installing a 2 zone central heating system

[doitmyself]

some of the downstairs rads are connected to the upstairs return and some of the upstairs rads are connected to the downstairs return - is this ok or will there be a risk of return circulation?

Are you saying that some downstairs rads are fed from the downstairs circuit but are connected to the upstairs return, and some upstairs rads are fed from the upstairs circuit but their return is connected to the downstairs circuit?

 

[Tinno]

All downstairs rads are connected to one flow, all upstairs rads are connected to the other flow, each flow will be connected to their own 2-port motorized valve which is controlled by their own programmable room thermostatm one upstairs and one in the lounge.

Now...my query is with the "return" connections. I have two sections of 22mm pipe, one for upstairs rads, one for downstairs rads and they are joined near the boiler and then obviously connected to the boiler. However, because of distance away it was more convenient for me to connect a couple of the downstairs rads to the upstairs "return" . Like wise with a couple of rads upstairs, because of the location of the downstairs "return" it was more convenient to connect them to that "return" instead of the upstairs return....hope this makes sense. I'm just wondering if their will be a problem with the way i have connected the rads to the "return" pipes.

 

[Tinno]

hi doitmyself,

just read your post again, didn't know why i have tried to clarify it because you have got it exactly right.

 

[doitmyself]

So the flow and return pipes for each circuit did not run together? That's very unusual.

I think there may be problems when it comes to balancing the system.

If you want to ensure there is no reverse circulation you should install one-way valves in each branch before they merge.

 

[stevetheplumber]

you can use s plan on a combi but the wiring is often different depending on the combi your using
most combis have a link wire installed to link two terminals all external controlls are switched across the two terminals when using s plan these two terminals are run through the aux switches of the valves power from the boiler goes to grey and orange is the switched feed back to boiler

 

[Tinno]

thx stewetheplumber, not quite at the wiring stage yet but that info will come in very handy when i eventually get there.

hi doitmyself - the flow and return for upstairs run together and flow and return for downstairs run together, they are not actually located downstairs as we have a concrete floor. both are located in between the joists of the bedroom floors as in the diagram above. its just that one circuit is situated in one side of the house and the other circuit is situated the other side of the house. About 6ft between them. didn't want to overload the holes in joists....between 0.25-0.4 neutral axis and all that. Saying that, the plumber and electrician who have been there before have put holes ALL over the place and not in the neutral axis,,,,,cowboys!!!!!! I think i'm gonna reconnect the 2 downstairs rads that are connected to the upstairs return etc...it will take away the doubt i have. Did you take a look at the diagram.....what do you or anybody think of it, does it look okay?

 

[doitmyself]

Can't see anything wrong with your diagram. You just need to size the pipes correctly.

 

[Tinno]

Thx doitmyself...that gives me piece of mind. On the diagram the thicker line is 22mm and the thinner line which is the pipe off the 22mm to radiators is 15mm. Do you think this will suffice?? cheers

 

[doitmyself]

On the diagram the thicker line is 22mm and the thinner line which is the pipe off the 22mm to radiators is 15mm. Do you think this will suffice??

It all depends on the number of watts the pipe is carrying as this determines the flow rate (litres/sec) through the pipe. Both 15mm and 22mm pipe can carry the flow, but the speed will be higher in the smaller pipe. (Think of a motorway. Both a two lane and a four lane would be able to carry 5000 cars an hour, but the cars will have to travel faster on the two lane motorway).

See the two links I gave earlier.

 

[Tinno]

I'm now thinking i have gone OTT with the 22mm looking at the table from the link. In copper 15mm velocity in a closed system has a minimum of 3.63Kw - 18.10Kw max. Is this the same as plastic, cos I am using HEP20. The guys at wavin advised that 10mm could only be used upto 1.75 Kw and could only be run a max distance of 5m and that includes flow and return in that 5m. I've basically ran the 22mm through out the house and then each radiator is tee'd off with 15mm no matter what size the radiator since the distance to most of the radiators is at least 5m, maybe one or two are slightly less. Should I have fed several radiators with one 15mm pipe when I tee'd off the 22mm? rather

 

[dontknowitall]

I don't think you can go OTT with a 22mm heating circuit and 15mm individually to/from most or all radiators. It will probably last for much longer than a microbore system and put up with more neglect.

 

[Tinno]

hi dontknowitall, thx for the advice...so theres no need to rip out some of the 22m and swap it for 15mm to feed several rads in order to keep the velocity above the min requirement (what ever that is in plastic piping - same as copper?).


Obviously, i'm putting the heating myself, its a big job in terms of labour and i want to get it right first time. I want a system that is efficient and lasts a long time. I think the advice that i am getting from this forum is going a long way to making sure that happens, so thx to everyone who has contributed, especially doitmyself. Anymore info and advice would be great.

 

[dontknowitall]

I don't know it it's you or me muddled up here.

The heating circuit will be the 22mm flow from and continuing in 22mm return to the boiler.

Off this circuit you will tee in 15mm from flow of heating circuit to flow end of radiator and 15mm return from radiator to heating circuit return.

 

[Tinno]

yes, exactly....22mm running close to radiators then tee'ing off ith 15mm to the radiator. I'm just thinking that i may have gone too close to the rads with the 22mm. For example, i have a rad that is about 0.4kw, the 22mm goes close to this, i then tee off using 15mm, total length of 15mm being aprox 5.2m (incl flow and return). I'm thinking is the piping too big for such a small rad to get the flow of the water running at the minimum velocity??

 

[dontknowitall]

That's one of the reasons for fitting lockshield valves so you can regulate the flow of the water through the radiator.

What you're doing sounds fine.