What do you mean by most efficient? least energy use? then switched off overnight has to be that.

I don't see how it can. I've been a bit confused about this too, but so far as I can see the 'overnight set back' idea is merely so that the system can react a bit faster. I don't see how it can possibly save energy over turning it off.

I guess if the criterion is that it must be at 20C at 8am for getting up, and it takes 2 hrs from cold (10C?) to get there then the system has to run at full blast for 2hrs to achieve that (assuming that the floor fully cooled overnight). If you set-back instead then it stays at 14C all night so only takes half as long at full blast in the morning to achieve 20 (1hr). So I guess the theory is that if the extra hours of full uses more fuel than than the 7 hours of 'low' (from midnight to 7am, in this example) then the set-back scheme will save fuel. Maybe this can happen, but normally gas boilers maximise efficiency near max output. Don't know about heat-pumps.

Somone here must know...

If the room is warmer overnight then more heat will be lost.

The only way it could possibly be more efficient to keep unused space warm would be if the heating system was dramatically more efficient at low power than at high power. This seems unlikely and is probably the reverse of the truth in almost all cases.

cWatters,

that is what i am hoping, and will be programming it to be 'OFF' when it is not on, if that makes sense.

I am hoping the freestanding masonry chimney central to the living area will be radiating a good chunk of heat through the night, keeping the place warm, and preventing too steep a fall in temp.

No, the house is not passiv haus insulated, but it is well insulated, and the living area at least is fairly well draft proofed.

We'll see!

My question was based on the literature that comes with all of these systems, but it seems their 'lower temp, so cheaper' tag line is a non-sequiter with their operating advice

it is not freezing yet, by any means, and the plan is not to use the heating on a daily basis just yet, but we did play with it from Friday am to Sunday pm, by way of a test, before it is required in earnest.

SO, the literature said it should be "on' from 7.30 am to 11.00 pm, and then in 'setback' mode of 17 degrees through the night.

SO, we threw out the literature!

I programmed the thermostats to 17.5 degrees from 8.30 to 10.30, and 16.00 to 20.00, with the remaining periods at 10 degrees.

morning one was a little chilly. The system had to work to get the slab up to temp from a standing start.
However, once it warmed up, it got ahead of itself, and the rooms got to just under 20 degrees, even though the thermostat tripped the system off at 17.5. A bit of thermal inertia there.

The system only engaged for about 30 minutes in the evening, as the house held the heat.

Since Friday pm, the boiler has only been on for about an hour and a half in total, to retain the 17.5 degrees.

Generally ,it seems that cooking heat and people are really helping, and the temperature was not below 18.5 degrees all weekend (which is plenty warm enough for me) It would take very little to nudge it to 20 degrees if required.

The system comes on at 8.30am (if required) but this weekend there was enough latent heat to make the place comfortable - no chilly kitchen requiring heating from early on.

With the stove going, the floor should really be a stand-by item (and a bl**dy expensive one at that!)

My wife works from home, and the kitchen, living room and dining room (office) are all essentially one big space.

I am really pleased that the system is not on mega-drive all the time, and hope the same can be said in January.

The dog and kittens love the warm floors, and it is a very different feeling to radiator driven heat.


To put it into perspective, the old part of the house - bedrooms and bathroom - have not had any heating at all since early April. It is a poorly insulated and drafty stone building.
It is currently sitting at a steady 12 degrees. I love a cold bedroom (but i am generally on my own on this point!)

lots of work to do at that end of the house....!

Were there any hot spots? (I know the system design is supposed to avoid these but all the same?).

Do you have towel radiators?

I think I'd be inclined to keep my UFH on all the time, to take the chill off the stone floors, at (say) 15C and stick a log on the fire in the evening. The problem would be the morning shower.

I can't remember if you have the thermal store set up. A towel radiator circuit would be useful just to boost (and encourage) that getting out of bed bit in the morning or am I just complicating things too much?

Good to hear about the hotspots. I thought it would be hotter where the manifolds were situated, so 3 of them I've located in what I would like to be warm cupboards and the 4th is where I'm planning to put the cat's bed.

I've been warned that UFH isn't the most controllable - so I'll just have to work out what constant back ground temperature is good for us.

Can't bear cold bathrooms ...

we have 600x600 porcelain tiles that have a leather texture and look to them. Now that they are warm, they feel like leather too! Nice!

exactly!

we had visitors at the weekend who actually had to get on their hands and knees to prove to themselves it was porcelain!

It is not really as bizarre as it sounds - they look great

thanks for that, Dave

I think i will set the temp lower to resolve any overshoot.

It didnt come on at all yesterday. the whole area dropped a total of 1 degree in 24 hours. Of course, winter isnt here yet, but that is encouraging

mrswhirecat,

Have a read through this thread:

http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=189

weather compensation is an external thermometer which controls boiler power -- the idea is that the colder it is outside the more power is needed from the boiler.

These are very common on commercial buildings and almost non existant domestically.