Discuss Heatloss through internal ceiling in the Central Heating Forum area at PlumbersForums.net


Gas Engineer
Hello, i'm doing some heatloss calculations, going by a fairly old plumbing book.

The formula for calculating heatloss would be Surface Area x Temp Diff x U-Value = Heatloss

My question is, when calculating the heatloss through a ceiling, so downstairs to upstairs, the temp difference would be 0 (assuming the design temp is the same for both for sake of argument), making the heatloss 0, but I don't think that would be right would it? Heat will always be lost to upstairs by virtue of the fact that heat rises.

Or am I missing something here?

Appreciate any help.
Yep aslong as it’s occupied same as if it was on the first floor and there was a flat below
How did you get on with your calculations?
I think that you are correct in first post of this thread.

I checked the temperature of my lounge ceiling with an infra-red thermometer and it is warmer than the temperature at the thermostat in the lounge. Some heat will flow through the lounge ceiling to the bedroom above. This could be included in a heat loss calculation done on Excel if you estimate the temperature of the lounge ceiling and bedroom floor.

In this case you could also include in the calculation the fact that the lounge floor is cooler than the temperature at the thermostat, reducing the heat flow from the room into the floor. The additional heat loss through the ceiling might largely cancel the reduced heat loss through the floor resulting in only a small change to the total heat loss calculation for a lot of extra effort.

These heat loss calculations are approximate:
  • They don’t usually consider the additional heat loss from the corners of the building.
  • The outside temperature may not always be -3°C, or whatever temperature you choose.
  • Usually, there is no way of knowing how close the U-values used in the calculation are to reality.
  • Ventilation may be different from the assumptions
For reference I used the Myson heat loss calculator to check the size of my radiators:
Myson Heat Loss Manager - https://www.myson.co.uk/hlm/
It lists the heat loss from each element of each room.

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