Why Do Heat Pump Quotes Recommend Different Sizes?

Start with the job the equipment is supposed to do. Ask whether the proposal covers the whole home, a group of rooms, or part of the heating load alongside another system. Note whether the existing furnace or other heat will stay, and under what conditions the contractor expects it to run. If the two proposals cover different rooms or handle cold weather differently, write that down before comparing their equipment sizes.

Give both contractors the same description of the home and the same goal. Include any planned work that could change the design, such as new attic insulation or finishing an addition. Ask whether their numbers describe the house as it stands or after the work is complete. If the answer depends on improvements you may defer, ask what design the contractor recommends for the house you will actually occupy.

• Ask for the heat load calculation behind the proposed size, as BC Hydro recommends.
• Ask which equipment data supports the selection at the stated conditions, following the distinction between sizing and selection in Natural Resources Canada’s toolkit.

Separate the estimated heating load from the output of the proposed equipment. The load describes how much heat the home or area needs under stated conditions. Equipment output describes what the proposed system can provide under specified conditions. BC Hydro advises asking for a heat load calculation. Natural Resources Canada publishes sizing and selection materials for contractors working in Canadian climates. Ask each contractor to explain which figures they used and what the figures represent.

Request the indoor and outdoor model numbers and the proposed heating output at the outdoor temperature used for the design. Ask for the same units and conditions on both proposals. If one quote lists nominal capacity and the other lists output at a particular winter temperature, have the contractors rewrite those lines before treating the numbers as comparable. Also ask how they accounted for any cooling requirements you gave them.

Consider a hypothetical house where one quote pairs a smaller heat pump with the existing furnace and another proposes a larger heat pump for wider heating coverage. The owners expected both quotes to replace the furnace. Their first question should be whether both designs deliver that result. If one assumes the furnace stays, it is solving a different problem. Ask that installer for a revised scope if keeping the furnace is outside your brief.

Now suppose both contractors intended the same coverage. One used an estimated insulation level, while the other assumed attic work the owners have only discussed. Ask them to compare the same house conditions, identify which assumptions remain unverified and explain whether correcting them changes the recommendation. There can still be two defensible designs. The comparison should show the trade-offs and how each contractor plans to cover any difference between equipment output and the home’s needs.

Copy this request into your follow-up: “Please confirm which rooms this proposal serves, the design outdoor temperature and estimated heating load, the indoor and outdoor model numbers, and their heating output at that temperature. Please identify what supplies the remaining heat if needed, which parts of my existing system remain, and which assumptions still need a site check.” Attach the same home brief to both emails.

Put the responses into two columns and mark each answer confirmed, estimated, or open. Ask who owns each open check, what it might change, and when it will be resolved. For example, if a proposal depends on reusing ducts, ask what the contractor will assess before confirming that scope. Keep the revised answers with the quotes so that the design assumptions carry into the final written agreement.