Wondering what size furnace you need for a 1,000 sq ft house? In a moderate (Zone 4) climate, a 1,000 sq ft home needs roughly 43,000 BTU/hr of delivered heat, which means about a 60,000 BTU input gas furnace at 80% AFUE. The calculator below is pre-set to 1,000 sq ft — adjust your climate, insulation and fuel for an exact number.
🔥 What Size Furnace Do I Need? — BTU & AFUE Calculator
Find the right furnace size for your home in BTU. Enter your square footage, climate zone, insulation and fuel type — we calculate the heat output you need and the furnace input rating (adjusted for AFUE efficiency) so you buy the correct 40k, 60k, 80k or 100k BTU unit. For homes in the US, Canada, UK & Europe.
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📐1. Floor Area & Ceiling
Range: 100 – 10,000 sq ft (whole-home or a single addition)
Range: 7 – 20 ft. Taller ceilings need proportionally more heat.
🌍2. Climate Zone
Zones follow US DOE / IECC heating climate zones. Colder zone = more BTU per sq ft. Pick your country above to auto-set it.
🧱3. Insulation
🪟4. Windows / Glazing
💨5. Air Tightness / Drafts
Older, draughty homes lose heat through air leaks and need a bigger furnace. A modern, sealed home needs less.
🔥6. Fuel Type & Furnace Efficiency (AFUE)
Standard gas = 80% · High-efficiency condensing = 90–98% · Electric = 100%. AFUE is the % of fuel turned into usable heat.
Furnace Size for 1,000 Sq Ft by Climate Zone
The same 1,000 sq ft home needs a bigger furnace in a colder climate. These figures assume an 8-foot ceiling, average insulation and a standard 80% AFUE gas furnace (round up to the next standard size sold):
| Climate | Heat Output Needed | Furnace Size (80% AFUE) |
|---|---|---|
| Warm South (Zone 2) | 33,000 BTU/hr | 45,000 BTU |
| Moderate (Zone 4) | 43,000 BTU/hr | 60,000 BTU |
| Cold North (Zone 6) | 53,000 BTU/hr | 80,000 BTU |
How the 1,000 Sq Ft Furnace Size Is Calculated
First we find the heat output your home loses on a design-cold day: floor area × a per-square-foot heating factor for your climate zone (about 43 BTU/sq ft in a moderate Zone 4), adjusted for ceiling height, insulation, windows and air-tightness. That gives the delivered BTU/hr the furnace must replace. Then we divide by the furnace’s AFUE efficiency to get the input (nameplate) rating you actually buy — an 80% furnace needs a bigger input number than a 96% one for the same heat. Finally we round up to a standard size (40k, 60k, 80k, 100k, 120k BTU). Enter your real insulation, ceiling and fuel in the calculator above to fine-tune it.
Frequently Asked Questions
What size furnace do I need for a 1,000 sq ft house? A 1,000 sq ft home typically needs about a 60,000 BTU input furnace (80% AFUE) in a moderate climate, delivering roughly 43,000 BTU/hr of heat. In a cold climate size up toward 80,000 BTU; in a warm climate 45,000 BTU is enough.
How many BTU furnace for 1,000 square feet? Around 43,000 BTU/hr of heat output in a moderate climate. A standard 80% AFUE furnace turns that into a 60,000 BTU input rating; a 96% high-efficiency model needs less input for the same heat.
Should I get a high-efficiency furnace for a 1,000 sq ft home? A 90–96% AFUE furnace wastes far less fuel and needs a lower input rating for the same heat output, cutting running costs — worthwhile in colder zones where the furnace runs many hours a year.
Estimates vary by contractor. Compare free quotes from licensed local pros before you commit. Request a quote →
High-efficiency systems may qualify for utility rebates and federal or state incentives. Find current programs at ENERGY STAR & DSIRE.
Figures are reviewed by the Refcon HVAC engineering team using U.S. DOE, ENERGY STAR & ACCA Manual J data. Estimates only — confirm with a licensed pro.