Advice on low-profile UFH system in ex-council flat.

[toblerone]

Hello all. First time posting so apologies if this is answered elsewhere.

I am close to completing a purchase of my first flat, an ex-council place from the 1960s built in the usual concrete slab and brick.

At present there is some ghastly pipe work for the radiators sprawling round every room and up the walls to the bedrooms, it looks horrendous. I would like to install a wet UFH and have seen the low-profile systems from the likes of Nu-Heat and Wunda which are suited to retrofit projects like mine.

My question is would I need to add some extra insulation like Celotex PIR before laying the boards for the pipes or will the boards themselves be sufficient? I don’t want to lose too much floor height so looking to keep it as low profile as possible. Does anyone have a preference for either Wunda or Nu-Heat?

There is currently carpet and underlay which I want rid off immediately and would ideally do one big zone for the whole of the downstairs (approx 45m^2), as I intend to knock a few partition walls down to make it fairly open plan.

Initially I would also likely keep the rads upstairs as I can’t afford to do the whole lot in one and not sure it’s worth it in every bedroom. My install an electric one for the bathroom at a later date.

Any advice and guidance would be much appreciated!

Tobin

 

[Murdoch]

Do you have permissions in place to make such changes?

 

[Knappers]

Don't do it!
Redo radiators and pipework to current standards instead and spend as much as you can on insulation.

 

[toblerone]

Do you have permissions in place to make such changes?

I’m not aware of any permissions I would need for such an undertaking? Could you elaborate?

 

[toblerone]

Don't do it!
Redo radiators and pipework to current standards instead and spend as much as you can on insulation.

Is it not worth it without adequate insulation?

I can handle pipe work from my days with EDF however it’s not that the current pipe work is bad, more than it looks so ugly, with some going vertically up the wall in the corners. Maybe I’ll get some of those pipe covers I’ve seen in a few houses, they didn’t look too bad.

 

[Murdoch]

I’m not aware of any permissions I would need for such an undertaking? Could you elaborate?

if it’s a leasehold property, you almost certainly need consent from the freeholder to make alterations …. And some structural changes may need building control involved

 

[toblerone]

if it’s a leasehold property, you almost certainly need consent from the freeholder to make alterations …. And some structural changes may need building control involved

I’m not planning to make structural changes. I would be removing stud walls which does not require permission from anyone as far I’m aware, least of all building control.

 

[Ric2013]

A flat with an upstairs and a downstairs?

Not sure what you mean by 'the usual' concrete slab and brick construction. Council houses/flats are not all the same everywhere at once.

UFH can feel 'nice' at lower room temperatures, so might save you energy even if you lose some through the floor, though it depends how much you are losing.

I incorporated UFH into my timber ground suspended floor a few years ago and am happy with the outcome, but the floor is insulated and the U value (heat loss) is about 0.25 W/m2/°C, which, while twice that allowed for a new build (I think), is still pretty good. I don't think I'd have bothered with the UFH is the U value had been much higher. Hard to judge if the UFH actually gives more thermal comfort for the gas consumed. The UFH was installed as part of a complete overhaul of the ground floor and the new airtight and insulated floor replaced a combination of draughty floorboards and damp concrete, so efficiency and thermal comfort are obviously better.

 

[Knappers]

I don't like UFH at all.
It has its place and would be absolutely perfect in a well insulated newbuild, running on biomass or one that requires a constant temperature 24/7.
I think its popularity is mostly to do with the no rad aesthetic and a bit of keeping up with the Jones'

My issue with it in theory is the response times.
Generally in this country we run our heating on a schedule and like to have direct control over the temperature and times (its not just us being behind - we have very changeable weather). Radiators are great at heating spaces quickly and are very responsive, they can be accurately sized and easily controlled.
If you catch a bit of sun through a south facing window then your radiator will go off and stop heating within minutes, Where your underfloor heating will be pumping out for a fair while longer and the same is true in reverse like if someone left a door open for example.
So I wouldn't be keen even in a newbuild but as a retrofit I actually would refuse to fit (except maybe on suspended floor).
The worst thing is where you get a mix of rads and UFH in different interconnected areas, it's just impossible to effectively control the spaces independently.

That said I could get behind a trend to have both, maybe UFH sized to deal with heatloss and small rads to improve controlability or better still low temp perimeter heating and little rads under windows.

Rant over!

 

[Ric2013]

My issue with it in theory is the response times.

Agreed. I would never want it in a slab. I'm not sure how having to maintain a warm slab 24 hours a day is a good thing in variable weather. Mine is using spreader plates and the heat starts to come through in about half an hour. It works in my Victorian cottage because I'm centre terrace. Would be useless in an end of terrace of this age due to insufficient ouput.

Generally in this country we run our heating on a schedule and like to have direct control over the temperature and times (its not just us being behind - we have very changeable weather). Radiators are great at heating spaces quickly and are very responsive, they can be accurately sized and easily controlled.

If I'm just a bit chillier than usual and want a degree extra over and above the scheduled temperature, the UFH is fine. If I got back from holiday, it would indeed take its time.

If you catch a bit of sun through a south facing window then your radiator will go off and stop heating within minutes, Where your underfloor heating will be pumping out for a fair while longer and the same is true in reverse like if someone left a door open for example.

If you're only having to reheat the air due to a door being left open for a few minutes, air warms very quickly.

The worst thing is where you get a mix of rads and UFH in different interconnected areas, it's just impossible to effectively control the spaces independently.

Here I have to agree. We actually put a door across the stairs to keep the upstairs (i.e. bedrooms) at a cooler temperature and split the heating into two zones which is now working splendidly. That said, the tendency was for the first floor to overheat and for the ground floor to tend to coolness even when the house was entirely heated with radiators, and perhaps the UFH was not quite as bad (though hard to tell as the whole ground floor was refurbished).

That said I could get behind a trend to have both, maybe UFH sized to deal with heatloss and small rads to improve controlability or better still low temp perimeter heating and little rads under windows.

In theory, don't we size radiators for heatloss?

I think perimeter heating or small radiators near large glazed areas might be a good idea based on my experience. I have a weird extension with thermal bridging issues and too much glass. The far end is rarely warm. Trouble is finding space for a radiator up that end.

I agree UFH is a bit of a fad and that is why I wanted personal experience of it, depite being more inclined to plumb my own house with all the old or scrap radiators.

I also think you can never overestimate how pleasant having a floor temperature of 27°C instead of 18°C is, so I'd say UFH is always a bonus, even as a backup heat source. And the floors dry when you mop them.

 

[Knappers]

Heatloss is often misrepresented, technically it's just the heat a building (or part of) looses at set temp differential.
If you sized heating according to heat loss then it would only be good at maintaining a temp.
What is usually meant is heat-load which includes the output required to raise temp within specified time.

I'm perhaps in the minority but I don't think I'd get on with it, I like a warm floor in bathroom or at the pool but I generally can't stand being heated, the heated seat in car makes my skin crawl!

If I was building a house tho I would definitely atleast run the UFH pipework, weather I used it or not and your setup sounds good.

The wet (or electric) low profile systems i would only consider sound as floor warmers for comfort and not as viable complete heating solutions (regardless of what the sails department claims)

 

[toblerone]

A flat with an upstairs and a downstairs?

Not sure what you mean by 'the usual' concrete slab and brick construction. Council houses/flats are not all the same everywhere at once.

UFH can feel 'nice' at lower room temperatures, so might save you energy even if you lose some through the floor, though it depends how much you are losing.

I incorporated UFH into my timber ground suspended floor a few years ago and am happy with the outcome, but the floor is insulated and the U value (heat loss) is about 0.25 W/m2/°C, which, while twice that allowed for a new build (I think), is still pretty good. I don't think I'd have bothered with the UFH is the U value had been much higher. Hard to judge if the UFH actually gives more thermal comfort for the gas consumed. The UFH was installed as part of a complete overhaul of the ground floor and the new airtight and insulated floor replaced a combination of draughty floorboards and damp concrete, so efficiency and thermal comfort are obviously better.

Sorry, I wasn’t clear. In London, where I am attempting to buy, the majority of ex-local authority housing stock from that era (1960s) is of similar construction, generally being concrete floors and walls.

 

[Ric2013]

Heatloss is often misrepresented, technically it's just the heat a building (or part of) looses at set temp differential.

Which was my understanding of it. In practice, though, it is calculated at the lowest possible external temperature, so even without adding x percent, you already have an oversized system for most of the heating season (unless you're running radiators and weather-comp). Not so good if you come back from a few days away in mid-winter and the house is cold.

What is usually meant is heat-load which includes the output required to raise temp within specified time.

Then you need to know the rate at which the internal part of the building absorbs heat (which is called the [something]-value) rather than the U-value. Are heating installers really doing this though, or just calculating heat loss plus x percent?

I'm perhaps in the minority but I don't think I'd get on with it, I like a warm floor in bathroom or at the pool but I generally can't stand being heated, the heated seat in car makes my skin crawl!

If the floor is properly designed, it doesn't go above 27°C, which feels more like not cold rather than actually warm. If you're ever passing Colchester in winter, do let me know - as if I'm in and it's heating season, you can come and see what you think.

The wet (or electric) low profile systems i would only consider sound as floor warmers for comfort and not as viable complete heating solutions (regardless of what the sails department claims)

Here I have to agree. I used the uheat suspended floor system. It underperforms (possibly because I have natural timber floorboards on top which are less conductive than uheat recommends) in terms of claimed heat output/m2, but not by much. So I think it's fair to say uheat rated outputs are honest. But bear in mind you'd only get the full heat output if you haven't too much furniture covering your floor. I'm quite minimalist; not everyone is.

Nuheat claims much better heat outputs than uheat does. But, having not actually tested Nuheat, I cannot confirm if the claimed outputs are accurate and achievable.

It's also worth considering what would happen if the neighbours decide to stop heating their flats for whatever reason. The party wall/ ceiling above you becomes a source of heat loss. If that happens, you may find your UFH does not cover the increased heat loss or heat load required. If that is the case, would you use electric heaters as a temporary backup, or would you keep a radiator as a contingency measure? Or are you going to insulate internal party surfaces?

 

[Knappers]

In practice, though, it is calculated at the lowest possible external temperature, so even without adding x percent, you already have an oversized system for most of the heating season (unless you're running radiators and weweather-compd.

Maybe -5°C and 20°C so it could get quite a bit cooler and all boilers now will modulate down atleast 5:1 so no not oversized.
Weather comp/load comp will increase modulation but cert isn't required for it.

Then you need to know the rate at which the internal part of the building absorbs heat (which is called the [something]-value) rather than the U-value. Are heating installers really doing this though, or just calculating heat loss plus x percent?

Thermal mass but air volume will do. I use an online calculator to establish radiator sizes required and size boiler accordingly but I do think engineers should have a good understanding of the principles even if they're using a 'rule of thumb'. If you end up with rads that won't heat the house on the cold days then what's the point?

 

[Ric2013]

Meant oversized as in 'bigger than needed to keep room warm' hence spare capacity to heat the room from cold relatively quickly. Not sure if I made myself unclear earlier... probably.