Underfloor heating - need help with timings!

[AryaUnderfoot]

We have just had wet u/f heating installed in our new extension (6m x 4m rectangular room). We have had a 3 circuit manifold fitted and a screed floor poured over the pipes and trays. We will have an engineered wood floor.

The rest of the house has radiator c/h via a 24kW condensing boiler.

At the moment the c/h comes on 5:30am and goes off at 7:45am (we get up at 6 and leave the house by 9). The heating comes on again at 5:00pm and goes off at 9:30pm. I normally get home about 4:30 and advance the heating and it doesn't take long to warm up. The hot water is on a different timer programme.

The u/f heating is on a different circuit and will have it's own thermostat and 7-day timer. The problem is that I have no idea how to start coming up with timings that will work. I know it will take longer to warm up. Ideally, I'd like the room to be at a habitable temperature by 7:00 am, and then be at least starting to get warm when I get home from work.

Any advice will be greatly appreciated!

If the extension is well insulated and not somewhere you sleep, it may be best to leave it on all the time at a slightly lower setting.

This is my problem with underfloor heating, if you have it on a timer it always seems to be too hot or too cold, and never quite right when you need it.

But if you have good insulation it may not work out to use too much more fuel than you would with radiators.

wet UFH in a concrete floor, start with an hour or two before you want it, and turn off an hour before you go out. For the first week or so, it will get warmer quicker every day as the mass of concrete warms up, after that, you can tinker with the timings a bit. It will tend to give out heat, slowly, for hours after you turn it off, even if you don't keep the heating on.

Depending on how thick the concrete is, and if it has a slab of insulation under it, it will have a greater or shorter lag, and hold more or less heat.

Thanks for that. The concrete is between 3 and 4 inches thick above the pipes, and the trays are on top of big slabs of foam insulation, so hopefully we won't lose too much heat to the earth!

Sounds mad, but you may end up leaving it on from before you get back from work, overnight and using the set back thermostat to keep the temp a degree or two lower overnight. That way, the slab will not have to keep heating back up again. This may be more effecient that having it on for two short bursts. Our whole house is u/f heated and once the downstairs is warm the boiler barely clicks on.

For the first few days, I would leave it on all the time till the slab warms up fully and then tinker with it till you find the right balance, but don't keep switching it on and off as you would radiators.As Piglet says, you need it to come on further ahead than you would a radiator, but you can switch it off earlier as the floor will give out heat for ages. Once you get it right you should have a beautifully, evenly heated room.

Marking place.

I was always told to just leave underfloor heating on all the time, it is more cost and energy effecient than adjusting the temperatures.