Sizing a Electric furnace? An electric furnace is 100% AFUE — all the electricity becomes heat, so its input rating equals its output. It needs no flue, but electricity usually costs more per BTU than gas, so compare running costs before you buy. For a typical 2,000 sq ft home in a moderate climate needing about 86,000 BTU/hr of heat, a 100% AFUE Electric furnace must be rated roughly 100,000 BTU input. The calculator below is pre-set to a Electric furnace — enter your home’s details for an exact size.
🔥 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.
🌍 Prefer metric? Switch units here
📐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.
Electric Furnace Size by Home Area (100% AFUE)
Typical Electric furnace sizes for a moderate (Zone 4) climate, 8-foot ceiling and average insulation. The heat output needed is the same for any fuel; the input rating shown reflects a 100% AFUE Electric furnace:
| Home Size | Heat Output Needed | Electric Furnace Size |
|---|---|---|
| 1,000 sq ft | 43,000 BTU/hr | 45,000 BTU |
| 1,500 sq ft | 64,500 BTU/hr | 80,000 BTU |
| 2,000 sq ft | 86,000 BTU/hr | 100,000 BTU |
| 2,500 sq ft | 107,500 BTU/hr | 120,000 BTU |
| 3,000 sq ft | 129,000 BTU/hr | 140,000 BTU |
Electric Furnace Efficiency & Sizing
Furnace sizing has two numbers: the output (delivered heat your home needs) and the input (fuel the furnace consumes — the nameplate rating you buy by). Output = input × AFUE. Size your home to the output it loses on a cold day, then divide by your Electric furnace’s AFUE to get the input rating, and round up to a standard size. Because an electric furnace is 100% AFUE, its input equals its output. Enter your exact area, climate and insulation in the calculator above.
Frequently Asked Questions
What size Electric furnace do I need? For a typical 2,000 sq ft home in a moderate climate you need about a 100,000 BTU input Electric furnace (100% AFUE), delivering roughly 86,000 BTU/hr of heat. Scale with your home size per the chart above.
Does fuel type change the furnace size? The heat output your home needs is the same for any fuel. What changes is the input rating: a lower-AFUE furnace needs a bigger input for the same heat. Electric is 100% AFUE, so input equals output.
What AFUE should a Electric furnace be? Electric furnaces are 100% AFUE by nature. The bigger question is running cost — compare against a heat pump or gas furnace.
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.