Warming Concrete Floors

[Avadon]

Does anyone here have any good ideas that I can pass onto my builder in regards to insulating/warming as we prepare to pour the monolithic slab for my new shop.

 

I know concrete floors can be a major heat sink in a large shop and wick out the heat. My father was encouraging me to a contoured bed of pex set on chairs to run heated water through the concrete in order to warm the slab. I thought it was a great idea and would save a ton of money on heating the shop in the winter. That is until I realized that most of my machinery in my shop needs to be bolted with anchors into the concrete floor. Way to much risk hitting those water lines and if they are severed a huge ordeal to repair them.

 

What other ideas can I do?

 

I saw on a TV show they once put down rigid poly foam and then poured the slab over it. Do people do such a thing for outbuildings? And if so does this work to keep the shop from soaking up the cold from the ground?

[Avadon]

Looks like I sort of answered my own question on the insulated slab

 

http://www.daviddarling.info/encyclopedia/S/AE_slab-on-grade_foundation_insulation.html

 

However i'm still curious if anyone has heard of a way of a heated slab (with circulating water through pex) that is done in such a way that you can still drill and mount to the slab?

[Mainely,Bob]

I would definitely go with the heated slab. The highly technical process that allows this to work is commonly called prior planning. :blink:
Do some homework and make a digital floor plan or draw it out on graph paper and take all your machinery (drawn to scale) and position it where you think you`ll need it.  Bypass the machinery areas when you lay the Pex. The solid concrete will make them stronger and better bases for gear that vibrates of involves impact (such as power hammers). The only places you really need the heat is where you are going to stand for long periods of time, like around the layout and assembly tables and in the forge areas. You don`t have to run those lines thru the entire slab,you`ll be surprised how little actively heated slab it takes to warm an entire shop. Think about it for a minute, how much wall/ceiling area does an industrial radiant  heater take up in a factory? None of the many places I`ve worked had 10% of any surface taken up in active heating (many far less if they used a large thermal mass like concrete to back it) and I live in Maine.

[Jerry W.]

Frosty would probably be a good one to hear from on this one.

[Steve Sells]

or maybe a HVAC pro, since it is their job to know these things... I would just insulate the slab with the hard foam sheets and go from there.

[rlbaker]

We have PEX buried in the slab of our house, source of heat is propane. Thought it would give us a nice uniform heat all winter, discovered that it would be cheaper to  stuff dollar bills in our clothing to stay warm and thats with a professionally installed system with insulation under the slab etc.Now we just use wood to heat the house.Our situation may not be typical, but I would ask around to others that are using similar system to see if they are happy.

[Sask Mark]

The pex is usually tied to the underside of the rebar mats.  If you make sure the pex runs right underneath the rebar, there is less chance of striking it when you drill for your anchors.  Ideally you would know where your equipment will be placed and tie the anchor bolts for the equipment right into the rebar cages before you pour your concrete.  But, as Mainely Bob suggests, larger equipment should be on dedicated foundations that don't require heating.

 

When insulating, the insulation should not only run under the slab, but you want to isolate the slab from the grade beam/foundation wall so the wall doesn't become a heat sink.  I have seen designs where there is a skirt of insulation extending 4' outside of the grade beam as well.

 

Depending on your slab area and application, you might want to break up the heating into zones.  

[ianinsa]

Pex, is a good idea. firstly  planning helps,   secondly divide up your space into zones  with a ring main and in and out valves  ie you open a sections valve  and  shut a  valve on the ring to force the water through a zone this gives you the ben ifit of being able to only heat part of the space or all as you see fit  also if you dammage a zone you can just isolate it while you still use the rest.  Mark the walls where you run lines because you are going  to forget where you ran them(I'll give you a written g/tee on that.) after a reratively short length of time. 

Use a UMO burner  as a heat scource- you'l sav e a lot. Alternatively get a diesel burner and run it on black  diesel.

Good luck Ian

[Chinobi]

Hey Avadon,

 

We had a pretty good discussion about heated concrete floors and layout WRT future heavy machinery penetrations a few months ago, flip through this thread if you havnt already.

 

http://www.iforgeiron.com/topic/29684-floors/

 

to respond directly to your question though, i agree with bob: prior planing.  make good and sure you know exactly where those pipes are, and leave yourself some spots ahead of time where you can cut the entire section out if you plan to install a power hammer.

[DanBrassaw]

In response to rlbaker, I'll vouch 100% in favor of heated slabs. We have in one the basement of our two story woodshop/commercial space type structure, heated with an outdoor wood gasification furnace. It's GREAT. You can open the garage doors to pull vehicles in, or just leave a window open if you're doing something noxious. Once you close things back up, the heat in that slab will push the temperature right back up. We've found it to be significantly more efficient then the electric baseboards which we used to use, and a real boon when bringing cold vehicles dripping with snow in. Things dry out much more quickly.

[GMoore]

I live in Colorado, right up against the Rocky Mountains, and - although I am just a beginner - my shop heats up comfortably just from a combination of my coal forge, my gas forge, and a small wood stove.  If fact, I don't know anyone with a heated floor.  I'm getting ready to move to Oregon (near Sandy just below Mt. Hood.  I didn't realuze Oregon got that cold.

[itsme]

Having designed and installed many hydronic slabs, I will chime in on this. A boiler can circulate warm water through zones and provide the BTU's you need. You can use a wood stove to provide heat. Forced air, geothermal, whatever you choose, based on your heating requirements and available fuels, can work great. As long as it is designed for your application.

In Montana, if you use rigid foam under your slab, and around the perimeter you can drastically reduce the heat loss into the ground. In southern Florida it would be less important, because the ground doesn't freeze. In my shop, I have pex tubing and a boiler, but I rarely use them. Unless I want to heat the shop 24-7, it just isnt as efficent as heating with a wood stove. The response time for the boiler is too slow to be useful, and I have a wood shop, so basically free fuel.

In my opinion, heated slabs are more senseable in buildings where people live, rather than shops, because the heating requirements are constant, and the relatively slow response of a heated slab can be benificial. The perception that they are more efficient is debatable, since it takes the same BTU's to get a space to the same temperature no matter what delivery method you use (negating the difference in efficency of individual systems).

My 1200 foot shop never gets below 45 even when I don't heat it for a month in the winter. I attribuite that to the insulated slab preventing the ground from freezing under the shop, and the perimeter being insulated to 4 feet deep (along with the normal wall and ceiling insulation). My neighbor's shop drops below freezing every night. It takes more fuel (and time) for him to heat every day, because he starts at a lower temperature. To me, a well insulated envelope is more important than the type of fuel and delivery method.

 

So, to get to the meat of my answer, tell your builder to insulate the entire slab area with 2" of blue Dow foam(or some equivilant), and as deep at the perimeter as you can afford.

 

As an aside, it is easy to locate the tubing after the pour with a thermal camera (if you have access to one), or within 2" with a simple laser thermeter while the system is circulating as hot as possible.

[Judson Yaggy]

Take careful high res digital photos of the PEX installed but before pouring the slab.  Run out your tape measures from a known point and include a view of these in every shot.  Two tapes are best so you know locations in two axis.  This will be a lot of photos, a dry erase board in each series of shots that names camera shot angle and other relevant features helps.  

 

Skip the pex in areas that you know will have lots of penetrations in the future.

 

Use gozintas (modular system of embedded square tube receivers) that you install before pouring (pex goes around them).  This will reduce the amount of drilling into the slab that you will have to do later.  

[Avadon]

Thanks for all the great information here. I'll definitely be printing this out and keeping it as I weigh the decision to pex or not. I'm North of Redmond, in a small warm pocket of Central oregon. Now that doesn't mean we can't dip down commonly into single digit temps at night in the winter, and even infrequently go below 0dgs.

 

@Gmoore Sandy is west of the cascades, basically down in the Valley. You'll like it there. And no it doesn't get anywhere near as cold over there as it does where I am. I'm not even sure if you can get snow in the winter there, I think it's to low. It probably depends on your elevation. It's a totally different climate. We are in high desert so hot days/cold nights. Heat rarely stays in the earth. This area is like a giant block of aluminum, it can get hot and it can get cold and it is rarely in between that. lol

If you keep the rebar rather straight and attach the pex to the rebar it shouldn't be to difficult to figure out where to and where not to drill. The problem though, from what I've seen is the edges of the slab, where people commonly bolt down grinders, buffers, sanders, etc. That's where the pexi makes half circles as it reverses direction for the next straight away. It's that area I'm concerned about.

 

From everything I've read it does seem like it's more geared to living spaces or garages where vehicles are being maintained. Our local fire station apparently has a heated slab.

 

This area 30x60' probably won't even have a window and will have a limited amount of doors as I'm preparing for a high STC value (sound suppression) I definitely will as a minimum insulate the slab heavily.

[Avadon]

The pex is usually tied to the underside of the rebar mats.  If you make sure the pex runs right underneath the rebar, there is less chance of striking it when you drill for your anchors.  Ideally you would know where your equipment will be placed and tie the anchor bolts for the equipment right into the rebar cages before you pour your concrete.  But, as Mainely Bob suggests, larger equipment should be on dedicated foundations that don't require heating.

 

When insulating, the insulation should not only run under the slab, but you want to isolate the slab from the grade beam/foundation wall so the wall doesn't become a heat sink.  I have seen designs where there is a skirt of insulation extending 4' outside of the grade beam as well.

 

Depending on your slab area and application, you might want to break up the heating into zones.  

Can you provide some images of the way your describing the insulation. I get the insulation under the slab and a strip around the inside foundation wall. Are you saying to wrap insulation also around the outside of the footer wall? 

 

Can you help make more clear "I have seen designs where there is a skirt of insulation extending 4' outside of the grade beam as well." this part for me.

 

Thanks,
Av

[Avadon]

Lets say worse case scenario you drill and hit the pex. How is this fixed. Will you even know you've hit it? Can you tell if there is a leak in the system after you pour? How much of a nightmare is it to fix it?

[Chinobi]

if there is pressure in the line the water will make itself evident, if it was dry you will find out the next time you charge the system.  if you see bits of not concrete/aggregate in the cuttings that would be a pretty good indicator as well.

 

i cant speak for repairing something embedded within the slab itself, but i have repaired copper water line breaks underneath the slab, which involves breaking up a large enough pothole to gain access to enough pipe to replace the damaged section, replacing said pipe, then backfilling with an appropriate material and concreting up the hole.

 

regular water lines can be leak tested by capping the system with a pressure gauge and pumping it up to a set pressure and leaving it there for a predetermined time(might have to start the clock after the pipes have expanded and come to equilibrium), then check the gauge and see if it has dropped, indicating that water is escaping somewhere.  talk to the contractor and make sure there is a provision in your contract for testing of the finished system if it is not included.

 

if you plan your space out in advance you should be able to completely avoid the areas with plumbing during future equipment additions.  keep a very detailed set of as-builts of the locations and dont be afraid to leave yourself permanent markers as to where the pipes are.  could be something as simple as a chipped mark in the concrete at the perimeter walls or a nail in the baseboard.  something you can match up to the other side of the workspace and snap a chalkline between to give yourself a clear view of the 'no drill' zones to prevent disorientation.

 

as you say you are concerned about the perimeter of the workspace being the most likely candidate for bolted down equipment, find out just how large a footprint the hardware on your wishlist will have and leave yourself a buffer from the edge of the concrete that will be large enough to fit said hardware in, and do not place the pex within that buffer.  depending on your budget and just how foolproof you want to make it you could go so far as to place colored concrete, some kind of surface finish (color, or texture), or even just spraypaint some other visual markers to denote plumbed areas.  reducing the square footage of floor that is plumbed should also knock down the cost of the system, less materials required, less man hours needed to install, etc.

[Avadon]

if there is pressure in the line the water will make itself evident, if it was dry you will find out the next time you charge the system.  if you see bits of not concrete/aggregate in the cuttings that would be a pretty good indicator as well.

 

i cant speak for repairing something embedded within the slab itself, but i have repaired copper water line breaks underneath the slab, which involves breaking up a large enough pothole to gain access to enough pipe to replace the damaged section, replacing said pipe, then backfilling with an appropriate material and concreting up the hole.

 

regular water lines can be leak tested by capping the system with a pressure gauge and pumping it up to a set pressure and leaving it there for a predetermined time(might have to start the clock after the pipes have expanded and come to equilibrium), then check the gauge and see if it has dropped, indicating that water is escaping somewhere.  talk to the contractor and make sure there is a provision in your contract for testing of the finished system if it is not included.

 

if you plan your space out in advance you should be able to completely avoid the areas with plumbing during future equipment additions.  keep a very detailed set of as-builts of the locations and dont be afraid to leave yourself permanent markers as to where the pipes are.  could be something as simple as a chipped mark in the concrete at the perimeter walls or a nail in the baseboard.  something you can match up to the other side of the workspace and snap a chalkline between to give yourself a clear view of the 'no drill' zones to prevent disorientation.

 

as you say you are concerned about the perimeter of the workspace being the most likely candidate for bolted down equipment, find out just how large a footprint the hardware on your wishlist will have and leave yourself a buffer from the edge of the concrete that will be large enough to fit said hardware in, and do not place the pex within that buffer.  depending on your budget and just how foolproof you want to make it you could go so far as to place colored concrete, some kind of surface finish (color, or texture), or even just spraypaint some other visual markers to denote plumbed areas.  reducing the square footage of floor that is plumbed should also knock down the cost of the system, less materials required, less man hours needed to install, etc.

 

 

Thanks for the good info Chinobi. I was really hoping to not have to get into planning out the interior with exact detail of where things go. Not because I'm lazy, but because I have so many other projects, and even parts of this build planned to the exact nuance that I was hoping to not have to get that specific but I guess if I want the pex in the floors I just may have to do that. 

 

Has anyone ever installed shielding over the pex? I.E angle iron on it's 45dg. Or would this inhibit the heating too much?

[Avadon]

Can anyone give me a rough cost basis for this? Or at the very least some comparables. 

[WayneCoeArtistBlacksmith]

You can use a good adhesive caulk to hold your equipment in place rather than drilling holes in the slab.  I have my Big Blu 155 Max and my 8" post vise glued down that way and they both stay in place.  The post vise has a 15" square base for the stand.

[Chinobi]

what if you ever had to move it?  or sell it?

 

Av,

 

thats the beauty of the buffer zone, you only have to plan so far ahead as to say 'no pipes within 6 feet of the walls', then you can drill with impunity within that zone, just dont stray outside of it.

 

i had thought about recommending putting some kind of protection over the tubes, angle iron as you also proposed, or a piece of flat steel, or coloring the concrete directly above the pipes so the drill cuttings will show that you are about to hit pipe before you get there.  but that will add another item to your budget that can be avoided.

 

edit: pricing can vary widely by location when it comes to construction, you would be better served contacting a local contractor who performs this kind of work and asking them for a rough quote.  they may be able to settle some of your questions as well.

[Avadon]

You can use a good adhesive caulk to hold your equipment in place rather than drilling holes in the slab.  I have my Big Blu 155 Max and my 8" post vise glued down that way and they both stay in place.  The post vise has a 15" square base for the stand.

 

 

I heard about that stuff.. those adhesives really work that well? What are they called again and where do you find them?

[Avadon]

what if you ever had to move it?  or sell it?

 

Av,

 

thats the beauty of the buffer zone, you only have to plan so far ahead as to say 'no pipes within 6 feet of the walls', then you can drill with impunity within that zone, just dont stray outside of it.

 

i had thought about recommending putting some kind of protection over the tubes, angle iron as you also proposed, or a piece of flat steel, or coloring the concrete directly above the pipes so the drill cuttings will show that you are about to hit pipe before you get there.  but that will add another item to your budget that can be avoided.

 

edit: pricing can vary widely by location when it comes to construction, you would be better served contacting a local contractor who performs this kind of work and asking them for a rough quote.  they may be able to settle some of your questions as well.

 

Yah I'll see if my contractor can do this or if he subs it out. I wouldn't think it would be to expensive. Pex is pretty cheap. I saw 300' rolls all over ebay and they weren't that bad off. Even the largest regular was like $260.00.  I'm guessing off the top of my head the whole thing could be done, at least material wise for under 1 grand even with labor. But I'll find out.

 

Thanks for the help.

[Sask Mark]

Can you provide some images of the way your describing the insulation. I get the insulation under the slab and a strip around the inside foundation wall. Are you saying to wrap insulation also around the outside of the footer wall? 

 

Can you help make more clear "I have seen designs where there is a skirt of insulation extending 4' outside of the grade beam as well." this part for me.

 

Thanks,
Av

Basically, rigid insulation extends horizontally (slightly sloping away from the building) at the bottom of the grade beam.  This probably wouldn't be required in your area.  I have seen this used for shops that work on heavy equipment where I live.  The frost level here can go down 6' below grade, especially if heavy equipment drives on the ground in freezing conditions.  The idea of this insulation skirt is to try to reduce the amount of frost that extends under the grade beam and under the slab.  I looked through my archived drawings and couldn't find this detail but, like I said, I don't think it's something you need to worry about in Oregon.

 

As for material pricing, we pay around $3/sf for something like 2" Dow SM styrofoam.  If you are going to put some heavy loads on the concrete and are worried about crushing the insulation, then something like a Hi-40 foam might be more suitable.  It has a much higher compressive strength than regular foams.  This stuff is also usually quite a bit more expensive.  IIRC, we pay around $5+/sf for this product.

 

I recently bid on a job that has a hydronically heated ramp entrance to an underground parkade.  Here is a section through the slab from the structural drawings.  Please note all the dimensions are in millimeters.  It will give you an idea of the typical slab construction where I live (5+ months of freezing conditions, highly expansive clay native soils).

In-slab heating section.pdf

 

I'm not going to provide any costs for the system itself as there are too many variables.  If you want you can tie the pex in when you pour your slab and cap the ends of the pex.  That will give you the flexibility to add a heating system later for little up-front cost.  Just be sure to test the pex before you pour the concrete (pressure test as mentioned earlier).

[Avadon]

Thanks Sask Mark. I could definitely see where a heated ramp is not even a luxury but something mandatory. If you had even a small bit of ice you might not be able to get vehicles out and salting ramps is messy and throws the salt everywhere. Nice Drawing, very detailed. I doubt I'll bring many vehicles into this shop as I don't really work on cars. At most I may weld on a vehicle/trailer/etc for a customer but that's an extremely rare occurrence one that hasn't even happened so far. I'm going to build a garage for my vehicles on the other side of my property. A very small garage basically just big enough to fit two cars with little clearance. I'm a big "park the car outside kind of guy and live in the shop." I grew up working and basically spending tons of time in workshops so they are basically like living rooms to me with toys. :)  Thank you for all the information.