UFH - Overlay or mill out?

[DJB83]

Hi all

I am undertaking a major renovation of our home and planning to install wet UFH to all of downstairs.
Size is 50sqm with a recent extension adding approximately 15sqm on top of this.

My two choices are currently either an overlay system (18mm panels with 12mm pipe) from the likes of PolyPipe or to mill / channel out the existing concrete floor screed.
The advantage of the milling option is no additional floor height but the disadvantage seems to be zero insulation as the original solid floor has no insulation below.

I was recommended JK Underfloor heating which are a national company. Price wise, they are approximately £3k to mill out, lay the pipes (14mm) and fit a manifold. (This would then need to be connected by the heating engineer).

Does having 18mm of insulation (panels) on the floor provide any significant benefit? (Compared with simply inserting pipe into the existing screed)
Has anyone else decided between these two options?

In addition, I have been advised that my combi boiler can be used (with zone valves) but does anyone know if I need an extra pump at the UFH manifold (even though the combi is already pumped)?

 

[Notch7]

I had no idea you could mill out, new one on me

sounds noisy

 

[DJB83]

 

[Notch7]

disadvantage seems to be zero insulation as the original solid floor has no insulation below

I don’t think in screed under floor heating is worth doing if there’s no insulation.

 

[DJB83]

Any other opinions on this?

 

[Madrab]

Unless you can guarantee that the slab is insulated underneath (80mm min) then channelling out the slab isn't worthwhile IMO. Overlay is a very successful retrofit, you just need to manage the lost height. pipe size would be dependent on what heat loss characteristics are involved, it may need to be 16mm, unless you have already performed the heat loss calcs etc and have established 12mm will be enough.

The EPS400 panels will provide insulation and the foil overlay helps with heat spread into the floor covering. Floor covering can be laid directly on top. If you can add any more insulation underneath then that would be of benefit. Have fitted a number of overlay systems (Wunda EPS400 panels & 16mm PEX) and they work very well.

If you are adding anything but the smallest of UFH loops then a pumped manifold and 2 port valve system would be recommended. Also ensure that the system/boiler can support the extra loads.

 

[robinbanks]

the original solid floor has no insulation below.

I wouldnt pick either of your options unless you literally want to pour money into the ground forever more. 6mm of insulation between your warm pipe and your cold slab is incredibly minimal; your floor covering will likely be equally as insulating, meaning half the heat you pay for goes into the slab and the ground below

Break up the existing concrete floor and get rid, dig down and get rid, level out with compacted type 1, sand blind and DPM, lay 150mm of seconds grade PIR (bit more economical, doesn't matter if it's a bit wonky) and put a self levelling screed of about 40mm over. The UFH pipes staple to the PIR through the retention sheet that stops the screed running away, take all of a couple of hours to put in the pipes - the bigger job is the prep of the subfloor but 65sqm is easy enough as a DIY effort

If, magically while smashing out the slab you discover that it has a nice thick wedge of insulation below then happy days; cut the perimeter and replace concrete with 2 inches of insulation to thermally disconnect the slab from the walls and foundations, then channel it out or overlay, and adopt a pattern of using the UFH to heat the slab and keep it warm (ie put the heating on a constant low level rather than blast on/blast off) and start looking at other areas of the house to insulate and draughtproof