3 tee

[ShaunCorbs]

What’s your thoughts on this I’m thinking it’s going to gravity circ maybe

down blue arrow upstairs rads return
Up blue arrow cylinder return
Tee below up blue arrow left heating return right cylinder return

even if I install another tee to the right just for the boiler return so that the cylinder is the last I think it’s going to be very close and could gravity anyway but open to your thoughts

 

[Knappers]

I'm struggling to get my head round your beautifully precise schematic 😄. You worried about cylinder return backfeeding through upstairs rads?
If so don't think it will gravity circ through cylinder coil because of Coil orientation.
If it does are anti gravity valves still a thing?

 

[ShaunCorbs]

I'm struggling to get my head round your beautifully precise schematic 😄. You worried about cylinder return backfeeding through upstairs rads?
If so don't think it will gravity circ through cylinder coil because of Coil orientation.
If it does are anti gravity valves still a thing?

close the blue line is the boiler return back to the boiler so from the cylinder it has to rise then goes into the boiler so I think there s a chance of it going into the upstairs rads

 

[Knappers]

If the return from cylinder is lower than flow then I'd think you'll be ok, if they're level then I'd want either a long horizontal run from cylinder or a little anti gravity loop

 

[Chuck]

What’s your thoughts on this I’m thinking it’s going to gravity circ maybe

Unless I've missed something, I think you must mean 'reverse circulation' rather than 'gravity circulation'?

If so, I assume you are worried that a proportion of return flow from the cylinder is going to reverse-flow back up the ground-floor-radiators return then mix with the flow to the upper floor radiators and then back to the boiler via the upper floor radiator return?

So, 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.

Following the 3-tee rule would prevent reverse circulation if a single zone valve controlled both GF and UF radiators, which doesn't look like it's the case here. It won't do much to mitigate this 'starvation', which is present any system that doesn't have an independent pump on each zone. Even non-return valves don't fix it because it's a reduction in flow not reversal. It's just what happens when you put heating loops in parallel.

On the one hand people accept that 'when the cylinder starts heating the radiators get cooler'. On the other hand if you don't follow the 3-tee rule, the next guy who looks at the system will point out the fact to the owner and allege, rightly or wrongly, that the system is below par as a result.

Or I may have misunderstood what you were saying.

 

[ShaunCorbs]

did a drawing with a picture @Knappers @Chuck and your correct there is a possibility of the upstairs rads warming when the cylinder is only on via reverse circulation as the cylinder tee isnt the last tee technically the upstairs rads are

yes the ground and upstairs rads are one zone

horizontal pipes from top to bottom

rad flow up and down
ufh flow
rad return
hot 3.5 bar
cold balanced 3.5 bar
cold main 8 bar

would option 2 eg the separate pipe be better as the tees are close i cant see much benefit as there close

 

[Knappers]

Yea 2nd is better but putting 150mm gap between tees would be best, can you kick out to right at bottom?

 

[ShaunCorbs]

Yea 2nd is better but putting 150mm gap between tees would be best, can you kick out to right at bottom?

not really would have to see how much I could squeeze as the boiler is left hand return

 

[EvilDrPorkChop]

Personally, from experience I'd of said you've got more chance of the down Rads heating up than the upstairs.

Tee the Cylinder return up at the bottom (To the right of your current T), and bring the upstairs Rads straight down without a tee out. Hope that makes sense?

 

[Knappers]

Actually will be fine, if you get any heat in pipe then it still won't induce a flow