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Condensing Boilers & UFH
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Condensing Boilers & UFH

Jon Rposted on 05-07-06

I am trying to sort out the best boiler for an under floor heating system but I am having problems sorting out which to use. I would like a condensing boiler because fo their efficiency but the condensing mode 'return' temperature (from ufh) seems to be higher than what it will actually be. I have been told that the 'return' temperature needs to be 57C but the UFH 'return' temperature will be about 37C to 50C. am I missing something because the boiler manufacturers seem to think that this is ideal for under floor heating systems.

thanks for any help you can give
Nigelposted on 05-07-06
The return temp to the boiler needs to be below 57C so that it can be used to condense the flue gases. A return temp above 57C means the boiler will not be working in condensing mode and will be less efficient.

UFH is ideal for a condensing boiler. When using radiators you need to oversize them so that you can run a lower supply temp so that the return temp is below 57c. Many retrofit condensing boilers will rarely condense as the boilers will be sized for higher flow temps. Reducing the flow temp will prevent them from heating the room adequately. To get round this the flow temp is raised above the optimum and hence return temps are too high.

Liz Mposted on 05-07-06

As this sounds like a new installation, you have to install a boiler that is at least 86% efficient. That essentially means a condensing boiler. Why not talk to boiler manufacturers to find out how they would propose turning down the temperatures. My new boiler at home has a dial where you can reduce the temperature of the heating water. It doesn't have temperatures on it though. So the simplest way would be to install a standard boiler and just turn the heating flow temperatures to minimum.
Liz Mposted on 05-07-06
Oh yes. Underfloor heating systems usually have a manifold which mixes the heating water to the correct temperature for underfloor heating i.e. changes it from 80/60 to 45/35(say).
Tonyposted on 05-07-06
Choose any condensing boiler you wish some have additional electronics to help with ufh systems. Please use a thermal mixing arrangement to manage the ufh probably with a manifold and several loops of ufh pipes.
mickposted on 14-08-06
I have just laid 15mm underfloor heating pipes in the screed on the ground floor and under the floor boards on the upper floors. As I have not used spreader plates, to increse the heating output on all floors I plan to first supply a small radiator (with TRV) on each U/H heating loop, and use the radiator return valve regulate supply to each of the u/heating loops. I am planning to make my own manifold distribution system from 22mm copper pipe and tee pieces, with a pressure guage and a temperature guage on supply and return to monitor the arrangement.

This seems to me to be a simple and very cheap way to do things. What can go wrong? I do not plan to use any other circulating pump than the one fitted in combi condensing boiler. I do not see the need for a room thermostat either, as the TRV will regulate each room and the boiler temperature dial will control the C/H water temperature supply

I haven't bought a boiler yet or made the manifold

Am I mad or is this a possible working arrangement? Any comments will be appreciated.

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