As of June 16, 2026, a heat pump quote should not lock in the equipment size while the house itself is still changing. If attic air sealing, insulation, duct work or window improvements are likely soon, the contractor needs to know whether the heat pump is being sized for today's load or the load after those fixes.

That does not mean every homeowner should delay a heat pump. It does mean the quote should explain what assumptions were used.

ENERGY STAR's contractor hiring guidance says a contractor should inspect the home, and that sizing should consider the home's size, insulation level and windows. The Department of Energy's heat pump overview also points existing homeowners replacing gas heat toward weatherization for cost savings and comfort, especially in older homes.

The useful pre-quote question is simple: will the house lose or gain less heat after planned envelope work, and should that change the proposed heat pump size?

Start with the work that may change the load

Before comparing model numbers, write down any near-term work that could change heating or cooling demand:

  • attic air sealing;
  • attic, crawlspace or basement insulation;
  • duct sealing or duct insulation;
  • major window or door work;
  • a finished basement or addition;
  • an EV charger, induction range or other new electric load;
  • removing or keeping a backup furnace;
  • changing from central ducts to ductless zones.

Some of those reduce the heating and cooling load. Some add electrical demand. Some change comfort without changing the whole-home load very much. The point is not to guess the final answer yourself. The point is to make sure the quote does not pretend the house is static when you already know it is not.

If the contractor only asks for square footage, be careful. Square footage can start a conversation, but it is not enough for a final heat pump decision in a house with uneven insulation, leaky ducts or planned weatherization.

Ask what calculation the size is based on

A quote should not just say "three-ton heat pump" or "36,000 BTU system" without explaining the basis for that size. Ask the contractor:

  • Did you perform a room-by-room or whole-home load calculation?
  • Which insulation levels did you assume?
  • Did you inspect ducts, airflow and returns?
  • Did you account for air sealing or insulation work that is planned but not complete?
  • Did you size for heating, cooling or both?
  • What outdoor design temperature did you use?
  • What backup heat, if any, is assumed?

You do not need to become an HVAC designer. You do need enough detail to know whether the number came from the home or from a rule of thumb.

Oversizing can look comforting in a sales conversation because it sounds safer. But a bigger system is not automatically better. It can cost more, cycle poorly, miss humidity control, create noise or still leave rooms uncomfortable if ducts and airflow are wrong.

Finish obvious envelope work when timing allows

DOE's air sealing guidance frames uncontrolled air leakage as outside air entering and conditioned air leaving through cracks and openings. It also says homeowners should detect leaks and assess ventilation needs before air sealing. DOE's insulation guidance treats insulation as part of reducing heat flow through the building envelope.

If a home has obvious attic leaks, thin insulation or cold rooms, the cleaner sequence is often:

  1. Assess the envelope.
  2. Air seal important leaks.
  3. Bring insulation up where it is clearly weak.
  4. Revisit the heat pump load assumptions.
  5. Finalize equipment size, ducts, zones and backup heat.

The Consortium for Energy Efficiency's weatherization guide for homeowners makes the same practical point for heat pump planning: when weatherization is planned, size the heat pump for the reduced load after that work. Treat that as a planning principle, not as a promise that every home will need a smaller unit.

If weatherization cannot be finished before heating season, ask the contractor how the system will handle the interim period. The answer might involve retaining backup heat, choosing a variable-speed system, setting controls carefully or planning a follow-up adjustment after the envelope work.

Separate duct problems from equipment size

A heat pump can be correctly sized for the house and still perform badly through weak ducts. ENERGY STAR's contractor guidance says a good contractor should inspect ducts for leaks and insulation where applicable, and measure airflow.

Ask for duct details before you approve the equipment:

  • Are the ducts inside conditioned space or in an attic, crawlspace or garage?
  • Are visible duct leaks or disconnected runs included in the quote?
  • Is duct insulation adequate for the location?
  • Will the return air path support the proposed system?
  • Are some rooms likely to need balancing, zoning or duct changes?
  • If ducts are poor, is a ductless or hybrid approach being considered?

Do not let a larger heat pump become the answer to a distribution problem. If one bedroom is hot because the duct run is poor, more capacity at the air handler may not fix that room.

Watch the quote language around "future proofing"

Future proofing can be useful, but it can also become a vague reason to oversize. A homeowner may genuinely expect more electric load from an EV, a heat pump water heater, added rooms or a finished basement. Those changes should be named, not hidden inside a bigger number.

Ask the contractor to split the assumption:

  • Size needed for the house as it is today.
  • Size expected after planned air sealing and insulation.
  • Size impact of any known addition or major usage change.
  • Backup heat assumption for very cold weather.
  • Whether a variable-speed system can handle the range without short cycling.

This helps you see the tradeoff. You may choose a system that has some headroom. But you should know whether that headroom is for a real future load or just a sales cushion.

Do not rely on old tax-credit math

Incentives can affect timing, but they should not decide the equipment size. ENERGY STAR's air-source heat pump tax credit page states that the listed federal tax credit was effective for products purchased and installed from January 1, 2023 through December 31, 2025. If a 2026 quote still uses that credit language, ask for a current source and do not treat the credit as guaranteed.

The same applies to local rebates. A rebate may make a better system easier to afford, but the system still needs to fit the house. Ask the contractor to keep incentive estimates separate from the sizing calculation.

The email to send before signing

Send this before the quote becomes final:

"We are considering air sealing, insulation and/or duct work. Please confirm what load calculation or sizing method was used for this heat pump quote, which insulation and duct assumptions it includes, whether the size should change after weatherization, and what backup or control plan applies if the envelope work happens later."

The answer should be specific enough that you can compare quotes. One contractor may say the load is already low and weatherization will not change equipment size. Another may recommend finishing attic work first. A third may flag ducts as the real constraint.

Those are useful differences. They tell you more than a single price line.

The goal is not to make the heat pump project complicated. It is to avoid paying for a system sized around leaks, weak insulation or duct problems you were about to fix anyway.