On Sat, 6 Sep 2008 23:12:00 +0100, "Roger Mills"
wrote:

If the output is quoted at dT=60 and you're going to run it at a dT of 40,
then yes - that's right.

I was reading a brochure by Grant boilers which says: "Size radiators
with a mean water temperature of 60° C". So if the room temperature is
20C that's a dT=60-20=40C. Isn't it?

However, many manufacturers are now quoting the output at dT=50. The output
at dT=40 is about 76% of that at dT=50.

Thanks. I will save that for future reference. Where did you get these
factors? Are they all listed on the stelrad web site you mentioned
earlier?

Hopefully you won't *actually* need an output of 4.7kW, unless you've got a
very large room

I got my units mixed up. I know you'll tell me off for using BTUs but
the catalogues use them. I used an online calculator (I can't remember
which) and it recommended 3800 BTU. I downloaded the Barlo program and
that said 4700BTU, however I am not sure I put the right numbers into
the right boxes and besides, I didn't know what all my walls were made
of. I think I saw 4700 in my spreadsheet and thought it was Watts but
it was BTUs.

I need to check to see what dT the Barlow program was using, as it
might require an even larger rad if I have a smaller dT. It's for a
3mx3mx2.4m room but with a 2mx2m patio door.

Thanks,
Stephen.