Sizing a furnace in Denver? Denver sits in a cold heating climate (IECC Zone 5), so homes need about 48 BTU/sq ft of heat output — more than a milder region. A typical 2,000 sq ft Denver home needs roughly 96,000 BTU/hr of heat, or about a 120,000 BTU input gas furnace at 80% AFUE. The calculator below is pre-set to Denver’s climate zone.
🔥 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.
Furnace Size for Denver Homes by Area
Typical furnace sizes for Denver’s Zone 5 climate, for an 8-foot ceiling, average insulation and a standard 80% AFUE gas furnace:
| Home Size | Heat Output Needed | Furnace Size (80% AFUE) |
|---|---|---|
| 1,000 sq ft | 48,000 BTU/hr | 60,000 BTU |
| 1,500 sq ft | 72,000 BTU/hr | 100,000 BTU |
| 2,000 sq ft | 96,000 BTU/hr | 120,000 BTU |
| 2,500 sq ft | 120,000 BTU/hr | 160,000 BTU |
| 3,000 sq ft | 144,000 BTU/hr | 180,000 BTU |
Sizing a Furnace for Denver’s Climate
Because Denver has a cold climate, the furnace runs many hours through a long heating season — so efficiency matters as much as raw size. Size to the heat output your home loses, then divide by AFUE to get the input rating you buy: a 96% condensing furnace needs a smaller input number than an 80% one for the same heat, and burns far less gas over a Denver winter. Avoid grossly oversizing — an oversized furnace short-cycles, wears out faster and heats unevenly. Enter your home’s exact insulation, ceiling height and fuel in the calculator above.
Frequently Asked Questions
What size furnace do I need in Denver? A typical 2,000 sq ft Denver home needs about a 120,000 BTU input furnace (80% AFUE), delivering roughly 96,000 BTU/hr of heat. Smaller or larger homes scale per the chart above.
Why does Denver need a bigger furnace than a mild climate? Denver’s cold Zone 5 climate raises the heat a home loses on a cold day (about 48 BTU/sq ft), so the same house needs more furnace capacity than it would in a temperate region.
Is a high-efficiency furnace worth it in Denver? Yes — with a long, cold heating season the fuel savings from a 90–96% AFUE furnace add up quickly, and it needs a lower input rating for the same delivered heat.
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.