HVAC Load Calculator

Summary

Estimate the heating and cooling BTU load for a room using square footage, ceiling height, insulation quality, and climate zone.

How it works

1. Enter the room length and width in feet (or total square footage).
2. Set the ceiling height — taller rooms have greater volume to condition.
3. Choose an insulation level that matches your walls and attic.
4. Enter the window area in square feet and select the sun exposure.
5. Select your climate zone to apply the appropriate design temperature difference.
6. Click Calculate to see estimated heating BTU/hr and cooling BTU/hr.

Use cases

• Pre-sizing a mini-split or window AC unit for a bedroom addition.
• Verifying an existing furnace or AC is not grossly over- or under-sized.
• Teaching students the fundamentals of Manual J heat load estimation.
• Estimating HVAC needs for a detached garage or workshop conversion.
• Generating a quick BTU figure before requesting a contractor quote.
• Comparing how insulation upgrades reduce the required system capacity.
• Sizing a portable heater or window unit for a room without central HVAC.
• Planning multi-zone ductless systems by summing room-level loads.

Frequently Asked Questions