Q: Central Heating DHW Zone Valve size? Advice please.

[Mike Norris]

I have several questions coming up, but I'll start with this one.

I have a Gas CH system that has been converted to a fully pumped system, previously pumped heating, gravity HW.

The installer used two port zone valves for each circuit, and as it had been previously gravity fed (I assume this is the reason) the HW circuit is all in 28mm pipework - except for the zone valve! He has used a 28mm-22mm converter either side of the HW zone valve which is

22mm.

Questions are

1. Why
2. Will it actually make much difference?

Many thanks for any info.

Mike Norris

[Andy Hall]

Because he only had a 22mm one on his van or because that's all that the merchant had that day.

Not really unless you had a very large property and large boiler and cylinder where it was appropriate for all of the pipework (even pumped) to be done in 28mm.

.andy

To email, substitute .nospam with .gl

[Set Square]

28mm - needed for gravity circulation - is an overkill for pumped hot water - but it's easier to leave it in place rather than replace it. Fitting a 22mm zone valve to it is no problem whatsoever. A friend of mine has a fully pumped system, with separate pumps for HW and heating - and the HW circuit uses 15mm pipe - and works perfectly ok.

[sparky]

I did exactly the same when I changed my system to fully pumped that was three years ago and I've had no problems it just saves taking out all the

28mm

[Niel A. Farrow]

It's usually quite ok to go from 28 mm gravity to 22 mm pumped - the pump makes it more efficient because it's er, pumping, so not so much heat loss so you can use smaller pipes. So in your case I don't think it should matter. Neil