Central Heating Pipe Sizing

[***Tom11***]

Whats peoples views on what pipe size i should use in the following scenario:
2 x 3 bed houses being converted into a 4 bed.
13Kw heating demand fed via a Worcester 42Cdi Combi, 550Cdi high flow or 35i System boiler - Customer undecided yet although i have recommended due to hot water demand required to go with the system boiler and cylinder.

22mm from boiler and main skeleton or 28 mm and reduce to 22mm after some of the heat load has been took off to some of the rads ?

I was thinking 22m should be fine but upon checking through various sources i keep reading conflicting advice which is making me think possibly some 28 may be needed ?

 

[ShaunCorbs]

22mm as heating demand is below 40kw

I would go heat only / sys and unvented cylinder

 

[chris watkins]

Tom, I would suggest purchasing a copy of the Domestic Heating Design Guide & reading it.
Best £30 a heating pro like yourself will ever spend.

 

[***Tom11***]

We both know that a 4 bed 2 bath property should have sys/unvented but she is adamant she wants a combi!
So you think 22mm could cope with 40kw of heat load ? That seems excessive to me.
Im not saying you are wrong at all but i wouldnt have thought 22mm would cope with that much.
On looking at various threads there is conflicting information/answers.

 

[chris watkins]

I believe Shaun meant the 13kW from your 40kW combi.
22mm copper will carry around 23kW at a delta T of 20degC which is what you should be designing & selecting the emitters to Tom.

 

[***Tom11***]

Cheers for the info and the book tip, ill have a looksi for sure

 

[Sharp Point]

13kw heat load seems rather low for 2 x 3bed houses, are these old houses with very high levels of insulation or new build houses?

 

[garygvl]

5 bed new builds on some sites are only fitting 12kw boilers.

 

[garygvl]

Whats peoples views on what pipe size i should use in the following scenario:
2 x 3 bed houses being converted into a 4 bed.
13Kw heating demand fed via a Worcester 42Cdi Combi, 550Cdi high flow or 35i System boiler - Customer undecided yet although i have recommended due to hot water demand required to go with the system boiler and cylinder.

22mm from boiler and main skeleton or 28 mm and reduce to 22mm after some of the heat load has been took off to some of the rads ?

I was thinking 22m should be fine but upon checking through various sources i keep reading conflicting advice which is making me think possibly some 28 may be needed ?

40k combi only runs at 40k when doing hot water. not sure what worcester ouput on this combi is on heating only without looking at tech specs but expect it to be below 30k and as your heating demand is only 13k boiler will modulate down anyway so 22mm all you need

 

[Sharp Point]

5 bed new builds on some sites are only fitting 12kw boilers.

Yes I understand that, but I don’t think the op’s description of knocking two houses into one, will be new builds lol.....but I maybe wrong.