Heat Pump Size Calculator

The short version: BTU/h load = square footage × a climate-based BTU-per-square-foot factor × a ceiling-height adjustment × an insulation adjustment. The calculator above runs this for you and matches the result to an APOLLO model. For the full formula walkthrough and a general-purpose (non-heat-pump-specific) version of this calculator, see our BTU calculator guide.

For a typical 2,000 sq ft home in a moderate climate with average insulation, an APOLLO 3.5 Ton (42K BTU) standard-series unit is usually the right fit for radiant floor or fan coil distribution. Homes with baseboard or radiator heating typically need the APOLLO MAX 3 Ton (36K BTU) instead, since it delivers higher supply-water temperatures. Enter your exact square footage, climate, and emitter type in the calculator above for a number tailored to your home, or browse the full APOLLO lineup.

Residential heat pumps in the US are sized in tons (1 ton = 12,000 BTU/h) or directly in BTU/h. "HP" (horsepower) is a sizing convention used for some international and commercial equipment, roughly 1 HP ≈ 9,000–10,000 BTU/h, but it is not the standard unit for APOLLO residential models — all APOLLO capacities are listed in tons and BTU/h.

Standard APOLLO models deliver water up to about 131°F and are the default choice for radiant floors, fan coils, and air handlers. APOLLO MAX delivers water up to about 170°F, which baseboard heaters and cast-iron radiators typically need to perform properly. The BTU/h load your home needs doesn't change between the two series — only which product line can deliver the required water temperature. See both series side by side in the APOLLO collection.

Not necessarily bigger — but a different series. Baseboards and older cast-iron radiators were typically designed around higher supply-water temperatures than modern radiant floors or fan coils use. Selecting "Baseboard / Radiator" in the calculator above automatically routes your recommendation to the APOLLO MAX series, which is built for that higher temperature range at the same capacity tiers as standard APOLLO.

If you want both from one system, toggle "Heating + cooling" above. Standard APOLLO models handle both; APOLLO MAX is a heating-focused, high-temperature series, so a MAX recommendation with cooling needs is worth a closer look with our team. For a project-specific plan covering distribution, tanks, and controls, use System Builder.

Our largest single unit is the APOLLO 6 Ton (standard) or APOLLO MAX 5 Ton. Homes above that range typically need two units running in parallel rather than one oversized system — the right combination depends on your home's zoning and layout. Contact MBTEK or use System Builder for a multi-unit design.