UFH

[Huge]

One of the things I've always wondered about Under Floor Heating is ... Doesn't it behave like a huge storage radiator? Takes days to warm up and stays warm for days after it's switched off?

[Nightjar]

That certainly was the intention behind the electric element embedded in concrete type that was widely installed in the 1960s. I don't know about more modern systems.

Colin Bignell

[Toby]

It all depend on the thermal mass - if you have UFH pipes embedded in insulation, with a floor laid on top of that, then no, it would heat up and cool off relatively quickly.

[TheOldFellow]

Mine starts to warm up in the morning at 6:30 when my thermostat goes from 14 to 19. Sometime mid morning the thermostat is mostly off, and the slab is warm. The thermostat switches to 21 at about 4pm, and by the time I want to sit down in the evening the room is at 21. At 10:30 the thermostat switches to 14, and slowly the slab then cools keeping the house warm all night. I do have some auxiliary radiators for instant-ish heat in the bathrooms and bedrooms.

So hours, not days. The thermal mass is about 1.75 cubic metres of concrete screed over 100mm thick insulation (5m x 5m x 70mm) with buried 15mm pipe on 100mm spacing.

R. North Cumbria.

[The Natural Philosopher]

Broadly yes, it does. If its in a screed.

Under a wood floor its a lot faster responding.

The plusses and minuses of a long thermal time constant heating system have been endlessly discussed here before.

What you lose is the ability to rapidly change temperature, and the hidden costs associated with that in terms of boiler inefficiencies

What you gain is huge thermal stability and warm feet, which lessens the need for such high room temperatures and summer aircon. But means its expensive in largely unoccupied areas subject only to occasional use.

[Dave Liquorice]

Ah but you're not letting it get cold, so you only have to replace the heat it has lost. How long does it take for the house to get comfortable again if you let it get cold?

Not under floor heating and a bigger lump in this place, solid stone wall approx 8m x 6m x 0.5m right through the middle. If we let that get cold (by turning the heating down/off) it takes 3 or 4 days for the house to become comfortable again(*). But it don't half keep the place cool in summer and warm in winter.

(*) We only made that mistake once! The heating stays on 365 days a year.

[John MacLeod]

Which just about sums it up. If you use the premises 24/365 UFH in a solid slab is just about the ideal heat -- exceedingly comfortable and largely draught-free. But if your floor slab is thick and if you've carpets, the response time is going to be very slow.

I have it in half the downstairs of this house. My only regret is that it's not in all the downstairs. The rooms with the UFH are by far the most comfortable.

[The Natural Philosopher]

6-8 hours, maybe 12.

exactly. I calcualatd the time constant of this house is about 6 days.