*HELP* UFH overlay system with Insulation or Screed or (Insert answer)???

[Da-Dad]

Hi folks

 

Just your friendly neighbourhood UFH newbie here - I'm hoping you can help me out with some advice...I've spent HOURS researching and still cant come to a decision *my mind is gonna blow!!!*

 

We really would like Wet UFH in our Bungalow that is undergoing renovation (has a combi boiler radiator system), the key concern is keeping the profile as low as possible (only 78 inch height on the doors openings) and ensuring the system is still efficient and affordable.

 

The floor of the house is concrete, think there is no insulation in there since it was built like 50+ years ago.

 

The other insulation is average (double glazed, cladded roof with some ceiling insulation 20mm) and there is only the one floor with ceiling + roof. But the main living room and dining room area will have a row of bi-folding doors.

 

We would be finishing half the house in carpet and the rest in tiles/laminate.

 

To try and keep the profile low (max 65mm profile), an overlay system seems much better at only 15-22mm depending on the supplier.

 

1) Is an overlay system going to do the job heating up the house?
My research and the suppliers says the heating will be ok, but surely the heat-loss due to no insulation in the concrete below will be substantial and kill my energy budget *scary*.

 

2) Will adding in some insulation help with this?

E.g. layering upwards:

30mm Celotex
18mm Overlay UFH system
20mm floor finish carpet/laminate/tile

 

Will adding a 7mm superfoil (space age looking stuff) high thermal resistance layering be a worthy investment over Celotex?

 

3) Would side insulation, like a foam or celotex like material make a big difference? I've read some comments that this makes a nice difference?

 

4) Are there any good quality for the price suppliers anyone can vouch for? I have looked at like 7-8 and really can't tell which once offers the best advice + product (Wunda, NuHeat, Continental, theunderfloorheatingstore, Warmup etc)

 

5) Maybe going with some kind of 40mm screed + 20mm floor finish is best (no insulation underneath?)

 

 

Thank you so much!
 

[Jeremy Harris]

Bear in mind that to work with any reasonable degree of efficiency an underfloor heating system needs at least 100mm of decent insulation under the pipes, ideally more (we have 300mm of EPS and we still lose about 10% of the heat into the underlying ground).

 

UFH is always less efficient, and so more costly to run, than radiators, especially as a retrofit to a building that may not be very well insulated, and so needs the floor to run at a higher surface temperature (the higher the UFH temperature the greater the heat losses down into the underlying ground).

[Temp]

Think I would stick with rads. We have 80mm of celotex under our UFH and wish we had more.

[ProDave]

Another vote for stick with radiators.  I suspect with the insulation levels of the house, the UFH would have to run at a high temperature and that really would want a lot of insulation underneath it.  Forget the multifoil stuff that won't add much. If it was as wonderful as claimed then insulating houses would be easy.

[Da-Dad]

Thanks-you for the kind replies folks, its not looking good for the ol UFH........big but - I had a chat to my builder, we could raise the height of the door frames to help accommodate.

 

So maybe something like max 90mm profile (all included):

1. 50mm celotex insulation
2. 7mm superfoil insulation
3. Some type of side insulation on edges of all rooms
4. 15mm overlay UFH system
5. 16mm floor finish 

I would go for using more tile floors in the heavily used rooms as they are better conductors and hold more heat -  would the above be do-able in the context of I still expect 20%+ heat loss downards.

 

Is there a supplier whose overlay solution is better at insulating or raw efficiency than others? Most of them claim their solution has "insulation already provided" in the overlay boards!

 

 

 

[PeterW]

Bin the super foil. It will do nothing under a floor as it works by reduction of radiated heat, of which there is none in that build up. 

[Nickfromwales]

+1.

Radiators will be the only way to get a decent amount of heat into the house in the arse-end of winter, when your retro-fit UFH would seriously struggle. 

Infiltration will be your biggest killer with every draught removing your hard earned heat and wastefully dumping it to atmosphere, so invest all of your budget into insulation, and draught-proofing, and enjoy a reasonably toasty home.

2 hours ago, Da-Dad said:

 

1) Is an overlay system going to do the job heating up the house?

Not unless you dig out the floors and start over again, go draught proofed, and insulate well.

 

A simple home-exercise for you would be to go to the local plumbers merchant with your rooms sizes, ask them to get your BTU/kW per-room requirement, and then cross-reference those numbers with the equivalent W/m2 output of the chosen overly system and see if you think it will cope. Remember that you need to factor in any fabric upgrades, and arrive at a realistic heat loss figure, before moving towards a decision.

Measure twice, cut once

 

[Cpd]

2 hours ago, Temp said:

Think I would stick with rads. We have 80mm of celotex under our UFH and wish we had more.

Always trying to get to grips with what’s a minimal build up for UFH ..... my cottage refurbishment has been on hold due to ill health and family priority’s but I want to get it going again next year, I am taking the time to review some of my original designs and this thread has prompted me to look at my hopes to retrofit UFH. In short it’s a very small footprint house approx 10x5 meter internal floor area with 2.2 m ceiling. I can get a max of 90mm calotex into the floor and had intended to use UFH run of the ASHP with it also running radiators in the two bedrooms upstairs and the bathroom. I hear people say 100mm is a realistic minimum, @Temp says 80mm not enough and I am smack in the middle with a possible 90mm ! The downstairs room would be very well sealed  with 100mm calotex in the walls and the ceiling is well insulated between floors, upstairs is even better insulated with 200+ in the vaulted ceilings and 100mm in the walls.  Is UFH still an option in a small build like this where there is only 90mm of possible floor insulation ? 

[Conor]

11 hours ago, Da-Dad said:

Thanks-you for the kind replies folks, its not looking good for the ol UFH........big but - I had a chat to my builder, we could raise the height of the door frames to help accommodate.

 

So maybe something like max 90mm profile (all included):

1. 50mm celotex insulation
2. 7mm superfoil insulation
3. Some type of side insulation on edges of all rooms
4. 15mm overlay UFH system
5. 16mm floor finish 

I would go for using more tile floors in the heavily used rooms as they are better conductors and hold more heat -  would the above be do-able in the context of I still expect 20%+ heat loss downards.

 

Is there a supplier whose overlay solution is better at insulating or raw efficiency than others? Most of them claim their solution has "insulation already provided" in the overlay boards!

 

 

 

 

Raising the floor will make your rooms feel smaller.  Even 90mm is noticeable. 

[Jeremy Harris]

11 hours ago, Da-Dad said:

Thanks-you for the kind replies folks, its not looking good for the ol UFH........big but - I had a chat to my builder, we could raise the height of the door frames to help accommodate.

 

So maybe something like max 90mm profile (all included):

1. 50mm celotex insulation
2. 7mm superfoil insulation
3. Some type of side insulation on edges of all rooms
4. 15mm overlay UFH system
5. 16mm floor finish 

I would go for using more tile floors in the heavily used rooms as they are better conductors and hold more heat -  would the above be do-able in the context of I still expect 20%+ heat loss downards.

 

Is there a supplier whose overlay solution is better at insulating or raw efficiency than others? Most of them claim their solution has "insulation already provided" in the overlay boards!

 

 

 

 

 

As mentioned, multifoil type "insulation" just doesn't do anything at all in a location where there is no radiant heat to reflect back, so would be wasted space and money.  The very best insulation is either vacuum insulated panels or aerogel, but both are eye-wateringly expensive.  The next best is PIR foam (Celotex etc), then EPS/XPS.

 

This spreadsheet will allow you to calculate the floor temperature needed for your house heating requirement, and also give the heat loss from UFH to the ground for any insulation used: Floor heat loss and UFH calculator.xls

 

As above, UFH will always be less efficient than radiators, as there will always be a greater heat loss down to the underlying ground, or cold undercroft space for a suspended floor. UFH may also struggle to heat a house that has a high heating requirement.  As a reasonable rule of thumb, UFH can provide around 50 to 60 W/m² of floor area at the most, and works best if delivering a lot less than this.  30 to 40 W/m² is a fairly good target.  You can determine the heat output per m² of floor area needed by just dividing the total house heating requirement (in W) by the UFH area (in m²).  For example, for our house the UFH area is about 70m² and the heating requirement in extremely cold weather is about 1,600 W, so the worst case for the UFH is about 23 W/m², well within the range where UFH will work reasonably well.

[scottishjohn]

well as usual I look at it another way 

yes keeping rads looks right one way ,but that still does not stop the heat going down through the concrete floor ,maybe you use rads and still lift floor by adding insulation layer under it next to concrete?

all you can say is by its nature rads will throw heat up wards away from floor 

I retro fitted UFh in a suspended wooden floor  with very little under insulation and the result was a 20% drop in heating costs --all i changed was rads to UFH--same lpg boiler -feeding a thermal store which the ufh coil ran through .

 I routed out the chipboard flooring and lined the slots with foil tape --fitted pipes then screwed down 6mm ply all over floor ,then ceramic tiles -- not a job i would do again -

If doing it again-I would lift the floor level or drop the joist height and double them up to put strength back ,but it meant i could do it without destroying the house 

.

everything that has been said about drafts+air leaks is correct -- that was the first thing i noticed after UFH --you could feel a cold from windows as you walked past them --so curtains were essential on these older double glazed units-- curtains seems something which is not done with a lot of new builds--must be all  exhibitionists!!.

thr other main thing was that the floor heated up all the furniture and anything close to floor --heat rises then before it gets to ceiling it drops again --radiators send heat straight to ceiling FIRST.-try standing on a chair and feel how hot it is at ceiling level in house with rads

I would agree that rip out start again would be good ,but I also think the 50mm of phonelic foam as underlay with pipes inserted init ,then  ply+ceramic tiles or some sort of hard floor   will work just fine 

that will keep height down --if you can stand more height --all the better --but you gotta kill the drafts as  they will be low level taking your heat away from the floor before it gets to you .

phonelic foam   =0.020

pir foam =  0.023

Edited July 3, 2019 by scottishjohn

[Jeremy Harris]

1 minute ago, scottishjohn said:

well as usual I look at it another way 

yes keeping rads looks right one way ,but that still does not stop the heat going down through the concrete floor ,all you can say is by its nature rads will throw heat up wards away from floor

 

 

There's a big difference in heat loss between UFH and radiators though.  Radiators don't change the heat loss through the floor at all, whereas UFH does, by a great deal.  This is simple physics, in that the rate of heat loss is directly proportional to the temperature differential. 

 

For a room at 21°C with radiators, then the floor will be a little cooler than this (because of surface resistance), say 20°C.  The differential temperature from the floor to the underlying ground will therefore be about 12°C for typical UK ground conditions (tends to be about 8°C all year around). 

 

For the same room, at 21°C, heated by UFH at a rate of 50 W/m², the floor surface temperature will be 25.8°C and so the temperature differential will increase from 12°C to 17.8°C, an increase of nearly 50%.

 

[scottishjohn]

 

I have no issue with your numbers --but that is not what the man was asking -he don,t want to rip his house to bits

my physics say heats rises #

 its the principle that matters

with rads you heat the ceiling first then the room fills downwards from the ceiling 

UFH heats the floor then the furniture  and you,then  rises to a point where it cools  then drops and recirculates and so ceiling could  be cooler ,dependant on height etc ,than where you are and where you need it

you will note I suggested if keeping rads he insulates concrete floor to stop it sucking heat downwards anyway and even agreed that new slab would be better.

 and if he is doing a real up grade then maybe he should seriously consider re -boarding with 37m foam backed plasterboard--that will help a a lot with heat loss through walls and ceiling ..

50 year old house will have next to sod all wall or ceiling insulation .

I know from when i did my house that it made a big difference in heat loss and noise level  

[scottishjohn]

I do not think the heat loss will be as bad as you suggest as the sort of system he is contemplating is not a "thermal store",nearly said "thermal mass", like a normal concrete slab and will change temp very quickly in comparison to a thick concrete slab

-and so he will not loose as much   because he is not putting it into the slab --but upwards and outwards when he needs it .

I know its not a simple thing ,but i have lived with a system similar to this and it works fine and better than rads ,which is the point --it is a good half way house  and as he is using gas then no need to charge up the floor at night on cheap electric ,as most do with ASHP etc 

and mains gas is still cheapest option for most people  

[Jeremy Harris]

4 minutes ago, scottishjohn said:

 

I have no issue with your numbers --but that is not what the man was asking -he don,t want to rip his house to bits

my physics say heats rises #

 its the principle that matters

with rads you heat the ceiling first then the room fills downwards from the ceiling 

UFH heats the floor then the furniture  and you,then  rises to a point where it cools  then drops and recirculates and so ceiling could  be cooler ,dependant on height etc ,than where you are and where you need it

you will note I suggested if keeping rads he insulates concrete floor to stop it sucking heat downwards anyway and even agreed that new slab would be better.

 and if he is doing a real up grade then maybe he should seriously consider re -boarding with 37m foam backed plasterboard--that will help a a lot with heat loss through walls and ceiling ..

50 year old house will have next to sod all wall or ceiling insulation .

I know from when i did my house that it made a big difference in heat loss and noise level  

 

 

The convective properties of heat don't change anything at all, as the key thing as far as heat loss through the floor is concerned is really just the temperature differential across it.  Increase this and the heat loss increases in proportion.  Increasing the temperature differential by 50% increases the heat loss through the floor by 50%.

 

The bottom line is that UFH will always increase the heat loss through the floor.  Even with our 300mm layer of EPS under our floor the heat loss (in cold weather) from having UFH is about 24% higher than it would be if we had radiators. 

 

The bottom line is that if you are prepared to pay for the increased heating requirement that arises from having UFH then that's fine.  You are, and we are too.  In our case the extra we pay because of the higher heat loss from the UFH is tiny, because our overall heating bill is pretty small, even with the additional losses from having UFH.

[Jeremy Harris]

2 minutes ago, scottishjohn said:

I do not think the heat loss will be as bad as you suggest as the sort of system he is contemplating is not a "thermal store",nearly said "thermal mass", like a normal concrete slab and will change temp very quickly in comparison to a thick concrete slab

-and so he will not loose as much   because he is not putting it into the slab --but upwards and outwards when he needs it .

I know its not a simple thing ,but i have lived with a system similar to this and it works fine and better than rads ,which is the point --it is a good half way house  and as he is using gas then no need to charge up the floor at night on cheap electric ,as most do with ASHP etc 

and mains gas is still cheapest option for most people  

 

What do your calculations of the heat loss through the floor show, then?

 

Are there factors other than the total floor U value, the surface resistances and the temperature differential that we are all unaware of (including those in the business of specifying and installing heating systems)?

 

If you know of specific factors that everyone else is unaware of, then it would be useful to state them here, so we can all correct the mistakes we've been making for decades.

[scottishjohn]

3 minutes ago, JSHarris said:

The bottom line is that if you are prepared to pay for the increased heating requirement that arises from having UFH then that's fine.  You are, and we are too.  In our case the extra we pay because of the higher heat loss from the UFH is tiny, because our overall heating bill is pretty small, even with the additional losses from having UFH.

so what you are saying is is that radiators are a more effiecient system than UFH and we should all be using rads

[Jeremy Harris]

10 minutes ago, scottishjohn said:

so what you are saying is is that radiators are a more effiecient system than UFH and we should all be using rads

 

 

I'm saying two things:

 

1) UFH always, without exception, has a higher heat loss rate than any other heating system that does not directly heat an external surface (unless you can provide evidence that shows otherwise).

 

2) UFH provides a clutter-free way of heating that can feel more comfortable, but that comfort and convenience comes at the expense of higher running costs, due to the additional heat loss.

[scottishjohn]

I have no calculations, just the one that matters --how much energy i have to pay for  and that said 20%less with suspended floor retro fit UFH  than with rads 

maybe that is the way  then air gap and insulated suspended floor with thin screed if looking for best economy  in heating costs ?

or should it be same 300eps then slab ,then 100mm eps and ufh then choice of floor ?

what do your numbers say to that ?

 

[oranjeboom]

@Da-Dad I was in a similar situation as you. Renovating bungalow with 2 extensions that were going to have UFH, so needed to tie that in with the bungalow heating system also. So wanted UFH throughout. Looked at various options, tried to squeeze in as much insulation, but it still meant I was wasting a huge amount through the old concrete slab (that had no insulation - a 1950s bungalow, DG and poorly filled CWI). I almost went for a retrofit, overfloor UFH system that quite a well known online UFH specialist firm were trying to convince me would work fine with their minimal insulation.

 

I ended up digging the whole slab up down to 1/2m below floor level  and laying 300mm+ of EPS/celotex, then with UFH meshed in concrete (turned out to be a nightmare as the guy who did the pour, was an utter muppet...another story). So it can be a lot of hassle for having UFH. Those modern oversized radiators can look good on rooms if you site them carefully where they won't be in the way if you ever decide to change room layouts. Have you considered, EWI to reduce the heat loss through walls? And supplement your loft insulation if needed.

[Ian]

Re the efficiency discussion comparing UFH to radiators, I’ve found with our UFH that, for the same levels of comfort, we can set the thermostat to a lower temperature than would be the case with a conventional radiator system

[scottishjohn]

1 minute ago, Ian said:

Re the efficiency discussion comparing UFH to radiators, I’ve found with our UFH that, for the same levels of comfort, we can set the thermostat to a lower temperature than would be the case with a conventional radiator system

thats exactly what i found 

[scottishjohn]

maybe we should be building with strip foundations then subwalls and fill inside them with 300-400m insulation and fully floating floor on top of it with UFH built in ?

no big heat store in floor then --so only heat it when you need it - temp will change very quick then  and low heat losses?

[Onoff]

13 minutes ago, scottishjohn said:

maybe we should be building with strip foundations then subwalls and fill inside them with 300-400m insulation and fully floating floor on top of it with UFH built in ?

no big heat store in floor then --so only heat it when you need it - temp will change very quick then  and low heat losses?

 

In effect what many have done here. Biggest problem seems to be the places can be TOO WARM and require cooling.

 

I can only dream of such a problem!

Edited July 3, 2019 by Onoff

[scottishjohn]

with only a very slim biscuit screed then it should not be as big a problem cos you won,t be holding heat for so long or have as much of a "thermal mass" to heat up ?