slab heat for a garage

[SolarAndWood]

I am about ready to pour a slab for my boss's 4 car garage. He already has radiant heat and I think even though he has little interest that it would be stupid to not heat the slab or at least not have the option to in the future. The closest corner of the garage is about 70 feet from the pair of boilers in the basement. The garage measures roughly 24x60. Any thoughts as to how you would go about it and what I would have to do to the control system?

 

[EffectaBoilerUser (USA)]

I agree with you.

I would at least put the pex tubing in the floor for future use. Based on the dimensions you give you should have approx. 5 zones at 288' each for the 1440 sq. ft. floor (the rule of thumb is 250-300' max pex tubing per zone-any longer and the water gets too cold by the time its at the end of the pex loop).

You can control it using a 6 zone manifold that gets its water from the current boilers in the basement.

The other item you don't want to forget is to put foam insulation under the concrete floor before you pour the cement (usually 2" of foam).

Any other questions please let us know.

Mr. Effecta

 

[lawandorder]

i did that with our garage a few years ago havent hooked it up yet beacause the garage still isnt insulated yet we have three loops of 290 ft each with a manifold in the boiler room off of the garage

 

[SolarAndWood]

Thanks Mr E, and nice looking websites. The inside of the house where the garage joins is a crawl space with less than ideal access. Is there any downside to putting the manifold in the garage? I assume the manifold would be a dumb system and the entire garage is either on or off?

 

[SolarAndWood]

i did that with our garage a few years ago havent hooked it up yet beacause the garage still isnt insulated yet we have three loops of 290 ft each with a manifold in the boiler room off of the garage

That is my thinking as well, get it in and have the option later.

 

[btuser]

What's the fuel source and what would it cost to heat the slab? Is there conditioned space above the garage or is it just a garage? My thought is how much does it cost to heat a garage, and to add that to the cost of the tubing + insulation that may or may not ever get used. I'm guessing 3 grand at the minimum to insulate and run the pex? If the garage is going to be heated 24/7 regardless then its probably cheaper in the long run to heat the slab. Expensive toy cars would be worth it. However, if its just going to be there so someone can work in comfort a couple times in the Winter then I'd have a hard time paying for it.

 

[SolarAndWood]

Just a garage and it will never be worked in while he owns it. We see extended periods below freezing. My thought was to keep it warm enough that the crap melts off the cars and his expensive toy car never freezes. I figure foam under the slab is a good idea anyway and we are going to use the same amount of mesh. So, I think it comes down to 1500' of pex, ties and a day to lay it out before the pour. As for how much heating oil it will take, he has a 5000 gallon tank and its not because he likes to be a few years ahead.

 

[DaveBP]

This question of whether to insulate and install PEX tubing in an upcoming slab pops up all the time here.

I don't think any slab in the northeast states should be poured without insulation and vapor barrier, even if you know for absolute certain that it will never be heated.

1" extruded styrofoam will keep the slab from getting damp from condensation when you have humid weather in the summer and every rainstorm when its warm. A dry slab will stop everything sitting on the slab from getting rusty, mildewed and "dry rotted".

To me the budget comparison is between vapor barrier and 1" T&G styrofoam (of whichever brand) for an unheated slab against one more inch of foam and the cost of the tubing.

 

[SolarAndWood]

Thanks Dave, that is a great way to present it to him.

 

[lawandorder]

Dave. We did that when we built 7 years ago and everyone thought we were crazy. We insulated the floor with the vapor bariier before the concrete was poured because we knew we would be finishing the basement and didnt want to deal with moisture and it is extremely dry, no moisture, odor etc....

 

[hedge wood]

When I build my shop 8 years ago no one around here was doing slab heat but we put the insulation and pex in the slab any way and had a hard time finding someone that would pour the concrete over the pex. Six years later I finally put a wood boiler in and hooked up the slab up and I just love it, way better than the furnace I used for six years in the shop. Know every one is doing slab heat in our area. Tell him to spend the money on the pex and insulation if he never uses it the next guy might and that would be a selling point to the place.

 

[SolarAndWood]

Its a go. So, vapor barrier and 2" of foam board? Any recommendations on slab height, mix, etc? The calculator at Pex Supply said 1600 - 2100 ft of 1/2 inch. Sound right?

 

[woodsmaster]

If the garage is only for cars 4" would be thick enough. I would use a 6 bag mix. With pex, foamboard, and manifold I would think you will have around $1700 in material. I recomend doing a pressure check before the pour
and have pressure in the lines during the pour with a couple couplers on hand just in case of a leak. Use the square panel mesh and not the rolled stuff. Theyalso make 1" chairs for the mesh to sit on that work nice.

 

[SolarAndWood]

Thanks for the pic. If I go 2", I'll have 2K in the foam alone. Then about ~$750 in pex, manifold, misc stuff for hanging. I told him 3K and an extra day to lay it out over what it would have taken without it. The 3K would be offset by about $750 if we at least did 1/2" anyway.

 

[woodsmaster]

Foam went up some since I bought mine in the spring. I give $21.00 a sheet. May want to check home depot prices, they were the cheapest when I did mine.

 

[woodsmaster]

even at $29 a sheet for 2" foam ( the current price around here) plus 7% sales tax that comes to around $1400.00 for foam.

 

[SolarAndWood]

Foam went up some since I bought mine in the spring. I give $21.00 a sheet. May want to check home depot prices, they were the cheapest when I did mine.

$40.69 a sheet at Home Depot, checked yesterday. Looks like it is up 50% since I bought a couple skids of 1" for the exterior of my house this spring. Most building supplies seem to have gone up significantly over the last few months.

 

[woodsmaster]

Just checked Menards $26.57 Almost worth a drive to Ohio lol

 

[SolarAndWood]

Ha, a boat trip down the Erie and across Erie to Sandusky would be a great trip.

 

[ewdudley]

Be sure to check 84 Lumber and Erie Materials.

 

[SolarAndWood]

I'll shop it around before I buy, I use HD for estimating purposes. Your project looks great by the way.

 

[rkusek]

[del]]wow $40 bucks seems outrageous. must have gone up. Menards seem to sell 2 grades of 2" also if I remember...The lighter stuff was around $17-18 and then heavier designed to be buried (they told me) was about $20-21 and never seemed to go on sale. Ulimately, I decided even $20 would cost me too much for my 30x60 building especially when I could not find a concrete finisher who knew what I was talking about or had ever poured a radiant floor. Fortunately, with my R19 walls and R38 ceiling the shop heats very easily with a homemade air heat exchanger. Radiant is still the way to go however if you can do it.[/del]

 

[rkusek]

wow $40 bucks seems outrageous. must have gone up. Menards seem to sell 2 grades of 2" also if I remember...The lighter stuff was around $17-18 and then heavier designed to be buried (they told me) was about $20-21 and never seemed to go on sale. Ulimately, I decided even $20 would cost me too much for my 30x60 building especially when I could not find a concrete finisher who knew what I was talking about or had ever poured a radiant floor. Fortunately, with my R19 walls and R38 ceiling the shop heats very easily with a homemade air heat exchanger. Radiant is still the way to go however if you can do it.

 

[easternbob]

solarandwind,
You might want to check out these guys, they have a warehouse right in Syr. http://www.thermalfoams.com/
I used 2" ESP foam the (1.5 pound is what they told me you need under a slab).
It's cheaper than the XPS foam but lower r-value. If you want more r's you can go with 3" and it will still be cheaper

 

[btuser]

It seems like the foam is going to kill you. I heard a rumor that a great majority of your heat loss happens near the footing, and insulating in the center of a slab is not cost effective. In the center of the slab you may only need to continue the vapor barrier.