KW/BTU rating for replacing a rad in 1 room ...

[ChrisR]

No. No. No.
Not if the other rads were designed with different numbers.
Balancing isn't that precise though.
Eg with 15 degree room temp,
80 - 70 gives a rad average 75 giving difference to room temp 60
80 - 50 gives a rad average 65 giving difference to room temp 50

so the output changes by only about 17% for a big imbalance.

Heating installers can disagree over rad sizes by two to one easily, though. I've seen them 35% the correct size.

 

[steved101]

so what your saying is if i am slightly out if doesn't matter??

 

[D_Hailsham]

Balancing isn't that precise though.

That's because systems are always a compromise. Balancing instructions are based on the assumption that all radiators are correctly sized.

 

[ChrisR]

Yes it's all pretty rough. All sorts of factors don't get included in the sums, then you alter a trv somewhere which alters the balancing, then we all leave the doors open anyway!
Balancing in practice is about making sure there's enough flow through each of the rads. "Too much" and the average temp goes up a degree or three - no big deal. It isn't an industrial situation where there are huge pumps costing so much to run that everything's tight.

 

[jon26]

To accurately size a rad. you need to take into account, 'U' values i.e. building construction, glazing area/type, floor area, ceiling/roof area length of outside wall, no. of air changes, internal external temperature, flow and return temps, delta T factors... so on and so on.

Just get one that look like the original and oversize it abit, you won't be far off

 

[Agile]

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?

If your radiator was goiving off 1200 kW then you should run out of the house as it would be glowing white hot and the house would be burning!

Most rads are between 0.5 and 3 kW.

The rating is in plain kW which is the continuous heat output.

Tony

 

[steved101]

I meant Watts not KW sorry!!

Still I am not sure about balancing my new rad. If I do just do it by guess work surely it may restrict flow to the others in the house?