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Heating BTU Calculator

Estimate the heating power in watts and BTU needed to heat a room based on its area and climate.

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Enter Area (m²), Climate and the Heating BTU Calculator works out Power needed, Power needed straight away. For instance, with Area (m²) = 20 and Climate = Mild it returns Power needed = 1,600 W and Power needed = 5,459 BTU/h.

How to use it

  1. Enter your values: Area (m²), Climate.
  2. Read the result instantly: Power needed, Power needed.

Frequently asked questions

What does the Heating BTU Calculator actually compute?

It takes Area (m²) and Climate and derives Power needed and Power needed from them. The calculation is live as you type, so the result updates on every change.

What information do I need to provide?

2 values: Area (m²) and Climate. Nothing else is required — no account, no file upload.

Can you show a worked example?

With Area (m²) = 20 and Climate = Mild, the calculator returns Power needed = 1,600 W and Power needed = 5,459 BTU/h. Those figures come from running this exact tool, so you can reproduce them by entering the same values.

What happens if I enter larger values?

It moves a lot. Using Area (m²) = 22 and Climate = Moderate instead, Power needed goes from 1,600 W to 2,200 W — which is why it is worth testing a few scenarios rather than trusting a single figure.

Which “Climate” option should I choose?

You can pick between « Mild », « Moderate » and « Cold ». Each one changes what the calculator works out, so switch and compare — the default is « Mild ».

What does it give for smaller values?

Scaled down to Area (m²) = 18 and Climate = Mild, Power needed comes out at 1,440 W. The relationship is worth checking at both ends before you rely on a single result.

When would I actually use this?

Putting a number on a bill: what an appliance costs to run, whether a solar array covers the load, and how much heating a room actually needs.

What is the most common mistake?

Confusing power with energy. A kilowatt is a rate and a kilowatt-hour is a quantity; a 2 kW heater on for half an hour uses 1 kWh, and only the second figure appears on a bill.

What is the difference between the Heating BTU Calculator and the Solar panel calculator?

This one returns Power needed and Power needed; the Solar panel calculator returns Panels needed and System size (kWp). That is the whole difference — open the one whose figure you need.

Is there a tool for the next step?

Amperage Calculator is the closest one after this: Convert a load in watts and a supply voltage into the current drawn in amps.

Further reading

All guides →
How-toWhat Size Heater Do I Need? Sizing BTUs by Room and ClimateSize a heater from room area and your climate: a BTU-per-square-foot rule gives the heat output, with watts and kW for electric units.ComparisonHeat Pump or Gas Boiler: the SCOP Your Local Prices DemandBefore any grant, the price of electricity divided by the price of gas sets a seasonal efficiency the heat pump must beat just to break even on running cost. In late 2025 that number was 1.53 in Portugal and 2.79 in Germany — and on old radiators a German heat pump can cost more to run than the boiler it replaced.How-toHow Much Does a Space Heater Cost to Run?Multiply the heater's kilowatts by hours used and your price per kWh — a 1.5 kW heater for 5 hours a day adds up fast at typical tariffs.How-toWhat Size Water Heater Do I Need?Match tank size to household size and peak-hour demand: roughly 40–50 gallons for two people, more as bathrooms and simultaneous use grow.How-toWhat Size Generator Do I Need? Add Up Your Running and Starting WattsSize a generator by listing the appliances you must run, adding their running watts, and allowing headroom for the surge when motors start.ComparisonInsulate or Replace the Heating: Which Repays First, and Why the Answer InvertsPut both on one axis — euros paid per kilowatt-hour a year of permanent saving — and the comparison becomes decidable. The same loft job costs 0.83 euros per kilowatt-hour a year in a 1965 house and 5.00 in a 2005 one, a factor of six. That, and not the age of the building by itself, is what inverts the verdict.