I'm in the process of converting an old barn into a heated shop and the old milk house into an office, we have the new rafters and false ceiling installed and the milk house is done except for the new ceiling and insulating, now for the tough questions, anybody use in floor heat in their shop where your putting in heavy equipment, I was thinking about 8 inches of cement in the floor but the cement guys are telling me 10-12 and not to put down the two inch insulation board under the cement period, they claim it'll crush due to the weight and cause the floor to crack over time and to just tie the heat tubes to rebar and lay it down first so its under the cement, the second problem is they are also telling me that in floor heat won't work good in cement that thick. I'm slightly confused on all this, first everyone recommends to insulate under the cement and thats what we did in the milk house but is it really needed if I only heat the shop to around 50-55 degrees, thats the temp of the ground anyhow inside a building thats heated so why would heat be lost into the ground if its already 50 some degrees and heat rises doesn't it? The next part of my question is why wouldn't the heat make it up through 10-12 inches of cement if heat rises? it makes it through 6 inches just fine, why not thicker? Would the cement and weight of what your running on the floor crush the 2 inch thick foam board under the cement? Is that thickness needed for heavy equipment? I plan on putting in a service pit to work on and service equipment and and want to make it all heavy enough to back loaded lowboys in and right now we weigh in at 110,000 lbs so I want to make it good enough to not worry about cracking the cement, my largest excavator weighs in at 60,000 and the cement people are worried about the vibration and weight in a short area. I don't want overkill but not to undersize it either. Someone out there has got to have experience with this and basically none of the cement guys have done anything with heavy equipment and don't know for sure, its kinda unique and not a big demand for like houses and driveways so I understand where they are coming from as far as experience goes. Tanks in advance for any input.
I used a product called slab shield under my floors with radiant tube heat. It is a lot like bubble wrap insulation but has a foil layer as well as 2 flexible foam layers. It is only 3/8 thick and does the job. As for the concrete thickness I would think you want at least 10 inches on the main drive path with minimal stone under it. I used wire and fiberglass reinforced concrete and have not had any breakage but my weights are more like 20,000 not 110,000. I did my center section as a separate slab and went 6 inch or more on it. You could also run the radiant around the rest of the shop and not do the center where the heavy weight will be concentrated. I strongly advise sleeving the tube where it passes from slab to slab with a bigger diameter plastic conduit. This will prevent pinching the pex as the slabs shift.
Bill on the hill ...Do you like that heat ??? A sawmill near me put floor heat in there shop and i heard one of his boys say it was great till you gotta get on creeper ?? Too hot ..
I'm a GC with several years of experience in pre-engineered steel buildings for shops, warehouses, offices etc. Although not, an engineer, I've had experience. Although I didn't actually install the floor heat tubes, I did the concrete and worked with the guys who did install the tubes in a few projects. To me, as far as the floor cracking or crushing, the biggest most important thing is the base. Make SURE you have a well compacted stone base. If the base gives, the floor will give, whether it's 4" thick or 15" thick. As far as cracking, all concrete cracks. Generally it's shrinkage cracks. Typically I'll see shrinkage cracks every 25-30' across a floor slab. the best method of controlling cracks is sawed joints. Saw 1/4 of the floor thickness. (Make sure you don't saw into the heat tubes.) An ideal way to assure the slabs don't misalign at the controlled cracks is by installing bars specifically to adress that. I'd recommend a #5 or #6 bar every 2' -4' along the controlled crack point. Grease half the bar so the floor can expand. Don't grease the other half. If it were my floor, I'd start with a stone base. A minimum of 6", probably more. Then I'd have an unreinforced mud slab, maybe 4" thick. Then a layer of 1" Blue Dow board, maybe 2" since your in Iowa. Then, #3 or #4 reinforcing bars on a minimum of 24" centers in each direction. If you're really concerned, #4's on 12" centers. Tie the tubes on the rebar grid, then place a 6" floor on top of that. If you're concerned 8" thick. You never mentioned what type of machinery you have. If it's tracked machines, remember the tracked machines are designed to distribute weight. A 50,000 pound wheeled machine would stress a floor more than a 110,000 pound tracked machine. Lastly, I'll say this. A heated floor is really nice. Open the wide shop doors to bring a machine in, the cold rushes in, close the doors, and the area is instantly warm again. It really is nice...VERY nice. If you looked at all the costs involved in a heated floor, and studied the energy savings compared to a couple of unit ceiling gas fired heaters, would a heated floor really ever pay for itself? But, if it's just something you want...and can afford it That's my opinions, for what it's worth.
Randy, in 2003 I built a new 70x120 ft shop with in floor heat. The heat I used was off-peak electric. I dug down 4ft all the way around the perimeter of the building and stood 2" thick styrofoam. the material inside the building was thourghly compacted sand with a 6inch base of 3/4inch minus road gravel, the cables had been plowed into the sand to a depth of about 12 inches. I then pour 4 inches of concrete in all bays except for one heavy duty bay where 6 inches was installed. I routinely place 120000 pd, loads on this bay with no problems what so ever in the bay itself. The only problem I've had is on the apron outside the building. The D8's coming and going in the bay has broken the apron on the outside end even tho they come in on conveyor belting. I hope this helps you in your decision makeing...good luck....oh one more thing, I buryed a 300 gal. barrel outside the building with a floor drain arrangement on the inside to dump used oil in...
I have both tracked and wheeled equipment, when we have the lowboys loaded we plan on backing them in so technically we would have up to and over 110,000 on my lowboys at times and want to unhook them so we can do repairs on the equipment dead while loaded, I've had a need for that quite a few times over the years, we can get them loaded wounded but have to fix them while on the lowboy and are planning for it to happen again. My shop will only measure 30x80 but the end 20 ft. will be for tooling and shop benches so only 60 will be used to back stuff in. We were hoping to pour the floor in sections 15 ft wide at a time so we can handle the flat cement work ourselves, we plan on having two layers of rebar every 24 inches each way on center at two different levels but stager the levels so we end up with a grid of rebar ever 12 inches when viewed from above. I originally wanted to tie the tubes to the bottom set of rebar but the cement crews I've talked to about pouring the service pit walls told me not to do that because it would weaken the floor by having hollow plastic tubes imbedded in the cement, thus making a hollow void and weaken my cement, don't know if it would or not but maybe it makes sense. The cement guys I've talked to were not as worried about the rubber tired machines and weight as the tracked stuff from the vibration aspect, even if I'd back them in on rubber belts, they all claimed the vibration was way worse than any constant pressure from more concentrated weight on smooth rolling tires. That surprised me but I don't have enough experience to argue with them either, any thoughts on that aspect from anyone else? Impact, the blue board your talking about is that the foam board most use for insulation? The guys around here are telling me not to put it in because that will be the weak point that can give and actually cushion and cause the cement to give when we drive heavy stuff in. Their concern was why put down the compacted layer of rock and have a soft spongy layer between the rock and the cement, they are telling me not to put anything down for insulation and just eliminate it, one told me to put the small thin layer of the flexable insulation thats only about 1/2 inches thick, his opinion was that way you put some down and I only have 1/2 inch to compress causing fewer problems later on down the road as far as crushing it from heavy weight. I honestly don't know or have any experience with any of it, we've put it in my folks basement and garage floor but maybe a car has driven on it and nothing heavy and thats a proven design and we knew it would work. None of the cement crews I've had look at would would put much of anything down first except for the one who recommended the 1/2 inch thick stuff, they all claimed it would crush and cause the cement to give up and down over time as much as the thickness we put in and cause the cement to fail over time and buckle. Any thoughts on this, are they right or wrong, if we didn't insulate it would all the heat go down into the ground like the heating guys are saying instead of up like common sense would predict. The heating guys don't have any idea of the crushing idea the cement guys are concerned with, they only know heating and the proven practice of insulating under the cement, as they say, nobody seems to agree on anything here, the cement guys think one way the heating guys the other. The heating guys are telling me to put the heat tubes attached to the rebar and cement them in and the cement guys say no way that'll weaken the cement. None of this needs to meet any code, we're in the country so thank god I don't need to deal with inspectors too yet who would have another opinion still.
Yes, typical foundation insulation is called Dow Board. I'm not engineer, but, I've put down numerous slabs that have been engineered by a registered engineer. The new energy codes require (at least here in ky) a 2' vertical board around the perimeter just inside the footings. I'd think the requirement would be 4' vertical in Iowa. then they require a 2' wide band 1" thick around the perimeter laying horizontal just under the floor. I've installed dozens or hundreds of slabs in this manner and have NEVEr once heard of any problems whatsoever. I know i'm just "Some guy on the internet", but honestly, it's simply should not be a concern. I wouldn't know where to send you to verify that information though. Same thing with the hollow tubes casts in the concrete. Not a concern. For loaded semi trailers grossing 110,000, I'd probably want 8" of concrete. The difference between a 6" slab and a 8" slab in a 30' x 60' area is only 11 yards. At $100 per yard, $1100 may be a good investment. As far as heat migrating through concrete, concrete is practically a 0 R-value. Yes, heat rises, but, if it was insulated beneath, it'd have no choice but to go up.
Several posts have mentioned that "heat rises" which is correct only respecting the air in your shop so install ceiling fans. Hot air rises because it is lighter (less dense), not because it is hotter than cold air. As far as heat flow in a solid, like your floor, heat will only flow from hot to cold. If the ground under your slab is as hot or hotter than the slab then the heat will rise to heat the air in the shop. If the slab is hotter than the ground beneath the slab, heat will flow into the ground. If your slab is hotter than either the air above or the ground below, you will have heat going up and down. That is why you should have some insulation to keep the heat in the shop where you want it. I don't know what the compressibility of insulation is (consult the manufacturer or an engineer) but if it was buried deep enough, any load above would be spread over a large enough area to not compress the insulation too much, same principle as burying a culvert under a road. I know the highway dept. here has installed styrofoam insulation under major highways where they have serious frost heaving problems. Perimeter insulation as mentioned by others around the slab would also be beneficial.
I have worked in shops heated by the slab heat and it is very comfortable. The concrete stays warm and dry and it recovers from doors opening quickly. Since you plan to do 15ft. slabs in a 30 ft. area consider zoning it into 4 zones. Each zone would be 15X 40 and allow for good heat transfer. I zip tie my tubing to wire but rebar will do just as well to hold it in place while pouring. I am in the process of building a second greenhouse for the wife and it will have pex tube in the floor the same as the one I did last year. I have it in my porches as well as my basement floors. I used the same soft foam insulation under the tube in all of them. Once you have a heated floor you will never want to go back to overhead heaters.
Impact and norite, thanks for the info, around here they are saying to keep the tubes below the cement and not in it at all. I originally wanted two layers of rebar one at about 3 1/2 inches up from the bottom and the other 3 1/2 inches down from the top and tie the heat tubes to the bottom rebar but all the cement guys are saying no, but get this, they want me to use wire mesh and tie the tubes to that and lay it in the bottom and cover it up and put no rebar in above, that would be the reinforcing, I've spoke to six differnt cement guys and this is the same story I've gotten use the mesh on the bottom for the rebar and foreget anything else? My thoughts are what good is it doing under the cement to put the mesh or rebar and nothing above, that was somewhat idiotic I thought but can all of them be wrong, their reasons were the tubes in the cement would create a hollow space and weaken it. My thoughts were two layers of rebar would be better than one under the cement and tie it to the bottom layer and it would have to be stronger than even with the tube in it to ever weaken it. One guy told me he did his himself for his house and to staple the heat tube to the insulation board and put rebar above, thats what I did to the milk house and basement and garage but the cement was only 4 inches thick there and everyone seems to be in agreement that it would work fine on 6 inches thick but not thicker so my thoughts were to put it basically in the cement 6 inches from the top and incase it in the cement. The heat guys are telling me on 6 inches or less staple it to the insulation board and don't have an answer on thicker cement period but they insist it needs to be under the cement not in it. My initial concern with stapling it to the insulation board was if rodents got under the cement they could basically live in the insulation baord and chew holes in the lines causing them to leak but if it were incased in cement then nothing could destroy the lines but again I do a lot of demolition and it seems every buiding we destroy has critters living in or under the cement. Maybe its nothing to be concerned with but thats my concern, if they ever got under the cement and into the insulation it would heaven for living for them all winter, mice never had it so good if they found that place to live.
Randy are you doing the install of the heat yourself or are you going to hire it out?? you should contact your supplier for the tubing/heat equipment they will be more than happy to help you with how deep in the concrete it needs to be or any other concerns that you may have! there are several makers of the tubing/furnaces they all have the engingers to serve you if you have any questions just message me i have put in several of these systems
I attached my tube to the wire and just pull it up about 2 inches as we poured the concrete. This lets the wire do it's job and gets the tube up in the concrete where it belongs. I agree on the critters getting in under for a warm house and once they chew a hole in it that section is done for.
First off...cement will not hold worth a darn...really powdery and loose. Concrete on the other hand, that will do you good. lol, when you work for a company that sells concrete they have a big issue when you call it cement. Curious as to where abouts you are located Randy? Better to go thick than too thin. I know my uncles floor never had anything but some fines under it where the tube laid on and it works wonderful. Trbo
You could use welded black pipe for the zones in the floor- would solve most of the issues discussed sofar...
I am planning on building my 3 bay shop next year and I am a concrete contractor. I will have 2" rigid insulation along the foundation walls and 2' along the perimeter of the floor. Then I will have an 8" base of 3/4 clean stone compacted a layer of the bubble rap foil insulation for the base. Then a 6" 5,000psi slab with #5 rebar 12" OC with 2 1/2" steel chairs holding it in the center of the slab with the pex tubing tied to it. After it is poured and bull floated we will add a dry shake emery powder to it before floating to give it more strength and impact resistance. PS: You mentioned you will have your lowboy in there sitting on the floor unhooked from the tractor. If you know where it going to sit you can place some steel plate insterts before hand and pour around it to help spread the spot loads. You would have to pour a seperate spread footing and anchor some type of beam with a plate welded to top at the right elavation and then can pour around it when doing your slab.
Nac, how thick is the buble rap foil insulation and why not use the 2 inch rigid insulation under the main cement? I"m curious as to why your doing it that way is all, I've seen and heard of that foil stuff, thats the stuff that comes in rolls and is about 1/2 inch thick? or am I wrong on that, also what the dry shake emery powder, I've never heard of that before. For the spot load this is what we were thinking, let me know if I'm nuts for thinking it this way, we want to unhook the lowboys loaded because if we need to do repairs on the machine thats dead and can't unload it my shop won't be long enough to shut the door with the tractor hooked up but will work fine to unhook it and shut the door, my building for the remodel is only so long and thats all we have to work with for now. Anyhow we were thinking about pouring a footing about 8 iches thick under the entire width of the lowboy and then turning a railroad rail upside down and welding a flat plate on it say 4 ft wide by 10ft long and about 1 inch thick and also another plate under it so it sits flat on its own and just cementing it in so we end up flush with the top of the floor and having the floor about 10 inches thick for the work area where we would be driving and parking equipment. We were also thinking about doing the same thing somewhere else in the shop floor for having a place under vehicles and equipment that we could actually use as a welding area and also to jack up heavy stuff and have it centered in the shop bay but go with a plate about 10 ft square and do the same footing and railroad rail design. I"ve never seen it done before but one of my sons came up with that idea and I kinda liked it. I don't know if it needs to be 1 inch thick or could go less since it would be literally cemented in and have a footing under it and about 9 more inches of cement under the plate, maybe I'd only need a plate 5/8 inch thick I have no real idea of what it would take, I can't see it ever bending but more of an area to distribute the weight and also use as a welding and cutting area so we don't need to constantly have to put tin down first to protect the cement. Thanks for the imput guys it really helps to ask for idea ahead of time rather than wishing we would have done it differently later.
The stuff we have used is TekFoil Reflective/Bubble Bubble/White Poly it is about 3/8"-1/2" thick. I like it because it is easier to use and probably cheaper. You can look in to Anti-Hydro A-H A-2 Emery Shake-on. There are other manufactures out there also like Euclid. If you go with a very wide plate you have to make sure when you place your concrete it get left with no voids
I put pex in the slab of my building, 1/2" pex under # 4 bar on 12" center, 5" slab over pink board. It works, I've learnt it requires a lot of hot water and time to get increase in slab temp and that heat radiates toward the cold, whether that be up down or sideways.
there is a guy on the www who sells plans for hydronic floors but he needs the plans. (door locations etc.) and for a 40 X 60 will build the plans for about $400. A wise investment i figure.......and the lastest word is........nix bubble wrap under the cement - - whatever you put under there better be ''unchangeable". and sced. 80 pipe may (MAY) not break but the concrete will so you better stick to the latest industry std. for piping.........and as mentioned above......make you floor plenty thick, you only do it once!
Randy, Martin Implement John Deere dealer in the Quad Cities has rail poured in there concrete, where they run the tracked equipment Not sure if they have floor heat. I have bubble wrap and it works fine, it is in my house and garage. A friend has both foam and bubble wrap he said the foam keeps his shop about two degrees warmer than the bubble wrap, does. In floor is the way to go. We built a building last summer and used the 4' styrofoam forms with 6" of concrete, then the styrofoam walls with OSB on the walls. He still doesn't have his heat in the floor hooked up but is is heating a 2000 sq. ft. shop with a little milk house heater. We put the metal shop ceiling and foamed the joints and the perimeter, then celulose insulation on top. The celulose stops the air flow, fiberglass is used in a filter and lets air through.
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.
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.
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.
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.
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.
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.
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.
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.
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.
(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.
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?
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.
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
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.
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.