BTU Calculators online give different result for a bathroom!

2 Nov 2006
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United Kingdom
Hi, I'm after some advice please regarding the different results I'm getting from various online BTU calculators.

Our bathroom (new extension) measure 3.0m (L) x 2.6m (W) x 2.3m (H).

The room is fully insulated to current building regulations with one external wall with a pitched roof, one velux window, wooden floor with garage below.

Not sure which BTU to trust! The maximum BTU is 3575. The radiator will have a TRV to turn down if too hot.

Does the BTU sound about right please?

Thank you.
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if you have a trv, you can oversize the rad and the only result will be that the room warms up faster as the trv will close the rad when it is warm enough; it won't waste any energy
Hi Bengasman, thanks for your reply, I really wanted to get as close as possible as space is a premium where the radiator needs to go.

If I can help it I don't want to oversize too much.

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Hi Gas4you, perfect! Your cals will enable me to get a slightly small rad now.

Thanks for your reply!
Do you know if the FLOOR is insulated?

I would fit about 1.2 kW or larger because I dont like to be cold in a bathroom where i take of my clothes.

Furthermore if towels are used to cover it then the heat output drops off dramatically.

Hi Tony,

Yes the floor is insulated to building regs. That's a good point about the towels. Thank you!

I've looked at Purmo rads as they seem to have more output compared to others of the same size.

I've looked at Purmo rads as they seem to have more output compared to others of the same size.

Never used them so can't comment, but check that they are quoting the outputs the same as other manufacturers. They should all be quoting at 50C mean temp difference now.

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