25000 BTU Cast Iron Radiator Supplied With 15mm Piping

lebigmacncheese

Hi,

Just wondering if it's ok to install a 25k BTU cast iron rad using 15mm pipe, or should i install 22mm?

I found some figures in a post below....these deltaT's relate to boiler supply and return i think? But wouldn't a radiator like this supplied with 70 degree water return it at a much lower temperature (effectively extracting most of the heat carried by the water)?

with 20 degree drop and 1.5m/sec flow you can have up to 18kw on 15mm

with 20 degree drop and 0.3m/sec flow you can have up to 3.4kw on 15mm

with 11 degree drop and 1.5m/sec flow only up to 10kw on 15mm

with 11 degree drop and0.3m/sec flow only up to 2kw on 15mm

John.G

What is the total length of the pipework, ie are you taking the flow and returns from existing 22mm piping?

lebigmacncheese

It's got it's own supply and return from manifold under the stairs 4m away...

John.G

If your boiler temp is 70C and if you can accept 21734btu (6.37kw) as the max rad output then you require a flowrate of 9.12LPM with dT of 10C, flow/return of 70/60C. 8M of 15mm (OD) piping will have a friction loss of ~ 1.3M so assuming rad v/v + rad loss of 1m then total = 2.3M, if you use 22mm piping then pipe loss ~ 0.25M....total loss ~ 1.25M. IMO better off with the 22mm piping otherwise you will have to run the pump at a higher head than normal but no big deal really with a sealed system but a no no with a open vented system as you are inviting vent pump over and air ingress.

If you are happy with a rad output (max) of 18629 (5.46kw) then the total piping loss is only ~ 1.3M with 15mm piping and a dT of 20c, 70/50C flow/return

lebigmacncheese

Thanks for the response, 15mm pipes are already in the ground so will have to make do I think.... See how it works out

John.G

If your rad is a tallish column rad then you would be well advised to insert a flow diverter (if not supplied) as the rad might literally take hours to heat up otherwise, they look like this and cost ~ €30 and are installed at the hot side.

lebigmacncheese

Thanks for that tip...yea its 990 tall, 6 column x 2.3m wide....

lebigmacncheese

Ho wmany mm would this add to the pipe centres John?