Questions on underfloor heating in a flat and insulation required

[Honza]

Hi,

I am planning flat renovation and was wondering a few things with regards to UFH - did some basic research but it's not my area of expertise at all so thought I'd ask here as I was getting some conflicting information from various people / vendors:

• Wet vs electric UFH - it seems that wet is generally better (more heat, cheaper to run) - does electric have any advantages (other than being easier to install)? I was told that electric UFH generally is connected via one cable per 30 square meters (so for my 80sqm flat it would be 2-3 cables) - for more power it can be connected by one cable per 10 square meters. Is that a good idea?
• Insulation - what are your recommendations please? My flat is on first floor (there is another flat below mine), built in 1970s, concrete / screeding floor, presumably no insulation between floors (cannot confirm for certain unfortunately). I was told that there are systems which are as low as 1.5cm and do not require insulation (in case they are used on concrete / screeding floor) and the heat loss is only around 6-10% or even less when the flat below me is heated - is that right? If so, I am struggling to understand why there are people out there recommending 5-20cm insulation layers. Ideally I would like not to increase floor height too much (2-3cm maximum if possible) but not lose too much heat through the floor - would space blanket or something similar be good enough for the UFH to work and heat the flat sufficiently so that I can get rid of radiators?
• Flooring - originally I wanted hardwood flooring but having read some pros and cons, I am leaning more towards luxury / rigid vinyl floors or maybe mineral core floors (for living room) and tiles for kitchen / bathroom - are those generally suitable? Are there any better options?
• Heated skirting boards - again, have read about these, looks like they might be a good option for smaller areas (kitchen, bathroom etc.) - does someone have experience with them, any recommendations?

 

I should add that the flat is in London where the winters are usually not too cold but certainly don't want to end up freezing if it ever gets to -10 outside  

 

Any thoughts / opinions are welcome - preferably in layman terms if possible, am not a builder or an expert.

 

Thanks

[Olf]

7 hours ago, Honza said:

I am planning flat renovation

What is your current peak energy use for heating, what is total and available (not permanently covered by furniture) floor area?

I assume you have already radiators, so no need for a new boiler?

Are you planning any energy efficiency improvement jobs during renovation?

 

7 hours ago, Honza said:

Wet vs electric UFH

If you define 'better' as 'longer and more disruptive installation but 1/3 of heating cost long term' then wet is better How long are you planning to stay in that place (what is you return on investment period)?

You never mentioned funky stuff like wall/ceiling electric radiant panels - some people like it, even for the art some of them offer

 

7 hours ago, Honza said:

am struggling to understand why there are people out there recommending 5-20cm insulation layers

Cause on the ground floor even with 30cm EPS one loses 10% of heat as sacrifice to Mother Earth, and that at very low floor temperatures. Search here for horror stories of people who were conned into installing UFH without insulating and burn money yet freeze. Even with flat below, if you have to have high floor temperature (because of losses elswhere, hence do your homework in figuring them out) you may end charitably reducing bills of your neighbour.

 

7 hours ago, Honza said:

I am leaning more towards luxury / rigid vinyl floors or maybe mineral core floors (for living room) and tiles for kitchen / bathroom - are those generally suitable?

Tiles are always a winner for UFH, with vinyls do check spec of what max temperatures they like. With the bathroom be especially careful about calculating losses through walls, window and ventilation and all the holes through the wall vs available floor area (as bath, toilet etc take relatively large proportion). You'll likely end up with need for heated towel rail (which is helpful anyway).

[Honza]

Thank you Olf for your thoughts. To answer your questions:

• Peak energy use for heating - don't know I'm afraid, probably around average just like everybody else
• what is total and available (not permanently covered by furniture) floor area? 80 square meters total, not covered by furniture would be around 50-60 I'd assume? There would not be UFH under kitchen cabinets, bath etc. But presumably there would be under bed / wardrobes as those can move from time to time
• I assume you have already radiators, so no need for a new boiler? I plan to get rid of radiators and get a new combi boiler (the current one is very old)
• Are you planning any energy efficiency improvement jobs during renovation? No - there's already double glazing windows. Other than that there's brick walls but as it's a flat, it's not up to me to insulate the walls
• If you define 'better' as 'longer and more disruptive installation but 1/3 of heating cost long term' then wet is better  How long are you planning to stay in that place (what is you return on investment period)? - Thanks, that's basically how I define better in this case How long to stay - don't know, could be as little as 3 years or as long as 10-20 - I see UFH as an investment (if done right - which is why I am asking all these questions) even if I decide to sell / rent the place at some point
• You never mentioned funky stuff like wall/ceiling electric radiant panels - I prefer simple solutions that work - if there's better (cheaper etc.) ways to heat the flat (particularly smaller rooms like bathroom etc.), I'm all for it
• Cause on the ground floor even with 30cm EPS one loses 10% of heat as sacrifice to Mother Earth... - is there any simple rule of thumb here? For ground floor yes, insulation seems necessary based on what you're saying - for first floor I am being told the heat losses are not significant (6-10% or so maximum) without any insulation - is that right?
• Tiles are always a winner for UFH, with vinyls do check spec of what max temperatures they like - I'll definitely have tiles for bathroom and kitchen. For living room and bedrooms, probably luxury vinyl - which from what I have read so far, should be suitable for UFH.

[Olf]

On 09/05/2023 at 23:33, Honza said:

don't know I'm afraid

You should be able, just look at your energy bills for last few months: pick the worst month, divide by 20 (30 would give average day, take the coldest day needed 50% extra) and you'll have your target.

 

On 09/05/2023 at 23:33, Honza said:

No - there's already double glazing windows. Other than that there's brick walls but as it's a flat, it's not up to me to insulate the walls

What about draughts? I had double glazed windows and behind mastic there were finger gaps around them: filling with foam did not take long and the difference is massive. You'll find many holes through the wall bringing frosty air in when you need it the least.

 

On 09/05/2023 at 23:33, Honza said:

for first floor I am being told the heat losses are not significant (6-10% or so maximum) without any insulation - is that right?

Unlikely, and depends on many factors, some beyond control, so claiming '10% maximum' is an outright lie.

Heat transfer through the floor = U (heat transfer coefficient [W/(m²K)]) x area [m²]x (floor surface temperature - what is under temperature)

Well insulated (current BR) ground floor have U=0.13, let's say your flat have U=0.5. Let's assume your floor temperature (with UFH) would be 30°C and your downstairs neighbour at the ceiling it is at 20°C.

0.5x80x(30-20) = 400W, times 24h makes daily total of 9.6 kWh, @ 10p/kWh it would costs you £1 a day to heat your neighbour.

When you get figures for heating energy needed, it should be easier to get percentage for your case.

[Honza]

Thanks, Olf - the thing is I only just bought the place and will be moving in after reconstruction, so don't know the heating costs, other than the fact that it's standard brick built block of flats with double glazing windows.

 

Certainly around windows I asked the builders to fill any gaps / cracks there - thanks for highlighting it, very good point.

 

For the insulation / system, my builder suggested using moulded foam panel (something similar to Underfloor Heating | Foam Insulation | Engineered Foam Products - though don't know the exact brand / type - can ask if there are differences there) to be put on the screeding. The thickness of the panel is around 2cm at the thickest point and around 3mm at the thinnest (where the UFH pipes will be) - is that sufficient, or do I need to put something more under the moulded foam to insulate more? I am really struggling with floor height and would prefer not to increase it more than necessary - around £1 a day 'wasted' would be acceptable for me, there will always be some heat losses - but significantly more than that would be a problem.

[Olf]

On 14/05/2023 at 21:30, Honza said:

don't know the heating costs, other than the fact that it's standard brick built block of flats

That would then leave you with

 

 

On 14/05/2023 at 21:30, Honza said:

The thickness of the panel is around 2cm at the thickest point and around 3mm at the thinnest (where the UFH pipes will be) - is that sufficient, or do I need to put something more under the moulded foam to insulate more?

This is to hold the pipes only Also, version with bonded aluminium layer acting as heat spreader will have higher emission (what you showed makes floor warm over the pipes only). And very likely will need some screed on top, so make it 3cm from current floor level.

 

On 14/05/2023 at 21:30, Honza said:

I am really struggling with floor height

UFH retrofit does not marry well with finished floors.

Back to basics, why are you so fixated on it? You have radiators in place, you could just do nothing. Depending on the layout, you could try skirting heaters though there doesn't seem to be experience with them on the Forum and they look like poor value for money for output tbh.