is there any good rule of thumb to use when calculating the KW/BTU output rating needed to heat a room, when changing a rad? I know U_Values are used for when instaling a boiler/heating/hw from scratch, but is there a simple way to roughyl work out the amount needed when choosing just 1 rad for 1 room, eg for replacement?
KW/BTU rating for replacing a rad in 1 room ...
- Thread starter steved101
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I have also found this info, which seems OK, would you agree that is is correct/pretty precise?
CHOOSING THE RIGHT RADIATOR
To calculate the BTU/hour required, just follow these simple steps or use our BTU calculator at www.diy.com:
* Multiply the room's height, width and length to get the volume in cubic feet
* For bedrooms, kitchens and hallways multiply the volume by 4
* For bathrooms, living and dining rooms, multiply the volume by 5
* If the room has large windows or exposed walls, increase the total by 10%
All outputs shown in this brochure are based on a mean temepratue of 70 degrees C and an ambient room temperature of 20 degrees C.
EXAMPLE
A bedroom 12 feet wide x 10 feet long x 8 feet high has a volume of 960 cubic feet. This is multiplied by 4 to give 3840 BTUs
Now, just select the appropriate sized radiator for the BTU/hour required - always choose the next size up if the exact size is not listed.
TO CONVERT BTUs to WATTS multiply by 0.2931
CHOOSING THE RIGHT RADIATOR
To calculate the BTU/hour required, just follow these simple steps or use our BTU calculator at www.diy.com:
* Multiply the room's height, width and length to get the volume in cubic feet
* For bedrooms, kitchens and hallways multiply the volume by 4
* For bathrooms, living and dining rooms, multiply the volume by 5
* If the room has large windows or exposed walls, increase the total by 10%
All outputs shown in this brochure are based on a mean temepratue of 70 degrees C and an ambient room temperature of 20 degrees C.
EXAMPLE
A bedroom 12 feet wide x 10 feet long x 8 feet high has a volume of 960 cubic feet. This is multiplied by 4 to give 3840 BTUs
Now, just select the appropriate sized radiator for the BTU/hour required - always choose the next size up if the exact size is not listed.
TO CONVERT BTUs to WATTS multiply by 0.2931
As rads have been specified in kW for the last 30 years or so then I would be suspicious of any program which called itself a BTU calculator.
Also a mean rad temperature of 70° is not correct for a condensing boiler.
There are so many variables that a competent heating engineer would take into account but for a DIYer the best option is to just replace with a similar size if the output has been satisfactory.
Any rad of the same size will give approximately the same output but modern ones will usually give a little more than old ones.
If the old one did not have fins then use a finned one as extra output does no harm.
But do fit a thermostatic rad valve with the new one.
Tony
Also a mean rad temperature of 70° is not correct for a condensing boiler.
There are so many variables that a competent heating engineer would take into account but for a DIYer the best option is to just replace with a similar size if the output has been satisfactory.
Any rad of the same size will give approximately the same output but modern ones will usually give a little more than old ones.
If the old one did not have fins then use a finned one as extra output does no harm.
But do fit a thermostatic rad valve with the new one.
Tony
Where did you find this rubbish?
was in a b & q designer rad catalogue.
to be fair, the mean temp of a rad is usually 70 and ambient room usually 20-21. and i do not have a condensing boiler, just a normal potterton (nearly 20 yrs old)!
i know there are ways to calcualte more exact, eg taking into account double glazing, external walls, etc but i thought this way seemed pretty accurate, for just replacing 1 radiator (not installing a whole new set)!!
One other point, i cannot seem to find any info on how much KW/BTW a normal sized single panel single convector rad gives out. Any links? I know one thing for sure, these designer rads give off LESS KW/BTUs than normal rads!!
to be fair, the mean temp of a rad is usually 70 and ambient room usually 20-21. and i do not have a condensing boiler, just a normal potterton (nearly 20 yrs old)!
i know there are ways to calcualte more exact, eg taking into account double glazing, external walls, etc but i thought this way seemed pretty accurate, for just replacing 1 radiator (not installing a whole new set)!!
One other point, i cannot seem to find any info on how much KW/BTW a normal sized single panel single convector rad gives out. Any links? I know one thing for sure, these designer rads give off LESS KW/BTUs than normal rads!!
Say no more!!
Provided your existing rad is a standard panel rad, with or without fins, an not an old fashioned cast iron type or a fancy designer type, most rads of a similar size are virtually the same in output.
Look in Stelrad Elite Catalogue to find one similar size and type to your existing rad and you are sorted.
thank you for your help. i will do that. if i find my existing rad, for eg/ gives off say 1200 KW/hour then I should choose one (even a designer one)! with the same rating/next size up?
Also I am not having a TRV on it, just a normal manual wheelhead rad valve as my original bathroom rad didn't have a TRV and all the others in my home do. I know some boilers allow all to be TRV'd, but I will be having it on full all the time anyway as it is in the bathroom so a TRV would make no difference.
One last point-any good link to a store where I can buy clip on type rad/pipe thermometers so I can balance the rad correctly when changing? I have been after some for a while now but screwfix, b & q, etc don't seem to sell any!
Also I am not having a TRV on it, just a normal manual wheelhead rad valve as my original bathroom rad didn't have a TRV and all the others in my home do. I know some boilers allow all to be TRV'd, but I will be having it on full all the time anyway as it is in the bathroom so a TRV would make no difference.
One last point-any good link to a store where I can buy clip on type rad/pipe thermometers so I can balance the rad correctly when changing? I have been after some for a while now but screwfix, b & q, etc don't seem to sell any!
Yes, the same or slightly greater
That's understandable
Clip on thermometers are very slow reacting to temperature change. A better bet is an infrared thermometer. Maplin sell one for £20
£20 sounds good. I had heard they were better, just thought they were in the region of over £100! DO they have a website where I can order/any link would be appreciated (sorry I'm being cheeky)!!!
Thanks again though, you're help has been top notch. Much appreciated.
Thanks again though, you're help has been top notch. Much appreciated.
DO they have a website where I can order/any link would be appreciated (sorry I'm being cheeky)!!!
Two options:
1. Type Maplin into Google
or, if you are really lazy
2. Go to Infrared Thermometer
A tip.
Infrared thermometers will give different readings depending on the type of surface. so the copper/painted pipe will show a different temperature to the chrome of the valve. The solution is to wrap some black insulating tape round the pipe and measure the temperature from the tape.
You need to hold the gun as close to the pipe as possible as they have a fairly large "spread"; like a torch beam. The other thing to remember is that the laser beam may not be shining on what you are measuring when you are very close or the thing you are measuring is very small.
I wouldn't buy an IR thermometer just for balancing one rad, it isn't that critical.
Try any sizing calculator you like, for your other rooms first. You'll find a variance, mostly in one direction or another. Use the same variance. Some plumbers always under or oversize radiators, and there's little point having just one which is way off the rest. Eg if they're all a bit small you'll have to keep the boiler temp high, and one big rad would be a nuisance.
Try any sizing calculator you like, for your other rooms first. You'll find a variance, mostly in one direction or another. Use the same variance. Some plumbers always under or oversize radiators, and there's little point having just one which is way off the rest. Eg if they're all a bit small you'll have to keep the boiler temp high, and one big rad would be a nuisance.
surely if I just measure the flow and return before changing the radiator and on installation of the new one, if I open the lockshield up to get the same temp drop across the flow and return this will be OK and easily done using a thermometer??
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