best piping layout to make the most of combi boilers?

[xelaris]

I'm aware a good flow is a good start to ensure a good supply to combi condensing boilers, and therefore a 22mm pipe is recommended...then, I've heard that a direct connection from the stopcock without tees would ensure the maximum flow available....but without tees?! So one is supposed to feed the rest of the house after the boiler?! Am I right?
Anyhow, I'm on the early stages of planning a new piping layout (connecting to a new main and getting rid of old lead pipes) - so any suggestions are welcome.

 

[MJGas]

How do you connect the cold after the combi?

 

[ALCPlumbing]

Only if you don't want cold water in the house. You'll obviously have to tee off before the boiler. A combi is fed with a 15mm mains pipe and as a result you'll never have great flow which is why you wouldn't use one where you have more than one bathroom.
J

 

[xelaris]

How do you connect the cold after the combi?

well, that's my question (wasn't that clear?) - a tee is required before the boiler - still, I've read something which suggest otherwise...(if I find the source I'll post a link in here...)

 

[xelaris]

Only if you don't want cold water in the house. You'll obviously have to tee off before the boiler. A combi is fed with a 15mm mains pipe and as a result you'll never have great flow which is why you wouldn't use one where you have more than one bathroom.
J

The minimum requirements for my Biasi is 22mm...
I guess with central heating on and a second toilet is when problems starts to appear - that's why I'm considering going UFH for heating and Combi for two separate toilets and 2 showers - maybe it's worth considering 2 combis (remain to be seen if the water flow is going to be adequate).

 

[Gas2Air]

Only if you don't want cold water in the house. You'll obviously have to tee off before the boiler. A combi is fed with a 15mm mains pipe and as a result you'll never have great flow which is why you wouldn't use one where you have more than one bathroom.
J

The minimum requirements for my Biasi is 22mm...
I guess with central heating on and a second toilet is when problems starts to appear - that's why I'm considering going UFH for heating and Combi for two separate toilets and 2 showers - maybe it's worth considering 2 combis (remain to be seen if the water flow is going to be adequate).

What are you talking about? Have you any idea?

 

[Steelmasons]

The minimum requirements for my Biasi is 22mm...
I guess with central heating on and a second toilet is when problems starts to appear - that's why I'm considering going UFH for heating and Combi for two separate toilets and 2 showers - maybe it's worth considering 2 combis (remain to be seen if the water flow is going to be adequate).

Stop being ridiculous.

 

[newbuildinstaller]

unvented cylinder for high water demand NOT two combis.

22mm to a combi is pointless as the biggest can only deliver 16l/min (easy for a 15mm pipe to cover)

Too much water through your Biasi will lead to luke warm water

 

[roguetrader]

No tee's needed, feed everything with hot water, helps keep the WC pan clean too.

 

[Dan Robinson]

Being a Biasi the OP won't have to worry about a lack of cold water... now the flow rate?

That's another matter

 

[Happyplumber]

You will be lucky to get 10 LPM out of Biasi on good day with sunshine and 30C outside !


Two Biasi's is that an idea of Hell on earth!

 

[Tipper]

....22mm to a combi is pointless as the biggest can only deliver 16l/min (easy for a 15mm pipe to cover)

It's not actually pointless just that most plumbers don't bother to do it!

The point about a larger bore pipe to the combi is to reduce the pipework losses before the combi and thus get better pressure and hence flow after the combi. Similarly for the outlet pipework but having a large pipe takes longer for the hot water to get to the outlets and wastes a lot of heat so it's not done.

The other thing worth thinking about is keeping the inlet and outlet pipework as simple as possible and as 'straight' as possible because every bend adds to the losses in the pipework by a large margin and reduces the flow to the outlets. Swept bends are much better than elbows and in my opinion Speedfit fittings in particular with the sleeves that go with them are far too restricting.

 

[newbuildinstaller]

....22mm to a combi is pointless as the biggest can only deliver 16l/min (easy for a 15mm pipe to cover)

It's not actually pointless just that most plumbers don't bother to do it!

The point about a larger bore pipe to the combi is to reduce the pipework losses before the combi and thus get better pressure and hence flow after the combi. Similarly for the outlet pipework but having a large pipe takes longer for the hot water to get to the outlets and wastes a lot of heat so it's not done.

The other thing worth thinking about is keeping the inlet and outlet pipework as simple as possible and as 'straight' as possible because every bend adds to the losses in the pipework by a large margin and reduces the flow to the outlets. Swept bends are much better than elbows and in my opinion Speedfit fittings in particular with the sleeves that go with them are far too restricting.

IT IS POINTLESS

a combi will only provide say 11 litres/min @ a 35* rise so you try putting 20Litres/min through it and see what happens.

If you have ever installed a combi on a old vented system the cust will nealy always find the bath tap runs cold if fully opened

Guessing you aint a plumber just a google warrior

 

[TCCHeating]

Similarly for the outlet pipework but having a large pipe takes longer for the hot water to get to the outlets and wastes a lot of heat so it's not done.

Agreed, but it is done often, you won't find many combi installations in an ex cylinder cupboard not connected to the old 22mm hot water pipework.

 

[Steelmasons]

Got some 15mm Yorkshire bends circa 70's tipper. get real man.

When was the last time you saw a soldered bend used under the floor or surface??????