Hydronic Floors & Hot Water Heat

[Jcoon]

I'm insulating the footings 4' deep and under the entire slab.

Friend of mine has been in his shop 3 years. He insulated as I described above. He says the grass stays green about a foot out around his shop. That's an example of how far concrete will radiate heat.

So you’re saying that with full insulation his grass is still green? What kind of temps do you guys experience in the winter? What does your friend think he could have done differently?

 

[ovrszd]

teejk,

Yep, climate has a lot to do with design. I only said I would not insulate under the middle of the slab, but of course you must insulate on the edge and in under it for the first couple of feet too. Especially in in colder climates. Also, there is no need to heat right up to the edge of the slab inside. Hold the heat back and let it fade out near the edge.

Loosing enough heat out through the edge to keep a lawn green in very cold weather is terrible. Nobody would advocate that! Heat loss in that situation is through conduction, not radiation.

And how would it be prevented?

 

[ovrszd]

So you’re saying that with full insulation his grass is still green? What kind of temps do you guys experience in the winter? What does your friend think he could have done differently?

We aren't extremely cold. Frost depth of 36" or less.

Could have put the footing insulation on the outside. But then it would be exposed to the elements at and above ground level. Which won't work. He likes to have 6-8" of exposed concrete around his building. I'm going to 2-3".

 

[Jcoon]

We aren't extremely cold. Frost depth of 36" or less.

Could have put the footing insulation on the outside. But then it would be exposed to the elements at and above ground level. Which won't work. He likes to have 6-8" of exposed concrete around his building. I'm going to 2-3".

We can see 30 below and our frost line 42 inches. I would not put the insulation on the outside of the footer wall due to the fact that The concrete in the wall will be heated from the inside floor I would definitely put insulation on the inside of the wall acting as a break between the floor and the footer wall.

 

[CalG]

We can see 30 below and our frost line 42 inches. I would not put the insulation on the outside of the footer wall due to the fact that The concrete in the wall will be heated from the inside floor I would definitely put insulation on the inside of the wall acting as a break between the floor and the footer wall.

The heated slab should be separated from the footings. But there need not be insulation between. Any gap will act as a thermal break, rigid insulation is hand however.

I used 1X 4 pine. vapor barrier on the out side. against the footing.

Alaskan slabs are an entirely different situation. The hydronic heat is best put in a slip sheeted thin slab poured over the base slab.

 

[ovrszd]

Here the slab is poured to sit on the footing. Where the heat escapes is thru the floor thickness at the outside edge that has no insulation.

Footing insulation is on the inside. Floor insulation is umder slab. So that leaves a gap. Hydronics piping is recessed a foot or so from the outside edge of the slab.

 

[teejk]

Here the slab is poured to sit on the footing. Where the heat escapes is thru the floor thickness at the outside edge that has no insulation.

Footing insulation is on the inside. Floor insulation is umder slab. So that leaves a gap. Hydronics piping is recessed a foot or so from the outside edge of the slab.

Leaving a foot or so is a good idea. Figure that sooner or later a wall is going to be erected which may involve drilling/nailing. The last thing you want is to puncture the tubing. Also plan ahead for any future partition walls.

 

[rScotty]

We used Rehau brand pex here (5/8" in the shop, 1/2" in the house). Benefit of the larger diameter is longer loops. Downsides are that fittings are not generally available in the hardware stores and any leftover tubing is not really good for anything whereas the 1/2" can be used for potable water at least in the Rehau brand (I can't speak for other brands). As for abuse during the pour, I think the stuff is much tougher than you think plus the loops are spaced 12" apart and our concrete guys were careful to avoid stepping on it. Another benefit of the Rehau brand is that the lengths are marked every foot...easy to know when you are at a loop's limit and time to return to the manifold and start a new loop.

Is Rehau brand the best? Any one brand better than another?? Reason I ask is that my house (2006) is built with Kitec XPA. I've not had any problems with it, but have heard of people running super high pressures & temperatures who have. Personally I think the knock on Kitec is out of line, & it is OK for most applications. At the time, Kitec was the supposed to be the best.

And what kind of connection method is favored now? Does anyone still use the XPA type with the O-ring?
rScotty

 

[teejk]

Is Rehau brand the best? Any one brand better than another?? Reason I ask is that my house (2006) is built with Kitec XPA. I've not had any problems with it, but have heard of people running super high pressures & temperatures who have. Personally I think the knock on Kitec is out of line, & it is OK for most applications. At the time, Kitec was the supposed to be the best.

And what kind of connection method is favored now? Does anyone still use the XPA type with the O-ring?
rScotty

Dunno which is the best. Like most things I rely on my plumbing/heating guy who may have started with Rehau and stuck with it because he had no problems with it before. As for any pex I understand there are pressure limits (my boiler only operates at 18psi, the shop water heater at less than that). Fittings/connections...seems most now use the crimp ring because it's quick and only requires a single tool.