Heat loss calculator

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All tools › Warmth and power

Heat loss calculator

Watts through the walls, the windows, the roof and the air.

It runs entirely in this browser tab: nothing you type is uploaded, and it makes no request of any kind.

Settings

Air changes an hour
In tenths: five is half an air change an hour, which is a normal house. A number from 0 to 30.
Allow for thermal bridges
Leaving them out is why a hand calculation always comes in low.
Thermal bridges add
A share on top, because modelling every junction is a different job. A number from 0 to 40.

How to use it

  1. Paste your text into the box above, or open a file.
  2. Adjust the settings beside it until the result is what you wanted.
  3. Copy the result, or save it as a file. The result updates as you type.

Questions

Where do the coverage rates and densities come from?
They are the published typical figures — what a tin of emulsion claims, what a cubic metre of dry sand weighs, what a bag of screed covers. They are printed on the result so you can compare them with the bag in front of you, and the bag wins.
Is the ten per cent reserve part of the calculation?
No, and that is why it is a setting. It is a trade convention for breakage and offcuts, and the quantity without it is shown on the same result, so you can order either.
Can I use this instead of a heating engineer or a structural check?
No. A heat loss from six fields is an order of magnitude, not a design: a standard calculation takes every room, orientation and junction separately. The snow tool weighs snow; whether your roof carries it is on its drawings.
Does anything I type here leave the page?
No. There is no account, no server and no network request. What you type stays in this tab, and in the link if you choose to share one.

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