PEX Radiator pipes - in screed or insulation

[Brian in Dorset]

I am about to install a celotex + anhydrite screed floor above the existing concrete floor and rear extension (B and B)

 

I want radiators rather than UFH and if possible use 15mm PEX so no joints underfloor. I will have  22mm from unvented tank on first floor landing to manifold in the hall. Pipes to run in 15mm PEX to each room.

 

I am looking for the best way to run the PEX in the floor.

 

I have a few ideas such as trunking/conduit in the insulation coming up through the screed by the radiators.

 

Alternative is to run in the screed a bit like UFH pipes with clips.

 

Last option i have come up with is to channel into the original concrete floor and run PEX in trunking under insulation.

 

Anyone any ideas and/or experience of such things and can offer any other ideas and/or hints and tips.

 

Thanks

 

Brian

 

[Russell griffiths]

Re think your screed choice, you want cement based not gypsum based, so not anhydrite 

Anhydrite screed requires sanding to remove the top layer, it’s also a bit dicey getting tiles to stick to it. 

[Mr Punter]

You may want to avoid having the rad pipes heating the screed.  They run much hotter than UFH and you will get hotspots in the floor.  In the middle of the insulation layer would be my favourite but I don't know what depth you have.

[JohnMo]

15 hours ago, Mr Punter said:

You may want to avoid having the rad pipes heating the screed.  They run much hotter than UFH and you will get hotspots in the floor.  In the middle of the insulation layer would be my favourite but I don't know what depth you have.

He could be running low temp rads, high efficiency modulating boiler or ASHP?

[NewToAllOfThis]

I know not an answer but similar topic and probably 'teaching your grandmother to suck eggs' but maybe useful to some on here.

 

I have just run PEX for radiators upstairs so ran them in the ceiling and clipped to Posi joists with the 15mm copper clips with no problem.

 

I haven't fitted the radiators yet but have managed to run the pipe in the service void and put a sharp 90 degree bend on them so they can be connected directly to the radiators eliminating any hidden joints and keeping everything off the floor and avoiding the skirting.

 

Make sure you use a spring bending insert, available from Screwfix and do a few practice bends with bits of spare pipe if you need a tight 90 degree bend.

 

Make sure you get the PEX to radiator valve connectors rather than generic type as they are slightly different sizes. 

[markocosic]

If doing that for downstairs make sure that you don't create an "n" shape with your PEX...

 

...because that will be a swine to get the air out of.

 

 

Ideally your "horizontal" runs to/from the "drops to downstairs radiators" will have a constant slope "upwards" to somewhere that the air can escape, such as the "rise" to an upstairs radiator.