan, 18.9¢/kWh from 1 November 2026. In winter it runs on weekdays from 7–11 a.m. and 5–7 p.m.; on the ULO plan, on-peak is 37.7¢ on weekdays from 4–9 p.m. Learn more
Ontario Building Code (OBC): The provincial regulation that sets minimum construction standards in Ontario, including energy efficiency requirements under Supplementary Standard SB-12. Renovations needing a building permit must meet the code. Learn more
Outdoor reset control: A boiler control that adjusts supply water temperature based on outdoor temperature, running cooler on mild days. It improves comfort and helps condensing boilers reach their rated efficiency. Learn more

P

Passive House: A rigorous building standard focused on airtightness (0.6 ACH50 or less), high insulation, high-performance windows and heat recovery ventilation, resulting in very low heating demand. Learn more
Payback period: How long an upgrade takes to repay its cost through energy savings, calculated as net cost divided by yearly savings. It ignores comfort, resale value and future price changes, so treat it as one factor among several. Learn more
Peak demand: The highest rate of electricity use, in kW, at a given moment, as opposed to total energy used, in kWh. Ontario residential customers are billed for energy, but household peak demand matters for electrical service sizing. Learn more
Phantom load: Electricity used by devices that are switched off or in standby, such as TVs, game consoles and chargers. It typically accounts for about 5–10% of household electricity use. Learn more
Pre-installation approval: Approval required from the Home Renovation Savings Program before heat pump work begins. Starting work without it can make you ineligible for the rebate. Learn more
Programmable thermostat: A thermostat that follows a set schedule of temperatures by time of day and day of week. A smart thermostat adds remote control, learning and energy reports. Learn more
Propane: A fuel stored in a tank on the property and used for heating and water heating where natural gas is not available. Propane-heated homes count as non-gas-heated for Home Renovation Savings heat pump rebates. Learn more

R

R-22: An older refrigerant used in air conditioners and heat pumps made before about 2010. It is no longer produced or imported in Canada, so servicing R-22 equipment is increasingly costly. Learn more
R-410A: The refrigerant used in most air conditioners and heat pumps sold from about 2010 until the early 2020s. It is being phased down under federal HFC regulations in favour of A2L refrigerants. Learn more
R-value: A measure of how well a material resists heat flow; higher numbers insulate better. Many older Ontario attics have R-12 to R-20, against a recommended retrofit target of R-50 to R-60. Learn more
Radiant floor heating: Heating through warm floors, using either hot-water tubing (hydronic) or electric mats. Electric mats suit small areas such as bathrooms; hydronic systems are better for whole floors. Learn more
REA: Registered Energy Advisor, a professional licensed through a service organization to perform EnerGuide home energy assessments. An REA is required for the HRS assessment stream. Learn more
Refrigerant: The working fluid a heat pump or air conditioner circulates to absorb and release heat. Handling refrigerant in Canada requires an ODP certificate. Learn more
Regulatory charge: A line on your electricity bill covering the costs of running the provincial grid and electricity market, along with some programs. It is set by the OEB and is the same across the province. Learn more
Retail energy contract: A contract with a licensed energy retailer to buy electricity or natural gas at a fixed or variable price instead of the regulated price, usually for several years. Prices are often higher than the Regulated Price Plan; read the OEB's guidance first. Learn more
Return air: Air drawn from the house back to the furnace or air handler through return grilles and ducts. Too few returns, or blocked ones, cause pressure problems, noise and uneven temperatures. Learn more
Rigid foam insulation: Board insulation such as extruded polystyrene (XPS), expanded polystyrene (EPS) or polyisocyanurate, typically R-4 to R-6 per inch. It is commonly used against basement walls because it tolerates moisture. Learn more
Rim joist: The band of framing where the floor joists meet the top of the foundation wall. In many Ontario basements it is uninsulated and leaky, making it a common air sealing and insulation target. Learn more
RPP: The Regulated Price Plan, the OEB-set electricity pricing that most Ontario homes pay. It includes the Time-of-Use, Ultra-Low Overnight and Tiered price plans. Learn more
RSI: The metric version of R-value, used in the Ontario Building Code. To convert, RSI multiplied by about 5.68 gives the imperial R-value; for example, RSI 8.8 is roughly R-50. Learn more

S

Save on Energy: The IESO's brand for Ontario's electricity conservation programs. It co-delivers the Home Renovation Savings Program with Enbridge Gas and runs the Energy Affordability Program. Learn more
SB-12: Supplementary Standard SB-12 of the Ontario Building Code, which sets the energy efficiency requirements for houses, including insulation levels, windows and equipment efficiency. Learn more
SEER2: Seasonal Energy Efficiency Ratio 2, the cooling-efficiency rating for air conditioners and heat pumps under test standards in place since 2023. Higher numbers mean less electricity used for the same cooling. Learn more
SHGC: Solar Heat Gain Coefficient, the fraction of solar heat that passes through a window, from 0 to 1. Lower values block more summer heat; higher values let in more free winter sun. Learn more
Short cycling: When heating or cooling equipment turns on and off very frequently. It usually signals oversizing, airflow problems or a misplaced thermostat, and reduces comfort, efficiency and equipment life. Learn more
Smart meter: The digital electricity meter installed in Ontario homes that records use by the hour, which makes Time-of-Use and Ultra-Low Overnight pricing possible. Hourly data is available through your utility, often via Green Button. Learn more
Smart thermostat: A Wi-Fi thermostat that can learn schedules, be controlled by phone and adjust for occupancy. HRS has offered a $100 rebate on qualifying models through the product route. Learn more
Specific yield: The annual electricity produced by a solar array per kW of capacity. In southern Ontario, a well-oriented, unshaded array typically yields about 1,100–1,250 kWh per kW per year. Learn more
Spray foam insulation: Insulation sprayed as a liquid that expands and hardens. Closed-cell foam provides roughly R-6 per inch plus an air and vapour barrier; open-cell is lighter and less insulating. It is common on rim joists and in hard-to-reach areas. Learn more
Stack effect: The natural upward movement of warm air in a building, which pulls cold air in at the bottom (basement) and pushes warm air out at the top (attic). It is why sealing the attic floor and rim joists matters most. Learn more
Standby losses: Heat lost from a hot water tank and pipes while water sits unused. Insulating pipes and keeping the tank at a sensible temperature, around 60 °C, reduces these losses. Learn more
Static pressure: The resistance to airflow in a duct system, measured in inches of water column. High static pressure from undersized ducts or restrictive filters reduces airflow and efficiency, especially with heat pumps. Learn more

T

Tankless water heater: A water heater that heats water only as it flows, with no storage tank. It avoids standby losses, but gas models often need larger gas lines and venting, and electric models need very large electrical capacity. Learn more
Thermal bridging: Heat flow through materials that conduct heat more easily than the insulation around them, such as wood studs or concrete slab edges. Continuous exterior insulation reduces thermal bridging. Learn more
Tiered pricing: An Ontario RPP option with two flat prices: Tier 1 at 11.2¢/kWh and Tier 2 at 13.2¢/kWh from 1 November 2026. The residential threshold is 1,000 kWh a month in winter and 600 kWh a month in summer. Learn more
Time-of-Use (TOU): Ontario's default residential electricity price plan, with off-peak, mid-peak and on-peak prices that depend on the time of day, day of week and season. Learn more
Ton (cooling or heating): A unit of heating or cooling capacity equal to 12,000 BTU per hour, or about 3.5 kW. HRS heat pump rebates are calculated per ton of capacity. Learn more
Transportation charge: A line on your Enbridge Gas bill for moving natural gas through pipelines to Ontario. It is separate from the gas supply and local delivery charges. Learn more
Triple-pane window: A window with three panes of glass and two sealed gaps. It typically reduces heat loss compared with double-pane windows and can be worthwhile in colder parts of Ontario, but costs more and is heavier. Learn more
TSSA: The Technical Standards and Safety Authority, which regulates fuel safety in Ontario, including gas appliances, fuel oil tanks and propane, and licenses gas technicians. Learn more
Two-pipe system: A central heating and cooling system common in older condos and apartments that can deliver only hot water or only chilled water at a time. The building switches between heating and cooling seasonally. Learn more

U

U-factor: A measure of how much heat passes through a window or door; lower is better. In Canada, window ratings are often shown in metric U-values (W/m²·K). Learn more
ULO: The Ultra-Low Overnight price plan, offered by most Ontario LDCs, with a very low 3.7¢/kWh price from 11 p.m. to 7 a.m. and a high 37.7¢ on-peak price on weekdays from 4–9 p.m. It suits households that can shift large loads overnight. Learn more
Unit sub-meter provider: A company licensed by the OEB to meter and bill individual suites in condos and apartment buildings. Its bills should show commodity, delivery and other charges and the Ontario Electricity Rebate. Learn more

V

Vapour barrier: A layer, often polyethylene sheet, that limits moisture moving from warm indoor air into walls and ceilings where it could condense. In Ontario it is usually placed on the warm (interior) side of insulation. Learn more
Vermiculite: A pebble-like, grey-brown loose-fill insulation found in some older Ontario attics. Some vermiculite contains asbestos, so do not disturb it; have it tested and, if needed, removed by a qualified contractor before attic work. Learn more

Z

Zoning (HVAC): Dividing a home into areas with separate thermostats, using motorized dampers in ducts or separate indoor heads with a mini-split. Zoning can fix uneven temperatures but must be designed so the equipment still gets enough airflow. Learn more