Using a Condensing Boiler with a Single Pipe Radiator System

Dear UK-DIY,

I am in the process of replacing my very old gravity fed CH and HW system. To simplify the job and because of the size of the property, I have opted to convert to a simple vented fully pumped "Y" plan system for CH and HW.

I have a semi detached property with just seven radiators and one bathroom (although adding an on suite shower room at a later date is not out of the question). The existing setup has more than enough head to power the one shower without the need for a pump.

I have taken a segmented approach, replacing the radiators last year and the rest of the system (hot water tank, pipe work conversion to fully pumped system and new boiler) this year. So far I have replaced the old copper cylinder with a new Part-L compliant one and am running all hot water from the immersion heater until the indirect and boiler installation is completed.

I have installed all the pipe work for the indirect system, including new pump and three port mid position valve; however I now face a challenge. In plumbing terms, the house is split into two parts, the one hundred year old main building, and the newer extension to the rear. The old part has four radiators connected to a 22mm single pipe system; the extension has three radiators which are plumbed using a

15mm two pipe flow and return system.

I am planning on having plumber install a Worcester Greenstar 15Ri to this new setup, but from what I understand condensing boilers rely on a significant temperature differential between flow and return in order to modulate properly and that single pipe systems often do not provide enough of a temperature drop between flow and return.

Because of the age of the house, converting the four radiators in the two bed rooms and two living areas on the existing single pipe system to a two pipe flow and return version would be a major challenge requiring a significant amount of additional work.

I appreciate that the problem with single pipe systems is their lack of efficiency, however since replacing all the radiators, I used the heating with just new radiators during the winter and I found that the radiators on the single pipe section got hot at the same rate and achieved the same operating temperature as those on the two pipe system - hence my reluctance to make any changes!

I guess my question is, In order to meet the any new regs and get best efficiency from my new boiler, am I going to be forced to add another pipe to the single pipe system to convert the whole thing to a two pipe system?

Many thanks in advance!

James

Reply to
James
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The continued use of the single pipe system is not ideal. However with care about the balancing, thermostatic valve settings and location of the thermostat it should be possible to make it work, albeit with some control limitations.

Reply to
Ed Sirett

Would you be able to meet the requirement for TRVs on each rad though?

Reply to
John Rumm

Thanks for your comments, all very much appreciated!

When I replaced the radiators last year, I took the opportunity to put TRV's on all apart from the two in the main living area (where I intend to locate the thermostat when its installed). I balanced the system as best I could and set the TRV's according to the use of each room.

What I found was that even on the single pipe system all the radiators worked well (really quite surprisingly well infact - given what I had heard about single pipe configurations) and all the TRV's seemed to be working just fine.

Whilst I fully understand its not ideal, the work required to put in the second pipe is a major job to do properly, I have very old walls and plaster which i'm really not keen to chase out in order to put in new pipework (i'm not looking to create a bigger problem than I already have!)

Ed, when you mention control limitations - what are you thinking ? are you considering the inability to implement any zoning ?

Thanks again

James.

Reply to
James

What you heard about single pipe systems was probably wrong. Mostly it is based on a lack of understanding of how they work because they aren't installed or taught today. There is nothing fundamentally wrong with them. They are more difficult to calculate and setup in the first place, but yours was probably installed back in the days when heating engineers did still know how to do that.

Reply to
Andrew Gabriel

Not so much that. Of course the single pipe run cannot be subdivided but the TRVs will make it more controlled.

I was thinking that there may be issues with balancing the single pipe against the two pipe stuff. It all depends on the layout.

You can think of the single pipe part as a large single big radiator (which happens to have parts in several rooms). It has a larger flow/return temp differential which is great with a condensing boiler.

Does the living room have any additional sources of heat? (fireplace or large southerly facing window?) In which case it may not be the best place for the over all heating thermostat.

Reply to
Ed Sirett

Thanks again for the very useful information.

The living area has two radiators (neither of which have been fitted with TRV's) and is quite a large open area. It has an open fireplace which we use in the winter at one end.

I am planning on purchasing a wireless thermostat and timer (probably the Honeywell CMT927) which has an optional table top stand to sit on a bookcase or shelf. In this way, I can move the device around to find the best location and then if necessary mount it permanently.

As a result of your advice, I have a much better understanding of the single pipe system now and feel confident in bringing it up with whoever I find to fit the boiler.

James

Reply to
James

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