Floor heat without under slab insulation

[Beemer]

Our state requires perimeter insulation as well as a thermal break for the slab at the exterior edges. Looking at the pictures posted though we generally have foundation walls.

 

[Youngandfree]

What diagram? I didn't post one.

There were 2 diagrams at the beginning of thos thread, with text in between them. One describing your mention of foreign build design with foam 4ft below the slab, and then a diagram with your slab and foam below it with an ice stem wall. Don't know where they went. Is it a different thread by someone else? sorry. Two threads with similar themes going.

 

[JJ Quick]

I am no builder, nor am I an engineer.
I do know for fact that the eaerh is a Huge Heatsink.
Why would you not insulate sub slab?

 

[jmdirk]

While everyone is arguing about what I meant and if we should lock the thread, I think you wound up getting to my point by accident.

I don't heat the shop to a very high temperature. 15 degrees (60) is normally the maximum, if I was painting I would temporarily bump it above that using the forced air, but I run hot naturally and if I'm wearing coveralls I prefer it to be cold. My assumption at that point is the delta between the shop and the earth at about 5' is not very much, so you're starting to split hairs on how much heat is moving. I'm totally willing to be wrong on that, hence why I commented that doing the "L" horizontal insulation to the footer would make sense versus nothing but the ICFs. But I'm questioning just how much heat is going to soak into the ground and not be recovered versus saturating the mass under the slab and more or less staying there to be slowly released back into the shop.

Most of the slab heated shops I've dealt with have issues with the temperature not regulating as the thermostat that is controlling the heat is sensing the air temperature and not the slab temperature, and will wind up firing the boiler at an extreme when it is a cold snap which results in the slab just being way too hot for when the cold has passed. Now, I don't know if those are insulated slabs or not (again, code requires the perimeter foundation to be insulated, but that is a change from only a decade ago), so maybe their issue is not what I'm perceiving it to be and the slabs aren't insulated, and that is causing the issue.

I guess what I am also not considering is that the glycol will be 40 degrees (105) and that would be the number for the delta to ground temperature, versus the 15 degrees (60) that would be my normal maximum shop temperature. In which case it then means you need insulation somewhere under the slab. Maybe? I have to think about if it works that way or not.

Ok, I'm located near Ottawa, so we don't get -40, but -30 or a bit lower, is rare, but not uncommon. I have a similar sized shop, 30 x 40, and in floor radiant using a 10 kW boiler. 3"insulation under the slab (monolithic shallow foundation) and horizontal skirt insulation out 4' from the edge of the building

You're right about the regulation of temp. With in floor radiant being very slow to react, there are a few things that can be done to mitigate that. One being having a boiler with an outdoor reset feature (poorly named IMO). ODR monitors the outdoor temperature and then regulates the output of the boiler (when it's warmer out, it scales back the boiler output) so as to not over shoot so bad. The other is to regulate on the slab temperature rather than the air temperature.

Regarding your point about the temperature differential between your shop and the temperature of the ground, I can tell you that the slab temperature is always 3-4 degrees Celsius warmer than the air temperature of the shop. So if I've got the shop set to 15C, the slab is going to be at 18-19C. Or about 15 degrees warmer than the average soil temp you cited below. And that's with 3" of insulation under the slab.

Without insulation, you'd have to pump a heck of a lot more energy into the slab to maintain the same slab temperature. I'm just not seeing a good reason to omit the underslab insulation. I've seen multiple threads on here and when I was researching installing my system where people did not install the insulation, even in much more temperate climates, and they regretted it.

 

[willymakeit]

Building a 40x40 and code requirements mean the perimeter foundation is ICF for 4' below grade on top of a footer.

Can I skip insulating under the slab despite doing in floor heat?

I know some of the winter greenhouses here are being built with a "heat battery" in the floor by filling the foundation area with sand and dumping heat into it starting in the fall, and they've found it helps a lot with regulating the temperature through the winter. Basically building a massive amount of thermal mass. Will that same concept work in this case, or is it just asking for massive inefficiency?

Northern BC location, typical to see -30 to -40ish, but typically it's closer to freezing (no units of temperature because who cares). I plan to have a large forced air unit in one corner to blast after the doors have been opened or if something needs to be dried out, but I prefer the quietness of the in floor and it keeping the slab comfortable otherwise.

Where you are located I would insulate underslab. I do large buildings in S. mo. ,S lake City and Illinois and we didnt. By large Im talking3-500,000 sq ft

 

[2drx4]

Since people wanted me to update on what we wound up doing. Wound up going with conventional formed foundation and foam on the outside of it, and foam under the slab. Builder and I decided that ICF wasn't going to be ideal. He felt that any frost protection around the foundation was unnecessary, as in he has never done that and we have fairly ideal control of water so it will be dry, so we did not do that.

So the whole thread is fairly pointless.