Sanity check - pipe layout

[Mjward]

Hello

After a lot of procrastinating I've decided to go down the Hep2o PEX route for our random house (basically a mix of rads fed by a one-pipe system and UFH fed by two segregated boilers).

In a nutshell, the boiler is in the basement, the ground floor has 2 rads and the first floor 5 rads. The plan is to fit a 22mm equal tee in the basement, to branch off a feed to the 2 ground floor rads and another up to the first floor, again branching off to feed first floor rads. Will be running 15mm copper tails direct from all the rads into the 22mm via a 22-15-22mm reducer. Will be identical setup for both flow/return of course.

Now the 2 questions I have:
(1) I've mocked up a pipe layout below, thick lines = 22mm pex, thin lines = 15mm copper. Is there anything glaringly obvious that won't work with the layout suggested?
(2) I currently have an unvented system, megaflow cylinder, cold water tank etc etc. I'm getting a plumber out to put in a new combi boiler. Is it logical for me to rip out the old one-pipe system and fit the above flow/return first or have the new boiler fitted and then run the pipework? I guess the angle I'm coming from is in terms of when the plumber removes the cylinder etc from the system, is there any benefit to either going first.

 

[Ben-gee]

Speak to the plumber who is doing the job- we all have our ways of organising a job, but we’re not doing this one.

 

[SJB060685]

You would first need to do a heat loss survey to find the boiler/emitters size required. After that you can begin to calculate/size the pipework etc.

 

[Mjward]

Roger that. Re heat loss, that's already been done. Plumber has recommended 35kw combi and I've got the BTU calcs but I think with 22mm spine and tailing off to rads in 15mm you can't really go wrong.

Will get plumber to choose which order he prefers the work in if there is no standard best practice.

In terms of the proposed pipe layout in the diagram, this seems the most efficient (shortest) route

 

[SJB060685]

Plumber has recommended 35kw combi and I've got the BTU calcs but I think with 22mm spine and tailing off to rads in 15mm you can't really go wrong.

If your load is actually 35KW (which is quite large) then 22mm primaries from the boiler is too small and you will get underflow problems. You would need 28mm initially from the boiler and branch down to 22mm when you can.

 

[Mjward]

If your load is actually 35KW (which is quite large) then 22mm primaries from the boiler is too small and you will get underflow problems. You would need 28mm initially from the boiler and branch down to 22mm when you can.

My sense is the 35kw was specced by the plumber for the better flow rate in the bathroom.

My gut feel was slight overkill. On my calcs the CH requirements are around 12kw (split across 9kw of rads and 3kw of UFH). There is one bathroom. Water pressure is very good. Gas feed is in 22mm.

I believe in copper 22mm can handle up to 40kw and given the CH is lower than the DHW I would have thought 22mm could handle the larger boiler but will bow to the experts. Would I be capped at 30kw boiler in your opinion?

 

[SJB060685]

You can run any amount of power through any size pipe but 35kw through 22mm would cause a number of problems. Now you say the CH load is smaller (which I should of considered because you did say it was a combi) then I won't mention those problems as 22mm for your load will be fine.

 

[Mjward]

You can run any amount of power through any size pipe but 35kw through 22mm would cause a number of problems. Now you say the CH load is smaller (which I should of considered because you did say it was a combi) then I won't mention those problems as 22mm for your load will be fine.

Perfect and sorry for confusion!