foamstaples vs wire mesh for Pex install

nickh1

I'm looking for opinions on pex install using foam staples vs tying to wire mesh.

The floor is 6000 sq ft in an equipment repair shop. Plan is for 2" of foam, 6" of concrete with fiberglass rebar on 18" centers on chairs.

I have stapled the pex to the foam in the past and picked up a stapler on ebay fairly cheap. It is about $.10 a sq ft more to use 6x6 wire mesh to tie the pipe to. One advantage I see is even without lifting up the mesh, the pipe is at least 1/4" off the foam rather than touching it. I'm still debating between 1/2 and 5/8 pipe. but either way, will probably be on 12" centers.

Should I try to hold the mesh up an inch?


Background of the project.

I posted about the building in question a few years ago when I replaced the boiler. It is a repair shop on a farm. I'm working on a plan to remove this steel building and build a larger one on the same foot print. The existing slab doesn't have near enough pipe install, but I'm going to leave the slab alone and add more concrete on 3 sides. My plan is to over build with extra pipe to over compensate some. I'm not concerned about uneven floor temps. Building will be supplemented with radiant tube heat as required.



I did a search but didn't find much, feel free to pass on old posts if it has been covered.

HomerJSmith

I would think it would depend on whether you need the wire mesh in the concrete. The pex should be installed at about 2" from the top of the slab for the best radiation. If it is a 3 or 4" slab I would use wire mesh and elevate it so the pex is 1-1/2 to 2" below the surface.

hot_rod

I too would do everything possible to get that tube near the top of the pour. Put the mesh up on bolsters.
The concrete installers will hate you.

The performance and cost of operation will payback for the entire life of the system. Tube at the bottom of a pour is the very worse location.

I'd also go 6" on center if budget allows. You only get one chance to get the tube right

https://www.pmmag.com/articles/87540-depth-perception

TAG

Hot Rod: Have always wondered about this and constant circulation -- keeping it near the top is going to be quicker response --- and having been around quite a few in my life my guess is you get a bit more radiation from the hotter lines where the tube is. But -- overall with constant circulation though the winter ....how much do you think it really matters -- getting that extra inch ?

I have seen that graph before .... but -- it's not saying if that's after running for a week with the slab at temp.

The OP has 6" slab -- think that will matter. I'm doing 4" slabs and always 6" loops.

I also worry about damage -- when you build a house there are walls going up. I always worry about some guy and a power nail

HomerJSmith

Don't worry about the power nailer. Use a IR camera and mark out the tubes.

You need to determine whether you are going to use 1/2" PEX. The mantra is a loop not more than 300'. But I always make my 1/2" loop less than 250'. Minimum bend radius for 1/2" is 6" and for 3/4" PEX is 8". To minimize the bend I will use a counterflow pattern, 90 deg bend, rather than a serpentine pattern which is 180 deg bend. Sometimes I use a heat gun to warm up the pipe before bending to minimize a chance for a kink.

It all has to do with the size of the pump that you would need.

hot_rod

Well there are certainly tradeoffs in each decision. Two inches below should be out of an anchor shot reach. If drill in or drop anchors are needed or desired, I would keep tube out of those areas. Same with spot footings or any location where equipment mounting is needed. With todays inexpensive camera drones I would film every slab installation for record. Combined with IR you should not need to hit a tube.

Tube depth is a lot like insulation thickness, what is the tradeoff? For awhile areas in Canada, under their hydronics code, were required to use 4" of foam under slabs. This brought the radiant market to a near standstill as the insulation costs were a dealbreaker. Intent was good, logic was sound, but...

Not sure how often a 6" slab is really required? A properly installed and reenforced 4" slab should carry all but heavy, point load equipment.

At around 4000 lbs per yard that difference between a 4 and 6" pour adds a huge mass to accelerate and decelerate. If you are in an area with wide and often temperature and load change, I would not burden the system with that much flywheel unless absolutely necessary, it will be a control challenge. I'd add a slab sensor well for sure.

We have enough data now on how slabs perform, looking back 20- 30 years I find the slabs, when data logged and studied perform very close to the simulation models that Siggy and others have modeled. Same with Dales transfer plate FEA work from early on. Better than hearsay and guesstimates

Bottom line each and every job and installers has choices, and information to determine pros and cons.

Shallow tube, tight spacing is another "future proofing" measure, allowing the lowest possible SWT to "get 'er done" now in in the uncertain energy future.

GroundUp

Response time is always going to be slower with the tubing on the bottom versus suspended. With that said, the average building with a radiant slab is set to a given ambient air temp and maintained there whether that means constant circulation and varying water temps or on-call circulation with fixed water temps. This has been beaten to death and the professionals always push the tubing to be suspended, but I like to see for myself what makes things tick so I did this very thing in my own shop. Half of the slab is stapled down to 2" XPS and the other half is tied to #4 rebar suspended with the bottom of the tubing exactly 2" above the XPS. This is a 4.5" slab so nearly dead center of the pour. I have been monkeying with it almost daily, changing water temps and air temps, logging the temps with my FLIR camera at varying stages of the heating cycle. My conclusion is this: it doesn't matter. The benefit is immeasurable. A couple days ago this was brought up on another site and someone mentioned that the tubing on the bottom of the pour would require 8-10 degree higher supply water temps in order to reach the same surface temperature. If both SWT were far too high or we were trying to bring the air temp up 20 degrees, then I would agree there is a difference relative to the response time. However, there comes a time at thermostat satisfaction when almost the entire mass will reach the same temperature. Directly above my suspended tubes I find the surface to be 1 degree higher than anywhere else in the slab once the equilibrium has been reached. For the normal Joe just always keeping his shop at 65 degrees, it's not worth the work of bending over 6000 extra times nor the extra cost of the mesh for the $2 a year energy savings. Concrete is fairly conductive, and the whole mass will be within a couple degrees from top to bottom once the equilibrium is reached.

TL;DR the takeaway, in my opinion as someone who does hundreds of thousands of feet of radiant in slabs every year, is that it doesn't matter. Given the size of your space, 5/8" tubing would give you longer loop lengths and both speed up the process as well as simplify installation with minimal tradeoff. Efficiency wise, you would be able to run a slightly lower water temp using 6" spacing so there is a few bucks to be saved monthly versus a 2x upfront cost for double the tubing. Never in my life have I seen a radiant slab with 12" spacing that wouldn't adequately heat the space with 130 degree water (uninsulated below), and never have I installed one that wouldn't heat the space with 100 degree water (2" XPS below). It was -35*F here a few weeks ago, one of the coldest areas in the US. The only reasons for tighter spacing inside a shop are to prevent icing near the doors, better recovery time, or to lower SWT and gain a little efficiency. My vote goes to 2" XPS (or more) with 400ft loops of 5/8" stapled to it at 12" spacing. Don't make it more difficult than it needs to be.

HomerJSmith

Personal experience certainly counts. Once cast in concrete, it's a done deal. I would rather go with what the engineers say. Cost is insignificant. If it doesn't perform to specs, then what?

"Experience is what you get when things don't go the way you planned."

GroundUp

I'm all about listening to the engineers, but to me it's a lot like taking financial advice from a poor person or weight loss advice from an obese person. Until you can show me one single real world application where a residential space cannot be heated with 12" tube spacing in a 6" slab, I'm going to put my money on what I know for a fact works.

hot_rod

GroundUp said:

I'm all about listening to the engineers, but to me it's a lot like taking financial advice from a poor person or weight loss advice from an obese person. Until you can show me one single real world application where a residential space cannot be heated with 12" tube spacing in a 6" slab, I'm going to put my money on what I know for a fact works.

You were doing good until you put the "but" into your sentence. It's like saying you believe the rules of thermodynamics BUT not when it is an inconvenience

Hot goes to cold, period.
The rate of heat transfer depends on the delta, period.

GroundUp

hot_rod said:

GroundUp said:

I'm all about listening to the engineers, but to me it's a lot like taking financial advice from a poor person or weight loss advice from an obese person. Until you can show me one single real world application where a residential space cannot be heated with 12" tube spacing in a 6" slab, I'm going to put my money on what I know for a fact works.

You were doing good until you put the "but" into your sentence. It's like saying you believe the rules of thermodynamics BUT not when it is an inconvenience

Hot goes to cold, period.
The rate of heat transfer depends on the delta, period.

That's not at all what I said, because thermodynamics is proven by science. I would love some proof that my FLIR camera is wrong and some guy who said otherwise is right- inconvenience has zero to do with anything.

Hot goes to cold=My point exactly. Heat transfer is dependent on delta=also my point exactly. Is the heat more likely to travel through R4 of concrete to get to the 65 degree space on the other side or R10 of foam to get to the 55 degree space on the other side? I do not mean to be argumentative, but I defy you or anybody else to prove to me that 2" of suspension makes a measurable difference or that 12" spacing will not adequately heat any one properly insulated residential space. I have proof right under my feet that it doesn't matter enough to measure.

hot_rod

GroundUp said:

hot_rod said:

GroundUp said:

I'm all about listening to the engineers, but to me it's a lot like taking financial advice from a poor person or weight loss advice from an obese person. Until you can show me one single real world application where a residential space cannot be heated with 12" tube spacing in a 6" slab, I'm going to put my money on what I know for a fact works.

You were doing good until you put the "but" into your sentence. It's like saying you believe the rules of thermodynamics BUT not when it is an inconvenience

Hot goes to cold, period.
The rate of heat transfer depends on the delta, period.

That's not at all what I said, because thermodynamics is proven by science. I would love some proof that my FLIR camera is wrong and some guy who said otherwise is right- inconvenience has zero to do with anything.

Hot goes to cold=My point exactly. Heat transfer is dependent on delta=also my point exactly. Is the heat more likely to travel through R4 of concrete to get to the 65 degree space on the other side or R10 of foam to get to the 55 degree space on the other side? I do not mean to be argumentative, but I defy you or anybody else to prove to me that 2" of suspension makes a measurable difference or that 12" spacing will not adequately heat any one properly insulated residential space. I have proof right under my feet that it doesn't matter enough to measure.

The data is in the post a couple up from here, and again below. Where is your data? And who claimed 12" on center would not adequately heat a 20- 25 BTU/ sq ft load?

18- 24" o.c. can adequately heat a shop as far as that goes.

Simply put , tighter space and tube near the surface will have increased input, all other variables being equal. For the same thermodynamic reasons that a tighter delta T across the loop increases output, more of the surface area is heated to drive the exchange.

Your beef seems to be the labor or PITA part of elevating the tube? That's fine but is not about the science of heat transfer.

https://www.pmmag.com/articles/87540-depth-perception

If you have read this, what part do you disagree with?

HomerJSmith

This is a story related to me by an acquaintance in the business. A contractor was doing a SIM sys and he laid out 1000' coil of 1/2" of pex and then pumped thru it with glyco, too. The problem was that the end of the slab was cold and wanted to know what to do (rather desperately I suspect) to fix it. The cost of fixing it was exorbitant if one had to do it all over again. The poor contractor ran out of heat energy before the fluid passed thru the tube. The fix was to pump from one end and then pump from the other end and repeating this procedure.

This stuff is complicated and has to be planned correctly. I would rather depend on an engineer that works for a company dealing in infloor pex than a guy standing on the corner with holes in his shoes for the needed information to do the job correctly. We all got to where we are today by the things we learned from someone else. Not all information has the same equivalency tho. I trust informed consensus. Isn't that what this site is all about?

GroundUp

hot_rod said:

GroundUp said:

hot_rod said:

GroundUp said:

I'm all about listening to the engineers, but to me it's a lot like taking financial advice from a poor person or weight loss advice from an obese person. Until you can show me one single real world application where a residential space cannot be heated with 12" tube spacing in a 6" slab, I'm going to put my money on what I know for a fact works.

You were doing good until you put the "but" into your sentence. It's like saying you believe the rules of thermodynamics BUT not when it is an inconvenience

Hot goes to cold, period.
The rate of heat transfer depends on the delta, period.

That's not at all what I said, because thermodynamics is proven by science. I would love some proof that my FLIR camera is wrong and some guy who said otherwise is right- inconvenience has zero to do with anything.

Hot goes to cold=My point exactly. Heat transfer is dependent on delta=also my point exactly. Is the heat more likely to travel through R4 of concrete to get to the 65 degree space on the other side or R10 of foam to get to the 55 degree space on the other side? I do not mean to be argumentative, but I defy you or anybody else to prove to me that 2" of suspension makes a measurable difference or that 12" spacing will not adequately heat any one properly insulated residential space. I have proof right under my feet that it doesn't matter enough to measure.

The data is in the post a couple up from here, and again below. Where is your data? And who claimed 12" on center would not adequately heat a 20- 25 BTU/ sq ft load?

18- 24" o.c. can adequately heat a shop as far as that goes.

Simply put , tighter space and tube near the surface will have increased input, all other variables being equal. For the same thermodynamic reasons that a tighter delta T across the loop increases output, more of the surface area is heated to drive the exchange.

Your beef seems to be the labor or PITA part of elevating the tube? That's fine but is not about the science of heat transfer.

https://www.pmmag.com/articles/87540-depth-perception

If you have read this, what part do you disagree with?

Besides everybody claiming that a simple shop slab needs to be designed by an engineer to determine tube spacing and loop length? I guess nobody. My point is simply that 12" OC is adequate and it does not need to be overthought.

Yes, I have read that column dozens of times, and it is one of the reasons I designed my slab the way that I did. John's data is computer generated while mine is real-world. I would be happy to share my FLIR data showing that the surface temp differential is minute, and that the BTUs emitted to the space are almost identical regardless of depth. I worship the ground that John and yourself walk on, but this is one particular subject on which I will not accept "because I said so" as fact. What makes John's data more factual because he has an engineering degree? Numbers don't lie. I always wondered about this and nobody could show me a real world comparison (not the computer generation you shared from Siggy) so I built a model myself to collect the data. My data collection says that the difference is nearly immeasurable. Yes, it is different and yes, closer to the surface does yield more BTU- I have never disputed that. The fact that the difference is SO minute is what my beef is about. When everybody who can read a book preaches that all slabs NEED to be engineered or they won't work properly, that gets under my skin because it's absolutely false. I'm all about doing things properly, but this isn't the difference between a 15-42 and a 26-150. It's the difference between a 15-42 with 120V and a 15-42 with 118V. It doesn't make enough of a difference to matter. We're talking fractions of a percent, not an 8-10 degree SWT spread as you've suggested.

hot_rod

Well, my data suggests differently, and matches closely to the modeling.The major tube manufacturers use this same modeling to build their output charts you see in the design manuals. Many will show 6- 18 or even 24" spacing options. I think the RadPad simulator goes out to 18"

So basically I could supply the slab with tube centered in the 4" pour with 73°SWT and get the same output as the slab with tube at the bottom running around 112°SWT, as clearly seen in these demo panels.Granted these are not a true scientific demo. I had the Fair tripod mounted trying my best to get the exact same shot over the several hours of run time. Ambient temperature did go up a bit, so a bit of wiggle room in the data collection.

I suspect some of the nob panel performance is related to the tube not being completely encased in concrete, touching foam nobs, or at the bottom with no concrete contact. Nobody has put a number to that, although they could, and should in fairness to the industry. Is it a 10, 15, 20% hit in performance??
The tube is actually 5" below the surface on the nob panel as I poured a full 4" over the top of the nob. I'm not sure what the accepted practice is with nob panel pours, measure from the top of the nob for slab thickness?

And if you believe the Viessmann "arrow chart" data there is some benefit from running the lowest possible SWT in terms of boiler efficiency and economics for the life of the system. Depending on where energy prices go, that could equate to thousands of dollars difference in operating costs. More than offsetting the cost of additional tube, I suspect.

I'm not questioning your 12" jobs getting the job done, covering the load, but it is hard to argue that putting more energy into the slab with additional tube contact does not have enough of an effect to consider. Tube is cheap in the big picture.

As far as your aching back, you need to hire some young "tube-sters"

HomerJSmith

TIME-It's the variable here. How fast does the planned installation reach set point? Put the pex loops at 2" centers with 110 deg water @ .75 gpm. All things being equal, put the pex loops at 12" centers. Which one will reach set point faster and at what energy cost?

With 12" center with heat energy migration out of the building envelop at some outside temperature, it may never reach set point.

People want instant gratification, that the world we live in. Would a customer prefer reaching set point in 2 hrs or reaching set point in 6 hrs?

Not all installations are the same. The variables between jobs demand planned consideration to meet project goals.

12" or 2", it all depends.

hot_rod

HomerJSmith said:

TIME-It's the variable here. How fast does the planned installation reach set point? Put the pex loops at 2" centers with 110 deg water @ .75 gpm. All things being equal, put the pex loops at 12" centers. Which one will reach set point faster and at what energy cost?

With 12" center with heat energy migration out of the building envelop at some outside temperature, it may never reach set point.

People want instant gratification, that the world we live in. Would a customer prefer reaching set point in 2 hrs or reaching set point in 6 hrs?

Not all installations are the same. The variables between jobs demand planned consideration to meet project goals.

12" or 2", it all depends.

Actually there was a study done with 4" on center years ago! One of the tube "staple up" brands considered 4 tubes per bay instead of two at 8".

The output of any radiant panel has to do with the average surface temperature. You see some striping on most all tube installations. Tighter tube, less temperature stripes= higher average surface= higher BTU/ sq ft output.. Or lower SWT potential as shown in the demo panels, however you want bio cut it.

The centered tube, and the 6" OC tube should be of particular interest to those that insist on setting back, or leaving the shop cold until needed.

GroundUp

Reaching setpoint is entirely variable based on what is asked of it. Are we maintaining a 70 degree ambient air temp or are we bringing it up to 70 from 40? Response time from a cold slab will be reduced slightly by suspended tubing, yes- I have never disputed that. Overall energy input? Negligible difference. Maybe 2% in a properly enveloped slab. Between heat calls, what is the temperature of the slab with relevance to the tube location? Where do we put slab sensors so as to not be influenced by the tubing during circulation? If the temperature halfway between the tubes is the optimal spot to maintain a given slab temperature (it is), that should say enough about the conduction of the concrete to know that there is an equilibrium reached after the heat call has subsided.

Bob, that's great and everything but how long had the water been circulating when that data was recorded? Why was the SWT so high? You could circulate that same 73* water constantly and maintain nearly the same BTU output with the tubing at the bottom of the pour versus 2" up. This all goes back to the response time which I never disputed in the first place. I guess this is a new test for me if I can get my mixing valve down to 73 degrees, I'll run the pump for 24 hours straight and record the surface temp in both halves to see where the difference ends up. I can already say with 99% certainty that it'll be inside of 1/2 a degree difference (and if my RadPad is accurate, the BTU output spread is nearly immeasurable), but just for you I'll try it and let you know for sure. I again never disputed the fact that more tubing can equal more BTU in a given time frame, but why does it matter unless for recovery's sake? We're not using setback thermostats with radiant slabs. Recovery is largely irrelevant. There is no sense in paying a grunt for 12 hours with 2x material cost to perform a task with the same overall outcome that I can do alone in 3 hours using staples for half the material cost. It's silly unless the desire is to regularly bring the slab up from cold.

hot_rod

My goal in all of this is to provide the energy and cover the load with the lowest SWT. If hydronics and radiant is to survive the mini splits, VRF, electrification movement which has money and power behind it, we need to think differently.

Designing systems with the lowest possible SWT allows us to embrace the new technologies and use the energy most efficiently. With changing climates, flywheeling slabs become more of a concern, lower SWT and tighter tube spacing and tube close to the load helps address that also. Nobody should have to open doors and windows to control an overheated space caused by mostly avoidable design practices.Or wait a day or more for a slab to ramp up.

2 hours of run time on a very low load condition with 112 SWT only produced a surface of 73° on the deep tube slab. What do you suppose that slab would look like after 2 hours of 73 SWT? Where would you suggest that energy difference went. Imagine if these slabs were sitting on 32° ground for the test.

And that is the whole point of my suggestions that tight tube spacing and tube close to the surface allows lower SWT, less energy consumption by providing lower SWT, higher mod con efficiencies, faster response, and ability to leverage all the current technology, A2WHP for example. If you want that 2- 3 COP you need to design for the lowest operating temperature conditions.

So basically we disagree on the definition of negligible Since you have provided no numbers to make a comparison?
To me these numbers and pics speak for themselves, most customers and designers would probably agree, engineers or not. In the end the customer is paying the energy costs they should be allowed to decide.
The more tube you sell the more money you and the "grunt" make

If I follow your logic it seems you should be considering at 18- 24" spacing? If 18"on center covers the load, eventually, why do 12?
I'll bet your answer to that would be the very same as what I just layed out here.

HomerJSmith

GroundUp, laying Pex in 3 hrs gives you a real competitive advantage. Hell, at my advanced age, it take me 3 hrs just to get a roll of Pex out of the truck.

HomerJSmith

Yes, hot_rod, you're right. I never want to argue against you, I think I would get the "short end of the stick". That's an economic term, by the way. AKA: Tally Sticks.

From what I observe in the Economic arena, we have reached peak energy and it's down hill from here. This is because of diminishing energy resources (the low hanging fruit has been picked resulting in higher costs, think Fracking) and increased competition for those remaining resources from other countries. This isn't good, God help us. They say all Wars are resource Wars.

The last 1-1/4 century, oil energy has resulted technology, food production, and population growths. It is inevitable that energy cost will rise, not only because of monetary inflation, but of shortages, too. Oil was a blessing for civilization, the question is can it be replace at reasonable commensurate cost.

I foresee greater regulation, greater technological manufacturing techniques to squeeze a greater energy output out of a energy cost straightjacket.

Yup! What good is a state of the art radiant sys if the energy necessary to run it is missing in action or too expensive to operate. If you make it as energy efficient as possible, you may have a chance. You owe that to your customer or is the primary consideration to take the money and run?

GroundUp

@HomerJSmith I've slowed down from my earlier days, but a single zone slab of say 2000 sq ft can easily be done in 3 hours by myself. Back in the old days 1000 linear feet per hour was the norm.

Bob, was that slab 4 degrees along with the ambient air temp when you started? What was the flow rate? Under what circumstances would there ever be frozen ground under the insulation below a slab? I am all about increasing efficiency, but realize there is a point of diminishing returns. Spending XX to save X is ridiculous. Notice these programs/engineers that are designing around 6-8" tube spacing claiming it as necessity are the same ones who design with a 110+ degree SWT. We both know that the average new construction home or shop can easily be heated with 90* SWT on design days, and efficiency doesn't get much better than that does it? That can easily be accomplished with 12" spacing if the system is properly operated. Perhaps some of us are not in bed with the tubing manufacturers and do not wish to charge our customers double for twice as much tubing as is required for an efficient heating system? I definitely understand your passive aggressive notes about 18-24" spacing, but the reality there is that is does stripe and obviously requires a higher SWT. So yes, I agree with the more=better philosophy but again with the diminishing returns. There is a much larger differentiation in going from 12" to 18" than there is going from 6" to 12". Anyway, I did provide you with numbers on FB the other day and you never responded. But since you asked, when the data was collected I was running an 80* SWT with a 9* delta. Flow rates of .75 GPM per loop, 6 loops of 1/2" pex at 12" spacing. 3 loops stapled to the foam, 3 loops tied to #4 bar in the center of the slab. ambient air temp of 65 above both halves, with 2 different thermometers. Surface temp of 68 degrees on the stapled half, 69 degrees on the tied part using a FLIR camera as well as a cheap infrared gun. The tubing could not even be located as the entire slab was within 1 degree.

HomerJSmith

GroundUp, your observations would probably be a great thesis for a PE graduate student.

But, I would rather error in favor of hotter and costlier than colder and cheaper. I can fix hotter, but not so easily colder. I guess I could increase the SWT, but that has limits.

hot_rod

Decisions, decisions I agree about diminishing returns, when the western Canadian code required 4" under slab that didn't work out so well, they backed off. The insulation cost more than the slab and tube It drove buyers away from radiant, probably went too far for the $$ exchange also. I'd like to think most of us have moved on from bubble foil to a true R-10 2" board minimum. Even the styrofoam coffee cup analogy couldn't salvage that sales spiel. Same applies to tube spacing, it is a $$ choice. Bottom or mid slab is more of a labor choice. I'm getting ready to build about 1200 sq ft of shop, foam and mesh is quite a bit cheaper than nob board, and my back can handle that size, so for me the tube spacing and mesh lift is an easier decision.

Same applies to building a new structure, how much will a person spend on insulation and construction methods to get into those single digit per square foot heatload/cooling load numbers? That certainly makes the HVAC guy or gals job easier, getting the load way down. The building after all is the driver of the load and operating costs.

At some point appliances and lighting, computers and occupants cover the heat load and we are out of business. At 10 and below BTU/ sq ft, does residential slab radiant even make sense? You certainly will not have "warm floors" even on design days. So much for the smiling toe, kids on the concrete/ tile floor promotion.

If the load can be covered comfortable with 12" oc and 90 SWT, not much benefit from going to 6". My point is trying to get ALL hydronic systems below 120, maybe 80- 90 SWT for radiant slabs.

Look at every job to see where the $$ makes sense. One or the radiant manufacturers would send me tube spec at 8", some times 9", doesn't need to be 6 or 12 I suppose.

Large workshops, equipment storage, etc can work okay with 18", barefooted comfort is not usually a concern.

HomerJSmith

https://www.pmmag.com/articles/101229-john-siegenthaler-tell-me-more-about-nubbed-foam-panels

Zman

This is a conversation I have with clients regularly. I like to select a design day water temp then design the tubing layout around that temp based on the heat loss of the space. An interior closet might just have a run of 12" up the middle where the floor in front of a large window wall would likely be run at 6". This makes for a nicely balanced system.

As far as the depth of the tubing goes, whenever possible it should be elevated, however, unless you can convince the structural engineer to specify rebar on chairs (and the owner to pay for it), the concrete guys will almost always leave it on the bottom.

One might think that you could just tap the gentleman pouring the floor on the shoulder and remind them the the slab will be stronger and the heat will work better if they would kindly pull the mesh to the center of the slab. I would not recommend trying that unless you are wearing full body armor.

TAG

Being a serial rehabber for the past 30 odd years. You can dream all you want -- getting it done is another thing. Pick up Fine Homebuilding/ TOH mag ..... online at GBAdvisor. It's all great until you try and find someone to execute the plan within a budget. What is the percentage of new construction w/ any type of hot water heat?

Have done some really cool spaces ... old factory form the 20's /1890's city fire house/ 1850 bank barn ... my new project is a 1870's church. Have built new glass and steel/ concrete modular (smaller vacation houses) and rebuilt many old stone/ brick. Getting the proper contractor is always the hard part.

With flat work (concrete) -- the best guys for a given project most times are not radiant experts. Do they do radiant slabs -- yes. But -- it's not day in day out. It's safer doing standard construction w/ 2" of foam and mesh. Everybody has a different idea .. KISS rules. In the end the most important thing is to end up with a finished slab as close to perfect as possible.

Used Warmboard back around 2004 when it was a new project -- gone in every project since someplace ... always with contractor resistance. No one wants to do something new or different vs the last time.

hot_rod

slab radiant has been around long enough that most concrete installers are aware of the special needs. If you let them know beforehand that they are working over tube it should not be an issue.

All the commercial projects I have done have had bar on bolsters or chairs, the way it should be, and the engineering dictates. Concrete guys don't complain about those pours. Nor would they remove the lifts 6X7 #10 mesh in my opinion does little to add strength to a slab, especially at the bottom of the pour. IF the job requires reinforcement, fiber mesh or rebar is a better choice. Rare to see a footing or foundation without rebar, that ends up in the correct spot more often than not.

If you want the tube in the pour where it should be, find concrete installers that will work with you. There are plenty around. Many that I worked with had their own radiant slab home and shops, they more than others appreciate radiant concrete. So they know the drill.