Insufficient power to heat room with UFH

[edb49]

I've got an underfloor heating installation in a room in my house. In the recent cold weather, it hasn't been able to raise the temperature more than 15c above outside.

The room is about 30m^2 in area, and about 7m^2 does not have underfloor due to built in cabinets. It is an extension built in 2004, so modern insulation standards. It is quite exposed though - no rooms above/below it, and North/South/East sides are exposed. Only the west wall connects to the rest of the house. Also has four sets of French doors, which add up to 17m^2.

I see my choices as:

1) Increase the output of the UFH
- Replace carpet with a more conductive material e.g. laminate. I don't fancy this because it will ruin the feel of the room.
- Rip out floor and relay UFH with pipe centres @ 100mm instead of 200mm. Expensive, messy, etc.

2) Decrease the heat loss of the room
- The room should be fairly well insulated as it is built in 2004, I think the biggest improvement I could make would be the French doors switching to triple glazing. Potentially cheaper than ripping up the floor?
- I can't insulate the floor without ripping up the UFH.
- The walls/roof could be improved a bit but going from a U factor of 0.3 average to 0.2 won't be enough to make a difference to the room.

3) Add a secondary heat source
- It is a pain to get a radiator in due to the pipework in our system going nowhere near the room.
- At the moment I have a cheap electric convector in, but not a very satisfactory solution, and over the long run it is expensive.


Have I covered all the bases? Any suggestions on what would be the right thing to do?

 

[sherbert]

Can you turn the temp of the Water going through the UFH .... look at the manifold ..

also did you have underlay fitted and if so was it suitable for UFH ... it could be acting like a coat and stopping the heat from coming out

 

[big-all]

plinth heaters

not cheap to run but will be minimum disruption or visual impact
http://www.diy.com/diy/jsp/bq/nav.j...mpid=4&tmad=c&ecamp=cse_go&CAWELAID=611365513

 

[Corgigrouch]

Plinth heaters cand tend to be noisy, especially budget ones

 

[JohnD]

has four sets of French doors, which add up to 17m^2.

this is likely to be a very big heat loss. Start with heavy lined curtains and keeping them closed. Experiment by taping clear plastic sheeting across the reveal. My BiL built two pairs of double french windows, one set opening out, one set opening in. Extremely good for cutting heat loss and also very soundproof. The inner set need not be double glazed, but you do neet to doughtproof the inner set well to prevent misting.

Otherwise think about a gas heater in the room, but please not a fluless one. Gas coals are also very uneconomical, though cheery.

 

[doitall]

How are you running it, and what was the total pipe length in the floor., what size pipe etc,etc. and what temperature are you it at, you should be able to ramp it up to 42c ish unless there's wood over it.

 

[Agile]

I hope that this thread will act as a warning to all those who imagine that UFH is the solution to all heating!

The reality is that it CAN give god results in a large area , say over 20 sq m as long as its properly designed and installed. That means taking very great care to calculate the heat losses and match that with heat output.

In this case we dont know all the facts and there is an implication that the floor insulation under the UHF may not be present or very good.

The pipe spacing is 200 mm which is rather wide but that all depends on the floor covering. A tiled surface probably is the easiest but in this case we have carpet which significantly reduces the heat output from the UFH.

There may be some minor improvements that can be made in this case but I expect the pipe spacing will be the limiting factor.

Remember when designing that a higher heat output will do no harm but an inadequate output can only be augmented with above floor heating.

Tony

 

[doitall]

200mm centers is ok Tony provided they've used 16-18mm pipe.

And yes if it's designed right you can heat any size room, the secret is keeping all the loops the same length, and preferably not longer than 120m, per loop.

 

[edb49]

Can you turn the temp of the Water going through the UFH .... look at the manifold ..

The water going through the UFH is already quite hot - 65c flow and 62c return at the manifold. I think if I put the overall temperature up it would effect the comfort of other areas by getting them too hot.

also did you have underlay fitted and if so was it suitable for UFH ... it could be acting like a coat and stopping the heat from coming out

Yes, there is underlay. I didn't fit any of this though, we bought the house in this state! The underflay is about 7mm thick, and has a rubber diaganol pattern on the screed side.

plinth heaters

not cheap to run but will be minimum disruption or visual impact

Prefer to avoid electric heaters, we plan on keeping the house for a long time so will be expensive in the long run.

How are you running it, and what was the total pipe length in the floor., what size pipe etc,etc. and what temperature are you it at, you should be able to ramp it up to 42c ish unless there's wood over it.

The pipe is grey, approx 20mm exterior diameter and is marked Hepworth Hep20. I don't know the total pipe length, the only other info I have on the system is that the flow rate is 4ltr/min for each loop.

 

[simond]

Pipe temperature is already too high.

UFH should be designed, and this one clearly hasn't. There appears to be some doubt about the presence of any insulation under the floor screed.

So we seem to have some fundamentals missing.

You could try improving the insulation of the room using some temporary secondary glazing.

But if you are already putting 62C through the screed without counteracting heat loss I don't give you much chance of making the system deliver. It is fundamentally wrong.

So add a rad!

 

[doitall]

Why do I have a bad feeling they have used Hep²0 water pipe, which has very good insulation properties. and not underfloor heating pipe.

The water going through the UFH is already quite hot - 65c flow and 62c return at the manifold.

If this is the loop temperature, there should be 20-30c difference between the flow and return, or the heat is just going round in a circle and not letting it into the floor, as above loks like the wrong pipe.

 

[muggles]

Agreed with the above, sounds like a poor install, probably with the incorrect pipe type used. Your only sensible solution here (IE without digging the floor up) may be to add a rad. Is it just the one room that has UFH or all the way through?

 

[edb49]

Why do I have a bad feeling they have used Hep²0 water pipe, which has very good insulation properties. and not underfloor heating pipe.

It is a grey pipe and about 20mm diameter; the UFH is 'working' in the other 3 rooms it is installed in though.

The water going through the UFH is already quite hot - 65c flow and 62c return at the manifold.

If this is the loop temperature, there should be 20-30c difference between the flow and return, or the heat is just going round in a circle and not letting it into the floor, as above loks like the wrong pipe.

This is the temperature on the flow and return on the manifold to the boiler. There isn't a 20c difference on the flow/return of the loops though, I can tell you this by touching them. (Don't have a temperature probe to give readings though.)

 

[edb49]

Pipe temperature is already too high.

UFH should be designed, and this one clearly hasn't. There appears to be some doubt about the presence of any insulation under the floor screed.

There is some insulation under the screed I believe. Had to dig up a bit of the kitchen floor (which also has UFH installed at the same time) and there was a small layer of celotex (20mm if I remember) underneath the screed.

 

[edb49]

Agreed with the above, sounds like a poor install, probably with the incorrect pipe type used. Your only sensible solution here (IE without digging the floor up) may be to add a rad. Is it just the one room that has UFH or all the way through?

It's four rooms downstairs that have the UFH. The existing rads therefore go nowhere near this room, adding to the pain of installing an auxiliary rad.