Reverse circulation, return tee?

[Super_Paulie]

Gentlemen.

Got a few days to hammer out some plumbing, so I'm going to lay the flow and returns for my ufh.

 

For context, combi is in the loft, ufh (manifold, pump, wiring center etc) is ground floor. 2 port valves can live in the void/cupboard within the defunct chimney breast just below the boiler on the first floor.

 

So I've designed a dedicated flow and return, but my question is at what point can I join the return to the primary heating return? Does it have to be higher than the last radiator so as to avoid return circulation? If so, how high is high enough, is it physically above the last radiator or can it come from the same/last tee.

 

Cheers gents. Pictures a bit of a bodge, best I can do on my phone!

 

 

Edited June 23, 2023 by Super_Paulie

[JohnMo]

Sorry an answer to your question, but be careful with your zone sizing, as combi boilers tend to be huge kW wise.

 

If you have too many small zones, your boiler could just short cycle, not really effective at producing heat, but very effective in using lots of gas. This is especially true in the shoulder heating months when demand for heating is low.

[Super_Paulie]

2 hours ago, JohnMo said:

Sorry an answer to your question, but be careful with your zone sizing, as combi boilers tend to be huge kW wise.

 

If you have too many small zones, your boiler could just short cycle, not really effective at producing heat, but very effective in using lots of gas. This is especially true in the shoulder heating months when demand for heating is low.

4 zones, around 90m each is currently designed so hopefully that is ok for the combi. Just the reverse circulation I was hoping someone could clarify for me. Cheers for the response John 👍

[JohnMo]

Do mean mean 4 zones (independent thermostats) or 4 loops?

 

90m loop could be well less than 1kW, our combi had a min turndown of 6kW.

[Super_Paulie]

Sorry, loop. 4 (or 5, I forget) loops split between 3 thermostats. It's all been designed, I don't know the ins and outs at the moment as I don't have the documents handy.

Any thoughts on the reverse circulation, that's where I'm at today.

 

Cheers

[JohnMo]

Your return leg tee, placed close to the boiler rather than further away.  So at loft level. Would be my view on it.

 

20 minutes ago, Super_Paulie said:

It's all been designed,

Design by an UFH heating company? If your boiler min turndown is circa 1.5kW you could be fine, anything more than that you will have short cycling with one or two zones on and the rest off. You need about 50L of water engaged to allow 6kW of heat input not to end up short cycling for example.

[Super_Paulie]

15 minutes ago, JohnMo said:

Your return leg tee, placed close to the boiler rather than further away.  So at loft level. Would be my view on it.

 

Design by an UFH heating company? If your boiler min turndown is circa 1.5kW you could be fine, anything more than that you will have short cycling with one or two zones on and the rest off. You need about 50L of water engaged to allow 6kW of heat input not to end up short cycling for example.

Yeah designed by a few companies but most came back the same. No one mentioned short cycling but I guess they probably wouldn't... I'll get my lines in and then get back to the research, cheers John.