in floor heat and cement thickness

[watglen]

I have a lot of heated floors around here in barns and shops. Houses too.

As far as the shop floor goes most of the guys on here are telling you the same thing. Dig down around the perimeter and install styrofoam board. That helps prevent the heat from escaping out around the edges of the slab.

For your kind of loads i would go heavy in the truck bay, 10" sounds about right. The rest is good at 4-6"

Under the slab i like double bubble, the foil covered bubble wrap. You should check the engineering for that stuff cuz under concrete there is an up and a down. Along with providing a heat break, it also creates an impermeable moisture barrier. Keeping the moisture from coming up through the floor helps as much as anything to create a warm dry floor. I put a minimum of super 6 poly under all concrete to keep the moisture out. Also it keeps the moisture in the slab during curing, which enhances its strength. You definitely want that.

( here is a an aside: Around here they build barns out of a product called royal wall. Its a pvc wall structure that snaps and slides together to form a hollow pvc wall. The insulation is already in the panel, you slide the rebar into voids, and vibrate the whole thing full of concrete from above. You end up with a wall that is pvc on both sides, insulated, and reinforced concrete throughout. The important part is this, because the concrete is encased in PVC it cures really really really slowly. The water stays in place for months. Try to drill a hole in the wall after that. You can destroy carbide bits like butter. Its the toughest hardest nastiest glass-like concrete you'll ever see. I've heard of test results as high as 50kpsi from a 3500psi mix.)

Long story short, you want to keep the water in the concrete as long as you can. So you need to put some kind of plastic under it. I use double bubble and tape the joints.

After that, the most important thing is rebar, lots of it. Way too many people skimp on rebar, and the is about the dumbest thing you can do. Concrete contractors hate the stuff for some reason, they never want to put it in, so they tell you not to put much in.

For your floor i would lay 2 lifts 20mm bar on 1' centers both ways minimum. I may even go to a full 1" bar under the truck bay. I would cut wood blocks 2" tall, and lift set the bottom layer on them. Use blocks or stakes to place the second layer about 3" down from the top of the slab. Tie 1/2 ipex to the bottom layer, on 1' centers around the perimeter, 2' centers everywhere else.

You should likely pump the concrete on a floor that size, it will save a lot of trouble keeping all that rebar from collapsing ect.

Under the door area, and anywhere that you have heavy traffic, dig down a bit deeper, maybe 16-18" the thicken the slab. Create a rebar beam and place it in the void. This will prevent cracking around the door area. If the floor is raised a bit (and it should be) a tracked vehicle will teeter at the threshold, and you know what happens next. The extra thickness will prevent cracking.

Depending on your drainage conditions you may or may not want 3/4 clear under the slab. If you have good drainage, you don't need it. Make sure you are virgin soil, not fill. If you have to raise the elevation, then you need it. If you use the gravel, you need a way to remove water from that layer, like a sump pump if nothing else. Also, you will want someplace to go with your sink drain or whatever, a sump pump works good for that.

Set your final elevation as high as possible, cuz in 15 years it'll be too low (for good drainage). Driveways always come up, floors always go down.

After the concrete is in and setup enough to walk on, lay super 6 on it and leave it for as long as you can. A week or more is great, the longer the better. That will help create some super tough concrete.


Sorry for the length on this post. There's lots to concrete floors. You only get one chance to screw it up.

What are you going to use for a heat source? I just installed a 250,000 btu tankless water heater in my barn, and it works great. Im really impressed with it, and i think my gas bill is going to be much nicer.


Good luck.

 

[Randy88]

Watglen, thanks for the info, I've never heard of royal wall before, I'll do some checking on the net to see for sure what its about. We are waiting for spring to pour cement for my pit and floor, my cement guy was wanting to do it but needed the big overhead door put in first, but due to structural issues we need to do more inside work first and warm weather to put the door in place due to pouring cement footings in to hold it up and its really cold here now. We worked all weekend taking out the old cement and jackhammering out three feet of frost to get down to a flat level area so we can drive skid steers around and start the insulating and closing up the walls so electrical conduit can be run.

Last year we finished up a remodeling project on my folks house and I thought that was bad enough for scheduling and changes and the scenario's that go with that, but there are a lot of knowledgable people that know about houses, remodeling old barns, theres virtually nobody that has any experience and we get conflicting answers on every issue that comes up and it gets down to nobody has any first hand experience only ideas and theories.

We are currently investigating insulation for the walls and ceiling and have asked about 30 different business's and people and have 30 completely different answers as to how to go about insulating cement foundations and cement block walls and irregular shaped wall cavities and how to venulate all this to prevent moisture problems in the future.

My kids keep telling me after its all done I should write a book about how not to remodel a barn and the adventure of sorting through all the conflicting information out there and how confusing it all is and what we should have done instead of what we did do.

As for heating we are hooking it up to an outdoor wood boiler that also heats our house, right now we have the mlkhouse heated but not insulated, we are still discussing the most cost effective way to go about that, thus, its not done yet, we are however more confused than before we started asking questions about insulation though. I was all prepared to have it spray foamed until I was told what it would cost, apparently other areas are slightly different in pricing than around here, the 20-4-50% higher ended up being 5-8 times higher than any other way and the sticker shock got me, I even asked several times if I heard it right and even made them give the quote in writing so I could see it to let it sink in before believing it. The second spray foam guy was higher so I knew it wasn't a fluke or mistake so we are back to asking questions again.

I only found one cement guy who would do rebar??? All others told me to lay down mesh and tie my infloor heat tubes to it and leave it under the concrete and pour over it?? We are going with two levels and somewhere between 12-18 on center both ways and stager the levels but we'll wait until we get started and see how it looks and comes out when we are laying the rebar at the time. I believe in rebar and a lot of it, always have, I grumble when I'm breaking out old cement thats full of rebar but the harder it is to break up the better it was for strength and burability, I'm hoping someone else can break this up someday and I'll be long dead by then and somebody else can grumble about it then.

I don't think I'll use wood blocks to prop up the rebar, because I thought it would cause a void in the cement so we are thinking about the plastic feet, am still looking for metal benches but haven't found any yet, I was hoping to find something to hold up the lowest layer and then between the layers as to not have a plastic void all the way to the insulation with every bench used, maybe its just my way of thinking but a void that goes from the insulation to 3/4 way up in the cement and as many as it would take would have to have detramental effects but maybe not. We discussed welding it all together but didn't know how and get the insulation under it and vapor barrior as well. We have looked into the formed layered mesh or whatever its called and putting more rebar in that but haven't got that far yet, we have too many problems to solve before those are here.

We are open to any input on any topic because right now we couldn't get any more confused and practical knowledge and experience is way better than than any theory or unproven or untried idea. I'm not really a drinking person but if I ever get this done and working and we have heat and can work in the warmth and not the cold I think I'll have multiple strong drinks to celebrate provided I can afford them by the time I'm done.

 

[norite]

I don't think I'll use wood blocks to prop up the rebar, because I thought it would cause a void in the cement so we are thinking about the plastic feet, am still looking for metal benches but haven't found any yet, I was hoping to find something to hold up the lowest layer and then between the layers as to not have a plastic void all the way to the insulation with every bench used

The rebar supplier should have little wire supports called chairs to hold up the rebar above your insulation or failing that you could use a concrete brick as a spacer.

 

[watglen]

If you can find those little cement blocks they are ideal. I have only seen those once, but have no idea where to find them.


If you put this much thought into it's going to be great when its done for sure.


Actually, you should be posting pics as you go.

 

[Randy88]

I've never heard or seen any concrete bricks before, the chairs are made of plastic and we have been using them in what we've done so far, I was just worried how much that many plastic chairs would weaken the concrete, there would be a void were the support was or a place for it to crack and as many as it would take I thought it would be a lot of places to crack because it would take literally thousands of them to hold up two levels of rebar spaced that close together, maybe not but thats what I thought, correct me if I'm wrong though, never seen the wire supports, I asked my supplier and he had only plastic ones.

As for pictures, well I'm not that tech savvy I have no idea how to do that let alone anything about camera's or whats needed to do that, I've read about how to do it but had no idea what anything they wrote meant or were referring to, thus far I've been able to handle posts and thats about it.

 

[RobVG]

Just a warning, I'd avoid "Munchkin" boilers. We've had several problems with ours. Igniters , thermocouples plugged drain and such. Service tech said they were supposed to be really good when they came out but they've have turned out to be job security for him. It is under warranty and we can get a complete new unit but it will be the same pos. Probably going with forced air next year.

 

[watglen]

Rob, it funny you should mention the Munchkin boiler. I actually have one of those and its been pretty trouble free. Maybe 1 service call/year. I think its around 400K BTUH. Mine heats a heating loop, so i never really shuts down.

I would buy another. In fact i almost did.

 

[RobVG]

I'm glad you've had a good experience with yours watglen.
I wouldn't have said anything if the Tech hadn't mentioned the problems he was seeing.

 

[norite]

I only found one cement guy who would do rebar??? All others told me to lay down mesh and tie my infloor heat tubes to it and leave it under the concrete and pour over it?? We are going with two levels and somewhere between 12-18 on center both ways and stager the levels but we'll wait until we get started and see how it looks and comes out when we are laying the rebar at the time.

I would check with the PEX tubing supplier, you may need to put mesh down anyway to secure your tubing so it doesn't float when poured. 12 -18 inches may be too far apart. I would still put the rebar as you planned.

 

[dsergison]

(i just saw norite already covered this)

Heat does not rise.
hotter, less dense, expanded air rises.
heat just radiates from, or conducts through objects.

there wont be any air, or any warmer gas rising through your concrete.
thus the heat will have no prefference to go "up" through it.

if your heating element is on the bottom of an un insulated 12" slab. it will need to heat a ton of concrete above, and even more earth below. this will really not be efficient. the earth is one hell of a big heat sink.

if you insulate it you wil eventually be able to heat the entire 12" slab. it wont heat up fast but it wont cool fast either. this may or may not be acceptible. if you like it heated all the time, great. if you wanted to save energy by turing it off at night..... not so great because it will take all day to warm up again.

one might assume you wish to use hot water heat because you have cheap acces to somehitng to burn? radiators and a fan would serve you better perhaps.

 

[Randy88]

We have free access to plenty of wood to use as a heat source, we are wanting to leave it warm from fall till spring pretty constant, we are also going to put in some hot water radiators with blowers behind them so when we fill the shop with really cold machines we can kick them on and help it to warm things up quicker, I've talked to several and about half say to do it the other half say forget it, I've located some takeout units at a discounted price for the radiator/blower units so I figured why not install them. If all esle fails they are a second backup source in case something would happen to the lines in the floor or a section of them anyhow.

From all I've read and heard anything with hot air blown heating causes the heat to rise to the ceiling area and it'll be like 100 up at the celing and almost freezing at the floor, thats why we wanted to go with in floor heat instead, eveyone tells me its more consistant between the floor and ceiling as far as temperature differences.

But armed with the knowledge of heating the cement floor does it really matter where in the cement the tubes are located? I thought about a third the way up from the bottom inbedded in the cement rather than under the cement completely, or is it better under it or even in the middle of the slab? Anyone want to venture forth an opinion on that? I figured it would eventually heat the entire slab no matter where the heating tubes were located and if its insulated under it the heat should rise up, but if they were in the center of the slab would the heat rise first or go down first and then rise? I've been told each way, its more efficient to have them under it because then the heat only has to go up, if its in the middle it has to go down and then up again? Or was the heating specialist giving me a lne of bs and it makes no difference at all?

 

[Auctioneerhere]

I have a 5000 sq ft shop with radiant floor heat. I put all the tubing on the rebar & it is in a 5 inch slab w/ each door having about 9-12 inches on concrete on the lip tapering back to 5 in. thick.

On the sides of the building we ran the 4 ft board laid flat around the outside edge, If I remember right we also put plastic down under the whole pour.

To each his own, but I would not have the tubing in the gravel below, I would put it in the pour up 2 in. from the bottom. Make sure when you pour, to have your tubing pressurized with air. this way if you do have a leak {shovel or something cutting a line} you know about it.

Did this 12 years ago. Have not had one problem since. I installed all the tubing & manifolds myself.

 

[dsergison]

please undo your false notion about heat rising. and please dont take offense at my saying that.

warm air will rise, yes. that's called convection. it ONLY applies to gasses or fluids which change density and can flow. it does not matter HOW the air gets warmed. floor or radiators, your choice. no difference.

here is the deal. your are pretty much correct about it not mattering where you heat the slab, as long as it is insulated underneath. the slab is a pretty fair CONDUCTOR of heat and has a huge mass. it would not matter where the heating loop is installed it will all heat up more or less uniformly and quite slowly.

eventually your warm slab top surface is going to transfer heat into the soles of you feet by conduction. It will also radiate heat by infared radiation, and it will warm up the air in contact with it by conduction.

fans are your freind. people put big ceiling fans in homes, offices, buildings etc... to stir up the air specifically to avoid having a warm air layer on the ceiling doing no good.

the heat in you slab will not travel up/down/sideways from the coils. it will travel AWAY from the coils towards whatever area is colder. If you insulate below it, great, the entre slab will warm up and do some real heating of your building. If you dont insulate under it your going to be heating up mostly mother earth because conduction through the earth is more efficient than radiating to the air.

I will try to find some #'s to support this and put some real quantity to it. -call it my physics homework

 

[dsergison]

i would like to add, i prefer to work near those infared heaters. even if a door is open and you are hit with cold draft, the heaters keep you warm because they are radiating heat directly on you. unless your under a machine where the "sun don't shine" then you get no warmth from the heater.
i dont like sweaty feet. i dont think i would like floor heat much,

i'm hard to please.

 

[norite]

i would like to add, i prefer to work near those infared heaters. even if a door is open and you are hit with cold draft, the heaters keep you warm because they are radiating heat directly on you. unless your under a machine where the "sun don't shine" then you get no warmth from the heater.
i dont like sweaty feet. i dont think i would like floor heat much,

i'm hard to please.

Radiant infrared heaters use less gas than forced air heaters but are less comfortable because they don't warm up the air and as you said underneath a vehicle is going to be cold and wet. The reason we heat garages is to bring in equipment to melt the ice off them and to work on them, often underneath them. This is where in floor heat is superior to any other heating system IMHO.

If my feet are warm I can put up with the cold, if my feet are cold I'm cold all over.

 

[Randy88]

I'd have to agree with norite on this one, I've worked under equipment for the last 25years in front of a space heater and I'm beyond tired of it, I want something to warm the floor up so the underside of the machine is warm when I'm working on it instead of my backside being cooked and the front side and feet and hands freezing, I am putting in the hot water forced air heaters because they are cheap and can be hooked up to my existing hot water lines, they are only for secondary heat and for emergency situations or to speed up the warmng process.

The cold feet statment says it all, I"m the same way, when my feet are cold its time to quit or look for a warm area to get back warmed up.