Shop Floor Radiant Heat ???

I am building a 30x40 pole barn/shop. I am considering adding a PEX (any better choices?) loop or 2 to the slab in case I want to add a boiler in the future for heating. I am in SW MI so we see some cold days in the winter.

Right now I am looking at 2" of foam board underneath and along the perimeter/grade board. It sounds like a lot of the heat loss form this type of heat edge loss at the slab. Thinking of 6" slab so less chance of cracking and less chance of hitting a loop if adding anchors.

Looking for tips, thoughts, better ways to do this whole process? If you did this did you like it?

Thanks,

 

Been in on a few designs, here’s what I’ve learned:

More/closer loops along the perimeter. Nothing anywhere near where you think you might want to anchor anything into the floor, unless you set the anchors when you pour.

Do NOT ever let that slab go cold. The BTU’s it will take to bring that thing back to temp will bankrupt third world nations.

Consider a secondary heat source to bring the space up to a higher working temp than you keep the floor.

 

Did it in my basement and garage. You have to use a special Pex with an oxygen barrier, not much more expensive than regular pex.

When I had it all laid up I made a blueprint on graph paper with measurements from hard points so I can locate in the future to avoid hitting a line if I drill in.

300 foot circuits 12 inches apart. 2" foam down then wire mesh sheets to secure the tubing to. Pretty easy but takes a bit of time. Get PVC sweeps to run the tubing up so when they pour the Pex is protected and it's a nice clean installed look.

 

Pressure test it BEFORE you pour the crete.....

I know a guy down the road who put a system under his driveway to melt the snow. 2 loops, and only 1 works....Pretty expensive fix at this point.

Other wise go for it. I know a few people who have it either in their houses or shops, and it's nice. Nobody has a bad word to say about it.

 

Neighbor did his 28’X40’X10’ stick-built with hot water heated floor. He used 4” foam under the floor and heats with a 40gal water heater. But, he has at least a couple hundred feet of pex in the floor. IIRC, his runs are ~2’ spacing and there are 8-10 runs. I know he limited his pex length per run to roughly the same length, each. I watched the Super Bowl laying on the floor, one year, with the thermostat set at 60°F. It’s the most comfortable shop I’ve ever been in. He claims ~$30/mo to heat it.

A couple I know were looking at a pole-style, commercial building for their business. I brought them over to my neighbor’s on a ~15°F day, opened both overhead doors to let the warmth escape, closed them, and the place was toasty in ~10min. They were sold. Their pole-style building is 40’X70’X10’ and heated by a tankless, in 2 zones. The place is heated 24/7, with the entire place lit 6 days/wk, during normal business hours, and customers constantly in/out. Their highest utility bill has been $175. They’re completely blown away, because their previous building was ~2/3 the square footage and were paying almost 4X as much in the winter, trying to heat an uninsulated block building that always felt freezing cold. It had two furnaces, for 2 zones, and both furnaces ran all the time.

Hot water heat in the floor is the only way to go.

 

My neighbor drove 2pcs of rebar into the ground and mounted a 2”X4” to the rebar, close to the height of his floor, as a place to affix his stubs to. Once the concrete cured, he cut and ground the rebar flush with the floor. His runs ended up looking really nice.

 

For sure pressure test. You should actually pour with the system pressurised to around 50-60 PSI as it helps hold the shape of the Pex and if someone hits a loop while the cement is wet you'll know it and can act fast to repair it (have some extra Pex and couplers on site when the cement is being put down)

 

Just finished a 50x60 here at home. Try to keep loops somewhat equal and no longer than about 300ft. Did 6in spacing at walls, and 1ft through rest of shop. 3000ft of Uponor 1/2" tubing. Use an preformed insulation that includes the channels for the pipe to save a TON of time doing the install. I used Hot Rock Panels which is local here. Find someone with a pipe roller/carrier thingy that allows you to just unroll the tubing off. Installing pipe only took maybe 1.5hrs.

 

The important stuff regarding loops has pretty much been covered. I've installed miles of radiant tubing and have never seen a leak. Not sure why others have had issues.

@ChemGuy what kind of heat source are you using?

 

When you say wire mesh, like a second special wire mesh or the normal wire mesh you use to reinforce slabs?


Any special connectors needed or standard PEX type?

I will probably use Propane and a small water heater or boiler. I am also considering an outdoor wood boiler for the house and running lines for the shop as well.
Not looking to make it tropical in there....maybe keep the slab ~50F or so. And add in some warm air heat for when I want to be out there all day.

I know its not a lot of sq ft but would 2 loops make more sense? I was thinking of covering the whole floor with each loop each loop rather than zones. That way if one loop dies I still have some heat in the whole slab. Or should I do 3-4 zones and maybe leave 1-2 dormant as back ups? I see an online place selling 1000' of tube for this for like ~$220...so a little cost now for extra tube isnt a big deal.

Thanks,

 

I'm going thru this now with a 32' x70' pole barn. I'm planning on using 3/4" pex in a 5" slab, heat source will be the same outdoor wood boiler I use to heat my house, I bought a 75 gal boilermate type tank that uses a 1 1/4" heating coil that the outdoor boiler connects and will use the onboard aquastat to control the tank temp. The 75 gals will be plumbed into the infloor heat with a 30% glycol mix. For insulation I am going to use a slab shield with 2" foam on the perimeter, I did this same insulation in my house and it's worked well. I hope to start framing in a week.

 

Nice.

What brand/model boiler do you use? Any issues?

 

It's a Central Boiler Classic pre-EPA version, holds 400 gals, it has multiple outputs and I just trenched the insulated pipes in last week.
I bought the boiler used but the previous owner took good care of it just got tired of hauling wood. I keep an eye on the chemical concentration in the water and test it twice a year to be sure it's in the correct range (it usually is), I don't run it year round so when it's off I fill it so it overflows the top to minimize rust, since they operate at 0 psi when I restart it in the fall the water expansion just overflows the top to self level. I change the door gasket every once in a while. The damper solenoids can take a shit sometimes so I keep an extra on hand, they always seem to go when it's 0*F out and the wind is blowing.

For your floor insulation I've had good results with the roll out slab shield, 2" foam is better but you have to watch which ones you get as there are 3 versions I believe with different compressive load ratings. Also look on Craigslist for poly-iso sheets from roof tear offs. I used this at my in-laws but the source dried up for some reason. We got 1.5" 4x8 sheets for $8/ea

 

The purpose of multiple, shorter runs is because of heat-loss out of the water over the course of the run. If you do really long runs, the temperature drop from manifold-to-manifold is going to be huge. You don’t want that, because at the feed point the floor will be warm and at the return the floor will be cold. Shorter runs are better for temperature stability.

Your manifold setup will need valves on every run. This would allow you to have zones in your pex layout if you wanted, but also, can allow disabling should you drill the floor and hit a run, find you didn’t need as much heating capacity as you originally thought, or whatever.

In a single-room building like a shop, zones aren’t important. But, in the case of the aforementioned couple, they have an area of their building that must be kept cooler than the main space. For them, a separate zone was essential.

You say you want to maintain ~50°F floor temperature, but, that’s not how these systems work. If you set your thermostat at 50°F, your floor temp will probably be 70°F or more, because the water temperature is more than your air temperature. 60°F on my neighbor’s thermostat feels like 75°F, because the floor is warmer than the air and the heat is radiating upward. Laying on the floor, working under a vehicle, can be too warm, depending on outside temperature. He’ll just turn off the system to disable the thermostat, then, crack an overhead door to get cool air coming across the floor where we’re working.

If you decide to go with a heated floor, initially, you’re going to have to mess with the system, until you find what temperature works best for your needs. But, once you figure that out, it’s a “leave it alone” deal. When the cold season starts rolling in, get the system up and going to take advantage of the existing warmth in the floor, then, leave it alone for the season. You can’t turn it on when you’re going to be out there, then, turn it off when you leave. The system will/can take a day or two to stabilize temperature.

 

Even wall mounted radiant is excellent, and less expensive.... heats the floor also when exposed. Had it at my last shop, and you could open the doors when it`s ass cold outside, and as soon as you close them, you`re warm...and heats the floor really well.

Less initail cost, fewer potential problems. My techs loved it.

 

If you're sticking with gas fired, buy a proper boiler. Guys frequently try to use tankless water heaters, but it's a bad idea. They're generally over 100k BTU, so it seems like a good idea on paper. Trouble is, a tankless water heater is designed to produce a massive delta T (~75 degrees) at very low flow rates (~2-3 GPM). A boiler is designed to produce low delta T (~20 degrees) at massive flow rates, ~10-15 GPM.

Your heating output is determined by flow, not BTU output, so your 140,000 BTU water heater is only capable of producing about 30,000 BTUs of actual heat to the building.

300' is the absolute maximum loop length and I actually like to keep perimeter loops even shorter. You can only move 13000 BTUs through 1/2" pex, and once the heat is used up, it's gone. Better way too short than even a little too long.

If you go with a wood boiler, make sure you separate the wood boiler loop from the system loop with a heat exchanger. Wood boilers are open systems, so your indoor boiler will disintegrate if they share water.

 

The mesh was pretty light gauge 5x10 foot sheets, normal stuff for reinforcing slabs but needed also to tie the PEX down. Use standard PEX type fittings. If the guys doing the concrete are good and have done this, they will pour, then pick the mesh and pull it up a couple inches so the PEX sits in the middle of the slab vs sitting on the bottom.

I used the Owens Corning Foamular 150 R10 foam board (4x8 - 2" thick) for the insulation. Home Depot had it at the best price due to quantity and the load rating is correct. Plus if you have some left over easy to take back.

I got supplies from https://www.radiantec.com - they will build your manifolds for you if you don't want to do it yourself. They will also blueprint it for you if you and quote the whole thing for materials, but your not committed to buy. It will give you a nice layout for tubing. I ended up buying the PEX and manifolds there as they did all the engineering for me but sourced the rest sourced locally. They are a great resource and have tons of manuals and guides on their site. Check em out.

Fill with glycol/antifreeze mixture so if you ever let it sit it wont freeze and bust anything.

 

Ive heard some people use he thermostat in the slab. Thats what i was planning to do. Rather than
thermostat the air.

Anyone do that?

 

I think you'd be disappointed going this route but you could try using this
https://www.supplyhouse.com/Johnson...MIpbeI2urt6gIVj4TICh3cywDBEAQYAiABEgLU0_D_BwE
If it doesn't work like you expect you could remove/replace the element and relocate it so it's sensing air temp
I use this in my current shop with a Reznor propane heater
Edit: you need to get a 24vac wall wort to run it or have some other 24vac source
https://www.amazon.com/Transformer-...24v+plug+in+transformer&qid=1595867258&sr=8-5

 

OK. I did see some people using/recommending a slab and air sensor. My idea was to adjust the slab temp to where i like the temp and the $$ and leave it. As its a shop Im using occasionally or even daily for a couple hours I didnt want to keep it 75F all day. I was hoping I can keep the slab around 50-55 F and the air would be tolerable and then add in forced air for when i want to warm up an and work there if needed. Or possibly turn it up a couple days ahead when i know Im going to be in there all weekend.