Retrofit UFH Dilemma

ChrisF88

First Post so apologies guys!

We are having a rear single story extension in a few weeks. This new area will be insulated to standard which is great but the existing house has no floor insulation at all. It's beam and block and very thin screed so having it insulated almost impossible.

We are thinking of having an overlay UFH fit in the entire downstairs and then either tile everywhere or LVT/PCS. As the UFH is so close to the surface I am hoping it will work well enough, but wondering if anyone else has tried anything similar or has any advice on feasibility or flooring type etc.

The main reason for us wanting UFH is the comfort you get when it's on and also sufficiently heating the living area without rads giving uneven heat.

Thanks in advance

ComicGeek

The existing floor will need a higher output from
the UFH, which means running the water through it at
a higher temperature than ideal. To heat effectively (and not damage the floor finish above), you need a layer of screed or cement board above to distribute the heat evenly - that generally adds an additional minimum 10-20mm to any build-up (which itself might be 20mm) Some slim fit systems have insulation built into the pipework trays, but you're still looking at a significant depth.

With UFH and existing houses, there is nearly always some rooms that you can't get enough heat output from the floor area available. So that is always a risk without a full design and heat loss calculations.

No point spending lots of money on it if it doesn't work properly at the end.

ChrisF88

ComicGeek said:

The existing floor will need a higher output from
the UFH, which means running the water through it at
a higher temperature than ideal. To heat effectively (and not damage the floor finish above), you need a layer of screed or cement board above to distribute the heat evenly - that generally adds an additional minimum 10-20mm to any build-up (which itself might be 20mm) Some slim fit systems have insulation built into the pipework trays, but you're still looking at a significant depth.

With UFH and existing houses, there is nearly always some rooms that you can't get enough heat output from the floor area available. So that is always a risk without a full design and heat loss calculations.

No point spending lots of money on it if it doesn't work properly at the end.

Thanks for your response. I am looking at the wunda overlay system. 22mm board with pipes built in and then literally tiled straight on top with heat resistant expanding adhesive so it should be pretty quick response times. I'm just worries of the heat output will be enough to actually heat the room to the required temp.

grumbler

ChrisF88 said:

...the existing house has no floor insulation at all. It's beam and block and very thin screed so having it insulated almost impossible.

With extremely thin layer of insulation (if any) between the pipes and the screed you'll be wasting a lot of energy on heating the screed, the blocks and the cold air flowing under the floor.

Doozergirl

UFH works very differently and I've always been nervous to put it into people's houses when they aren't very well insulated.  

There's no option to just turn the heating up.  There's no warm spots to lean yourself on a radiator when it gets a bit nippy.  If your house cannot retain the heat well, it just will not get warm.   I live in a house with UFH so I have experience of it working well but this house is insulated and airtight.  Even then, when you come in from the cold getting 'into your bones' it takes a while to warm yourself naturally.   

A massively expensive risk, IMO.   No doubt there are people that can do heat loss calculations for you and if you're determined to go ahead I'd recommend doing that.  

ComicGeek

ChrisF88 said:

ComicGeek said:

The existing floor will need a higher output from
the UFH, which means running the water through it at
a higher temperature than ideal. To heat effectively (and not damage the floor finish above), you need a layer of screed or cement board above to distribute the heat evenly - that generally adds an additional minimum 10-20mm to any build-up (which itself might be 20mm) Some slim fit systems have insulation built into the pipework trays, but you're still looking at a significant depth.

With UFH and existing houses, there is nearly always some rooms that you can't get enough heat output from the floor area available. So that is always a risk without a full design and heat loss calculations.

No point spending lots of money on it if it doesn't work properly at the end.

Thanks for your response. I am looking at the wunda overlay system. 22mm board with pipes built in and then literally tiled straight on top with heat resistant expanding adhesive so it should be pretty quick response times. I'm just worries of the heat output will be enough to actually heat the room to the required temp.

The Wunda website states that their standard overboard system can't be used for tiles, so worth getting their input on the most appropriate system for you. Every manufacturer has slightly different products.

If you don't have enough cover between the pipes and tiles then you just won't get a good spread of heat, and the overall heat output will be lot lower. You need to know the exact depth of adhesive needed to assess total buildup - most UFH manufacturers have detailed measurements on their websites, I can't see anything on Wunda.

You could always get them to do a design for you and then post the details. 

ChrisF88

grumbler said:

With extremely thin layer of insulation (if any) between the pipes and the screed you'll be wasting a lot of energy on heating the screed, the blocks and the cold air flowing under the floor.

The idea I have been told is that the 16mm pipes sit in an insulated backing board with aluminium lining so that heat reflects upwards (in theory). I can see how it works in theory but my concern is whether it works in practice. It's a shame there isn't a way of speaking to someone who has had the systems installed without insulation so I can ask if it works.

ChrisF88

Doozergirl said:

A massively expensive risk, IMO.   No doubt there are people that can do heat loss calculations for you and if you're determined to go ahead I'd recommend doing that.  

I have phoned several companies and no one is willing to give me any calculations or any recommendations and will only show where the heat is lost using thermal imagine which is frustrating.

ChrisF88

ComicGeek said:

The Wunda website states that their standard overboard system can't be used for tiles, so worth getting their input on the most appropriate system for you. Every manufacturer has slightly different products.

I would be going for the rapid response panels which you can tile straight on top of. Hopefully with the tiles being so close to the pipes they will warm nicely and if the entire downstairs is doing this simultaneously surely it will heat well? 

ComicGeek

ChrisF88 said:

ComicGeek said:

The Wunda website states that their standard overboard system can't be used for tiles, so worth getting their input on the most appropriate system for you. Every manufacturer has slightly different products.

I would be going for the rapid response panels which you can tile straight on top of. Hopefully with the tiles being so close to the pipes they will warm nicely and if the entire downstairs is doing this simultaneously surely it will heat well? 

If the pipes are too close to the tiles then the water temperature has to be lowered to prevent the hottest parts of the floor from exceeding 29 degrees. The spaces in between the pipework loops are then going to be cooler than this. With the right thickness of adhesive cover the whole floor can be heated to 29 degrees, thereby increasing the overall heat output from the system.

So if you need a higher output to meet the space heating requirements, then you must allow for a thicker topping to the pipes. You can guess, or get proper heat loss calculations done and a UFH design. Not something that anyone should throw in and hope it works.

grumbler

ChrisF88 said:

grumbler said:

With extremely thin layer of insulation (if any) between the pipes and the screed you'll be wasting a lot of energy on heating the screed, the blocks and the cold air flowing under the floor.

The idea I have been told is that the 16mm pipes sit in an insulated backing board with aluminium lining so that heat reflects upwards (in theory). I can see how it works in theory but my concern is whether it works in practice. 

If this were true we would be able to build our houses from thin foil reflecting heat back inside. In practice radiation is only one way of heat transfer along with conduction and convection. In your case it's conduction that is important and the only way of reducing it significally is by adding thick layer of insulation. That's why the current requirement for beam&block floors is, IIRC, 10 cm of foam insulation (that normally has a reflective foil as well to reduce radiation)