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Discuss Is it OK to plumb new radiator off pipes from existing radiator? in the Plumbing Forum | Plumbing Advice area at PlumbersForums.net

Hi all,

Question from a complete non-expert - I'm about to have some extension work start in my house and for radiators in the extension space, my builder has suggested he will use the plumbing from an existing nearby radiator to plumb the new radiators. Is this OK/typical to do? Is there anything I need to watch out for?

My simple non-expert brain says ideally the new rads would be plumbed direct to the boiler but I can also see the impracticality of going all the way back to the radiator when in order to do that there would be disturbance to internal floors or running pipes outside where they will be more prone to freezing although in this latter case I'm sure they can be protected appropriately.

Also, all the rads in my house are controlled by motorised TRVs (Honeywell Evohome) so I can turn them on/off individually. Will I be able to do that with the new radiators which have been plumbed from another existing radiator's pipes?

TIA!
 
1. Builders are generally not plumbers and have a less than perfect grasp of what is important.
2. The key issue is whether pipes run off existing radiators will, given the heat usage of the existing radiators, be able to supply sufficient heat for the extension. As a rough (not guaranteed) guide, tapping into 22 mm flow and return pipes will probably be OK, tapping into 15 mm pipes MIGHT work if all radiators so fed on the same pipework are small to medium sized, and it will probably never work if tapped of microbore pipework.
3. You wouldn't run right back to the boiler, as, depending on the type of boiler / system you might well be bypassing some or all of the controls. You should, if possible, tee into the flow and return "spine" of the system, which will probably be 22 mm, or even 28 mm pipework.
4. Motorised TRVs control individual radiators, so I wouldn't see any problem with your using them on the new radiators.
 

Last Plumber

Esteemed
Plumber
Gas Engineer
Advent Win
As above, the flow rate is important. You need to find out the size of the existing pipes and the current demand placed on them to ascertain whether they will supply enough for the new additional rads.
A good Plumber/Heating Engineer should be able to tell with a few quick calcs.
I wouldn't guess if I were you, if it doesn't work you will end up paying twice.
 

centralheatking

Esteemed
Plumber
Hi all,

Question from a complete non-expert - I'm about to have some extension work start in my house and for radiators in the extension space, my builder has suggested he will use the plumbing from an existing nearby radiator to plumb the new radiators. Is this OK/typical to do? Is there anything I need to watch out for?

My simple non-expert brain says ideally the new rads would be plumbed direct to the boiler but I can also see the impracticality of going all the way back to the radiator when in order to do that there would be disturbance to internal floors or running pipes outside where they will be more prone to freezing although in this latter case I'm sure they can be protected appropriately.

Also, all the rads in my house are controlled by motorised TRVs (Honeywell Evohome) so I can turn them on/off individually. Will I be able to do that with the new radiators which have been plumbed from another existing radiator's pipes?

TIA!
ALERT ...your builder is not a plumber, you are correct to be wary, No its NOT correct to do as this none qualified person suggests. He will know nothing about your system and most probably take your money and mess things up. Get advice from PF and find a totally independant inteligent heating engineer in..he will look after you and if your clever observe your 'builder' at the same time. PF is awash with got a builder in posts and my heating and plumbjng is messed up...heating systems are really quite
clever nowadays ...well beyond any brick monkeys. centralheatking
 
Thanks both. The builder uses specialists for electrical work, plumbing work etc. so I expect the plumber to be aware of all this - I just haven't spoken to anyone except the project manager.

This evening I will report back with the size of the existing pipes and the dimensions of the existing radiator so you know the existing demand. In terms of new rads in the extension, I expect there to be 3; 2 in a large room and 1 in a smaller room.

I don't know for sure but I have a feeling the "spine" of my system is underneath my tiles and flooring which means connecting off that as @steadyon has suggested may not be possible although now I know this I will ask the question if this can be checked because they do need to disturb a small section of existing floor.
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ALERT ...your builder is not a plumber, you are correct to be wary, No its NOT correct to do as this none qualified person suggests. He will know nothing about your system and most probably take your money and mess things up. Get advice from PF and find a totally independant inteligent heating engineer in..he will look after you and if your clever observe your 'builder' at the same time. PF is awash with got a builder in posts and my heating and plumbjng is messed up...heating systems are really quite
clever nowadays ...well beyond any brick monkeys. centralheatking
Understood - as well as double-checking with my builder/PM I might seek advice from a heating engineer by posting on here in the right section!
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Actually, there isn't much on the directory here. Can anyone recommend how I can go about finding a reliable heating engineer in my area?
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I've checked and the size of the existing pipes seems to be 15mm. The radiator in question is single panel 1.6m x 0.5m.
 
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