Radiant Floor Heat

Just got a 36x48 pole barn put up to use as a shop/garage and was considering installing radiant heat in the floor. The floor will be 5" thick and saw cut into 12'x12' squares. I've been doing a bit of reading and have gotten conflicting views about putting insulation under the slab. Some say you need it, some say you don't, what do you think? Most seem to use the blue or pink board insulation anywhere from 1 to 2 inch, with the poly vapor barrier under the insulation. My other concern is how much will that insulation compress with the weight of the concrete on top? I don't want the floor to start cracking when I bring in a 33,000 lb truck and start jacking it up. I will most likely also be installing a wood stove, whether I install the radiant heat or not.

I have a 5" floor with double bubble under it. I would use 2" and double bubble next time. The bubble is aluminum on one side so it provides insulation plus vapor barrier. I would not worry about the weight on the styrofoam, there are thousands of installations out there with it.

FLOOR HEAT IS THE BEST WAY TO KEEP WARM AND COMFORTABLE../ and weel worth the investment to do it rite ..
and insulate with the best ,,.do your homework ,, i promise you will be glad you put heat in the floor ,, the ambient temp in your building may only be 45 degrees , but you will always be warm ,, also when opening the bigg doors to move stuff in and out ,, you will regain heat so much faster , in a floor heated shop

Mine is installed without insulation under it and I regret it.
It works perfectly, no problems as far as heating or cracking.
I just think the insulation would have saved me quite a bit of
money in heating costs.
Insulation not just under it, but around it on the outside as a barrier.
Mine has been in place for 11 years. No problems, just hurts the wallet!

Do not skimp on under floor insulation. There are different grades of foam insulation. 15#, 25#, and another heavier one too, can't think of the rating now. You need 25# under the floor. Make sure you know which foam you are getting prices on. Most people don't know there is a difference.

Several things to do and not to do:

1)Buy the 5000 lbs mix concrete. It will cost just a little more but is 40% stronger than the normal 3000-3500 lbs mix.

2) Use fiber in the concrete AND rebar.

3) Have the gravel under the concrete well compacted. Not one of those little walk behind vibration units either. I used a end loader with a full bucket of gravel. I rolled every square inch with the front tires to pack it solid. If the gravel is dry then you will need to wet it down some as well.

4) DO NOT cut seems in the concrete if you are using hot water floor heat. If you do then just go ahead and cut the lines before you put them in. They will leak after a few years at every sawed joint. With good solid fill and good quality concrete and rebar every two feet on the square, you will not have cracks. My main shop floor is 48 x 60. It is one single pour and does not have a single crack after 15 years.

5)Put at least 2 inches of insulation under the pipes. It will pay back over time. The pressure of the floor is spread over the entire surface of the insulation board. It will not crush.

Caution!!! Dig footers down several feet around the out side of the building. I would really go down to the frost line myself. Mine are dug four feet here in Iowa. The need for footers it to stop rodents from getting to the insulation board. Buddy put his in using a floating slab. The floor cracked in about three years. The one end sank. We had to break it out. Rats had chewed all of the board up.

6) Use a vapor barrier. Just a good grade of heavy plastic sheeting is good enough. Put it under the insulation board. I used 10 mil under mine.

7) Five inches of concrete is on the light side for a shop floor. Remember this will be for the rest of your life. So a few dollars for extra concrete will be cheap spread over many years. I would go 6 at the minimum and 8 is better. If you can only afford 5 then make sure and have good thick footers at each door so the equipment will not break the edge pulling across it.

The floor is the most important thing in a shop. If it is not correct then the rest of the shop is effected. Also something I did on my shop. It has two inches of fall in the 60 foot length. I hate floor drains. So I just sloped the whole floor out the door. Never have had any issues even washing things in the shop. Just open the door a inch and let the water run out. My doors faces south so the water runs off the approach slab and usually melts of without causing any problems.

For a small shop like that I would go for one single Reznor propane unit hanging, and facing the doors. Wire it up with a digital thermostat.
40 degrees overnight and when not in use. Wick it up to 59 for shop use. It will be ready before you get the job started.
What kind of insulation do you have?Walls, ceiling? Doors?
And it would help to know where in the world you are?

Foil backed bubble is what the company I bought the PEX from recommended, they told me you must have a barrier between the concrete and the earth or you are heating the ground too.40X60X16

I'm in Southern New Jersey, close to the Delaware Bay. The doors are insulated and I have insulation under the roof and, so far, have one wall insulated. The rest of the walls will be done between now and next winter with fiberglass batt. I'm also going to add insulation to the bottom of the trusses

JD seller is right. I built my shop in Wi. just like he said. The insulation you use under the concrete is POLYSTYRENE. It's the kind that snaps when you bend it. I would not put any drain in the floor. I used to put snow and ice covered vehicles in my shop at night and in the morning the vehicle would be dry and so would the floor. My son put a 2'by 12' X8" deep pit and floor drain in his and all he has is a pit full of dirt no water, and a place he can't ride a creeper over. My new garage floor here in NY is poured over the old cracked and rough 1932 concrete with bubble wrap between the new and old. 22' X 33' and I heat it with a 28 gallon water heater.

I agree with almost all of JD's points except I used a 6 bag mix on the concrete and a 6 inch slab thickness. Reinforcing is important. After many years in the concrete business, concrete poured at a depth of 6" will crack, that is why in factory floors there "control joints" cut for usually every 400 sq. ft and some type of expansion joint placed also. Do NOT saw cut a floor with radiant heat. If you nick one pipe....lots of work and headaches. The control joints should be cut with a jointer tool when finishing the floor. The reinforcing will take care of the floor "moving" at the control joints.
Use at least 6x6 mesh 8 gauge or 1/2" re-rod on 1.0' centers each way.
My barn floor is 62'X42' and is a dream to work on. I also have a center trench drain connected to double trap sump pits to retard oil leaks.(Haven't had one yet)As also was said...don't try to save on the floor or the insulation and you will be a happy camper for many years to come.
Larry NEIL

If you like wet cold floors then go with a hanging heater. The in floor heat is the best investment I have made in any of my shops. I have built three.

The first was just a remodeled hog barn. I heat it with hanging heaters. If you pulled in a vehicle that was covered in snow the next morning the vehicle would be nice and dry but the floor would have water puddles on it until you pushed the water out the door.

The second I made two big mistakes in: 1) The ceiling was not tall enough. I went 14 foot and that made my doors be 13 foot and they where not all enough for some combines nor a ceiling crane. Second I tried to heat it with a wood stove with propane back up. Still had the cold floor problem and wasted time in messing with the stove. Wood stoves cost you money in many ways. One of them being the time it takes to fire them and remove the ashes etc. The time that I could have been spending generating income.

The one I have now I put in floor heat and made it 16 foot tall at the walls and 18 foot in the middle. It makes working in the winter so much easier. My heating cost are down as well. The heat is much more even and you don't have as hot of ceilings. The only mistake in this one is the main door is not big enough. I put in a 20 foot door and I should have went with a thirty.

The most important thing is to insulate around the perimeter. If you don't want to put foam under the floor due to cost and/or weight concerns, trench around the perimeter and put 2 inch foam down at least two feet. Even if you insulate under the slab, you'll want to put 2 inch insulation inside the skirt boards. (Miter the upper edge of the insulation and you'll be able to trowel your concrete over the insulation.)

Standard polystyrene insulation like you'll find at Home Depot is only 15 psi compressive strength. For slabs, you should try to find at least 40 psi. There are even higher strength planks; Dow Corning lists 60 and 100 psi versions, although I imagine they'll be difficult to obtain in the small quantity you need.

What I did with my slab to save cost was to only pour it four inches thick around the perimeter and six inches thick in the middle, using two inch thick insulation for the outer six feet and one inch inside. Most of your heat loss will be around the perimeter, and typically you won't be parking big vehicles along the walls. (The doorway was left six inches thick.)

To avoid breaking your water lines, figure out in advance where you'll cut your slab, and sheath the PEX at those points so the slab can move without cutting the tubing. I used a split corrugated tubing for this purpose.

Reinforcement is a must. I used wire mesh, but if I was to do it again I'd probably use rebar. The mesh is a hassle because you have to pull it up as you pour.

I purchased my PEX supplies from Mountain View Supply. This was several years ago, prices and service were good then.
Mountain View Supply

Hangar 17 at JFK has radiant floor heat. Great system because when the doors are opened to roll aircraft in or out a tremendous amount of heat is lost but the recovery time with warm floors is practically instantaneous. Mechanics always complained about the floors being too hot, though.

Another thing while planning. In my shop I have an inner room 16x22x10 where I do most of my more time consuming work. I keep it at 50 degrees and bump it up a little when I am in there. The outer part 40x50x17 is kept at about 40 degrees by the heat escaping from the inner room. I heat with a little catalytic propane unit for very little money.

All good ideas but the concrete still won't be worth a darn if its poured too wet nothing more than a 4" slump and have a certified tester there to call the shots.Adding Superplastersizer will make the concrete more workable and keep the finisher happy.

First off the rebar goes over the tubing and yes you need to saw cut the floor but only an inch deep, if you dont the floor will crack where it wants and then the tubing will leak. 5000lbs mix????? Go with 6500 at a min. Fibermesh is a waste of time, that has been proven

Insulate around and UNDER the floor. You want to heat the floor, not the ground underneath it.

I was a vice president of the Michigan Radiant Panel Association, and represented Slant Fin in Michigan. Insulation on the edge of the slab and under the slab is essential. I heard some horror stories when no insulation was used in a radiant installation. One do-it-youselfer in the upper peninsula of Mich found out he was heating the world when the ground 3 feet all around his home never froze in the winter and he had $300 a month LP bills (12 yrs ago). There have been studies that have found up to 50% savings in the heat bill in certain instances. Look at the picture posted of the even heating, with scorched air, you are heating the ceiling and upper walls and losing many BTU"s that way. I see many of you have found out how excellent radiant heat is. There is no more comfy or frugal way to heat almost anything. More info is available at Dan Holohan"s website, heatinghelp.com. Dan has a book there available written for the layperson on radiant heat and other books on hot water and steam boilers and heating. This type of heat can be retrofitted to many structures as well.

Floor of my 40x72 was poured to slope to drains in the center of two bays. (1/4 distance from each end wall). You can pour a bucket of water in any corner and it runs to the drain. No wet floors.

How do you get 6500lb concrete? Cement won't do it
and would be borderline adding Celica Fume.Fiber isn't any good? Fellow I think you need to stop BSing and learn something about concrete.

I would put in a wood boiler before I put in a wood stove. The floor will warm up and cool down real slow. It is best to get your heat from there. You could heat the floor with wood and have other as a backup.

Sorry 6500 psi concrete.

Install white steel ceiling and then blow in insulation. I am in SD and I use just 350 gals propane to heat the entire shop for the winter.