central heating pipe sizes.

[CliveM]

In a fully pumped central heating system, is 22mm pipework ok for both the heating loop and HW loop?

If some of the HW pipework was gravity using 28mm pipework - is it ok to run a section of 22mm when the system is fully pumped?

[Tim S]

Yes. I have never seen bigger than 22 used except for the thermo-syphon systems (which are an awful idea IMHO).

HTH

Timbo

[Tim S]

For the heating loop - depends on the length of runs and how many rads are coming off each spur.

Assuming normal house (you don't have a mansion?):

22 is big enough for the core runs from the boiler/pump. You can go down to 15 for spurs feeding a upto couple of rads. There's probably a correct way to calculate it with tables but if in doubt keep the pipes on the right side of too big as you can at least balance the flow at each rad and you won't have to switch the pump upto full pressure (which gets noisy in my house) to stop one of the rads running too cold.

I'm not a plumber - this is based on observation of working systems.

HTH

Timbo

[Andy Hall]

It depends on the size of the system and boiler rating but unless the house is large, has a high heating requirement due to poor insulation or has main pipe runs of more than a few metres then 22mm is conventional.

If you have a diverter valve or zone valves such that the heating and HW are not n simultaneously then 22mm for fully pumped where there was

28mm gravity should be fine.

.andy

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[Set Square]

Yes. But if the 28mm is already there, there's no need to rip it out and replace it.

If a single pump is going to be used to pump CH and HW simultaneously, you may need an adjustable gate valve in the HW circuit to allow HW/CH balancing to be performed.