Increasing heating pipework capacity...

[MattChan]

I have 5 downstairs rads which are all fed from one 15mm flow and one 15mm return from the pump and boiler upstairs! The 15mm was all put down when the house was built 20 years ago so is buried in the concrete floor.

I believe 15mm pipe is good for about 3kW of heat. Which I assume is lower than the output of my 5 rads.

It would be fairly easy for me to tap off the 22mm pipe where it leaves the pump and give another 15mm branch downstairs to supply the hall and kitchen rads. This would then mean the current 15mm is only supplying 3 rads.

My main question is, is it correct to cap the old supplies to these two rads or would it actually be better to leave those supplies be and just T the new flow and return into them. Effectively the second method would give two 15mm supplies to the downstairs heating circuit.

I was just wondering if this would cause any strange flow issues etc?

 

[bengasman]

15mm is ample for 5 rads

 

[chrishutt]

15mm is ample for 5 rads

It depends on the output of the rads, and what the temp. drop across the system is. A 20°C drop will almost double the carrying capacity of 15mm tube compared to a 11°C drop.

 

[Biggles..]

Old figures used to be 20000 btu's for 15mm and 40000 for 22.

If its double that for 20 degree drop(condensing boilers flow and return) then your laughing.

 

[ChrisR]

I was told 14,000 Btu/hr , =4.1 kW
There's no limit, as such. If you can get the water down the pipes.
The limiting factor is the water velocity because of the noise it can generate.
WHat boiler do you have, what pump, and how long is the longest loop of pipe. That will start big, probably 22mm, and somewhere drop to the 15.
If you have a condensing boiler it will probably be designed for a 20º differential, so as ChrisH says ......

Do the rads have TRV's?

You can prove the supply issue with a surface thermometer, which can be had for under £20.

 

[chrishutt]

Do the rads have TRV's?

Are you doing that deliberately Chris?

 

[D_Hailsham]

Take a look at Copper in Small Bore Heating Systems:

http://www.ukcopperboard.co.uk/literature/pdfs/Installation-Tips/Small-bore-heating-systems.pdf

If you want to estimate the output of your existing rads, the Stelrad Elite catalogue is a good starting place. Most rads installed by the typical mass house builder are Stelrad or similar.

http://www.stelrad.com/UK/docs/elite.pdf