How to estimate the heating power your house needs without an engineer. Enter the dimensions and temperatures — get the heat loss in kW, so you don't buy a boiler that's too big or too small.
What you'll learn
Before buying a boiler, the main question is how many kilowatts you need. Sellers often calculate "by area" (for example, 1 kW per 10 m²), but that's a rough estimate that easily misses. In this article we show how to get a more precise figure yourself in a few minutes.
What heat loss is
In winter a house constantly gives off heat to the outside — through the walls, roof, floor and windows. How much heat "escapes" per unit of time is the heat loss, measured in kilowatts (kW). The boiler has to replace exactly as much as is lost, so the boiler power = the house's heat loss (plus a small margin).
Heat loss depends on:
- the size of the house — width, length, height;
- how well insulated the walls, roof, floor and windows are (their U-value);
- the temperature difference — how warm you want the room and how cold it is outside.
Why "by area" is risky
Buy a too-large boiler and you'll overpay for the equipment, it will run in short bursts and wear out faster. Buy a too-small one and the house won't warm up in a hard frost. A calculation based on real dimensions and insulation gives a figure you can rely on.
A better-insulated house needs a smaller boiler. If you're planning insulation, first calculate the walls in the thermal conductivity calculator, then the heat loss: the boiler will come out smaller and cheaper.
How to calculate
- Open the heat-loss calculator.
- Enter the house dimensions (width, length, height).
- Set the temperature you want in the room (for example, +20 °C) and the design outdoor temperature for your region.
- Specify how well insulated the walls, roof and floor are, and the number of windows.
- Get the total heat loss in kW — that's the guide for the boiler power.
Безкоштовно · без реєстрації
Example
For a 10 × 8 m house 3 m high with average insulation, at +20 °C inside and −22 °C outside, the heat loss comes out at about 9–11 kW. That means a 12 kW boiler is plenty — not 20, as is sometimes proposed "to be safe".
And what will it cost
Once you know the kW, you can immediately estimate which fuel is cheaper for such a house — gas, a heat pump, pellets or electricity. There's a separate heating cost calculator for that and the article gas, heat pump or pellets — what's cheaper.
Frequently asked questions
What does the calculator account for? The heat lost through the walls, roof, floor and windows — the main loss paths for a private house.
What margin should I allow? A small power margin is sensible, but you don't need to double the figure — that's the typical overpayment.
Is it suitable for a café or shop? Yes, the principle is the same. See the article on heating for a business.
Теги: