What Size Furnace Do I Need?

The right furnace size depends on your home's square footage, insulation, climate zone, and layout. As a rough guide, central Illinois homes need about 40-45 BTUs per square foot. A 1,500 sq ft home typically needs a 60,000-70,000 BTU furnace. A 2,500 sq ft home needs 100,000-110,000 BTUs. But square footage alone isn't enough - a proper Manual J load calculation is the only way to get it right.

A furnace that's too small runs constantly, can't keep up on the coldest days, and wears out early. A furnace that's too big heats your home too fast, shuts off, then starts again minutes later - called short-cycling. Short-cycling wastes gas, creates uneven temperatures, and puts extra stress on components. Either way, wrong sizing costs you more in energy bills and shortens system life by years.

A proper sizing uses a Manual J load calculation that factors in: square footage, ceiling height, insulation quality, number and type of windows, how much sun exposure your home gets, basement type (finished vs. unfinished), and local climate data. Any company that sizes your furnace just by looking at your old unit or guessing based on square footage is cutting corners.

• 1,000-1,200 sq ft: 40,000-55,000 BTU
• 1,200-1,500 sq ft: 55,000-70,000 BTU
• 1,500-2,000 sq ft: 70,000-90,000 BTU
• 2,000-2,500 sq ft: 90,000-110,000 BTU
• 2,500-3,000 sq ft: 110,000-130,000 BTU

These are estimates for central Illinois. Your actual needs depend on insulation, windows, and home layout. Curious about costs? See our new furnace cost guide.

We perform a full Manual J load calculation before recommending a furnace size. No guesswork. No overselling. We size your system for your home - not for a bigger commission. Furnace installation available across Peoria, Pekin, Morton, Washington, Canton, and surrounding areas. To keep your home trouble-free, call (309) 347-5309.