What size heat pump do you actually need?
Get a starting range in 30 seconds. Then see why the real answer comes from a load calculation on your house — and why a tighter envelope buys you a smaller, cheaper system.
This is a rule-of-thumb starting range, not a Manual J. Installer heuristics run roughly 30–60 BTU/hr per square foot depending on climate; your envelope moves it further. Use it to sanity-check quotes, not to buy equipment.
Estimate uses a 15°F winter design temperature.
Keep this number with your project — it becomes part of Your Retrofit Plan.
We use this only to save your result. Create a free account with the same email and it appears in your plan.
What's next
Why this is a range, not a number
Square-footage rules can't see your walls. Two same-size houses can need systems two sizes apart.
The calculator above uses the same BTU-per-square-foot heuristics installers use for a first guess. What it can't measure is the part that actually determines your heating load: how much air leaks through the envelope, how much insulation is in the attic and walls, how many windows face which direction, and your local design temperature — the coldest conditions your system has to handle.
A Manual J load calculation measures all of that, room by room. It's the difference between "houses like yours usually need" and "your house needs." Every serious quote should include one — it's one of the first questions to ask an installer.
A tighter house needs a smaller heat pump
Envelope work isn't a separate project from the heat pump. It's how you buy a smaller one.
Flip the envelope setting above from "poor" to "good" and watch the capacity drop. That's not a calculator trick — air sealing and insulation genuinely shrink the heating load, which means smaller equipment, a lower installed price, and a system that holds up better on the coldest nights.
That's why the standard advice is to weatherize before the heat pump, and why the full retrofit sequence puts envelope work first. If the equipment has to come first — furnaces die on their own schedule — have the contractor size from a load calculation that assumes the envelope work you're committing to.
Oversized and undersized both cost you
Oversized: the common mistake
Short cycles, poor dehumidification, uneven rooms, more wear per hour of comfort — and you paid extra for the capacity. Contractors oversize defensively when there's no load calculation.
Undersized: the cold-snap failure
The house loses ground on design-temperature nights and backup heat (expensive resistance strips, if you have them) carries the load. Cold-climate sizing must use capacity at low temperature, not the nameplate number.
Capacity drops when it's cold — size for that
A heat pump's rated capacity is measured at 47°F. Output falls as the temperature drops — exactly when you need it most. Cold-climate models are engineered to hold much more of their capacity at low temperatures, and the good ones keep heating well below zero. If your winters are real, the spec that matters is capacity at your design temperature. Our cold-climate heat pump guide covers which models hold up and how to read the performance tables.
Sizing questions
How many square feet does a 3-ton heat pump cover?
It depends on climate and envelope. A 3-ton (36,000 BTU/hr) system might cover 2,000+ sq ft in a mild climate with good insulation, or under 1,200 sq ft in a cold climate with a leaky envelope. That spread is exactly why installers run a Manual J load calculation instead of using square footage alone.
Can a heat pump be too big?
Yes, and oversizing is the more common mistake. An oversized heat pump short-cycles: it heats the air fast, shuts off before it dehumidifies or mixes the air properly, and wears out components faster. It also costs more up front for capacity you never use.
Do I size a heat pump for heating or cooling?
In most of the northern half of the country, the heating load is larger and drives the sizing decision. In cooling-dominated climates it flips. A good installer calculates both and sizes for the dominant load, then checks the other mode.
What is a Manual J load calculation?
Manual J is the industry-standard room-by-room heat loss and gain calculation. It uses your actual walls, windows, insulation levels, air leakage, and local design temperatures instead of a square-footage rule of thumb. Any quote for a whole-home system should be based on one.
Get rebate alerts while you plan your system
Free weekly digest. Unsubscribe anytime. Privacy policy.
See what your state pays toward a right-sized system.
Heat pump rebates vary by state, income, and program. Find every program you qualify for before you sign anything.
Match my rebates