What to ask for in an HVAC load calculation

Questions covered in this guide

A bigger unit is not a complete answer

If the house has an uncomfortable room, start by describing when and where the problem occurs. Give the contractor a short record: afternoon or overnight, doors open or closed, upstairs or downstairs, and whether the problem affects one room or the entire house. This is useful project information even when you do not know the equipment capacity.

Ask for the inputs behind the result

A load calculation estimates the heating and cooling demand the equipment must serve. The Department of Energy explains that proper sizing considers the building rather than only its floor area. Ask what the contractor assumed about insulation, windows and air leakage, and whether recent improvements were included. Request a copy or summary you can keep with the proposal.

Separate demand from equipment selection

Ask the contractor to explain how the calculated demand leads to the proposed model. Request an explanation if a competing proposal specifies a different size. Treat the existing unit's label as a record of what is installed, not an automatic instruction to buy the same capacity again. ENERGY STAR identifies sizing as one part of installation quality, alongside airflow and other checks.

Use uncertainty to improve the bid

If insulation or an addition is poorly documented, mark that question for inspection. Avoid replacing missing information with an online square-footage rule. In your comparison sheet, record whether the calculation was completed, which scope it covers, and what remains unverified. Our planning calculator helps organize a budget; it does not perform a building load calculation or select equipment for your home.

Putting it into practice

A sizing comparison should record the calculation inputs and the explanation for equipment selection. Two different tonnage recommendations cannot be meaningfully reconciled by choosing the cheaper or larger one alone.

Sources and supported claims

DOE guidance on proper HVAC sizing considers building characteristics in determining heating and cooling loads.
Source ↗ · national · Checked 2026-10-12

ENERGY STAR identifies correct equipment sizing and airflow as installation quality considerations.
Source ↗ · national · Checked 2026-10-12