sizing primarys

[good old the jazz]

What the rules of thumb about sizing primary flow and returns on a fully pumped sealed central heating system?

The new 38kw boiler is approx 12m away from existing pump and zone valves.Existing primary f & r done in 22mm.

Thanks

 

[spacethegas]

chances are thats ok.
if you have 20 rads it may not.

 

[gas4you]

I would swap them to 28mm personally.

 

[larrytheleak]

It all depends on loading there are limits on how many litres per minute velocity etc
you need to make a diagram and work out demands on each circuit
i think there may be pipe size calculators on web somewhere
there is one for corgis for gas but they cannot agree how to use it

 

[JohnD]

I don't know, but i know someone who has a big house with 28mm out of the boiler, necking down to 22mm for upstairs rads and 22mm for downstairs, which seem sensible to me.

 

[good old the jazz]

So 28mm it is then.

 

[D_Hailsham]

22mm can carry 22kW max with an 11°C differential and 40kW with a 20°C differential.
28mm can carry 37kw max with an 11°C differential and 67kW with a 20°C differential.

These will give a max velocity of 1.5 metres/sec. Anything higher may cause noise in the pipes.