Two radiators on one 10mm pipe

[Jasontenn]

I’ve posted a few times on here about plumbing radiators using plastic push fit etc.

My house is a 1930’s semi the central heating is all 8mm and 10mm copper microbore fed from manifolds off 22mm feed and returns.

What I found when I lifted the floorboards in the hallway has confused me somewhat.

There is a long run of 10mm copper from the manifold in the dining room all the way to the hallway which must be a run of at least four meters (8 meters there and back). The radiator is a large 1800 x 600 which is boiling hot and heats quickly.

Now for the confusing part, tee’d off this 10mm is a three meter (6 there and back) run of 10mm copper into the living room feeding an even larger curved bay window radiator, which also heats quickly and gets very hot.

I’ve just replaced the hallway radiator for a larger 1900 x 600 double designer radiator and just cut the 10mm copper and used push fit to connect 10mm speedfit to 10mm plastic and into the valves.

Again this heats quickly and is very hot.

Everything suggests that this shouldn’t work. How can a 10mm tee off onto another radiator and one long run in effect power two rather large radiators without issue.

Is this an anomaly or is all the research I’ve been doing wrong. My understanding is that you can tee off 15mm and run another radiator, but not off 10mm.

What’s going on ??

I’ve added a couple of pictures of the pipes tee’d off the pipe going to the hallway. The large pipe is a gas pipe.

 

[denso13]

What’s going on ??

Nothing really, if it works it works.

I've done it a few times when forced to with no issues.

 

[Johntheo5]

Circ pump might be set to and running at a high head.

 

[Jasontenn]

Circ pump might be set to and running at a high head.

How do I check if it’s running at a high speed?

Is that bad and will it cause issues. I suspect it’s been running the same way for well over ten years.

 

[denso13]

How do I check if it’s running at a high speed?

Is that bad and will it cause issues. I suspect it’s been running the same way for well over ten years.

No, it's fine if you have no issues. 10mm can easily supply your two radiators, as you have found out.

 

[Jasontenn]

No, it's fine if you have no issues. 10mm can easily supply your two radiators, as you have found out.

Definitely no issues. All running fine and heat up nicely.

Everything I’ve read elsewhere says that it shouldn’t work but it does.

The rest of my house is 8 and 10mm copper and working fine. When I’m replacing radiators is it ok to keep it at 10mm plastic as I find that so much easier to manipulate and connect or do I need to go to 15mm plastic ?

 

[denso13]

10mm is fine, just keep the system well maintained and clean.

 

[Jasontenn]

10mm is fine, just keep the system well maintained and clean.

Thank you

 

[Johntheo5]

How do I check if it’s running at a high speed?

Is that bad and will it cause issues. I suspect it’s been running the same way for well over ten years.

Is it gas or oil fired, if oil fired the pump is (normally external) but I wouldn'y worry in the slightest about it, as said , its working fine, leave well enough, alone.

 

[Jasontenn]

Is it gas or oil fired, if oil fired the pump is (normally external) but I wouldn'y worry in the slightest about it, as said , its working fine, leave well enough, alone.

It’s a 2.5kw combi boiler in an upstairs cupboard powering seven radiators (one is a towel rail).

 

[Johntheo5]

The circ pump on a combi is used to circulate water through the radiators or through one side a small plate heat exchanger with mains cold water being heated on the other side of the heat exchanger so the circ rate (via a high pump head) is designed to allow full boiler output to heat the incoming cold water, so your 25kw? combi might have a pump head capable of circulating ~ 24LPM through the plate heat exchanger whereas your 7 rads might only require ~ 12LPM at the same dT of say 15C and ~ 12kW rad(s) output, or something along those lines.

 

[Jasontenn]

The circ pump on a combi is used to circulate water through the radiators or through one side a small plate heat exchanger with mains cold water being heated on the other side of the heat exchanger so the circ rate (via a high pump head) is designed to allow full boiler output to heat the incoming cold water, so your 25kw? combi might have a pump head capable of circulating ~ 24LPM through the plate heat exchanger whereas your 7 rads might only require ~ 12LPM at the same dT of say 15C and ~ 12kW rad(s) output, or something along those lines.

Yes my bad 25kw combi boiler. So I take it 7 radiators would be fine on this one. Does that take into consideration size of radiators. With having 7 could I add two more and it still be ok. I’m was hoping to add a very small single panel radiator on the landing 414 x 600 and perhaps add an additional double radiator in the kitchen dining room.

Or do you think I’m at my max with 7 and using 10mm microbore pipes.

 

[Johntheo5]

I find it hard to answer that one (re extra rads), probably no big problem if you are not using all the rads at one time, on your existing system you might be able to see the boiler flow and return temperatures, what is the make/model of the Combi?.

 

[denso13]

Or do you think I’m at my max with 7 and using 10mm microbore pipes.

Nowhere near it, just tee off the main circuit rather than the 10mm.

 

[Johntheo5]

I thought all the piping is 10mm??