What Size Furnace Do I Need for a 1,500 Sq Ft House?
Updated February 11, 2026
Just want the number? Use the furnace size calculator.
For a 1,500 square foot home, the furnace you need usually falls between roughly 45,000 and 90,000 BTU per hour of output. The reason that range is so wide is that square footage is only one of the inputs. Climate does most of the rest of the work, and insulation moves you within the band.
Here is how to turn that range into a single number for your house.
Start with your climate
The rule of thumb is BTU per square foot, and that figure climbs as you go north. A mild southern climate needs around 30 to 35 BTU per square foot. A cold northern one needs 50 to 60. The U.S. Department of Energy keeps a climate zone map you can use to place yourself.
For a 1,500 sq ft home, that works out to:
- Mild climate (about 35 BTU/sq ft): around 52,000 BTU
- Moderate climate (about 47 BTU/sq ft): around 70,000 BTU
- Cold climate (about 55 BTU/sq ft): around 82,000 BTU
These are output (also called heating capacity) numbers. A furnace also has an efficiency rating (AFUE), so an 80,000 BTU input furnace at 80 percent AFUE only delivers about 64,000 BTU of usable heat. When you compare quotes, make sure you are comparing the same thing.
Then adjust for your house
Two homes of the same size in the same town can still need different furnaces. The big swing factors:
- Insulation and air sealing. A tight, well-insulated home can drop toward the low end of the range. A drafty older one pushes to the high end.
- Ceiling height. You heat volume, not floor area. Vaulted or nine-foot ceilings add load.
- Windows. More glass, and older glass, means more heat loss.
Why bigger is not better
It is tempting to round up “just to be safe.” Do not. An oversized furnace heats the house in short bursts and shuts off, a pattern called short cycling. It wears out faster, costs more to run, and leaves rooms unevenly heated. Right sizing is the goal, not maximum size. The signs of an oversized furnace can help you recognize short cycling in an existing system before you replace it.
Get your number
Plug your square footage, climate, and insulation into the furnace size calculator and it returns a BTU range with the math shown. If you are also weighing a cooling system, the AC and mini-split sizing calculator works the same way.
For a sizing-critical or high-efficiency install, ask your contractor for a room-by-room Manual-J load calculation before you buy. Use the estimate here to sanity-check that a quote is not wildly oversized.