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I calculate I require a heat output of 8000 BTU,s for my living room.
I can only fix the radiator under the window against one wall. Will it work if I connect two double radiators, in series with a single thermostatic valve??
regards W :?

Many thanks :)
Will it work ok connecting in parrallel with my existing 15mm pipe drops??
and would both the thermostatic valves both need to be placed on the flow side or could i have one on the flow in 1st rad and one in the return on the 2nd rad?
Best regards W

If the radiators are connected in series you will find the second rad will heat up a lot slower and may not produce the same heat. Ideally the two rads should be connected in parallel and fitted with individual valves

Many thanks :)
Will it work ok connecting in parrallel with my existing 15mm pipe drops??
and would both the thermostatic valves both need to be placed on the flow side or could i have one on the flow in 1st rad and one in the return on the 2nd rad?
Best regards W

Yes 15mm pipe should provide enough flow for both rads if the rest of the system is piped correctly. You can place TRVs on flow or return legs if you fit bi-directional valves e.g. danfoss ras-d valves

You are on the edge of 15mm copper pipe work for 8000 btu's (2.3kW), so it depends how hard your pump is already working, as to if you will get sufficent heat through from your 15mm drops. (If it's plastic pipework then you have no chance). To assist your pump have the TRV's on the flow side of each radiator as that is the way they will give least resistance.

Thanks for all the help.
The 15mm copper down pipes are supplied off a 22mm copper circuit. There are only 3 other rads on the pumped heating circuit (one rad on gravity hot water 15mm off 28mm circuit.). The pump is on the boiler return right underneath the boiler.
Will the thermostatic valve on rad 29Living room) work oK on the flow pipe when it is effectively in between the two radiators which are only about 150mm apart??
Currently I have no room thermostat and am thinking is it best to contol the pump using a room thermostat in the living room (without any thermostatic valves on the living room rads) but keeping the thermostatic valves on kitchen and bedroom Rads??
Possibly not best practice but trying to improve system as effectively as poss.
Cheers W :?

The 15mm pipes will be more than adequate to run both radiators.
The regulations require timed and thermostatic control for heating and hot water on a standard system so your idea of installing a room stat is good one.
I presume you have a floor standing cast iron boiler when you mention a gravity circuit which probably means you have no temp control over your hot water. Ideally the system should be fully pumped with a zone valve on the hot water circuit controlled by a cylinder stat and a zone valve on the heating circuit controlled by a room stat and both through the time clock. The system could be altered to achieve this type of control but careful consideration must be taken with regards to the safety relief pipe on the system which probably comes from the flow pipe at the hot water cylinder, this type of work is best carried out by a qualifed heating engineer.

Will the thermostatic valve on rad 29Living room) work oK on the flow pipe when it is effectively in between the two radiators which are only about 150mm apart??

Not quite understanding the above could you please clarify.

As to TRV's on radiators current building regulations part L (J in Scotland) State that all radiators including add on's to existing systems must be fitted with TRV's and if moding a existing system with out a room stat then one must be fitted. Hope this helps.

Thanks for the posts :)
Certainly would like to add complete control of the system,was considering this when I take the inevitable step of having the boiler replaced.
Current boiler wall hung cast iron Ideal concord model.
In the meantime would it be Ok to add a 28mm motorised valve to the hot water cylinder flow pipe controlled by a cylinder stat but indepedent of the timer control?? (Potterton Mini Minder) I understand the motorised valve must not interupt the path to the expansion tank in the loft.
I'm working on the assumption that the bathroom radiator which is a permanently connected loop around the boilerflow/return will continue to prevent boiler overheating. As you suggest with no controls the hot water gets very very hot in the winter season when the rads are running. It also seems very inefficient that when the radiator thermostatic valves kick in the pump continues to run.

Regarding sitting room rad I was planning to replace the existing rad (a huge double rad about 8 foot long) with more modern
finned rads. For aesthetic reason I am considering using two rads(400mm height) but beacuse the distance (left to right) would be quite small I was wondering if the thermostatic valve on the flow to Rad 2 would be affected by the proximity of the rads themselves therefore closing it too quickly???
My intension was to run the pipes behind the radiators (rather than underneath) and drop down onto horizontally mounted themo valves.
Hope this makes more sense!!
I have been unable to find reasonably compact radiators with 8000 BTU rating.(hence the idea to use two in parallel)

If I fit wall mounted thermostat to control the pump, I assume I should set the thermostatic valves on the living room rads to a higher temperature than the wall stat to ensure the pump is switched when a comfortable room temp is achieved??

Thanks for all the help.
regards
W