Issues with radiator sizing

[jmcni]

Today i was asked to check the sizes of radiators installed (by a building firm) in a bungalow by a customer who has the problem of the rooms in question never going above 20 degrees. The Rads are however heating properly, and i am the second plumber he has asked to do so , he has asked me to look at as the last guy he had out confirmed his fears that the heaters were the wrong size for the rooms and he wants me to confirm this. below are the details and my resulting sizes recommended but before i submit my findings i would like to see if anyone is willing to agree or disagree with my findings.
The roofspace is insulated at the rafters but not on the floor

Room 1 : Living room/Kitchen (all one room) 4020 x 5030 x 2400

1 pvc door , 2 windows ( 1.8 x 1.5 m ) & ( 1 x 1 m )both pvc double glazed
Concrete floor, 2 external walls ( cavity )
= my approx 8735 btu`s Other plumbers approx 8706 btu`s Actual installed by builder 5433 btu`s

Room 2 : Bedroom 3180 x 2.4 x 2.4

1 external cavity wall , 1 wndow 1m x 1.5m, 1 internal block wall, concrete floor

= my approx 2637 btu`s other plumbers approx 2564 btu`s Actual installed by builder 1373 btu`s

 

[CMairiD]

Without know some other details, I've done a rough calc and come rather close to the figures calculated by you and the other plumber have come up with. Based on design temp of 21 and air changes of 2.

 

[AWheating]

dont you mean watts not btu's?

i would think between 2000 to 2500 watts min. try using the city plumbing radiator calculator.

unless you have u values of walls, floor and ceiling/roof you cant really do bang on cals. but the city plumbing calulator is normally close enough. add 10-20% if its an extra cold room.

 

[AWheating]

what size rad has been fitted?

 

[jmcni]

dont you mean watts not btu's?

i would think between 2000 to 2500 watts min. try using the city plumbing radiator calculator.

No mate i work it out in btu`s i didn`t realise that it mattered much if you used either it should be correct the translation of btu`s to watts for what i have posted would be room 1 2560 watts and room 2 772 watts either way your calculation is much the same as mine confirming i haven`t made a boo boo ! the slight difference in our calculations probably is due to me having the u values.

In any case i find it quite shocking that the builder was so much out with his calculations they have been out to look at it and even said the rad installed in room 2 was too big !

 

[jmcni]

what size rad has been fitted?

Room 1 had 2 single panels (myson) with 5433 btu between them (1592 watts)

Room 2 had one single panel (myson) with 1372 btu (402 watts )

 

[davebigpipes]

Your calcs are right but clearly they are undersized because they can't get it above 20 deg, just out of curiosity do you lads match the rad rating with the heat loss calc or do you oversize the rad slightly?

 

[SimonG]

Your calcs are right but clearly they are undersized because they can't get it above 20 deg, just out of curiosity do you lads match the rad rating with the heat loss calc or do you oversize the rad slightly?

Always roundup to next size rad.

 

[CMairiD]

Your calcs are right but clearly they are undersized because they can't get it above 20 deg, just out of curiosity do you lads match the rad rating with the heat loss calc or do you oversize the rad slightly?

Kinda depends on the property and the occupiers. If I have a solid brick property with an OAP who's always cold, then I'd probably go higher than the calcs.

If I have a well insulated home, then I'd probably stick closer to the calculated BTUs.

 

[stevetheplumber]

builders tend to use the deisel method of rad sizing as in deisel fit

 

[AWheating]

or the radiator they had left over from the last job.

 

[jmcni]

Your calcs are right but clearly they are undersized because they can't get it above 20 deg, just out of curiosity do you lads match the rad rating with the heat loss calc or do you oversize the rad slightly?

when i work out the heat loss i find 15 % of the total heat loss and then add it to it, this is what we were taught all them years ago , but i`m not sure if everyone does that as i have never came across such differences before

 

[jmcni]

builders tend to use the deisel method of rad sizing as in deisel fit

:hurray: very good

 

[pelerin]

Maybe I ought to create a new thread for my question below...

My friend reports his new condensing boiler does not seem to consume less gas than his old one. When we checked over Xmas (when it was fairly mild outside in South UK) we found the bolier return temperature was above 70 C for hours on end.

I've read somewhere that condensing boilers work best when the return temperature is about 50 C.

I guess this means increase the radiator sizes (or change single for double. or change non-finned to finned etc).

Any comments, you gurus ?

 

[AlexGas]

"Domestic Heating design guide" is the book to have, it tells you everything about the rad sizing and more.

 

[AlexGas]

Maybe I ought to create a new thread for my question below...

My friend reports his new condensing boiler does not seem to consume less gas than his old one. When we checked over Xmas (when it was fairly mild outside in South UK) we found the bolier return temperature was above 70 C for hours on end.

I've read somewhere that condensing boilers work best when the re

Here's some info from the book:

 

[sparra1100]

i always go a bit over so say 4000 buts for a room id go to 5000 just to make shore or if a room needs a 600x1000 single id go 1100 or 1200 depending on what i can get