Underfloor heating in insulated slab.

[gavztheouch]

I’m about to start my isoquick insulated foundation it’s 250mm thick insulation and 250mm concrete. Four layers of a393 insulation.

 

Just looking for advice on laying the pipes.

 

Should I pressurise them before the pour. If so air, water or antifreeze. It will be exposed to cold weather over the winter so if water I would need to drain down which might be tricky.

 

should the pipes be connected to the manifold before pour or after. I have seen both ways on in picture on this forum. Some pipes come pressured from the supplier with end caps. 
 

My mesh is 200mm spacings on the bars this would suggest 200mm centres on the pipes. I have a low heat demand I’m hoping this will be ok. Not worried if it is not as efficient as it could be.

 

The last point is the pipe diameter, as I have a large number of mesh layers (4) the build it could get tricky and any overlap or misfit will push the top layer of mesh higher, in turn encroaching on the 40mm of cover concrete. If I run a smaller diameter pipe as 12mm instead of 16mm I would gain some more space but the volume of water would be much less I think.

[JohnMo]

57 minutes ago, gavztheouch said:

Should I pressurise them before the pour. If so air, water or antifreeze.

I would a - leak is immediately visible (by watching pressure gauge). If water, do it with water and anti freeze or just air.

 

I filled mine with water and Screwfix antifreeze and left as it was, pressurised until I commissioned the UFH.

 

I installed the manifold on some marine ply and made a foot so it was self supporting and cast it into the concrete.

 

Run standard 16mm pipe. I'm on 300mm centres 200mm will be fine.

 

Depth depends on how you want to operate. 100mm deep allows batch charging overnight on cheap rate, 40mm maybe not.

 

Not sure I would bother paying for pre pressurised pipes. Pert-al-Pert pipe is nice to use as it has no memory unlike PEX.

[gavztheouch]

Thanks @JohnMo  great advice