CSA F280 load calculation for a building permit

The clause that creates the requirement

The requirement is not a local preference. Section 9.33 of the National Building Code — and the provincial codes that adopt it — requires that the capacity of heating and cooling appliances located in a dwelling unit and serving only that dwelling unit be determined in accordance with CSA F280, except that the design temperatures shall conform to Subsection 9.33.3.

That applies to residential occupancies falling under Part 9, where the appliances are permanently installed in the dwelling unit they serve. Which is to say: essentially every house and most small residential work in the country.

The practical consequence is that a permit application has to demonstrate the sizing was done to F280. Not assert it. The building department is not going to take the equipment schedule on faith when the clause names a standard.

The design-temperature trap

Read that exception again, because it is where otherwise-good submissions come apart: the design temperatures shall conform to Subsection 9.33.3.

Your software has design temperatures in it. They probably came from a weather-station dataset — NRCan HOT2000 values, or something derived from the same climate record. Those are good numbers and they are appropriate for design work. But the code sends the reviewer to the design-temperature tables in the code appendix, tabulated by municipality.

Those two sources agree closely far more often than not, because they descend from the same observations. When they diverge, the reviewer is working from the code table and you are not, and the conversation goes badly for the person who has to explain the difference.

There is a related trap in the geography. Weather-station datasets map a postal code to the nearest station with published data, which is usually fine and occasionally is not — a valley bottom versus the plateau above, a lakeshore versus twenty kilometres inland. Our design temperatures by city table shows exactly which station each postal code lands on, precisely so you can see when the substitution deserves a second look. For a permit, use the value the code names for that municipality.

F280 is a room-by-room method

This is the part that surprises people coming from block-load habits, and it is worth being blunt about.

CSA F280 provides a methodology for calculating room-by-room heat loss and heat gain throughout the dwelling unit. The room-level detail is not decoration — it is what makes the sizing defensible, and it is the input to the air-side design. A whole-house total tells you what equipment to buy. It tells you nothing about how much air the back bedroom over the garage needs, which is where comfort complaints come from.

So a whole-house block load, however carefully done and whatever standard it names, is a different artifact from a room-by-room F280 report. It is genuinely useful for sizing equipment and for catching a quote that is obviously oversized. It is not, on its own, the thing a reviewer is asking for when they ask for F280.

Some authorities accept a summary with building totals plus supporting room-level detail; some want the full room-by-room schedule; some have their own worksheet. Ask before you assemble the package.

What belongs in the package

Requirements vary, but reviewers are consistently looking for the same story: here are the conditions I designed to, here is the building I assumed, here is the load that produces, and here is why the equipment I chose matches it.

• Design conditions — heating and cooling design temperatures for the municipality, with their source named, matching the code tables the reviewer will check against.
• Envelope assumptions — assembly R-values or RSI, window U-factor and SHGC, areas and orientations, foundation type and below-grade detail. These have to agree with the architectural drawings in the same submission. Contradictions between the two are a fast rejection.
• Ventilation — the CSA F326 rate used and any HRV or ERV recovery credited.
• The calculated loads — room by room where that is what is expected, with building totals.
• Equipment selection — the chosen appliance and its capacity at the design condition, not its nameplate rating. For a heat pump, include the balance point and the supplementary heat below it; see heat pump sizing for why that is the number that matters.
• Provenance — who prepared it, what software and version, and the date.

Why submissions come back

Rarely arithmetic. Almost always context:

• Design temperatures that do not match the code table for that municipality.
• A whole-house total where room-by-room was expected.
• Envelope values that contradict the drawings — a wall assembly on the mechanical sheet that the architectural set does not describe.
• Equipment capacity quoted at rating conditions, so the reviewer cannot tell whether it covers the load at design.
• A heat pump sized as if it were a furnace, with no balance point and no supplementary heat shown.
• No name, no date, no software identified — a page of numbers nobody stands behind.

Where our tools fit, and where they do not

Being precise about this matters more than being flattering about it.

The free web calculator and the CSA F280 app both produce whole-house block loads using F280-12 methodology. The app adds detail the browser cannot — blower-door airtightness, HRV and ERV recovery, NFRC window overrides, heat pump balance point and supplementary heat — and puts the design conditions and assumptions on a PDF. Neither produces a room-by-room F280 schedule.

So they are sizing and verification tools. Use them to arrive at the right equipment, to check a subcontractor’s numbers, or to catch an oversized proposal before it reaches the homeowner. Do not present either output as a compliance document, and note that the app’s F280 coefficients are still being verified against the published standard — every result it produces says so.

If you are weighing which rulebook a job falls under in the first place, CSA F280-12 vs Manual J covers the differences.

FAQ