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What Is BTU to Watts? The 3.412 Factor Explained
The phrase shows up on calculators, HVAC product pages, and energy blogs. Here's what it means and when you need it.
The phrase, decoded
The phrase “BTU to watts” shows up on calculators, HVAC product pages, and energy blogs. It refers to a single conversion: turning a heating or cooling rating (BTU per hour) into an electrical power rating (watts). The math takes one line. The reason people ask takes a bit longer.
This guide explains what each unit means, why you’d convert between them, and how to spot the right number on a product label.
The two units in one sentence each
A BTU is the heat needed to warm one pound of water by one degree Fahrenheit.
A watt is one joule of energy delivered each second.
Both describe energy. They use different yardsticks. BTU comes from the imperial system and steam-era engineering. Watt is the SI unit from physics textbooks. Most of the world picked watts. The US and parts of the UK kept BTU for heating and cooling.
What “BTU to watts” means in practice
When you see BTU on a sticker, it almost always means BTU per hour (BTU/h). That’s a rate — energy moved per unit time. Watts are a rate too. The two are interchangeable once you apply the right factor.
The factor is 3.412. One watt equals 3.412 BTU/h. Flip it: one BTU/h equals 0.293 watts.
So “BTU to watts” is a division problem. Take the BTU/h number, divide by 3.412, and you have watts.
Examples:
- 5,000 BTU/h ÷ 3.412 = 1,466 W
- 10,000 BTU/h ÷ 3.412 = 2,931 W
- 18,000 BTU/h ÷ 3.412 = 5,275 W
Why anyone cares
Comparing heaters
Electric heaters are sold in watts. Gas and propane heaters are sold in BTU/h. To know which heats a room faster, you have to put both on the same scale.
A 1,500 W electric heater outputs about 5,118 BTU/h of heat. A 30,000 BTU/h propane heater puts out roughly six times more. Same room, very different results.
Sizing air conditioners
AC units list cooling capacity in BTU/h. Their electrical draw is in watts. The ratio (BTU/h per watt) tells you efficiency. A unit pulling 1,000 W and cooling at 12,000 BTU/h has an EER of 12. Higher EER means lower bills.
Solar and off-grid setups
Solar panels generate watts. To run a window AC off batteries, you need to know how many watts the unit will draw, not just its BTU/h rating. The conversion lets you size panels, charge controllers, and battery banks.
Generators and backup power
A portable generator rated at 3,000 W can run a 10,000 BTU/h portable AC (roughly 1,200 W of electrical draw) plus a fridge and some lights. Without converting, you’d be guessing.
How the number 3.412 came to be
The factor isn’t arbitrary. One BTU equals 1,055.06 joules. One hour equals 3,600 seconds. Divide and you get:
1,055.06 ÷ 3,600 = 0.29307 watts per BTU/h
Invert it and you get 3.41214 BTU/h per watt. Round to 3.412 for everyday math.
The constant has been stable since the 1950s, when international standards committees pinned down the exact joule equivalent of one BTU. Before that, several slightly different BTU definitions floated around (the “thermochemical BTU,” the “International BTU,” the “59 °F BTU”). The current standard uses the IT (International Table) BTU.
Reading a product label
A window AC label might show:
- Cooling Capacity: 8,000 BTU/h— heat removed per hour
- Power Input: 715 W— electricity pulled per hour
- EER: 11.2— cooling per watt of input
The 8,000 figure is the cooling output. The 715 is the electrical input. Both describe rates, but they aren’t the same thing. The AC moves more heat than it consumes in electricity — that’s the whole point of a refrigeration cycle.
A 1,500 W space heater is the opposite. Almost all the electricity becomes heat, so its output is close to 1,500 W × 3.412 = 5,118 BTU/h. No leverage, no multiplication. Resistance heating runs at near 100% conversion.
Common confusion
Mixing BTU and BTU/h.A “10,000 BTU room AC” almost always means 10,000 BTU per hour. The hour part is implied. Plug raw BTU into the wattage formula and the answer is meaningless.
Treating cooling BTU/h as electrical wattage. A 12,000 BTU/h AC does not pull 3,517 W from the wall. It pulls maybe 1,100 W and moves heat the rest of the way. The BTU number is output, not input.
Confusing kW with kBTU.A 24,000 BTU/h system is 24 kBTU/h (kilo-BTU per hour), not 24 kilowatts. Convert first: 24,000 ÷ 3.412 = 7,034 W = 7.03 kW.
Quick conversion table
| BTU/h | Watts | Equivalent |
|---|---|---|
| 1,000 | 293 | small fan heater |
| 5,000 | 1,466 | bedroom AC |
| 9,000 | 2,638 | mini-split head |
| 12,000 | 3,517 | 1 ton AC |
| 18,000 | 5,275 | 1.5 ton AC |
| 24,000 | 7,034 | 2 ton AC |
| 36,000 | 10,551 | 3 ton AC |
| 60,000 | 17,584 | 5 ton AC |
The “ton” column refers to refrigeration tons, an older unit equal to 12,000 BTU/h. One ton was originally the cooling effect of melting one ton of ice in 24 hours. The BTU/hr to tons converter handles the math for any value.
When the conversion lies to you
The 3.412 factor is pure math. It assumes you’re comparing equal forms of energy. Two cases break that assumption:
Heat pumps.A heat pump rated at 24,000 BTU/h might draw only 2,000 W. The math says 7,034 W. The gap is the Coefficient of Performance (COP) — the pump moves more heat than it consumes in electricity by pulling energy from outside air.
Combustion appliances.A 40,000 BTU/h gas furnace doesn’t run on electricity at all. Converting its BTU rating to watts gives a theoretical electrical equivalent, useful for comparison but not for sizing wiring.
What to take away
BTU and watts measure the same thing — energy flow — in different scales. The conversion is a fixed ratio: divide BTU/h by 3.412 to get watts. Use it when product labels mix units, when you need to size electrical gear, or when you’re comparing heaters of different fuel types.
Keep the number 3.412 in your head and you’ll cut through 90% of HVAC shopping confusion. Or skip the math entirely with the BTU/hr to kW converter.