In slab Radiant Heat

I was talked out of it by two different people in the industry when I built my shop. Their reasoning was the temp swings we see here in NC. Basically they said you'll get the floor nice and warm when it's cold out and then It'll warm up to 70 like yesterday and the slab will have bad sweating problems. I've seen lots of shop floors with sweeting problems without radiant heat but think that's a problem with % humidity such as leaving doors open or pulling in dripping wet vehicles when it's raining. Maybe bad slab prep would play a part too.
 
I put it in my shop 30x50 when I built it 15 years ago. Ran a small 5kw tankless water heater on it for a couple years. Only ran it on days where it didnt get above freezing or real close to it. Never had sweating issues from the heat. Cold is what makes something sweat, have you ever seen a warm cup of coffee sweat? The biggest thing is insulation and vapor barrier under the concrete. I used 2" closed cell foam and a heavy mil plastic under that also insulated around perimeter of slab. Water heater crapped out abot 5 years ago and havent replaced it, I can tell a diffrence on really cold days but thats about it.
If I built a shop again here in Sanford NC no I wouldnt do it. If I built one in a colder climate I would def. do it. Family member in Todd NC has a large shop 60X150 and it makes a world of diffrence when the floor heats running and not running. No sweating issues on his either.
 
Recently stayed in a cabin in Wyoming with it. That was the only heat source for the cabin and it would keep it at 70-72* all the time with it in the teens as the high outside. In the case of it out there, it qualifies for energy credits as the concrete stores the heat so they essentially get 50% off their per kwh rate after 5pm. We are going to do it when we build our barndo here in VA since most of the space will be polished and sealed concrete floors. I know of a couple people with it and never having the sweating issues. I'll run it off a wood boiler with provisions in the manifold for tankless water heater to be plumbed in when we get old and don't want to deal with the wood boiler.
 
Last edited:
I have a 28x40 shop with radiant heat and would not consider another without it. Built about 6 years ago, installed myself for about 2.5k for everything. I did a hybrid insulation with a heat sink in the center. Keeps shop nice and comfortable. Building itself is insulated well. Happy to share any info.
 

Attachments

  • IMG_20191111_072350927_HDR.webp
    IMG_20191111_072350927_HDR.webp
    242 KB · Views: 52
  • IMG_20200302_170656655.webp
    IMG_20200302_170656655.webp
    68.8 KB · Views: 35
StretchASU said:
Recently stayed in a cabin in Wyoming with it. That was the only heat source for the cabin and it would keep it at 70-72* all the time with it in the teens as the high outside. In the case of it out there, it qualifies for energy credits as the concrete stores the heat so they essentially get 50% off their per kwh rate after 5pm. We are going to do it when we build our barndo here in VA since most of the space will be polished and sealed concrete floors. I know of a couple people with it and never having the sweating issues. I'll run it off a wood boiler with provisions in the manifold for tankless water heater to be plumbed in when we get old and don't want to deal with the wood boiler.
Click to expand...
I looked into it for my shop that didn’t get built when I sold the farm.
I was told not to do it with epoxy floors because it could cause the epoxy to de stick…didn’t make sense to me, but again changed plans and never built the building. Just soemhting that’s worth investigating I guess
 
Ron said:
I looked into it for my shop that didn’t get built when I sold the farm.
I was told not to do it with epoxy floors because it could cause the epoxy to de stick…didn’t make sense to me, but again changed plans and never built the building. Just soemhting that’s worth investigating I guess
Click to expand...

Thats really odd. I know guys that use it in their car washes and have epoxy floors in some bays. I'm sure there is some special prep/primer and epoxy combo that needs to be used for the heat to not weaken the bond, but the floors never get THAT hot I wouldnt think. Like the place we stayed it was just a concrete stain and clearcoat sealer basically is all they had on the floor.
 
Concrete with a densifier and sealer from ghostshield has worked well. Easy to clean and concrete dust has not been any problem.
 
As others have said, cold slabs sweat. Epoxy adhesion issues are due to lots of things, mostly around shitty products and incorrect prep. The slab remaining a constant temperature isn't one of them. It doesn't really get hot. Vapor barrier is critical for any slab, heated or not.

Biggest issue you'll have is around future modifications to the slab - drilling any holes or making any cuts could mean cutting a line.
 
Our is on it attached to an outdoor wood boiler. The only heat source. It’s definitely gooder than forced air. But only if you keep the temp set - if you like tweaking it a few degrees here or there it’s not for you.

Most people don’t realize till they’ve lived it. It doesn’t really heat the “air”. It’s wacky, All your surfaces feel like your temp setting, but the air often feels slightly different. And because of this, if your floor track skips over say, a half bath in hallway, it will feel a big temp difference

You also need to have your plan pretty in place. If a kitchen island ends up over a track the cabinets underneath are like a mini sauna.

The shop hasn’t faced and floor drilling woes. Pallet racking for example is lagged to the block wall. A tin building with radiant floor and something like pallet racking may have issues…

Indoors is usually a gypsum floor. Let’s the heat thru well. A shop with “weight” is going to have a poured floor which doesn’t permeate the heat as fast but definitely adds a higher heating factor but this is where it counts even more so that you can’t really “tweak” the degree for a few hours

In the future on a new build I would still do it. In re shop build, the system does not work if you’re the type that turns it on only for weekend hobby work etc
 
Stuntman Autoworks said:
Ok, I think I'm going to skip the radiant heat, what about 2" underslab insulation, any reason to or not to get it?
@ckruzer
@shawn
@Ron
Click to expand...

Plastic sheet or butyl mat for lifetime overkill. Then XPS. Spray foam the joints.

If I was to experiment. I would lay xps, skip the foam, then layer the top in roofing butyl + tar. If it takes generations to decompose at the dump…. Lol
Slab insulation is more about preventing cold/moisture incursion than heat loss
 
Vapor barrier is critical. Underslab insulation is a waste of money around here if you don't have a heated slab.

Heated slab is nice for the thermal mass. Set it and forget it, doesn't matter if it's 4F outside, open the door, roll something in, close the door, still warm.
 
Back
Top