UFH - first time startup

$lim$hady

Hi All,

I have a question i'm hoping you can help with.
Contractor just finished installing a wet UFH system at my home, its on the ground floor and the coverage is 100SqM

We turned the system ON yesterday for the first time and has been running for 24 hours now. I set it to 30degres (low setting according to the manifold). I wasn't expecting the home to be hot in 24 hours but the question is: Should the flow and return pipe feel the same temperature by now?
All flow are warm and all returns are not warm although not cold either...

This was all installed by our plumber who is due back in 3 days but in the mean time i was curious about what i should expect to be happening by now.

Thanks.
Slim

DOBLY

Depending on the ambient temperature of your floor slab, it will take a number of days to warm the house up, likewise the return side of the pipes won't get to 30 degrees, because the loop will be transferring heat into the floor, for it to be radiated out into the rooms (as is the purpose of underfloor hydronic heating).
The rate to which the floor slab warms the rooms depends on a few factors - the heat input, the insulation levels (both under the slab and of the building as a whole), outside temperatures and system efficiency.
I would guess that in an adequately insulated house, in 3 days time you will be very comfortable, barring anything going drastically wrong.  From then on in will be a question of maintaining a balance that suits your personal preferences - whatever, it should be kind to your wallet, as heating water to 30 degrees is cheaper than heating it to the 60  that radiators require.

$lim$hady

Thank you Dolby, that is very helpful. I knew not to expect warm house in 24 hours but i was expecting return pipes to be just as hot as the flow but your reply explains why that would not be the case..
The house is well insulated (the whole place was gutted) so once the slab heats up, i'm sure i will reap the benefits. i'll come back to you in 3 or 4 days with an update.

dannnielll

There should be a temperature difference between the flow and return of 7 to 10 degrees. So you could expect a flow temperature of  35 Celsius and a return of 27 , giving a room temperature of  22.  If you are happier at lower then fine, just dial it back a little. The cooler you make the room, the closer the return and flow temperatures become, because the heat flow  to the slab is less
Actual figures from my system taken minutes ago.. the system would have been running for a number of weeks
House temperature 21.1
Target temperature 21
Exterior air temp 2
Supply line 34
Supply return 30.

And a half hour later supply 40
Return 33.
Air source heat pump...

Alps

Guys, just came across this thread whilst searching for something else.

I have a few questions please which I've been wanting to ask for ages.

I've had wet UFH for about 4 years. It has a screed depth of approximately 6 inches and on top of the screed is engineered wood. How long should it take for the UFH to heat up a 19x16ft room from 18oc to 22oc in winter?  In winter mine takes about 4-5 hours. Is this normal?

Also, if it takes this long, would it not use a lot more energy than a standard radiator, which took less than an hour to heat up my room?

Finally, does under floor heating use a lot more water than standard radiators?

DOBLY

There are many factors.
Radiators will act quicker than UFH, especially as the water temperature in a typical radiator system is much hotter than UFH.  But if the radiator is undersized, it will take an age to heat a large room.
UFH is designed to maintain temperatures, rather than provide an instant blast of heat.
With UFH, you are heating water to a lower temperature (range 30-50, typically 40 degrees), rather than the (range 60-80, typically 70 degrees) with radiators.
Providing the insulation is good, maintaining a room at 22 degrees using underfloor water at the UFH range will be more efficient & cheaper over the long run.

A six inch screed does sound a lot, but provided in is thermally broken from the ground under the house with a decent insulation layer (typically polystyrene), this will act as an efficient thermal store will will slowly radiate heat into the room, requiring less inputs from the heating system - that's the theory.

Water usage shouldn't be an issue - both should be closed systems.  The amount of water in a UFH loop may well be more than a radiator system - just depends how it has been specified, designed & implemented.

Alps

Hi Dolby, thanks for such a top reply.

I do indeed have insulation. It’s not polystyrene but the padded silver stuff  (forgot what you call it). It’s slightly under what depth I’d have wanted but have been told it’s ok.

I need to call out a plumber to check it over as the guy who fitted it turned out to be a bit of a cowboy! How do we check if the system is on closed loops? Also how to check what the UFH water heats up to? I have a feeling the plumber may have increased the temperature by a fair bit.

neilball

What kind of odded silver stuff did you use? Normally it would need to be solid insulation, either polystyrene or solid foam (Kingspan or Celotex) capable of bearing  the weight of the screed. This would normally be several inches thick in most cases.

If you’ve used the thin silvered bubble wrap style insulation then this will be having very little insulative effect I’m afraid. This is meant to be used in applications with clear air gaps on both sides of the membrane, so often gets used in roofing applications etc. Even then it’s hotly debated on the insulative benefits - it does act as an air barrier (preventing draughts), and as a radiant barrier (due to the silvered foil covering) but in scientific testing it generally performs poorly as a pure insulator (as it only has minimal air pockets).

Your screed depth is also a major factor in your room response times. 75mm of “regular” concrete screed is usually considered to be more common, and 55mm would be appropriate with anhydrite (flowing) screeds.

If you want to check temperatures then for a low cost you can get an infra red thermometer which looks a bit like a gun and reads surface temperature from what you point it at. If you want something more sophisticated that also allows you to take photos or videos for record keeping then look at the Flir One thermal imaging camera add i. for mobile phones - this give a clear visual indication of heat output and also allows you to add spot temperature readings overlaid onto the pictures.

neilball

I forgot to mention that I have 55mm anhydrite screed over my UFH, laid on 100mm of Floormate polystyrene insulation board. Floor coverings are a mixture of tile & stone with some 12mm engineered oak and laminate in some rooms. With a flow temperature from my heat pump of 38 degrees it generally takes 2 hours or less to warm up my rooms to their target comfort temperatures when the heating comes on (set for 3-4 hours, twice a day in most rooms). If the weather gets very cold (below -10 overnight) then I leave running 24/7 (and the rooms still cycle on and off as they reach setpoint) but still do not need to increase my heat pump flow temps.

This will be my 12th winter with the system, so it’s performance is proven over many years now.

Alps

Right, this post is going to bring back some bad memories.

I have 35mm of kingspan - far below the desired insulation. I also have 75mm of screed. Maybe a little too Much! Maybe not! Longer to heat up. But longer to cool down.

The guys doing the plumbing and screeding were different and in the end comms between them broke down. I too should have done more research myself before getting it all done. I know I shouldn't have to, but with hindsight it's better to play it safe!