New radiator pipe work - 10mm system. Can I use 15mm for just one room?

ChasingtheWelshdream

Hi all,

I am swapping one large radiator for two smaller ones (a very large on an internal wall, for two smaller ones under the bay window). The Btus are roughly the same, it will just make the room layout more practical.

The system is currently 10mm copper microbore, each radiator running from manifolds from the 22mm. The 10mm works well and I have no need to change it, but this has me scratching my head a little.

To go from one to two radiators, I was going to to put in a 2 port manifold on the 22mm and run new 10mm to each rad from there. However, I can't get a suitable manifold locally and always mindful of needing to rush out and get something if I muck up. So I am wondering about other options.

I could put a couple of reducing tees on the 22mm -  rather than a manifold - one for each rad. But again, I can't get a copper one of these locally and would need to buy online. I can get push-fit but I would prefer to keep it all copper if I can.

But I can get 22mm-15mm fittings by the dozen. So I wondered if it would be an option to tee in a 15mm flow/return 'circuit' to that room only, and then tee up to each new rad from this.

Now as a humble diy-er, I can't see there would be any issues with that as long as everything connects back to the 22mm properly.  But then again, there are usually things I haven't thought of and will always bow down to others' superior knowledge. 

So, over to you lovely lot. Can I mix and match 15mm and 10mm like this, or am I being dangerous?

Thank you as always. :-)

BUFF

as long as you balance things after installation I can't see an issue (certainly not dangerous) - but I am also a humble diy-er.

grumbler

I think it's absolutely fine to use 15mm, but 15 x 10mm adapters are easily available a SF

And if you already have one 10mm connection at the manifold, why not just to add a 10mm tee to split it to two radiators?

FreeBear

ChasingtheWelshdream said: But I can get 22mm-15mm fittings by the dozen. So I wondered if it would be an option to tee in a 15mm flow/return 'circuit' to that room only, and then tee up to each new rad from this.

Don't see a problem with this. You will (probably) need to balance all your radiators afterwards, so that will minimise the issue of 15mm pipe having a higher flow capacity compared to 10mm.

ChasingtheWelshdream

BUFF said:

as long as you balance things after installation I can't see an issue (certainly not dangerous) - but I am also a humble diy-er.

Reassuring, thank you. :-)

FreeBear said:

ChasingtheWelshdream said: But I can get 22mm-15mm fittings by the dozen. So I wondered if it would be an option to tee in a 15mm flow/return 'circuit' to that room only, and then tee up to each new rad from this.

Don't see a problem with this. You will (probably) need to balance all your radiators afterwards, so that will minimise the issue of 15mm pipe having a higher flow capacity compared to 10mm.

Lovely thanks. I am fiddling with the system a lot so will be re-balancing  everything properly once I am finished.

grumbler said:

I think it's absolutely fine to use 15mm, but 15 x 10mm adapters are easily available a SF

And if you already have one 10mm connection at the manifold, why not just to add a 10mm tee to split it to two radiators?

Sorry if I am misunderstanding you (I may be a couple of glasses of red down....) That fitting looks like a reducer insert for 15mm radiator valves, or is it something else? As far as I am aware (only by reading mind), 10mm should only be used for one radiator, and tee-ing into it would reduce the flow too much and struggle to heat up two rads on the same run, hence why I thought it couldn't be done. Or do you mean something else? 

The other thing I wondered about is to tee from 22mm to 15mm for a short distance, and then add 2 x 10mm tees into that, so that the majority is still 10mm pipe. The only reasons being (a), I have enough 10mm already and (b), there is enough space to manoeuvre 10mm runs without needing to make any joints. Having said that, I am using 15mm for final connecting pipes as I think it looks better, so would effectively be going 22-15-10-15. Which seems a little mad possibly.

I am thinking aloud.... Hubby has no interest in my ramblings so I do appreciate you all listening.   

ChasingtheWelshdream

To continue my wandering Saturday night ramblings.....

I have another two radiators to deal with later on, which are in the room directly below. These are both drop fed from the upstairs 22mm pipe but the installer had no regard for aesthetics, ruining some beautiful cornicing in the process. Future goals are to tidy this all up.

If I were to put the 15mm 'circuit' in the upstairs room as above, could I then drop this 15mm down to the room below, tee-ing off to the two downstairs rads as well? So four radiators on the same 'circuit' - two upstairs, two downstairs? (I don't know what else to call it, it makes sense to me!) It is hard to explain, but would make the downstairs much neater.

Something is telling me this is not the right way to deal with downstairs, but I'm not quite sure why....

grumbler

ChasingtheWelshdream said:

grumbler said:

I think it's absolutely fine to use 15mm, but 15 x 10mm adapters are easily available a SF

And if you already have one 10mm connection at the manifold, why not just to add a 10mm tee to split it to two radiators?

Sorry if I am misunderstanding you (I may be a couple of glasses of red down....) That fitting looks like a reducer insert for 15mm radiator valves, or is it something else? As far as I am aware (only by reading mind), 10mm should only be used for one radiator, and tee-ing into it would reduce the flow too much and struggle to heat up two rads on the same run, hence why I thought it couldn't be done. Or do you mean something else?

This adapter works with with all 15mm compression fittings, including those 22mm-15mm ones that you can "get  by the dozen" and 15mm radiator valves.

ChasingtheWelshdream

Ah thank you, I hadn't realised that. :-)

FreeBear

ChasingtheWelshdream said: The other thing I wondered about is to tee from 22mm to 15mm for a short distance, and then add 2 x 10mm tees into that, so that the majority is still 10mm pipe. The only reasons being (a), I have enough 10mm already and (b), there is enough space to manoeuvre 10mm runs without needing to make any joints. Having said that, I am using 15mm for final connecting pipes as I think it looks better, so would effectively be going 22-15-10-15. Which seems a little mad possibly.

Personally, I'd stick with 15mm all the way. Sticking bits of 10mm in part way will restrict water flow.

ChasingtheWelshdream said:

To continue my wandering Saturday night ramblings.....

I have another two radiators to deal with later on, which are in the room directly below. These are both drop fed from the upstairs 22mm pipe but the installer had no regard for aesthetics, ruining some beautiful cornicing in the process. Future goals are to tidy this all up.

If I were to put the 15mm 'circuit' in the upstairs room as above, could I then drop this 15mm down to the room below, tee-ing off to the two downstairs rads as well? So four radiators on the same 'circuit' - two upstairs, two downstairs? (I don't know what else to call it, it makes sense to me!) It is hard to explain, but would make the downstairs much neater.

I have a rule of thumb that says no more than three radiators per drop when using 15mm pipe. This seems to be a pretty common "rule" with most plumbers. That said, if the radiators are small, then you could get away with more. With 10mm pipe, I wouldn't hook up more than a single radiator per drop..

ThisIsWeird

10mm to each of the two rads should be fine. Sharing 10mm between the rads not so much.

ChasingtheWelshdream

Yes, I wouldn’t share 10mm between two radiators. 

I will leave the downstairs for now as I will probably be increasing the size when I get to them as well. One to think about later.

Right, off to loft some floor boards.

Thank you all, very much appreciated. :-)