Matt1976

Hi Everyone - retrofit (wet) UFH advice required

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Hi,

Finding this site really usefull but would like to hear peoples experience with the installation and merits of retrofit underfloor heating.

I live in a 2 bed semi detached built in approx 1996. I want to fit a low profile wet UFH system to the whole of the downstairs (approx 20 sq/m). I am told the floor is concrete block and beam with a screed on top, unknown insulation depth (would there be a standard depth on a house of that age? It is a barrett house if that helps!). I am hoping i would be able to install UFH over the top with one of the many low profile system available and it be reasonably efficient, but more importantly it will be the only heat source downstairs so needs to get the room warm (it will be open plan).

Hopefully that makes sense

Thank you, Matt

 

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Might be a shot in the dark but can you get hold of the building control drawings for the house to ascertain what insulation was used etc? Knowing the commercial house builders it’s likely to just meet building regs at the time so a lot less insulation than is needed today so you may well take a hit on efficiency. 

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Welcome.

 

A house of that age probably won't have any insulation at all in the floor I suspect, and being beam and block it's not really feasible to lower the floor to allow insulation to be added.  Unless your room heights are such that you can accept losing a fair bit of height by raising the floor I doubt that UFH would be a sensible option, I'm afraid.   Worth checking to see if you can determine how deep the floor is, just to be sure there's no insulation, but I suspect even if there is a layer it will be so thin as to make running UFH a very inefficient way of heating the house.

 

UFH is always less efficient than radiators, because of the losses down through the floor, even with pretty good insulation underneath it.  It does give the benefit of better comfort levels, plus freeing up space on the walls where radiators are, though.

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i installed the wet system by polypipe which is 12mm pipe in gloved 18mm polystyrene board in a victorian house which worked well..however, there was a neighbour downstairs, upstairs and to one side. In total, there were three heated sides (floor, ceiling, one wall), the flat itself was single glazed and uninsulated front and rear walls.

 

 

My observations - the pipe heat up the floorboards which heated the flat quickly due to non-screed and direct contact of the pipe to the floorboards, however, the flat cooled down within 2hours once the heating was turned off.

 

Most important observation was floor surface area heated, the flat was 38sq meter open plan and had UFH throughout, if it had been installed in a typical 4m x 4m room, the heat would NOT have been adequate. 

 

i currently have a similar system in my current house, this time i have screed on top of the pipes and 100mm of Polysterene between the joists, the open floor space is 65sq of open plan and end of terrace house. The same applies here too, heat is enough but more down to open space heated to make up for high heat loss.

 

if you have small living spaces, i will definitely say, it won't work, you need a well insulated place. if you have good open spaces, it may just be enough, proceed with caution,it will be a expensive experiment if you don't do the due diligence in advance

 

hope that helps

 

 

 

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12 minutes ago, wozza said:

That’s a very coarse way to introduce UFH. 

As you’ll have a lot of concrete to heat up and keep at temp I expect that the flow temp would therefore need to be considerably higher than if the pipes were in the slab itself. 

Thermally isolating the pipes from an existing ( therefore possibly insulation unknown / not present ) slab is paramount.

The overfloor systems deal with this in a far better way imo, and I’d only consider the ‘cut groove and lay’ system in a thin slab with known insulation, if I could self level ( therefore fully encapsulating the pipe for optimised heat transfer to the surrounding material ) and if I could tile or lay a decent thickness engineered floor to absorb and diffuse the heat as effectively as possible. 

 

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A while ago I wrote this simple UFH calculator spreadsheet that allows the losses and floor temperature to be worked out fairly easily, as long as you know how much heat you need to deliver to the room to keep it at the temperature you wish: Floor heat loss and UFH calculator.txt

 

The file is really a spreadsheet, but the forum software doesn't allow .xls files, so just save the file and then edit the suffix from .txt to .xls

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Thanks everyone for the info/advice. Sounds like it might be a risk. Will see if I can find out what insulation the floor has.

Thanks

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