3 tee

[Knappers]

Yes.
looks like a nice job tho fella.

 

[ShaunCorbs]

This is what it actually looks like upto date

 

[Knappers]

You decided to risk it then?

 

[ShaunCorbs]

Tbh I haven’t decided yet I’m going to get the boiler in there tomorrow and depending on space if it’s less than 4” I’m risking well having an experiment if I can get 6-8” I will change it

 

[Ric2013]

If I've understood what you're saying correctly, I think you're right, there's a potential issue. If the upper and lower rads each have their own zone valve I can't see that your going to get reverse circulation in the 'Why are my radiators hot in the middle of summer?' sense but there'll be some starvation of heat to the radiators when the DHW is heating and both rad zones are supposed to be on.

I don't follow you. You suggest elsewhere that the cylinder return could run back along the rad return. If the rad circuits are on, then how can the return from the cylinder possibly flow back against the current? Pumped water flow cannot in run two directions through the same pipe simultaneously, can it?

Obviously I get that having multiple circuits in use at the same time may reduce head and thus flow.

 

[Chuck]

I don't follow you. You suggest elsewhere that the cylinder return could run back along the rad return. If the rad circuits are on, then how can the return from the cylinder possibly flow back against the current? Pumped water flow cannot in run two directions through the same pipe simultaneously, can it?

Obviously I get that having multiple circuits in use at the same time may reduce head and thus flow.

At the time I wrote my answer, I was assuming that the upper floor and ground floor radiators had their own separate zone valves (there were several shown in the picture) but @ShaunCorbs said in later that they were on a singe zone.

In the actual system, I think that literal 'reverse circulation' can occur when the (single) zone valve to the radiators is closed and the DHW is heating. When the radiator-zone valve is open the 'reverse circulation' will be superimposed on, and hence reduce, the forward flow in part of the radiator circuit and might impair performance to a greater or lesser extent.

Take a minute to sketch a diagram of the pipework it'll make my thinking much easier to understand.

 

[ShaunCorbs]

They are 3 zones total ufh, rads, cylinder

 

[Ric2013]

At the time I wrote my answer, I was assuming that the upper floor and ground floor radiators had their own separate zone valves (there were several shown in the picture) but @ShaunCorbs said in later that they were on a singe zone.

In the actual system, I think that literal 'reverse circulation' can occur when the (single) zone valve to the radiators is closed and the DHW is heating. When the radiator-zone valve is open the 'reverse circulation' will be superimposed on, and hence reduce, the forward flow in part of the radiator circuit and might impair performance to a greater or lesser extent.

Take a minute to sketch a diagram of the pipework it'll make my thinking much easier to understand.

Okay, kind of got you now. Ta.

 

[Knappers]

Up the upstairs return and back via downstairs return via splitting tee on flow, induced by convection like on 1pipe system with cylinder return acting as a header.
Is the issue as I see it?...

@ShaunCorbs how did it go?

 

[ShaunCorbs]

Haven’t filled up but the distance between was less than 5” so opted for a nrv

 

[EvilDrPorkChop]

Haven’t filled up but the distance between was less than 5” so opted for a nrv

NRV on CH? They're only for water aren't they.

 

[ShaunCorbs]

NRV on CH? They're only for water aren't they.

yep and no you have the same in most boilers in there bypasses

 

[ShaunCorbs]

Nrv

 

[EvilDrPorkChop]

Are they even rated for CH? Don't think i'd be using one tbh

 

[ShaunCorbs]

110dc temp rated and 11 bar