How Many BTUs for a Poorly Insulated 25x20 ft Room?
A 25×20 ft room with 8-foot ceilings and poor insulation may require up to 20,000 BTU/hr or more for adequate heating.
How to use this tool
- Enter room length, width, and ceiling height in feet.
- Select insulation quality (average is most common).
- The result shows room volume and the recommended heater BTU output.
Calculate the heater size needed for a large, poorly insulated 25×20 foot room such as an older home, garage conversion, or sunroom.
Frequently asked questions
- How many BTU do I need to heat a room?
- Multiply the room volume (ft³) by a factor of 3–5 BTU depending on insulation quality. A 1,440 ft³ room with average insulation needs about 5,760 BTU/hr.
- What size electric heater do I need?
- Divide the BTU requirement by 3.412 to convert to watts. A 5,760 BTU/hr heater is approximately 1,688 watts (about 1.7 kW).