Furnace Size Calculator

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Estimate the required heating capacity (BTU or kW) for your home based on size, climate, and insulation.

Property Characteristics

Heated Area (sq ft)

sq ft

Climate Zone

Higher latitudes require more BTUs per unit of area to combat colder external temperatures.

Insulation Quality

Capacity Estimate

Sizing your system?

Provide your home's total area and select your climate zone to see the recommended furnace capacity.

About this calculator

Overview

Sizing a furnace correctly is vital for both comfort and energy efficiency. An undersized unit will run constantly without reaching the target temperature, while an oversized unit will 'short-cycle', leading to uneven heat, excessive humidity, and premature wear on the compressor and heat exchanger. This calculator provides a base capacity requirement for standard residential homes.

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Pro Tips

Improve your attic insulation and weatherstrip doors before upgrading your furnace; better efficiency might allow for a smaller, cheaper unit.
In coastal or southern areas, humidity control is as important as temperature; a variable-speed blower can help significantly.
This tool is for estimation only. A professional HVAC contractor should perform a 'Manual J' load calculation for final sizing.

Fun Facts

"A BTU (British Thermal Unit) is the amount of energy required to heat 1 pound of water by 1 degree Fahrenheit."
"In the metric system, heating capacity is primarily measured in Kilowatts (kW). 1 kW is equivalent to approximately 3,412 BTUs."
"The AFUE (Annual Fuel Utilization Efficiency) rating tells you how much fuel is converted to heat vs wasted; a 95% AFUE furnace wastes only 5% of its fuel."

Formula: BTUs = Area (sq ft) × BTU Factor (based on Zone and Insulation)