In short
A CSA F280 heat-loss calculation is the Canadian standard method for sizing home heating and cooling. It adds up the heat each room loses through walls, windows, ceilings, floors and air leakage at the local winter design temperature. The result is a design heat loss in BTU/h. A quote sized by square footage, or by copying the old furnace, is not a load calculation.
A CSA F280 heat-loss calculation is the page of numbers that justifies the size of a furnace, boiler or heat pump before anyone orders equipment. The standard is published by CSA Group as F280-12, and it is the Canadian counterpart to ACCA Manual J, the method American websites describe. It produces one figure for the whole house and one for every room, in BTU per hour.
What goes into an F280 calculation and what comes out
An F280 takes the physical house as its input and returns a design heat loss for winter and a design heat gain for summer. The designer works from drawings or a site measure and enters every surface that separates heated space from the outdoors or the ground.
- Wall, ceiling and exposed-floor areas, with the insulation value of each assembly
- Every window and door: its size, glazing type and the direction it faces, which drives summer heat gain
- Below-grade walls and the basement slab
- Air leakage, from a blower-door test where one exists or from the age and construction of the house
- Mechanical ventilation, such as the airflow of an HRV
- The outdoor design temperature for the municipality, taken from the climate data in the building code
Design temperature is not the coldest night on record. It is the cold-weather benchmark the code assigns to each municipality: colder than a typical January night, milder than the record low, and a little lower inland than beside Lake Ontario. The room-by-room results then feed the duct design, because a bedroom over a garage needs more air than an interior bathroom.
When Ontario requires an F280 and when it is only good practice
Ontario requires it wherever a building permit covers the heating system. The Ontario Building Code references CSA F280 for sizing residential heating and cooling, so the calculation is part of the HVAC design package filed for a new house or an addition. Building departments such as the City of Burlington, the Town of Oakville and the City of Hamilton review it alongside the duct layout.
A like-for-like furnace swap in an existing house does not usually go through that review, which is why most replacement quotes arrive with no load calculation at all. That is the job where it pays off most. A 1970s–90s subdivision house that has since gained new windows, attic insulation and air sealing loses far less heat than it did the day its original furnace was chosen. The replacement case is covered in do I need a heat-loss calculation for a new furnace.
How to tell a real load calculation from a rule of thumb
A real load calculation states a design heat loss in BTU/h at a named outdoor design temperature and shows the rooms that add up to it. Anything else is an estimate.
- BTU per square foot multiplied by floor area is a rule of thumb; it ignores windows, insulation and air leakage.
- Matching the nameplate of the old furnace repeats whatever sizing mistake was made decades ago.
- A furnace's output, not its input, is the figure to compare with the design heat loss; a large overshoot gives you a furnace too big for the house.
- A heat pump is checked at the design temperature using the manufacturer's cold-weather capacity table, not its nominal tonnage; where capacity meets heat loss is the balance point.
- The design heat gain, not the heat loss, sets the air conditioner size.
Square-footage charts still have a use as a sanity check, and our furnace sizing guide explains their limits.
What an F280 costs and what to do next
There is no flat price for an F280. The cost follows the size of the house, whether drawings already exist and whether a duct design is needed with it, so ask for it as a written line on the quote. For a new build or an addition, the calculation is the first step of new construction HVAC work, done before equipment is chosen.
If you are comparing replacement quotes, ask each contractor for the design heat loss in writing. To have a house or a set of drawings looked at, contact ZK Mechanical or call (647) 801-1252.
Questions people ask about CSA F280 heat-loss calculation
Is a CSA F280 the same as a Manual J?
They do the same job under different standards. Manual J is the ACCA method used in the United States; F280 is the CSA method written for Canadian construction and climate data. Run on the same house, the two land close to each other, but an Ontario permit package is built on F280, so that is the one a building department expects to see.
Do I need an F280 to replace my furnace?
A straight furnace replacement does not normally trigger a municipal review, so nobody will demand one. It is still worth asking for when the house has been insulated or re-windowed since the old furnace went in, when the old unit short-cycled, or when you are moving to a heat pump, where capacity at the design temperature decides whether the house stays warm.
Who prepares an F280 for a building permit?
For a permit submission, the building department expects the calculation from a designer who holds the qualifications the Ontario Building Code sets out for residential HVAC design. The summary sheet carries the designer's name, the design temperatures used and the total heat loss and heat gain. Ask to see that sheet; it is one page and it is the proof the work was done.