Would you REALLY always recommend running UFH constantly?

[Ric2013]

Been adding UnderFloor Heating to my own house and it's running provisionally. Controls yet to be wired. Can't think of ideal system but this is the best I can think of myself:

Since the UFH is auxiliary to a radiator (theoretically not enough output from UFH to hold its own in cold weather), I decided to try plumbing the manifold (with pump, mixing valve assembly etc) with flow and returns from the heating circuit and room temperature control using the same stat that runs the central heating. Timber floors and spreader plates, so response time isn't too bad.

Existing room stat is in the room heated by UFH - house is open plan and most of the heat goes upstairs anyway, but bedrooms do not overheat as they are controlled by TRVs and doors kept shut.

Basically, the UFH will come on when everything else is on. The radiator will provide the main heat, and then the UFH will help keep the room and floor warm. In warmer weather, the radiator can be shut off using the manual control valve.

I know it's usually advised to have the UFH on its own zone, but my thought is that all that will happen is that my old cast-iron-heat-exhanger-non-condensing boiler will cycle continually and reduce the system efficiency significantly (that would be an 8.5kW boiler running at 1.2kW demand... ) and heat losses from pipework would effectively heat the whole house to some degree anyway (centre terrace - so not a huge heat requirement) . The radiators in other rooms currently in use are just two - my bedroom (in practice, the TRV normally closes fully) and the bathroom (600Wish, but usually half-warm due to TRV).

Also, days like today the windows can be open most of the day and it seems wrong to have heating on with open windows. Last three days heating has been on for an hour or two each evening and then I switch it off and sit by the fire instead.

Does my reasoning about the UFH make sense to anyone else, given that I'll be the one using it? I know I'm weird, but I wanted a reality check when it came to system design.

 

[SimonG]

Just to confirm. Rads and floor come on together but you have thermostatic control on the floor water temperature?

 

[Chalked]

Will sort of work but your floor will slowly reach 60-70 degrees.!

 

[Ric2013]

Some confusion. To clarify:

Simon G: Correct - there is a thermostatic mixing valve on the UFH manifold and a floor sensor that will shut down the UFH if floor gets too hot.

Chalked: There will be a thermostat set on the floor to limit the maximum floor temperature by closing the zone valve to the UFH manifold and shutting down the UFH pump. This will not switch off the rest of the heating system.

 

[Ric2013]

Okay. I was searching for a relevant thread, but have decided to hijack my own post instead.

Update: the system works well for my requirements, except that the bathroom is often cold. The auxiliary radiator gets used in very cold weather, but usually the UFH is enough on its own. Bedroom radiators are normally turned off at TRVs (as bedrooms used purely as bedrooms don't really need heating IMO).

I was reluctant to add a second zone for reasons as in previous posts and because the part timber-frame and North-South orientation of the house means that the heat requirements vary dramatically and I couldn't decide which bedroom to put the 2nd thermostat in.

Since I now know that the bathroom is the one upstairs room that always need heat, and the last to be satisfied, would it make sense to have it as the thermostat room for heating zone two (bathroom and two bedrooms), leaving open-plan ground floor (UFH) as zone one?

This could be my heating system version 3 when I get around to it (sometime never probably).

I think that you can put a room stat in a bathroom so long as you're 60cm from the bath and on an RCD? Could go for wireless, would prefer 240V wired - I should be asking an electrician these questions, but the one I know usually asks me the questions when it comes to heating systems lol.

Am I vaguely making sense in my thinking or has anyone got any better ideas?

 

[Ric2013]

Just looked at John Whitfield "The Electrician's Guide [....]" and discovered that, at the time of his writing (early 17th edn), you could have a switch in a bathroom outside the zones, but it should be fed from a SELV supply outside the zones. Logically, then, it would make sense to see if there is a product that could be hardwired to the outside of the bathroom wall.
Something similar to this seems to be the ticket. I know it says for 'underfloor heating', but probably there's no real difference, or a non-underfloor version is also available.

Underfloor Heating Thermostat with Bathroom Remote Air Sensor

Anyone fitted one, and any experiences or recommendations?