# Best isnsulation under radiant tubing.



## Dune (Jan 18, 2010)

Hi, working on the big picture here, trying to plan what to try to accomplish this year. I really want to spray foam my rim joists. I also want to install stapleup radiant tubing, so am holding off on the rim joist job till the tubing goes in. Is there anyway I can use spray foam to insulated under the tubing? I am afraid it would eliminate the air space which seems needed to heat the floor. Help! I can't start the actual work till the planning stage is finnished. Thanks.


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## Gooserider (Jan 18, 2010)

I've seen mixed stuff on the use of spray foam under Pex...  At least some of the stuff I've seen seems to suggest that spray is OK if you put the pex up w/ aluminum transfer plates, which I think is a good idea in any case...  What I'd be somewhat worried about is whether or not the PEX could do any thermal expansion / contraction if it's foamed in place, and whether or not the foam chemistry is compatible w/ the PEX (If you read the manuals at least, it seems there is a lot of stuff you shouldn't get near it...)  The other possible concern I could see is the foam getting in between the PEX and the floor, and expanding so that you have an increased R-value to try and push the heat through...   

Hopefully HR or one of the other guys that does a lot of this stuff can give a more definitive answer, but my first guess might be to staple up some of the cheap bubble wrap radiant sheet insulation over the PEX, and then spray the space between the bubbles and the bottom of the joists...  

Gooserider


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## Frozen Canuck (Jan 18, 2010)

Dune said:
			
		

> Hi, working on the big picture here, trying to plan what to try to accomplish this year. I really want to spray foam my rim joists. I also want to install stapleup radiant tubing, so am holding off on the rim joist job till the tubing goes in. Is there anyway I can use spray foam to insulated under the tubing? I am afraid it would eliminate the air space which seems needed to heat the floor. Help! I can't start the actual work till the planning stage is finnished. Thanks.





You will want to insulate to the point where you reach the inside face of the wall in the floor above, all the way around, then install the radiant tubes & aluminum plates to help spread out the heat, then insulate over them, however we have never used spray on foam over the radiant tubes. We usually use reflective bubble foil or fiberglass or other batt type insulation. I believe that a spray on would leave you with warm strips in the floor above (something you will want to avoid) as it would stop the outward radiation of heat from the tubes.


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## Gooserider (Jan 18, 2010)

Frozen Canuck said:
			
		

> Dune said:
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Not arguing the point, but how much of the heat spread is through the air under the floor vs. through the floor material itself, and the aluminum plates?  I agree that doing foam w/o the plates would be a bad idea, but I don't see that foam over the plates would stop the heat spread through the plates and the rest of the floor material...

At least some of the places where they were saying leave a gap under the tubes were also the places urging plateless installs, which seems like a bad idea to begin with...  The places that said to use plates seemed less fussy about putting insulation right up against the tubing / plates...

Gooserider


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## in hot water (Jan 18, 2010)

I would highly recommend the aluminum transfer plates.  Plates allow you to use the very lowest temperatures to get the job done.  Same with some of the above floor products with aluminum, like the Roth panels.

The very best way to move the radiant is with a conduction transfer.  If you use transfer plates and fasten them tightly to the floor then spray foam works nicely.  I would check with the foam manufacturer and installer, and limit the temperature.  Most loads should be able to be met with 120F or less in good transfer plates.

If you do a suspended tube, then you need an air space as the heat transfer in convection and radiation.For that a bubble foil with an air gap then batts or spray foam for the r-value.

Pay attention to the rim joist detail.  All wood shrinks and you need to seal that rim joist from infiltration as the plates and joist dry and shrink.  And they do tend to shrink with radiant heat applied.  Fiberglass batts are not a good insulation for rim joists.

Grab a copy of Joe Lsitiburek's Builders Guide to Cold Climates.  Joe has the best methods and details for insulating regardless of your climate.  Get to one of his seminars if you can, he is a sharp and funny guy.

hr


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## Fred61 (Jan 18, 2010)

I think the spray foam will work well. I have some under-floor and some in-floor, some with plates and some without. I would definately use plates but would also install reflective material under tubing before foaming.


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## connerfur (Jan 18, 2010)

We are about to do exactly what you are asking about. As it was explained to me, by a mechanical engineer that works with heat transfer on a regular basis, using the spray foam over the pex will only aid in the heat distribution. I was concerned about the same things that you mentioned but I'm being told that the heat will spread more evenly throughout the subfloor using this method. He likened it, somewhat, to an installation in concrete. 

The only question I have is that our spray foam installer told us that most of the radiant jobs he sprays using Joist Trak have been over the silver tape which the radiant installer uses to cover the tube. The only reason I can come up with for that is to keep some of the foam out of the track to prevent the foam from popping it out while it expands. Has anyone heard of taping these before?

By the way, we had the walls and ceiling spray foamed last week and the process was much more messy then I ever imagined. I tried to download a couple pictures of the spray foam but the file was too large.


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## Hunderliggur (Jan 18, 2010)

You didn't say what is below your radiant tubing.  Is it conditioned space or an unheated crawl space.  We insulated the 2nd floor under floor radiant (with metal plates) with batt insulation but more for sound than heat.  Heat will generally rise and any heat that "falls" is just adding to the 1st floor space.  Ditto for the 1st floor radiant and the basement - we use our basement so a little "lost" heat is fine.  The spray foam will greatly limit your ability to add anyting (like wires, pipes, etc) in the future.  We d have a radian barrier (foil) below the pex. BTW - what do you folks have to pay for foam?  It is not popular around here.


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## connerfur (Jan 18, 2010)

We're going to run the whole house with radiant so basement, first floor and second floor are going to have the tubing. We also laid pex in about 2/3 of the slab last year before they poured the basement floor. We are working on running forced hot air as the primary "heat up" source and then having the radiant take over. This is a vacation home in norther NH that we plan on keeping at about 40 degrees when we're not there. 

We plan on about 2 inches of spray foam over the pipes but I'm a little concerned about running wire and plumbing after we spray foam. At the same time, I don't want everything encased in it either. 

The foam ran in the neighborhood of 80 cents per sq ft. per inch but we recieved more then we paid for. I think its difficult to control that stuff. We have 2 X 6 walls and paid for 4 inches but most of the bays are just about full. Same thing with the rafters. The only thing we did there was to build proper vents out of strapping and 1/2 rigid foam board and had them spray over the top.


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## sbleiweiss (Jan 18, 2010)

I have a question about how the foil faced bubble wrap insulation is applied under the radiant tubes. The stuff I have seen is in rolls about 4 feet wide. Is it simply spread across the bottom of the joists and stapled to them as one large sheet, or is it cut into strips and installed up inside the floor joist bays.


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## Hunderliggur (Jan 18, 2010)

I am sure others will have other opinions, but I don't see the value in spray foaming the radiant in conditioned spaces.  Yes, you will get more "precise" zone contol, but with radiant you are working on heating a thermal mass (the objects in the house - floor, walls, furniture).  Any heat "lost" (that would have ben reduced by the foam) is going to heat conditiond space anyway so it is not lost.  Additionally, the heat radiated into the cavity (i.e., floor joist bay) will assist in keeping your pipes from freezing.  I would keep the house up to 40 while your are away with radiant for that reason.  I also had the domestic water in the house plumbed with pex.  Each fixture is fed with its own 1/2" line from a manifold in the basement.  This has two advantages - one, it is very east to turn off the fixture when you are planning to be absent (and minimize potential water damage), and two, pex is more freeze tolerant than cpvc or copper (not that you want it to freeze).


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## Hunderliggur (Jan 18, 2010)

Radiant barrier - we cut ours to fit between the joist.  Cut the tightly wrapped roll with a cutoff saw before unrolling.  We installed an inch or so below the tubes.


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## connerfur (Jan 18, 2010)

That is the problem we face with this project, many opinions and all many of the are valid points.  At my full time home, I stapled up some radiant and did nothing under it just so I could heat the basement.  In a second room I used a foil faced paper because there was too much heat going into the basement and not enough in the mudroom.  

The point has come up several times during this project that at some point you have to draw the line at where to stop.


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## Jackpine Savage (Jan 18, 2010)

One variable you need to consider is what type of floor covering you are trying to 'push' the heat through. If you have carpeting for example you are going to need more r-value under the floor. Hot air rises but heat moves to cold. You may end up with too much heat in the basement. 

There was thread over on the RPAnet forum a little while ago about a heating contractor that did a plateless staple up and then put bubble wrap between the floor joists. Then unbeknown to him they came behind and sprayed in foam. He is thinking that the foam pushed up and eliminated the air space in the joists. But the bottom line was that the house wouldn't come up to temp. The best suggestion was to add baseboard heat.

I used poly encapsulated fiberglass batts r-13 under the warm sections of the basement and r-19 under areas that I prefer to remain cool. The poly encapsulated bats are nice to work with and the basement will remain unfinished for awhile so it will also keep the fiberglass particles from getting into everything.


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## connerfur (Jan 18, 2010)

Trying to find that article.  Do you have a link you can post?


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## coolidge (Jan 18, 2010)

Always alot of good info on this site.  I installed tubing(onyx) in my old farmhouse, basement and crawlspace. Cut some 2" Atlas board(reflective board insulation) to fit the bays, all different widths. And sealed the edges with sprayfoam. I had also planned on installing tubing in the upstairs floor while the ceiling was out but decided not too. Was going to use a product i have use several times before for this application called The Insul-Tray from www.insulationmaterials.com. After installation you could use a open cell foam at around 5" to give you your insulation. Cheap!  Not at all.   Effective? Lets just say i dont have any UNHAPPY customers.


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## Jackpine Savage (Jan 18, 2010)

connerfur said:
			
		

> Trying to find that article.  Do you have a link you can post?



Here is the thread I referred to: http://radnet.groupee.net/eve/forums/a/tpc/f/4771065301/m/424103362


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## in hot water (Jan 18, 2010)

The very fist step should be a room by room heatloss calc.  You need to know how much heat (btu's) the space needs before you chose the heating system.  Personally I think 25-27 btu/ square foot is a reasonable number to expect in a residential application.  Beyond that you may get some un-comfortably warm floor surfaces, and high supply temperatures.  Most building materials should not see above 140F applied to them, plywood, OSB, sheetrock, even concrete.  Ideally you could heat the space with 120F or less for quiet, safe radiant performance.

If a room has a load beyond that range I would add panel radiators as a supplement, as they are still radiant, not convectors like baseboard.  So they can operate at lower temperatures.  And they are easily zoned with TRVs on each unit.

Kicthens can be tricky to heat as you need to subtract out all the cabinets from the square footage (heat flux)  That can sometimes make it hard to get enough btus into the room, watch that load number carefully.  Although refrigerators and appliances do add some heat when running.

If you use the tight fitting extruded aluminum transfer plates they should not be any foam getting into the groove, but the tape is not a bad idea.

Spray foam does tend to stiffen the floor a bit as a bonus as each bay is "glued" to the next.  It does make getting to any plumbing or wiring a hassle as it is all one big foam block.  There should be room below the foam to add wiring or pipes later one.  Once the sheetrock is up, it may not matter.

If you go with fiberglass or other products, don't scrimp on thickness, never 4" batts 6 or more.  A lot more if you plan on carpeting (a bad match for radiant) but it happens.

hr


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## sbleiweiss (Jan 18, 2010)

Can you give some guidelines on calculating the BTU/hr delivered by PEX at various temperatures.
I read through that thread on radnet. My vote is that the foam pushed the aluminum bubble wrap up around the tubes cutting off any air convection around the tubing effectively insulating them. Air that can't move = insulation. Or maybe the insulation contractor pulled out the aluminum bubble wrap before foaming. Either way, if you do go with foam, make sure whatever you put in place does not get re-arranged by the foam expansion.
I have a situation where I want to add a radiant loop under a hardwood floor. The floor nails are protruding through the plywood deck, so installing aluminum plates would mean I would have to cut off all the nails. Is it worth the effort or can I get a reasonable result with suspended PEX? I have a great room with cathedral ceiling and baseboard heat. The baseboard was marginal with oil boiler temps in the 190 range. It is now inadequate with the temps that the wood boiler storage delivers, so I am looking at radiant to supplement the needs.


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## Dune (Jan 22, 2010)

Thanks for all the great replies. I have been out of town for a few days. The floor I want to heat is over a crawl space and I want insulation under the tubing because I am losing heat through the floor. It is a hardwood floor and I don't plan on running the water very hot, hopefully about 100.

I really want to use foam, since I am convinced it is more effective and the insulation guy owes me.


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## walpoledan (Jan 23, 2010)

If you don't need the airspace between the insulation and the subfloor and can therefore choose between foam and batts stuffed up tight I think that the primary determiner would be whether you have any need to try and control air infiltration or if it's just for heat migration. The foam is excellent at really locking the whole place down and keeping air from moving around but if all you're doing is keeping the heat upstairs from the floor below the foam is likely overkill. Not sure how tight your crawl space is but that's probably what I'd use to make the decision. I suppose if the foam guy owes you then maybe it's a non decision though ;')

I'm doing the same thing here in my house. I had the local Icynene contractor in doing some upstairs walls that I had torn apart but also had him shoot all the ends of the joist bays in the basement and I couldn't be happier. I installed the Joist Trak afterwards, just holding it back from the foam blob at the end of the bay (or shoving it in a bit if the blob was particularly intrusive) and have put 3.5" fiberglass up. This was over my sometimes heated by wood stove and mostly warm basement though so perhaps a different animal than your crawl space. The kicker for me for the decision was that I can access any tubing problems later by just moving the fiberglass and also it was pretty cheap at something like 25 cents per square foot.

Dan


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## Dune (Jan 23, 2010)

O.K., so I guess what I am seeing here is that I can/should insulate the rim joist first anyhow, and use aluminum plates with the tubing. Any compelling reasons to use the extruded plates rather than the formed thinner plates? I don't really see how the extruded plates can perform so much better as to justify the additional cost.


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## walpoledan (Jan 23, 2010)

As far as before/after on the joist bay spraying, I don't see what the problem is with installing the tubing afterwards. I actually considered it to be beneficial. My chief concern was making sure that I kept the heat on the inside and kept the cold away from the water filled PEX. So, making sure that the rim was sealed up before installing the stuff left me feeling more comfortable that it was continuous and no tube was hanging out in some odd cold pocket in the foam. I have no real basis for that though, just the way that I worked it out in my head so take that with as many grains of salt as you like.

As far as the extruded vs. thin plates go... I'm 100% on board with the rationale behind the extruded ones. Here's the way that I understand it. Advantage 1 is that the extruded plates get a good grip on the tube with good firm contact over something like 60% of the circumference of the tube. This alone provides better heat transfer into the plate from the tube. The thin plates just don't grip the tube in the same way. Advantage 2 is that the thicker aluminum really transfers the heat out more evenly to the far edge of the plate  than the thin plates, the thin ones just don't have the meat to move the heat as well. Those two things mean that in the real world you can get the same average floor surface temperature with lower water temperatures and also that you get more even floor surface temperatures. The next two advantages are less quantifiable but I think that they are there. Advantage 3 is that the extruded plates make it easier to install the whole thing. You put the plates up (making sure that they transition smoothly from one another) and then you bang the PEX up into them. If you do it with the thin plates you have to get the pex up there and then attach the plates around it before you actually attach the tube. Advantage 4 is that the thick plates tend to make much less noise than the thin plates given the same control strategy. Neither is silent if your water temp varies a lot but the thin plates (at least the ones that I've heard) sound like somebody beating a marimba in your basement (well... maybe that's a bit of an exaggeration but definitely louder <g>). The only disadvantage that I'm aware of is the cost and that's not a small disadvantage... I put more money than I care to think about into the damn joist-trak in my house but I do really think that it was worth it.

So... that's they way that I understand it. Sorry if that last bit came off like a rant, not tying to be the crazy soap-box guy, I've just been thinking about it a lot so it was right there ready to come out ;')

Also, just some random other thinking that I came up with while working on my system, I'm not sure what the conventional wisdom is on this site for tubing layout but I think that it's worth considering more, shorter loops than fewer longer ones. The classic theory (at least in the books and with my plumber brother in law <g>) seems to be to lay out 300' 1/2" PEX loops, home run them to the boiler room and call it. But, I think that if you break those up into multiple, parallel loops say at 100' or 150' you can run a much smaller circulator (005 instead of 007, speed 1 on your 15-58 or maybe even a Grundfos Alpha) and still push plenty of flow through and keep a reasonable delta T in there. Higher fitting cost with more loops because of having to make the PEX up to the manifold in more places is the trade-off but you can often use manifolds without the balancing valves because you're laying out more short loops so balancing is potentially done right to begin with so it might be a wash.

That whole loop length thing is a bit more "out there" but it's where I ended up and so far I'm pretty happy with things and running with a gerbil powered circulator which is nice so I figured I'd mention it.

Sorry for the long post...

Dan


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## DaveBP (Jan 23, 2010)

As a personal theory let me add...One of the reasons that the extruded plates work better than the formed thin plates is that when you screw the plates up against the subfloor (especially if it is nice flat plywood and not rough sawn plank) the extruded plates get drawn tighter over a larger area. That also promotes better conduction of heat from the water to the finished floor up above. But they are fiercely expensive.

I'm going to put my PEX on top of the subfloor but if I were to do it from below and use the thin plates I'd consider screwing wood strapping on both sides of the PEX channel after it was all done. Just to pull the aluminum up tight against the subfloor. I've seen some installations that looked as though the aluminum was only touching at a few points where it was stapled up. 

The faster heat can flow from the water in the tubes to the flooring and up into the air above, the lower temperature the water needs to be to keep up with the heat loss of the house. Lower water temps are better.


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