Getting close to pouring hydronic floor in new garage/shop. My plan was (from base), vapor barrier > 2″ blueboard > wire mesh > tie pex to mesh > concrete. Flatwork contractor suggested stapling pex to foam then mesh on top. Gives him more control on pulling mesh into slab and less “tube float” which evidently was a problem on a recent job.
Sounds like a decent plan to me…can y’all see anything I’m missing.
PJ
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Replies
Yes, I can see something you're missing. Your contractor is more concerned about pouring concrete than he is about how your heat tubes function.
If you are going to use wire mesh, you should tie the tubes to the mesh and pull them up in to the slab where they belong.
This business of stapling them to the foam and leaving them half covered with concrete is fine if you are looking for a fast installation. If you are actually concerned about doing the best and most efficienct job, then tie the tubes to the wire and put them where they belong...in the middle of the slab!
Use the appropriate ties ( such as Wirsbo's ) and make a hook out of a 16d nail and chuck it in to your battery powered drill and you can tie the tubes in no time. Use a tie every 18" and at the tips of the bends and you will never have trouble with tubes "floating".
Pressure the system to at least 60psi of air before and during the pour.
The difference in function is extremely minimal. granted tube float is a problem easily rectified by appropriate tie distances such as 18" as you note, and lifting is technically superior.But not by enough that I would ever care, nor adjust a calculation to reflect.In fact, simply having them slightly loose is quite adequate. the only possible issue here is less than full concrete envelopement around the pipe. The extra 2" of concrete over the top is of no concern whatsoever, since whether you are in the middle or the bottom of the slab, you pretty much have to heat the whole mass up to start heating. You just have slightly faster response time with higher tubing. and it is slight.Even NOT loose, you don't have anywhere near half the tube outside of the concrete with foam staples. A very small area where the tubing actually hits the foam, maybe.So the answer is no, he isn't really missing anything. as others have pointed out, the tubing can act as a "chair" of lower height for mesh if dead center mesh isn't needed, and provides more protection from control cuts and nails as well.-------------------------------------
-=Northeast Radiant Technology=-
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You and I will never agree on this, so I will agree to disagree. The only reason they ever came out with foam staples is to make installation faster, not to do a better job of heating a slab.
I don't see any sense at all in using this method with a concrete slab when you are using wire mesh for reinforcement. In a few hours, you can do it the "right way" and have a better system for your efforts.
Gypcrete will fill in better around the tubes when they are on the bottom, but even pea gravel concrete mixes leave voids around the bottom of the tubes.
Personally, I would never staple tubing to the foam in a house I owned.
BTW, hydronic heating experts like Dan Holohan don't agree with you about installing tubing at the bottom of a slab.
Edited 6/26/2007 8:58 pm ET by BoJangles
really? seigenthaler himself has modelled this. it's an insignificant difference. While Dan is a great guy, I'd rate siggy a step or two higher on the design ability scale.-------------------------------------
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You guys are making me realize that I need to look into this. I'm about to put together a radiant slab and as far as I know my sub likes to staple pipe to the foam. From a concrete point of view it would seem to create a less than ideal condition, with lines of weakness following the tubing. I may tie a mat of #3 18" OC on 1-1/2" dobies, so it may be a moot point anyway, because I can ask him to tie tubing to the bars. Or can I?
there is absolutely nothing wrong with tie tubing to mesh or rebar, as long as you do it to an appropriate on center.all I'm saying is, foam stapling works fine as well, and this myth about middle of the slab being in any significant way better is just that.. a myth. you don't lose much contact area, if any. The increased resistance of the concrete is infintesimal.You Might, maybe, worst case see up to a 5 degree shift in operating water temperatures, though I never adjust upwards and it's never bitten me. You might see somewhat decreased response time, but it will be slight.I'm not saying everyone should foam staple. I'm just saying it's not worth losing sleep over, and if faster installation is important or saves some money, it's a corner that can be cut with practically no real downside.BoJangles is mostly correct that that only real benefit is faster installation.. it's a *much* faster installation.. though it is more protective of the pipe as well. Not generally a major concern, but then, neither is tubing float or this marginal reduction in output.do what you like, basically.-------------------------------------
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David I tied my tubing to the rebar (18" o.c. on dobies) in our 1200' slab and had no problems when placiing/ finishing concrete. I would not be comfortable having rebar installed over the tubing, seems like a good chance for a nick or kink. Mike
Trust in God, but row away from the rocks.
I went with #3 rebar on 1" dobies and figure it puts the tubing centered about 2" above the foam. My radiant guy was a little unhappy tying tubing to the bars as opposed to stapling it to foam... apparently it's harder to control precisely where it goes... but he got it all in there and it's now entombed forever. The part I do not like is pinning down the interior wall plates. I'm using 2-1/2" split anchors and very carefully drilling 1-1/4" deep for them. Each time I drill I think about what a tube hit would be like... 1600 feet of tubing at 100 PSI all emptying right into my face. So far so good and I only have a few more to drill tomorrow AM. We used Combi-form to avoid having to cut the slab, although in theory a 1" deep cut should be no problem, as long as none of the tubing floated.
Well, since you respect Siggy...here is a quote from one of his great books:
He is talking about how the tubing should be tied to the mesh and pulled up in to the center of the slab, and points out that this sometimes doesn't get done properly.
"Even though the tubing may end up at the bottom , the system still will function well although a slightly higher water temperature is required compared to installations where the tubing is in the center of the slab" He goes on to say "The time required to warm the surface to normal operating temperature after a set back will also increase when the tubing is placed deeper in the slab".
Now I ask you....if you were in the original poster's situation and he could tie the tubing to the mesh in a few hours at most, why would you not do it??????
Bojangles, I can see both sides of the question and have read all I can Google. There might be another reason to leave the tubing low in the slab. I don't have immediate plans to do so but may want ot anchor something to the floor. The consistent depth to pex would make it easier to set anchors without risk.
PJ
Everything will be okay in the end. If it's not okay, it's not the end.
There is no such thing as setting anchors in a 4" heated slab "without risk". I would avoid areas where you may have to drill when installing tubes.
Proceed with caution!
And while you are at it....watch your temperature gauge on the boiler and see how long it takes to climb 5 degrees or more. That is how long you are wasting fuel by requiring a higher water temperature to heat the slab with the tubes sitting in the bottom.
But think about it a minute. Still air is an insulator. As long as any of the slab is cold, it should absorb btu's before the they are released to the air. Conduction is more effecient than radiation.
My gut tells me it don't make much difference.
Personally, I like tubing tied to rebar. If the concrete dudes can't properly place the rebar/mesh......
It does make a difference. The deeper the tubes, the more delay in emitting heat to the room.
The slab doesn't just sit there and wait to warm up to a certain temperature. The heat is conducted evenly off of the tube and the closer it is to the surface, the faster the surface will warm.
This is why you get cold or cool spots between tubes that are placed too deep or too far apart in the floor.
I agree with you that any competent concrete contractor should have absolutely no problem in dealing with mesh with heat tubes attached.
Some people just don't see the need for mesh in a floor. If they then also choose to staple tubes to the bottom of the floor knowing that it will be somewhat less efficient and responsive, then that is their choice.
I look at it this way. You are constructing a large and expensive radiator. I am willing to spend a little more time and money to make it the most efficient radiator possible under the circumstances.
This is why you get cold or cool spots between tubes that are placed too deep or too far apart in the floor.Whoops. Lost some crediblity there. That is backwards. Too close to the surface will make hot and cold stripes easier than too deep.SamT
I stand by the previous statement...but you are right, you can definitely get too close to the surface. I believe the IBR manual recommends a minimum of one inch. The effects are far more noticeable in thin slabs.
Think about something...they do not recommend placing the heating tubes close to the surface because it causes uneven heating and poor heat distribution. Now flip that slab upside down and this is exactly the setup you have when you staple tubes to the foam at the bottom of the slab. That is why every heating book, manual etc. that I have ever read wants the heat tubes placed in the center of the slab as the first choice in placement.
Any farther apart than 12" and noticeable striping occurs in all slabs.
Any deeper than 6" and you might as well forget about the system working properly.
Edited 6/27/2007 11:28 pm ET by BoJangles
Wow, that quote sounds exactly what I just said, doesn't it? "slightly" higher water temperature. I added a "slightly" to response time as well. Why would siggy saying exactly what I'm saying change my mind again?
I would not insist on tying tubing to wire mesh and lifting, because it doesn't make enough of a difference for me to care about.
I'm a low temperature fanatic... really... and this is a non-issue. It really is. You can be a purist if you want, but this really won't make any difference that will bother you in the field or in final system operation unless you're trying to do setback or something silly like that. If installation time can be cut 60 to 70 percent, I'm not going to tell someone it's a bad idea because of these VERY SLIGHT EFFECTS. especially if time is at a premium. Perhaps your labor is cheap.. I occasionally work with people whose time is worth $100/hour or more. I also work with other people who have other things to do. If they were really compromising their system performance, you bet your booty I'd put my foot down, like I do when they want to cut corners and use those worthless BFB or tarp insulation products.
But they are not. So I don't throw a hissy fit over it. In fact, I have no problem with it at all.
the big waste is when someone ties to wire mesh and doesn't lift. It's a waste of time, and it renders the mesh useless. But thermodynamically, I don't care about that either.
-------------------------------------
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Edited 6/27/2007 11:08 am ET by NRTRob
<<<Wow, that quote sounds exactly what I just said, doesn't it? "slightly" higher water temperature. I added a "slightly" to response time as well. Why would siggy saying exactly what I'm saying change my mind again?>>>Not exactly Rob, I invite you to revisit pages 330-331 of Siggy's text. Siggy does not quantify with "slightly" but rather "reasonably":
"Experience has shown that slab-on-grade radiant floors will still function reasonably well when the tubing is placed hear the bottom of a 4- 6- inch thick slab. Higher water temperatures will be required to maintain a given rate of heat output. The higher operating temperatures tend to lower the efficiency of heat sources such as ground source heat pumps and condensing boilers. They also increase the rate of downward heat loss to the soil." (Modern Hydronic Heating. J. Siegenthaler. 2nd edition. p. 331.)Furthermore, the potential extra expense of "$100/hr" labor you mention waiting may be offset by the potential savings in efficiency and future energy costs. Yes, I have lost sleep over preparing a radiant slab system. Why? Because once it's poured, the floor is there to stay not to be tinkered with, unlike above floor systems. The real issue here is how to maximize control over the system put in place.
http://www.pmmag.com/CDA/Archives/bcf53d9e1efc7010VgnVCM100000f932a8c0____it does make a difference, as I said. Perhaps siggy was a bit more pronounced in his statement than I remember.Still, using this model, to achieve that same 25 BTUs/sq ft with tubing dropped from a 2" centered height (the max recommended in a slab typically) to a 3.5" centered height, your water temperature would rise from 100 degrees in this model to perhaps 107 degrees.for a more typical load (25 is fairly high), you're probably looking at a 5 degree change or less. Sorry, as into low temps as I am, even I can't pretend 5 degrees is a particularly big deal on nearly any system.so sure, that's a real temp change. a deal breaker? not even close. the efficiency change on a geo system or a modcon would also be minimal. And loads higher than this on slabs are pretty rare in commercial situations, and in residential situations other parts of the system are more likely to be setting the max temp for your radiant system before your slab areas will.IF the water temperature drop translated into a lower maximum water temperature, and IF that were the max water temperature I were running a mod/con or geo system on, I might consider it more worthwhile, but even then not such a big deal, and in practically any other situation it is truly not very important. As for the response time issue, maybe that's more of a concern for others. We use control hardware smart enough to deal with it. If you do bang-bang slab control, you're probably going to have swings anyway. So again.. tying and lifting is techanically superior, yes. Not by enough that I would ever insist on it, nor condemn anyone else for not doing it, for any reason they care to justify their action with.-------------------------------------
-=Northeast Radiant Technology=-
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Ok, Just to sum it up. Siegenthaler, Holohan, and the I-B-R training manual all agree that it is better to install the tubes in the center of the slab and that installing them on the bottom is not as good ( to some unagreed upon degree ) .
I really have not seen the numbers to compare them scientifically. I believe you are better off both structurally and from an energy efficiency standpoint to do it the way they prefer.
If you have any documented evidence that there is no difference in performance of the system, you should present it. Just because you staple tube to the floor and the floor still gets warm doesn't mean too much. Somebody must have done their homework in studying this. How does anyone add up the inefficiencies, even slight, over the life of the system??
I'm sure this all came about when somebody invented the foam/tube stapler and then set out to justify it's use industry wide.
How does anyone add up the inefficiencies, even slight, over the life of the system??
The way you wrote that it seems you are thinking it's costing more money to get a btu of heat out of one system over the other. The heat transfer is slightly less, but that's not the same thing as actually losing heat ($) in the system.
Concrete conducts heat pretty darn well so all this is beating a dead horse. Effort and money would be much better spent on additional insulation, which will pay for itself over time and reduce heating loads, often significantly.
HVAC guys seem to keep it in their head that the heating/cooling loads are static when designing a system since they are in the business of providing HVAC hardware, and are totally oblivious to including insulation upgrades to make a more comprehensive and cost effective package for the long-term.
We should be spending 80% of our time on the 20% of design decisions that get the most bang for the buck to reduce overall costs. Pex placement in the slab isn't it. Any HVAC design that doesn't include insulation improvement also is missing the boat.
Cheers
Beer was created so carpenters wouldn't rule the world.
When you have to provide hotter water or run your boiler longer than you would when using another system, you are wasting fuel. It's simply a question about how much more fuel you are willing to burn for the sake of faster tubing installation.
Try turning a hot water heater down 7 degrees and see if it makes a difference in your heating bills. I guarantee you will see a difference and the same thing applies to a boiler.
All heating experts agree that the tubes in the center are more efficient. What I have yet to see quantified, is how much more efficient.
Obviously you have your reasons for using the stapling method. My point to the original poster was that in his situation (using mesh in the slab) I would tie the tubes to the wire and put them in the center of the slab.
If he was pouring a basement floor, where he probably wouldn't be using mesh, he wouldn't have much choice other than to staple to the foam.
When you have to provide hotter water or run your boiler longer than you would when using another system, you are wasting fuel. It's simply a question about how much more fuel you are willing to burn for the sake of faster tubing installation.
You're not getting the point about btu transfer. A boiler will only add as many btu's into the tank as have left the hydronic loop into the concrete and other surfaces along the way. If 95 btu's have been taken up by the concrete slab with a staple down system instead of 100 with the pex in the middle of the slab, those 5 btu's aren't lost out of the system and the boiler doesn't add 100 more, but rather only the 95 that were used.
Your example of turning down a hot water heater 7 degrees is a totally different situation since 100% of the water that goes out of the hot water heater leaves the system completely.
A few extra coils of pex would completely make up for the loss in btu transfer by having the coils resting on the foam. No higher temps needed, no extra anything. In most cases it's simply not needed since tube spacing is rarely too far apart. In fact I'll bet our radiant installs have 50% more pex than are actually needed in the coldest conditions, but it's quick, cheap and always works well. A small loss in transfer is meaningless since we've over built the loops to begin with.
As for pex against foam creating uneven heating, that simply doesn't happen since the temps even out as the heat rises through the concrete.
The temps against the foam aren't even, but that's a non-issue. We don't live on the foam side so it just doesn't matter since the temps even out between there and the slab surface.
There are many urban myths about hydronic systems that have been passed down from some very smart people who have made the mistake of writing books about optimizing the tiny details rather than empasizing good basics and attending to the other details on a cost/benefit basis. With no experience it's hard to know what those low value details are.
An in-slab hyrdronic system is about as simple and hard to screw up as it gets.
Good heating
Beer was created so carpenters wouldn't rule the world.
You are overlooking one major factor...the inefficiency of the boiler itself. Your example is only true when the heating unit operates at 100% efficiency. Most are nowhere near that, so any time the unit is running, heat is lost up the chimney and leaves the building envelope.
The goal is to heat the building using the lowest water temperature possible and minimizing boiler on-time. This is where your previous statement about paying attention to the sealing and insulating really pays off.
There are varying degrees of inefficiency in every system, depending on the boiler choice and the method of heat transfer.
Placing tubing near the center of the slab is simply more efficient than any other method when heating a concrete slab,and I don't think any heating expert would disagree with that.
There is no doubt you can heat a room with the tubes on the bottom, but how much extra this actually costs the owner over the life of the system is up for debate and depends on the heat source and a number of other factors.
An in-slab hydronic system is about as simple and hard to screw up as it gets
(Amen)
I just posted the article siggy wrote about this. Yes, it is BETTER to have the pipe in the middle. I don't know how many times I have to say that and agree with you, before you understand that I am not saying it is BETTER to install pipe at the bottom.The ONLY point I am making, is with siggys OWN numbers, it's NOT THAT BIG OF A DEAL.The difference in responsiveness is not going to make or break the system either. It's dwarfed, I would think, by the mass of the concrete itself in the first place. which is why it's generally a good idea, unless you're in a basement where loads don't change much or quickly, to use reset water temperatures, which minimizes overshoot. And/or intelligent thermostats that can "Plan ahead". Rapid response on temperature change is not a hallmark of slabs to begin with. A little slower response is, in most system, of no concern whatsoever.Neither is a 5 degree shift, most of the time.Frankly, I'd much rather fight over insulation, which has a much larger effect and is a much larger battle. Someone wanting an easier tubing installation doesn't trouble me at all. Based on SIGGY'S OWN NUMBERS.-------------------------------------
-=Northeast Radiant Technology=-
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Rob,
I think all but one of the BTers reading your responses completely understands your position. That's probably about as good as you're going to get :)
Don
fair enough. sometimes I try too hard ;)-------------------------------------
-=Northeast Radiant Technology=-
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Make that two.
I'm still waiting for Rob to provide data to support his repeated claims that stapling the pex to the foamboard will substantially reduce the operating costs when compared to a mid-slab installation.
Sorry Rob. Couldn't resist. :)"Listen, strange women lying in ponds distributing swords is no basis for a system of government."Jon
help help, I'm being repressed!-------------------------------------
-=Northeast Radiant Technology=-
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Thanks for the input. I'm going to do as described in original post, but probably will increase slab to 5" for good measure. I'm thinking mesh and fiber as a "belt and suspenders" appoach (love the saying, learned it here!)....sound good?
Will be asking for advice as I move along and bump into stuff I'm not sure about, maybe even stir up a good controversy.
Lately, I've been thinking about siding install. Sip wall with fiber cement. Fir out for drain plane or install right on sip over building paper? PJ
Everything will be okay in the end. If it's not okay, it's not the end.
Ok, Siggy has a new article about the optimum depth for tubing.
http://www.pmengineer.com/CDA/Articles/Column/BNP_GUID_9-5-2006_A_10000000000000153040
As Colonel Klink would say, "Verrrry Interesting"!. Rich, looks like I'm gonna have to run the boiler a little warmer if he's right....I put the pex down on the foam today!
View ImagePJ
Everything will be okay in the end. If it's not okay, it's not the end.
Looks good so far.
Siggy's temperature model curves have some glaring problems.
View Image
Using his model and simple A^2=B^2+C^2 triangulation, I noted the floor surface temperature where the floor was 3.7" from each pipe. The difference between the floor and 100* is the recorded Delta T. His model show a 2.1 degree error range. At any distance greater than 2" from the centerline, the modeled floor temperature for all pipes is identical +- the error range.
He suggests the pipes should be 1" from the surface in a 4" slab. This gives a heat stripe that varies 4.5* in 2" at the centerline and 9* across the entire 6" that is half way to the next tube.
He suggests that raising the height of the tubing lessens the power required to pump the same BTUs, but since all temps farther than 2" from centerline are equivalent due to the error range, all increase in efficiency would occur in the 2" either side of center, or only in 33% of the total floor area.SamT
Personally, I still think that halfway in a 4 inch slab is best.
And in the second last sentence, Siggy recomends halfway in the slab.
The real issue is will the owner of a 1200 square foot house see a difference in his gas bill. Probably not enough to lose sleep over.
It may be a significant issue on a 20,000 square foot warehouse.
Better to look at the system. If you use foam, bottom of the slab is ok. If you use foil, or no insulation, it would be better to have the tubes at the top.
My 18 year old is about to head off to University in a week. My gas bill for domestic hot water is going to drop. Probably in half. But my education bills are about to go way up.
Every change has a ripple effect. Some are just larger than others.
Edited 8/27/2007 1:34 am ET by rich1
"And in the second last sentence, "Dint cee dat. After I saw the discrepencies in the models' graph, I barely scanned some of the rest of the article, because I had made up my mind that his model was flawed making his conclusions invalid."Siggy recomends halfway in the slab."Even in the middle, his graph shows a 2* Delta T over 2" and 5* over 6". However, one fact trumps all models. I wonder what NRTRob has seen."If you use foil, or no insulation,"It would be better to not use RFH at all.SamT
What have you seen that applies to this?SamT
I'm not sure what you mean. I have not done the modelling, nor the experimentation I bet Siggy has and I would trust his numbers.-------------------------------------
-=Northeast Radiant Technology=-
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"I'm not sure what you mean."I figured that you had seen and measured the floor temp on several systems with the tubing at a few various heights and would know some factual numbers for the difference in floor temp from tubing temp. "I bet Siggy has and I would trust his numbers."Assuming the graph shown is a fair representation of the results he got, I don't.Using his graph for the calculated floor temperatures at various distances from the centerline of each tube, I calculated where on the floor surface would be 3.7" from each tube. This would be the X axis.I then extended down to each tubes floor surface temp curve and read the Y axis to find the calculated floor temp. Subtracting that from 100* gave the calculated Delta T of that point on the floor surface that was 3.7" from the respective tube.It probably would have been easier to understand if I had used floor temp instead of Delta T. The two are equivilant. One is temperature, the other is 100* - temperature. In Latin, this would be "it-so same-oh" :)Even though it might be easier to see by looking at floor temps, the reason I looked at Delta T is to calculate the models' error range and error %. The error range is (Max D-T minus Min D-T), or 2.2* and the error percent is (error range) divided by (average D-T). The average D-T is 20.175, so the error % 10.9%.Consider that the floor temp for all four tubes is within the error range of each other for half the floor area and for the top three tubes that is true for almost 75% of the floor area, even though the difference between successive tube elevations varies from 5/8" to 1.3" or more than a factor of 2.I presume that siggy has a budget allowance. He could have made experimental measurements for the cost of a couple sacks of ready mix, one sheet of foam and one stick of copper as long as he already had an infrared reading thermometer.As far as I personally am concerned, the only thing Siggy's model is good for is to show that there is one heck of a heat striping effect as you raise the tubing.SamT
he's doing straight forward FEA, as far as I know. I'm not sure what you think your permutation of his numbers is proving? You can't just pretend that temperature is equal 3.7" from the tubing, no matter how the tubing is positioned. The temperature 3.7" toward another run of tubing is likely to be warmer than the temperature 3.7" straight up in a thick slab, for instance.I think the calcs you are attempting are more complicated than you are giving credit for.But, they are more complicated than I have attempted myself, so don't think I am married to that thought, it's a bit beyond my attention span right now. This is just my initial reaction; for something this simple (tubing in concrete) I would trust FEA and siggy more than a permutation for sure.Heat striping is definitely real, that said.... check out thermographic pictures of tubing in slab sometime. very "illuminating".-------------------------------------
-=Northeast Radiant Technology=-
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Ok. At last, part two of does depth matter.
http://www.pmengineer.com/CDA/Articles/Column/BNP_GUID_9-5-2006_A_10000000000000165825
blarg! Nasty toes. Taste bad!!!That's more significant than I had expected.You'll be interested to note that we added some verbage to our systems to advise clients accurately about this after the last conversation, to make sure we didn't give anyone the impression that there was NO difference and so performance purists could make decisions as they wished.This isn't crippling, by any stretch, but it is significant enough that I'll have to strengthen the wording on that advisory.Thanks for bringing that back here Rich.-------------------------------------
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Yeah. on a 800 sq ft office/ house, no biggie.
Looked at a shop last night. 4000 sq ft. tubing in center. bubble wrap underneath. Oh well, better than nothing.
But ........
They used 4- 1000 foot rolls of pex. You guessed it. 4 loops.
Doing the math, going to be a strech.
They want to put up a 16,000 sq ft shop. I think they will talk to me first.
ouch!!!Hopefully it won't take a jackhammer to fix.We have worked with a reversing 4-way valve.. I think siggy drew it up originally, or maybe it was hot rod. heat half the loop at a time, switching every 20 minutes or so. It's a band aid, but better than a jackhammer in some cases.-------------------------------------
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Big pump and high temps. Might work.
Soooooooooooo.............
4000 sq ft with a heat loss of about 180,000.
4 loops requiring about 2.5 gpm each.
2.5 gpm in 1000' of 1/2 pex has a head loss of about 70 feet.
So 10gpm at 70 feet.
Found a grundfos that might work. tp100 series. 4" flanged feeding 4 1/2" lines.
Whatcha think?
70 feet of head is what, about 170 PSI?I think you'll be exceeding the pressure rating of the pipe.That load sounds pretty obscenely high.. 45 BTUs/sq ft?-------------------------------------
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Quick figures came out at about 38.
As much as I hated to, I think I've talked them into tube heaters.
This is a truss shop, but they don't have dust collection installed yet. Can only imagine what that would do the heat loss.
Once they work under tubes, I'm thinking they are going to want them for the new 16,000 sq ft shop.
You've already had lots of answers on the mesh. I'll say I don't think you really need a vapor barrier if you are going over 2" of foam.
Don't forget to make a thermal break around the perimeter, at least ½" of foam.
Are you putting the dust collection for your table saw under the floor? Power under the floor?
I considered the ductwork and power in slab, but I'm just about certain that either equipment will change or I'll want to move it. DC will run overhead...this stuff looks pretty cool for reconfiguration, http://www.nordfab.com/index.cfm
Some power on wall, table saw will probably get a ceiling drop.PJ
Everything will be okay in the end. If it's not okay, it's not the end.
Btu transfer between pex and concrete is so good that you will find little practical advantage to the pex in the middle of the slab vs stapled to the foam and any disadvantage can be overcome with a few extra coils, but in most well insulated applications that's splitting hairs and just not necessary. That's simply arguing over two good options.
Our standard pattern for well insulated new construction in pex 12" oc over 2" of foam. For material planning that's 1' per sqft of floor plus the legs back to the manifold with loops of 330' (1/3 a 1000' roll). Simple to extimate and effective in use.
I find it counterproductive to suggest that it's desireable to pull the mesh and tied tubing into the middle of the slab. We want both towards the bottom to reduce the risk when cutting contraction joints. We also increase the depth to 5" for both increased mass and further safety factor for cutting the slab.
If a slab needs reinforcement we'll add rebar over the pex and on chairs.
Costs will be lowest if the pex is stapled to the foam since it's a great deal faster and steel is expensive and is doing little else if just sitting on the foam holding the pex since the concrete can't get a good hold of it.
You'll also want to make sure the foam is taped well prior to placing the metal and pex. Tyvek tape works well and will hold water surprisingly well if applied to clean foam. Tape it down as you go and it will save you the grief of cleaning dirt and dust off the foam so the tape will stick.
If you have a sand/gravel base being put in under the foam you may want to consider putthing the foam and vapor barrier under the sand/gravel. This brings that mass into the building envelope and reduces the risk of slab curl or voids due to excess water collecting on top of the foam. There is very little extra cost and I'd argue it's less prone to problems.
Some may question the value of extra mass in a basement where temps will remain mostly constant during the day, but there can be huge advantages if there are air handlers that can circulate air throughout the house. The mass of the slab in the basement can be a heat sink for the upper floors helping to store heat during the day and release it at night (or via versa), reducing AC and heating loads. Essentially using passive solar practices and benefits in standard construction.
If you have no provision for moving air, a few Fantec remote fans and 4" or even 3" flex duct can be strategically placed to move air within the home. It's easiest if the existing hvac unit is run at low speeds in fan only mode to circ air between the floors.
Best of luck.
Beer was created so carpenters wouldn't rule the world.