Skip to main content

CSA F280 Heat Loss Calculator
(Ontario & Canada)

A quick heat loss and heat gain estimate for Canadian homes, built on the CSA F280-12 approach. Ballpark the furnace and AC size, then see what the full F280 calculation for your permit needs.

Back to Calculators

Where is your home located?

We use your location to determine the design temperatures for your region.

CSA F280-12 Design Temperatures

Your location determines the outdoor design temperatures used in the calculation. These are based on historical weather data (2.5% design conditions).

Heat loss calculations in Ontario and BC: what CSA F280 requires

Building or renovating a house in Ontario or British Columbia? The building department will usually ask for a heat loss and heat gain calculation done to CSA F280 before it issues the permit. Here is what the standard is, when each province asks for it, who can sign it, and where this free calculator fits.

What CSA F280 is

CSA F280, Determining the Required Capacity of Residential Space Heating and Cooling Appliances, is the Canadian standard for working out how much heat a house loses at the winter design temperature and gains at the summer one. The furnace, boiler, heat pump or air conditioner is then sized to match.

It covers houses and small residential buildings under Part 9 of the building code. It sizes the equipment and sets rules for choosing its output capacity once the load is known. It does not design the ductwork or the installation; those are separate steps.

The edition in use is F280-12. CSA has reaffirmed it rather than replaced it, which is why you see labels like F280-12 (R2021): the R year marks a reaffirmation, not a new method.

When Ontario asks for a heat loss calculation

The Ontario Building Code points to CSA F280 for sizing the heating and cooling equipment in a house, and building departments check the calculation at permit time. For a new house, a typical HVAC package is:

  • Heat loss and heat gain calculations
  • A duct design, with a duct layout that matches the architectural drawings
  • A mechanical ventilation design summary
  • The Schedule 1 designer information form

Renovations depend on the municipality and the work. Sarnia asks for the full package for a gut renovation or any renovation that includes a furnace replacement, and no mechanical documents with the application when an addition grows the conditioned floor area by 20% or less and keeps the existing system. Brampton asks for the calculation and a ventilation design summary when a home switches from electric, oil or boiler heat to a natural gas forced-air furnace.

Energy efficiency is a separate rulebook, Supplementary Standard SB-12. The compliance package the house is built to (insulation levels, windows, airtightness, equipment efficiency) is declared on an Energy Efficiency Design Summary, and building departments expect the heat loss calculation to match it.

The 2024 Ontario Building Code took effect on January 1, 2025, and applications filed after March 31, 2025 are reviewed under it. Work from your building department's current checklist, not an older one.

Who can prepare and sign it in Ontario

The designer has to be qualified and registered with the Ministry of Municipal Affairs and Housing. For HVAC design on a house, that means the HVAC-House qualification (the Building Services exam also covers it), and the designer lists their BCIN, the Building Code Identification Number, on the Schedule 1 form. A professional engineer licensed in Ontario can stamp the design instead.

Some design work is exempt from registration and qualification, and Schedule 1 has a line for stating the reason. Ask your building department before you assume an exemption applies.

For training, HRAI (the Heating, Refrigeration and Air Conditioning Institute of Canada) runs a Residential Heat Loss and Heat Gain Calculations course on CSA F280-12 (R2021) that municipal building officials and plans examiners recognize.

When BC asks for an F280 calculation

The BC Building Code 2024 is explicit: Sentence 9.33.5.1.(1) of Division B requires the capacity of heating and cooling appliances serving a single dwelling unit to be determined with CSA F280, using the code's own design temperatures.

It also added an overheating rule. For permits applied for on or after March 8, 2024, at least one living space in each new dwelling unit must be able to stay at or below 26°C at the summer design temperature, through mechanical cooling, passive design, or both. F280 is the method for showing it.

The province recommends doing the F280 calculation early in design, by a mechanical consultant or contractor or someone competent in HVAC design, using software verified under Section 8 of CSA F280. HVAC Designers of Canada keeps the list of verified programs.

Local governments enforce the code, some add their own forms and deadlines, and the City of Vancouver has its own building by-law. Check with your local building department first.

What this calculator does, and what a full F280 calculation adds

This free calculator

  • Uses the winter (2.5% January) and summer design temperatures for the city you pick
  • Holds 22°C indoors in winter, the living-space design temperature in the building code, and 24°C in summer
  • Treats the house as one block: floor area, ceiling height, stories, age, foundation type, insulation level, window type and window share of the walls
  • Estimates air leakage from the age of the house
  • Returns one whole-house load in BTU/h and kW, with a furnace range and AC tonnage

A full CSA F280 calculation

  • Takes measured areas and the actual insulation and window values for every wall, ceiling, floor and window from the drawings
  • Works room by room, because the duct design and register sizes are built from the room loads
  • Calculates foundation heat loss and air leakage with the standard's own methods, and can use a blower door test result
  • Includes ventilation heat loss and the credit for a heat recovery ventilator
  • Applies the standard's rules for choosing equipment capacity, and is signed by a qualified designer or engineer
  • In BC, shows the 26°C check for the designated living space

An estimate, not a signed F280 design

Use this calculator to plan, quote and sanity-check equipment size. It is not a CSA F280 calculation and cannot be submitted for a building permit. For the permit, hire a qualified designer (in Ontario, one with a BCIN and the HVAC-House qualification) or an engineer, and confirm what your building department needs.

For HVAC contractors

Heating season is when furnace and heat pump quotes pile up. Run the estimate with the homeowner to set expectations on size and budget early, then let the full F280 calculation settle the final equipment choice.

WorkZen for HVAC businesses →

Heat loss calculation FAQ

For a new house, yes. Ontario building departments ask for a heat loss and heat gain calculation, a duct design and a ventilation design summary with the permit application, prepared by a qualified designer. For renovations it depends on the municipality and the work: replacing a furnace or converting to gas forced air often triggers it, so check your building department's checklist.
No. It is a simplified estimate for planning, quoting and sanity checks. A permit needs a full CSA F280 calculation, worked room by room and signed by a qualified designer or engineer.
A designer registered with the province who holds the HVAC-House qualification (or Building Services) and lists their BCIN on the Schedule 1 designer form, or a professional engineer licensed in Ontario. Some design work is exempt; your building department can confirm whether yours is.
Yes for new homes. The BC Building Code 2024 requires the heating and cooling appliance capacity for a dwelling unit to be determined with CSA F280. For permits applied for on or after March 8, 2024, the design must also show that at least one living space in each dwelling unit stays at or below 26°C at the summer design temperature.
Both size home heating and cooling equipment from a heat loss and heat gain calculation. CSA F280 is the Canadian standard that provincial building codes refer to; ACCA Manual J is the American method. For a home in the United States, use our US heat load calculator, which follows Manual J.
For heating, the 2.5% January design temperature for your city and 22°C indoors. For cooling, the summer design temperature for your city and 24°C indoors. Your designer will confirm the design temperatures your municipality expects.
It depends on the heat loss at your winter design temperature, which comes from your location, floor area, insulation, windows and airtightness. This calculator gives a furnace range in BTU/h as a starting point. The F280 calculation decides the final size, and an oversized furnace short-cycles and wastes energy.

Sources

Checked October 2026. Codes and municipal checklists change, and your building department has the final word.