Pipe for UFH

[WWilts]

PEX
AL PEX
PERT

PERT AL PERT

 

Which pipe type is recommended for UFH and why?

[WWilts]

Some might find this info useful

 

https://www.beama.org.uk/static/8a453c69-defb-47c1-85af891729e44abe/BEAMA-UNDERFLOOR-HEATING-GUIDE-TO-TYPES-OF-UFH-PIPEWORK.pdf

 

Tradeoffs involved

[Nick Laslett]

There are lots of good posts here on different UFH pipes.
 

I tried to research the topic, but things like the 3 different types of PEX A, B or C. Different oxygen layers Al or EVOH. Number of layers and mixtures of material make it a challenge to understand.  

 

Wunda do 2 types of pipe 16mm Hdpe-Al-Pex for in screed and 16mm Pert-Al-Pert for overfloor, both with lifetime guarantees. 

https://www.wundatrade.co.uk/shop/home/water-underfloor-heating-solutions/joist-floor-heating-pipe/16mm-hdpe-al-pex-pipe/

 

https://www.wundatrade.co.uk/shop/home/quick-shop/wundatherm-quick-shop/pipe-quickshop/16mm-pert-al-pert-pipe/

 

Not many suppliers are specific about their pipe being okay to go into concrete slab.

 

I used the 16mm Hdpe-Al-Pex for my install. But my build is a long way from being finished, so difficult to know how to make recommendations about the UFH pipe. It survived the concrete pour and the ICF wall braces. 

[Adsibob]

Are all UFH pipes able to be laid at 150mm spacing, or will some have too high a turning radius to achieve this without kinking?

 

Edited October 4, 2021 by Adsibob

[Temp]

Think most can manage 80-100 mm bend rads.

[WWilts]

Which pipe will bend sufficiently & easily for 100mm spacing?

[vala]

@WWilts I think you'll need to do a light bulb end when bending to that radius. I've just laid UFH pipe at 135 centres and done the light bulb ends to achieve this.

Did do a test on an offcut to see how small a radius I could achieve however it kinked before 135mm.

Maybe it could be done with the use of a former?

[shuff27]

I've had an estimate (not a final plan as I haven't yet finalised my kitchen unit layout) from Screedit, one of those contractors which install the UFH kit & screed as a package.  They recommend 100mm pipe spacing when being run off an ASHP which seems logical for a lower water temp source - have other ASHP owners used this configuration, or just gone with wider gaps e.g. 150mm? 

[tonyshouse]

The lower the heat loss of the house, the lower the flow temperature needed and the wider apart the pipes can be and the less energy it uses 

[PeterW]

PERT and PEX are broadly the same thing - a polyethylene pipe, the difference being PERT has a modified binder to deal with continuous high temperature (ie 55°C plus) which isn’t needed in most UFH installations.
 

The AL layer is key to oxygen diffusion but has nothing to do with the flexibility or tightness of bends etc. 

 

100mm spacing is close and will use more pipe and will also need “light bulb” turns toward the ends as the bending radius will  not allow it to turn back on itself in 100mm. 
 

Bear in mind if you use 100mm you will get quicker response times as you can put more heat in, but it will still be the same amount of heat irrespective of the pipe spacing. 

[jack]

2 hours ago, shuff27 said:

I've had an estimate (not a final plan as I haven't yet finalised my kitchen unit layout) from Screedit, one of those contractors which install the UFH kit & screed as a package.  They recommend 100mm pipe spacing when being run off an ASHP which seems logical for a lower water temp source - have other ASHP owners used this configuration, or just gone with wider gaps e.g. 150mm? 

 

What're your heat input requirements? A number of us here with passive slabs have gone with 200mm spacing (the pipes are tied to the slab reinforcement mesh) and have no issues getting enough heat into our houses at low flow temperatures. At all but the very coldest outside temperatures I run mine at 25°C, which is the lowest temperature setting available with my ASHP.

 

It may also depend a bit on your floor covering. We have ~70mm of polished concrete on top of our 100mm slab, so there's a lot of concrete for the heat to diffuse across before it reaches the surface. I don't notice any "banding" of heat, although there are a couple of warmer patches where pipes are closer together due to routing. Perhaps it's different if the pipes are closer to the surface?

[ruggers]

On 06/10/2021 at 07:11, tonyshouse said:

The lower the heat loss of the house, the lower the flow temperature needed and the wider apart the pipes can be and the less energy it uses 

Just reading some old posts to gain some info. before I make a post of my own. I agree with what you say about the lower heat loss the lower the flow temperature can be.

 

But why do people always say with low temperature systems to go for as close spacing as possible so you can get the heat into the room with it being at reduced flow temperature. I've completed all heat loss calcs for a self build and know that I'll be aiming for 37.5C MWT on weather compensation so this will vary the flow. Indoor designed to 21°C at outdoor -3.6°C. I will probably have the house running at 19°C air temperature but if designed higher it allows some headroom.

I'm not sure if I go with 100mm centres throughout the ground floor 50mm screed or I have different spacings for the different heat loss rooms.

[JohnMo]

I used Pert-Al-Pert, because there is almost zero memory in the pipe.  Unroll, straighten by hand and it stays straight, clip it down and bend away, super easy to use.

 

I did 300mm centres in 100mm of concrete, flow temps at -9 were 33 degrees.  Designed it myself, instead of relying on a sales man to tell me I needed to buy several km's of pipe (which you don't) and a couple of manifolds to cope with the loops.  Works fine and dandy.