🔥 BTU Heater Calculator
Find the exact heating capacity needed for any room or space — in BTUs or watts
Bedroom
Living Room
Kitchen
Bathroom
Garage
Office
Basement
Sunroom
| Room Size | Sq Ft | BTU (Mild) | BTU (Moderate) | BTU (Cold) | Watts |
|---|---|---|---|---|---|
| Small bedroom | 100 | 3,000 | 4,000 | 5,000 | 1,465 |
| Average bedroom | 150 | 4,500 | 6,000 | 7,500 | 2,198 |
| Large bedroom | 200 | 6,000 | 8,000 | 10,000 | 2,930 |
| Living room (small) | 300 | 9,000 | 12,000 | 15,000 | 4,396 |
| Living room (avg) | 400 | 12,000 | 16,000 | 20,000 | 5,861 |
| Open plan | 600 | 18,000 | 24,000 | 30,000 | 8,792 |
| Large open plan | 800 | 24,000 | 32,000 | 40,000 | 11,722 |
| Whole home (small) | 1,000 | 30,000 | 40,000 | 50,000 | 14,653 |
| Whole home (avg) | 1,500 | 45,000 | 60,000 | 75,000 | 21,979 |
| Whole home (large) | 2,000 | 60,000 | 80,000 | 100,000 | 29,306 |
| Climate Zone | Description | BTU Multiplier | Good Insulation | Average Insulation | Poor Insulation |
|---|---|---|---|---|---|
| Mild (Zone 1–2) | South US, coastal | 0.75x | 0.70x | 0.80x | 0.95x |
| Moderate (Zone 3–4) | Mid-Atlantic, Midwest | 1.0x | 0.90x | 1.00x | 1.20x |
| Cold (Zone 5–6) | Northern US, Canada | 1.25x | 1.10x | 1.25x | 1.50x |
| Very Cold (Zone 7+) | Alaska, far north | 1.50x | 1.35x | 1.50x | 1.80x |
| Heater Type | Typical BTU Range | Best For | Efficiency | Watts Equiv. |
|---|---|---|---|---|
| Portable space heater | 5,000–10,000 | Small rooms, spot heating | 100% (electric) | 1,500–3,000W |
| Wall heater | 5,000–25,000 | Bedrooms, bathrooms | 100% (electric) | 1,500–7,300W |
| Baseboard heater | 500–2,000 per ft | Supplemental heat | 100% (electric) | 150–600W/ft |
| Mini-split (heat pump) | 9,000–36,000 | Rooms & zones | 200–300% COP | 1,000–3,500W |
| Gas furnace | 40,000–150,000 | Whole home | 80–98% AFUE | N/A |
| Propane heater | 10,000–80,000 | Garages, workshops | 80–95% AFUE | N/A |
| Infrared heater | 5,000–30,000 | Drafty spaces, outdoors | 100% (electric) | 1,500–8,800W |
| Boiler / radiant | 50,000–200,000 | Whole home, radiant floors | 80–95% AFUE | N/A |
| BTU/hr | Watts | kW | Typical Use |
|---|---|---|---|
| 1,000 | 293 | 0.29 | Very small space |
| 5,000 | 1,465 | 1.47 | Small room 100–150 sq ft |
| 10,000 | 2,930 | 2.93 | Medium room 250–350 sq ft |
| 15,000 | 4,396 | 4.40 | Large room 400–500 sq ft |
| 20,000 | 5,861 | 5.86 | Very large room 550–650 sq ft |
| 30,000 | 8,792 | 8.79 | Open plan 700–900 sq ft |
| 50,000 | 14,653 | 14.65 | Small home 1,200–1,500 sq ft |
| 100,000 | 29,306 | 29.31 | Large home 2,500–3,000 sq ft |
BTU, or British Thermal Unit, serve as a way to measure energy. It matches the amount of heat that is needed to raise the temperature of one pound of water by one degree Fahrenheit. One btu matches around 1 055 joules, 252 calories or 0.293 watt-hours.
That is like the energy that comes from burning one single match. Basically, btu helps to measure the thermal energy that some device puts out.
What is a BTU and How to Choose the Right Heater Size
When buying heater units, the numbers about btu show everywhere. One candle burning delivers around one btu. A floor heater with 1 500 watts makes about 5 000 btu.
A mobile patio heater can reach 40 000 btu, while a fireplace puts out around 90 000 btu. Those values make it easy to comapre various heating devices.
Electrical heater units reach 100 percent efficiency, turning power into heat. They reach a max of 1 500 watts, because that is the limit of a standard 15-amp circuit for continuous usage. Those 1 500 watts equal about 5 100 btu.
A heater of 1 000 watts, running one hour, makes 3 412 btu. Every electrical model with the same power gives the same amount of btu, no matter whether it costs 10 dollars or 80 dollars. The main difference between cheap and expensive versions is in how they spread the heat threw the room, not in the heat itself.
Heat pumps are an exception, because they make around three times more heat for the same power input.
Propane heater units come in many sizes. The mobile Buddy delivers 9 000 btu and works well in tiny spaces. The big Buddies reach up to 18 000 btu and can heat up to 400 square feet.
There is even a propane heater on a tank with 15 000 btu. For bigger areas, a propane heater with forced air can reach from 30 000 to 60 000 btu and heat up to 1 500 square feet with regular warm flow. Larger heater units with gas for garages, warehouses and industrial buildings range from 30 000 to 400 000 btu.
Catalytic heater units offer another option. The models of Olympian Wave come in three sizes: the Wave 3 from 1 600 to 3 000 btu, the Wave 6 from 3 200 to 6 000 btu and the Wave 8 from 4 200 to 8 000 btu. The Coleman ProCat is a 3 000 btu catalytic heater that you can use indoors.
Picking the right btu involves several things. A heater with lower btu pollutes less and causes less dryness, because stronger burning makes more moisture if airflow is not good. A water heater with high btu heats warm water more quickly, which is helpful during showers happening at the same time to keep flow.
The exact sizing depends on the area, insulation, windows andoutside temperature.
