pipe sizing.....

[jimst]

Usually the flow/return from a combi boiler is 22mm then tends to go down to 15 the further you get away from it. Is there a rule for this....ie if there are less than 2/3 rads to feed you can use 15mm?

I know it is ok for single rads...just wondered if you could go for more....

thanks......property is small bungalow with 6 rads 3 in either direction from the boiler.

 

[Biggles..]

15mm 13kw
22mm 26kw
28mm 46kw

Based on 20°C ΔT @ 1m/s

 

[jimst]

15mm 13kw
22mm 26kw
28mm 46kw

Based on 20°C ΔT @ 1m/s

Assume this apples to the rads...so if the total output of each set of 3 rads is less than 13kw I am ok with 15mm?

And where the 2 sets of pipework go to/from the boiler (28kw) it's 22mm.

thanks for your help.....Jim

 

[twgas]

13kw sounds a bit much for 15mm pipe, a fact and figures guru may well come up with the answer, although I know it's not exact because of the pipe lengths has a bearing on it.

 

[Biggles..]

If you want to be pedantic

0.14 x 84

0.14 is lps
84 is 4.2 x 20

11.76kw to be exact at 1m/s

Do you want the exact KW for the other sizes.

 

[compheat]

13kw sounds a bit much for 15mm pipe, a fact and figures guru may well come up with the answer, although I know it's not exact because of the pipe lengths has a bearing on it.

If Lee as taken the time to answer your question I wouldn't doubt his answer

15mm can feed a complete house depending on rad sizes, the average semi would only be approx 10kw.

 

[twgas]

I'm not trying to cause an argument, but, when I was installing I was always led to believe. 3 rads was the max on 15mm, allowing approx 1.5kw per rad.
I never designed the systems, apart from one at college for another trainee.

 

[Biggles..]

Then you were taught wrong unless of course you were taught for a Delta T of 10 which would be just under 6kw.

Rules of thumb are useless especially when the calc is so simple.

 

[CBF]

sorry but i disagree as well 11.76kw is 40,126 btu's & there is no way you can feed 40k btu's worth of rads on 15mm pipe, i would say 15mm will feed 4.40 kw 15000 btu's

 

[Biggles..]

Can you not read or do you just fail to under stand the calculation!

4.2SHC of water
20 delta t
0.00014m3 per linear meter of 15mm pipe

0.14litres/m

Calc done at 1m/s

0.14= KW / (4.2 x 20)

End of arguement.

 

[twgas]

sorry but i disagree as well 11.76kw is 40,126 btu's & there is no way you can feed 40k btu's worth of rads on 15mm pipe, i would say 15mm will feed 4.40 kw 15000 btu's

For a minute I thought the wife had put too much booze in my dinner.

 

[Dan Robinson]

Lee, what are you on about? It is patently obvious you have no idea .

 

[mickyg]

sorry but i disagree as well 11.76kw is 40,126 btu's & there is no way you can feed 40k btu's worth of rads on 15mm pipe, i would say 15mm will feed 4.40 kw 15000 btu's

based on what? hearsay

 

[CBF]

no based on experience, so you feed 40k of rads on 15mm then wonder why they don't work, plus Lee you are talking about pipework rads work on a delta t of 50 degrees not 20

i didn't know a pop band knew anything about heating calcs

 

[mickyg]

no based on experience, so you feed 40k of rads on 15mm then wonder why they don't work, plus Lee you are talking about pipework rads work on a delta t of 50 degrees not 20

i didn't know a pop band knew anything about heating calcs

experience is variable. Physics is constant. You cant argue with correct calculations because you have always done it that way.