BTU Calculators

[CHarr]

I've looked at a few online BTU calculators to get a feel for the capacity of radiators I require in a new CH installation, but I'm amazed at the variations in results for the same room sizes/assumptions.

B&Q's calculator suggested around 1250BTU for my bathroom, but others, twice that! I was wondering whether I could use a larger than average towel rail as BOTH radiator and towel rail, and plenty have a bigger capacity than that, but not twice as much. Does anyone have any experience of this configuration?

 

[HERTS P&D]

I got the tallest towel radiator for my bathroom 1800mm high, all I did then was to put a trv on it. It's good for hanging 2 full size bath towels.

Andy

 

[CHarr]

I got the tallest towel radiator for my bathroom 1800mm high, all I did then was to put a trv on it. It's good for hanging 2 full size bath towels.

Andy

... and good for keeping the bathroom warm too? I've got space for one 600mm wide, and have found one we like that is 1600mm high. The stated output is 1501 BTUs and its a dual fuel rail with a 400W element.

 

[Agile]

The UK has been decimalised since about 1970 !

heating power is measured in kW !

Tony

 

[HERTS P&D]

Yes. Keeps the bathroom very warm, that's why i fitted the trv so that it can be turned down.

Andy

 

[CHarr]

Yes. Keeps the bathroom very warm, that's why i fitted the trv so that it can be turned down.

Andy

Isn't it a building regs. requirement to fit a TVR, anyway?

 

[D_Hailsham]

B&Q's calculator suggested around 1250BTU for my bathroom

I wouldn't trust that calculator.

1. It doesn't ask any questions about insulation. This can have a considerable effect on the amount of heat required and consequently on the size of radiators and the boiler.

2. It still uses BTU's, which are only used by older generation heating engineers, e.g "Gas Board" employees. The current unit used is the kilowatt.

The best online calculator I have come across so far is this one: Radiator Calculator.

 

[CHarr]

B&Q's calculator suggested around 1250BTU for my bathroom

I wouldn't trust that calculator.

1. It doesn't ask any questions about insulation. This can have a considerable effect on the amount of heat required and consequently on the size of radiators and the boiler.

2. It still uses BTU's, which are only used by older generation heating engineers, e.g "Gas Board" employees. The current unit used is the kilowatt.

The best online calculator I have come across so far is this one: Radiator Calculator.

That's interesting, but it's a shame it doesn't state the underlying assumptions about different room types: it says 1688 BTUs (494 W) for my bathroom, but that would be only 894/(262) for a bedroom, and somewhere in between for a living room. I leave all my internal doors open, usually, and all the rooms are much the same temperature ...

 

[D_Hailsham]

it's a shame it doesn't state the underlying assumptions about different room types

I've tried hunting for the info by looking at the Page Source, but unfortunately all the important bits are hidden in another part of the system. So we don't know the assumed room temperatures, U values, air change rates etc etc.

You can find all this info in the link I gave and the assumptions used are sensible.

You said that this is a new installation. Have you designed it for a temperature drop of 20C so the return temperature is at or below 55C (condensing begins here)? This is now recommended in the Domestic Buildings Compliance Guide. If so you need to oversize your rads by 20% as they will be producing less heat than the catalogues show.

 

[CHarr]

... so you need to oversize your rads by 20% as they will be producing less heat than the catalogues show.

That's easy enough for normal radiators, but if I'm going to use a towel radiator on its own, then they inevitably have a limited output. If I go to 1800mm x 600mm (the biggest I can find) the output is still only 2620 BTUs / 768 watts, so the sky's not the limit!

I can see why higher output elements are specified for larger rails, but I don't want to overdo it. The inexpensive elements don't seem to be thermostatically controlled, and I'd guess that a 600w element would heat even a larger rail to a higher temperature than I really want in the Summer, when I just want towels to be dry, not warm (and I certainly don't want any heating for the room). Has anyone any experience of using smaller elements in larger rails - I was wondering whether 400w or even 250w would do the job?

 

[D_Hailsham]

... so you need to oversize your rads by 20% as they will be producing less heat than the catalogues show.

That's easy enough for normal radiators, but if I'm going to use a towel radiator on its own, then they inevitably have a limited output. If I go to 1800mm x 600mm (the biggest I can find) the output is still only 2620 BTUs / 768 watts, so the sky's not the limit!

There are always exceptions.