Heat loss calculator

[martin43]

I have tried six or so internet available calculators and of course got six different answers. Can anyone point me at one they have used and found reliable. Thanks
Martin

 

[Galoka]

not used any of the online ones - presumably they are making some slightly different assumptions about things?

I do have somewhere a copy of the the old Myson programme they produced (dunno if they still do), though back in the day when I did the CH in the old house I did it with a little spreadsheet.

 

[D_Hailsham]

not used any of the online ones - presumably they are making some slightly different assumptions about things?

I did a fairly detailed study of several online calculators recently and the assumptions varied considerably. Some of them were extremely basic, e.g measure the volume of the room and multiply by a factor depending on what sort of room it was; construction and insulation was not taken into account.

The best one I could find, when compared to Stelrad Stars for my house, was the Home Supply Radiator Calculator

 

[GavThePlumber]

If you want it calculated correctly, then you will need to do it long hand by doing a full design heat loss method and not rely on any assumptions.

 

[Elkato531]

All heat loss calculators rely on assumptions. One of the greatest is the assumption of an outside temperature of -1. This means that the actual heat loss will be lower than the calculated figure for the majority of the time but may be greater in the very low temperatures such as we have seen in the last couple of winters. A radiator with output at the calculated value may not be sufficient when it is needed most.
You should also bear in mind that radiator outputs figures are usually quoted for a Delta T of 50 degrees C. Most modern systems will be set up to run at a lower temperature than this where output will be lower. For these reasons, I would use a calculator as a guide to work out the minimum size radiator required but always oversize slightly and fit a TRV.