Underfloor heating off a combi boiler Help and information on all topics relating to your central heating, air conditioning and ventilation issues.

[phughes1979]

We've just moved into a new house (well, really old house actually) and we're renevating our living room. We've discovered it still has the original stone flag floor so we're taking this up, digging the floor out to lay a damp proof course and then laying the floor back down. Whilst doing this we're considering installing a underfloor heating system. We would require a single room system, the room itself is roughly 12 ft by 14 ft. Our hot water and central heating system runs off a combi boiler and I have a few questions related to this fact.

I've read somewhere that you should not turn the underfloor heating system off totally like with a conventional radiator system, but rather have it so it drops to a lower temperature. How does this work from a combi boiler? I've been told the water for the UFH will come from the same system as the radiators - does this mean that I will also have to have the radiators on permantly albeit on a low temperature? Could somebody explain to me how the set up works and is a combi boiler suitable to support a UFH system? (This will have to be fairly simplistic explaination - I'm definately not a plumber!)

[The Heating Doctor]

You can not have the underfloor coming from the radiator circuit, it must be a completely seperate circuit. You do not switch off underfloor heating, it has a manifold & circuit pump, blending valve and independent controls. From the boiler to the manifold, water gets there by the built in boiler pump and this circuit must have a two port motorised zone valve fitted. You must check with the combi manufacturer that they are happy for the boiler to supply a underfloor system, not all are and not all underfloor manufacturers say this is ok, but they do say it's up to the boiler manufacturer. The radiator circuit should also have a two port motorised valve fitted and timed through a programable room stat. This way the radiators can be timed to switch on and off regardless of what the underfloor circuit is doing. Both can be turned off in the summer. A competant electrician can work out the wiring which is not complex.