[Greenbuilding] Hydronic Radiant Underfloor Heating

[Chris Green]

Gary Viljoen wrote:
> Hi all,
>
> I am about to install an under floor hydronic system into the home I am
> building, and face two options given to me by ‘experts’:
>
> 1.	Lay the concrete surface bed.  Place polystyrene insulation on top.
> Lay the piping in the screed above this.
> 2.	Insulate below the surface bed with the piping in the concrete
> surface bed.
>
> Any recommendations based on experience?
>   
Either way, but the first way just adds extra work and probably uses 
more concrete.

My experience recommends this way:

1: Level and compact the soil/ gravel as best you can. You want to get 
it quite close to flat so there aren't any big voids underneath the 
rigid insulation. Also, getting the bed flat as possible cuts down on 
the amount of concrete you'll need.
2: Place 5 1/2"/ 140mm strips of 25 mm rigid insulation along the inside 
of the exterior wall footings or foundation to prevent heat flowing from 
the slab to the foundation and out into the great beyond.
3: lay down the poly and seal the joints and any big rips that might 
show up in it. A few little ones are okay. The poly can run up the side 
of the footings a ways. Also tape the poly to any plumbing pipes which 
stick up above the surface. I also use the tape to seal any open  pipe 
ends and prevent concrete from splashing into them (that can happen when 
pumping the stuff with a pumper truck...)
4: Place the rigid insulation. On one job we even taped the joints 
between the insulation, possibly because we didn't put poly down under 
it...or at least I don't recall doing that...
---if you're using foil covered insulation, the foil faces upwards.
5: place and tie the rebar as per the specifications. The rebar should 
be between 1 to 1 1/2" or 25 to 40mm above the insulation. There's 
little plastic risers that will set the rebar at the right height but 
chunks of broken concrete patio tiles work just as well.
6: lay out and tie the hydronics tubing to the rebar grid.
7: do a walkabout to inspect and adjust everything before the cement 
crew starts working. Repair any punctures the rebar has made in the poly...
8: pour and screed the concrete.

***If I think some patches of the compacted soil aren't quite up to my 
standards, I'll ask the rebar guys to throw an extra run or two in, 
reducing the spacing
from 2' to 1'. I had to do that on one job this spring.


Cheers,

Chris Green.