Scope. Sizing method, not program advice. Rebate amounts, eligibility and deadlines change often and vary by province — always work from the current terms of the program you are claiming. Nothing here is affiliated with or endorsed by any program administrator, CSA, HRAI or NRCan.

Your heating load is not your heat pump size

This is the single most common mistake in Canadian heat pump work, and it comes from carrying a furnace habit into equipment that behaves nothing like a furnace.

A furnace makes its rated output whether it is −5 °C or −30 °C outside. So sizing it to the design heat loss is reasonable, and CSA F280-12 sizes heating to the calculated design load without deliberate oversizing on exactly that logic.

A heat pump does the opposite of what you need. Its capacity falls as the outdoor temperature drops — precisely when the building’s heat loss is climbing. Two curves moving in opposite directions. Take a unit rated at 3 tons at 8.3 °C and it might deliver a little over half that at −25 °C, depending on the model.

So if you pick a heat pump big enough to cover the full design heat loss at the design temperature, you have selected a machine that is enormously oversized for the other 95% of the heating season. It will short-cycle through the shoulder months, control humidity poorly in cooling, and never spend time in the modulating range where its efficiency actually lives. You will also have paid for a great deal of capacity that gets used for a handful of hours a year.

The balance point is the real decision

Plot the building’s heat loss against outdoor temperature, then plot the heat pump’s capacity on the same axes. They cross somewhere. That crossing is the balance point: above it the heat pump carries the house on its own, below it something has to make up the shortfall.

Where you put that crossing is the sizing decision, and it is a judgement rather than an output. Push the balance point lower and you buy a bigger machine that covers more of the winter unaided, at the cost of money up front and worse part-load behaviour the rest of the year. Let it sit higher and you lean more on supplementary heat — electric resistance, or the existing furnace in a dual-fuel arrangement — which is cheap to install and expensive to run.

What makes this a Canadian problem specifically is the spread in design temperatures. A balance point that is perfectly sensible in Vancouver, where design is around −4 °C, is a completely different economic proposition in Winnipeg at −31 °C. You cannot carry a rule of thumb across that gap. Start from the real design temperature for the actual postal code — there is a table of them by city if you want to see the range.

The other half is supplementary heat. Once the balance point is chosen, the shortfall below it is arithmetic: the gap between the load line and the capacity line at the design temperature. That is the number that sizes the backup, and it is the number that tells the homeowner what their coldest week will cost.

What the programs actually ask for

The major Canadian incentive programs do not hand you a sizing method. They hand you the responsibility.

Ontario’s Home Renovation Savings Program, delivered through Save on Energy and Enbridge Gas, states in its terms that the mechanical system contractor is responsible for specifying the system — load calculations, sizing and selection — and that the heat pump must be properly sized to meet the building heat load and comply with applicable laws, building codes and permitting requirements. The same terms go on to say that a heat pump is not typically sized to deliver 100% of the peak heating load, because that leads to an oversized system that cycles frequently, and that contractors should design for energy savings and occupant comfort.

That is a program administrator telling you, in writing, not to do the thing the furnace habit tells you to do.

Most programs layer on equipment requirements as well — typically that the unit appears on the NRCan qualified product list for cold climate air source heat pumps or ground source heat pumps, and that the installing contractor is registered with the program. Those are eligibility gates rather than sizing guidance, but they are where applications get bounced.

Current program pages, since the details move:

Where the incentive pulls the wrong way

Worth naming plainly, because nobody else will: some programs pay by installed capacity. A rebate calculated per ton means a larger system returns a larger cheque, on the same job, for the same house.

The program terms simultaneously require correct sizing. So the paperwork and the payment structure point in opposite directions, and the person who absorbs the difference is the homeowner — through short cycling, poor dehumidification in summer, more starts and stops on the compressor, and a shorter service life.

The defensible position is simple and it also happens to be the one the terms require: size to the calculation, then claim whatever that size earns. If a reviewer ever asks why the system is the size it is, the answer is a load calculation with real design conditions and a stated balance point — not a preference.

What to put in front of the homeowner

Whatever the program requires, the document that ends arguments has the same bones:

  • The design conditions used, and where they came from — the postal code or municipality, the heating and cooling design dry-bulbs, and the source.
  • The calculated design heating and cooling loads, with the envelope assumptions visible rather than buried.
  • The selected equipment, with its capacity at the design temperature rather than its nameplate rating at 8.3 °C. This is the line most quotes leave out, and it is the one that matters.
  • The balance point, and the supplementary heat sized to cover below it.
  • Who prepared it and when.

A homeowner comparing three quotes cannot evaluate equipment brands. They can absolutely see which of the three contractors showed their work.

Running the numbers

The free CSA F280 calculator gives you a whole-house block load from a postal code in the browser, which is enough to sanity-check a proposal or catch an obviously oversized quote on the phone.

The CSA F280 app adds the parts this page is actually about: it computes the heat pump balance point and the supplementary heat requirement, takes blower-door airtightness and HRV or ERV recovery, and produces a PDF with the design conditions and assumptions on it. It works offline, which matters when the mechanical room has no signal.

Both are estimating aids. Neither is a room-by-room CSA F280 report, and neither is a compliance document — see what a permit submission actually needs.

FAQ

Should a heat pump be sized to the full F280 heating load?

Usually not. That logic fits a furnace, whose output does not change with outdoor temperature. A heat pump loses capacity as it gets colder, so sizing to the full design load leaves it badly oversized for the mild hours that make up most of the season.

What is the balance point?

The outdoor temperature where the heat pump’s falling capacity meets the building’s rising heat loss. Above it the heat pump carries the house alone; below it supplementary heat makes up the difference. Choosing where it sits is the actual sizing decision.

Do rebate programs require a load calculation?

The major ones put load calculation, sizing and selection on the mechanical contractor and require correct sizing to the building heat load. Ontario’s program terms say it explicitly and warn against sizing to 100% of peak. Terms vary and change — read the current ones.

If the rebate pays by the ton, should I go bigger?

Better cheque, worse house. The same terms that pay per ton also require correct sizing, and the homeowner pays for oversizing in comfort and equipment life. Size to the calculation and claim what that size earns.

Can I submit a whole-house block load?

Check the program and your AHJ. CSA F280 is a room-by-room method and a block load is a different artifact. Use the block load to design and sanity-check; do not present it as the compliance document.