Single pipe central heating systems - hybrid options?

[dhutch]

After some advice.

I have recently traced all the heating pipes in our house and discovered it is plumbed as a one pipe system.

There are actually in total five circuits each with there own balancing valve with only 2-3 radiators on them, it appears when new its was quite a high spec system, but I believe it will have been put in around 1965. Ring is 22mm, 15mm rad tails, 28mm back to boiler. Total of 18 rads and 2 towel rails.
Most of radiators work ok, but only if you turn the flow temp on the boiler right up and even then quiet a few are much closer to 'quite warm' than 'hot', with the return temperatures being very high, and where someone has bodged another two rads on for a porch/loo extension they obviously basically don't even get warm.
The boiler is a reasonably modern Viessmann Vitodens 100 35kW system boiler, which spends most of the time just ticking over, due to the high return temp.

Hence we are looking at what the options are in terms of improving performance, to get the time to heat the house more reasonable, and ideally to reduce the return temperature to improve boiler efficiency.

The way the pipes are run with 22mm flow and return basically parallel, it would not take much work anywhere there is access, to convert over to a two pipe system. This is great for the first floor where all the floors are up anyway for a whole house re-wire. However the ground floor is all under a fairly original looking oak flooring nailed into the floorboards, so lifting that is well down the desirable list!

In a moment of madness my current best plan is to convert the first floor (and the rad that descend off it) into a two pipe system including moving the porch onto this as we can drop pipes in a cupboard, and then run the output of the boiler through the two ground floor circuits first for the two main rooms and hallway (five rads), and then run the 'return' from that into newly rehashed two pipe system on the first floor and back to the boiler. Adjust the flow temp and pump speed to get a good return temp and overall performance.
My thinking being we get the best of both worlds, hot feed into the single-pipe system where we cant re-pipe it, and then nice easy to balance normal two pipe system for the rest of the house, with low return temps to boost?

I will get a drawing of the full system uploaded once drawn, but thoughts welcome!

Daniel

 

[dhutch]

Anyone?

 

[Neil9834]

Where do you stay?

 

[MeldrewsMate]

Hmm?
2 - 3 rads on each of 5 loops makes 15 maximum, but you say you have 18 rads + 2 ?
If each loop has a balancing valve try throttling back each to reduce the return temperatures.

 

[dhutch]

Where do you stay?

Not sure what you mean, we live in the house. Located on the Wirral.

Hmm?
2 - 3 rads on each of 5 loops makes 15 maximum, but you say you have 18 rads + 2 ?
If each loop has a balancing valve try throttling back each to reduce the return temperatures.

It's actually 17+2, I excluded the the two piggy backed extension rads, and there is one rad direct across the flow and return by the boiler, but get the picture.

I have spent some time adjusting the balance and got it better, including turning the one right by the boiler off. But the return temp is still huge compared to some of the rad temps and can't see how you can improve on that with balancing.

Thanks

 

[dhutch]

Our plumber came round last night and looked over the job again now we have uncovered the pipes we can as part of the re-wire.

Given the layout and the amount of compression fittings he has suggested we re-pipe the whole system including drops to each of the ground floor radiators in 10mm coated coil back to a backbone of 22mm, reusing what 22mm we have if and where practical. We did talk about 15 coated but he assures me even a very large rad is ok on 10mm as long as it's just the drop to one rad.

This will be pain in the room with oak cladding as it will have to come of in atleast one place, but is probably for the best in the long term I guess.

Daniel

 

[MeldrewsMate]

IMO two pipe systems are superior to single pipe in every way except in capital cost, however single pipe systems can work very well; for example I have two single pipe loops in my house, one for upstairs, and one for downstairs. The upstairs loop has 3 radiators (about 3kW load) and a balancing gate valve, downstairs has 6 rads and about 10kW of load. The loops are fed with 15mm copper in the screed, and whilst it is apparent that the downstairs loop is overloaded (in that the last rad takes a long time to reach full temperature) it is fortuitous that the two leading rads are in the lounge and the last is in the kitchen - the performance is very satisfactory for me, as the lounge heats quickest.

OP, on your system have you tried turning the pump speed lower, thus increasing the water dwell period and reducing the return temperature?

I would suggest that, if you are going to convert to a two pipe system, you make the larger radiator drops in 15mm pipe to help keep the velocity (and pipe noise) down. Do not try to mix single and two pipe systems - the result may be disappointing - so if you're going to do it, do the conversion completely.

 

[dhutch]

IMO two pipe systems are superior to single pipe in every way except in capital cost, however single pipe systems can work very well; for example I have two single pipe loops in my house, one for upstairs, and one for downstairs. The upstairs loop has 3 radiators (about 3kW load) and a balancing gate valve, downstairs has 6 rads and about 10kW of load. The loops are fed with 15mm copper in the screed, and whilst it is apparent that the downstairs loop is overloaded (in that the last rad takes a long time to reach full temperature) it is fortuitous that the two leading rads are in the lounge and the last is in the kitchen - the performance is very satisfactory for me, as the lounge heats quickest.

OP, on your system have you tried turning the pump speed lower, thus increasing the water dwell period and reducing the return temperature?

I would suggest that, if you are going to convert to a two pipe system, you make the larger radiator drops in 15mm pipe to help keep the velocity (and pipe noise) down.
Do not try to mix single and two pipe systems - the result may be disappointing - so if you're going to do it, do the conversion completely.

It might be that slowing the pump down would reduce the return temperature, its a system boiler so the pump internal and I've not had the covered off to see what speed it is set at. Obviously while a lower return temp may be better for boiler efficient, it will reduce the temp of some of the radiators, and make balancing all the circuits slightly harder as the total flow will be less requiring finer valve control.

Sounds like your system works well enough for you, as to an extent ours has this winter. However as we are expecting to live in the house for the next 30-50 years all willing, and have a full re-wire, redecoration, several replacement radiators etc planned if feels like the time to get it right.

The 10mm drops would be for just one radiator per drop, but they are large rads, something 600x2400 type 22 rad.

 

[garyo]

Do not try to mix single and two pipe systems - the result may be disappointing - so if you're going to do it, do the conversion completely.

Can I ask why? I'm considering this myself next year (two pipe section fitted to a new extension) my thinking being that I'd put that circuit on its own pump.

 

[MeldrewsMate]

Can I ask why? I'm considering this myself next year (two pipe section fitted to a new extension) my thinking being that I'd put that circuit on its own pump.

You can successfully eliminate many of the problems by introducing a secondary pump for the new circuit - at the cost of extra capital, extra electrical power (expense), and perhaps a little noise. If you are taking two tappings from the single pipe system to your pumped extension system then be aware that the return temperature from this extension will be (should be!) more than 10 C cooler than the flow, thus detracting from the flow temperature of the single pipe system downstream. The solution may be to take your extension flow and return directly from or near to the boiler and, if a system or combi (with inbuilt pump) remove the need for the extra pump.

 

[dhutch]

Just to post back to this, we have decided to condemn the pipes under the ground floor, given what we can see of the pipes in the first floor, and chase out the wall to run new droppers down for the ground floor rads. Expect they would have been ok for ages more, but a lot of compression fittings, including some with signs of weeping, plus obviously single pipe layout.

I did want to avoid this due to the mess and delay, however its gone well and been fairly quick as well as being a lot less chasing than the electrics due to there only being 1-2 rads per room and about 8-10 sockets/switches per room. Plus we have managed to get into the oak panelled room from the adjoining rooms, running pipes in behind the skirting and along to the rad. Ground floor droppers in 10mm coated coil, which on a 20c dt appear to give reasonable flows even for larger 600x2000 twin convectors.

All in all happy. We are aiming to be here 40+ years and even if we are not for some unforeseen reason then we can sell the house knowing it is done right.


Daniel

 

[Grumpy Gasman]

Ground floor droppers in 10mm coated coil, which on a 20c dt appear to give reasonable flows even for larger 600x2000 twin convectors.

All in all happy. We are aiming to be here 40+ years and even if we are not for some unforeseen reason then we can sell the house knowing it is done right.

“done right”
Using 10mm tubing?

 

[dhutch]

Ran a short separate thread on the topic, but while I questioned it myself, it seems that running individual droppers in 10mm, which then then join a 22mm back bone, gives reasonable flow speed for the size of rad were using. With the advantage that it can be run in the wall within the thickness of the plaster and in one run without joins.


Daniel

 

[Grumpy Gasman]

“back bone”?
What’s a back bone?

 

[dhutch]

I mean the pipes running back to the boiler. Each radiator has a pair of 10mm pipes going to it, which then connects to a pair of 22mm pipes, either directly or if more than a foot away via 15mm, which then take the combined flow back to the boiler. One pair of 22mm for each side of the house, doing the last run back to the boiler in 28mm.

Daniel