Staple-up radiant heat; Aluminum plat... - Fine Homebuilding

We are building a new sq ft house, well insulated with sip panels. While Warmboards are clearly the superior product, they are also $ more than what we can get Roth panels for, and an even greater difference for Zurn Thermal Track. Here are the questions:

1) I know that thick aluminum is better than thin, but how MUCH better? Roth and Warmboards are .02", and the thermal track is quite a bit thinner at .004". I figure that even if the warmboards were so efficient that they saved us $30 a month in heating costs (over the thermal track), it would take twenty years to make up for the greater upfront cost. Does anybody have knowledge about how much more efficient the thicker stuff is? And does it spread the heat more noticeably?

2) Does anybody have experience with Roth panels? Our concern is that the foam may compress over time. We are also wondering about installing hardwood floors over them- they say to use nailing strips in between the panels, although it seems awkward to do this around the places where the tubing bends. And there is no aluminum on the rounded ends- is this noticeable in the floor heating pattern?

3) Does anybody have experience with Zurn Thermal Track? Does the floor heat evenly in spite of the thin (and therefore lower conductivity) aluminum?

thank you for any input!
Laura

Thanks for your replies. Our total load is 35,000 btuh, and the basement level will be concrete slab, so we're looking at around sq ft of floor panels. The heat source will be a gas boiler. Wehave sip panels construction, with R27 walls and R42 roofs.

Three questions about the RHT panels:
1) It looks like in this sandwich construction, most of the aluminum is below a 3/4" layer of plywood. How much efficiency is lost by having this extra layer between the aluminum and the top flooring? Does the plywood act as thermal mass, or does it act as insulation?
2) I'm wondering about inverting the aluminum plates, so that they lay above the 3/4" plywood, and the u-trough for the tube lies in the gap between the boards. This would put the plates right up under the hardwood flooring. Seems like you would get much more direct heat transfer. Is there some reason why the system isn't designed this way?
3) Are the plates wide enough that they are continuous across the floor, or do they just run several inches on either side of the tubing? And how much effiiency is lost if there is not continuous coverage?

As for the thickness/thinness of the panels, are there some actual figures available for the btu output of these various systems, so that their relative efficiency can be accurately compared? Seems like a very murky area with lots of speculation, but maybe thats just the way it is for now.

NRT, are you saying that the warmboards actually produce the same output with 30 degree cooler water? thats a pretty huge difference.

thanks for your thoughtful replies. warmboard should be 20 to 30 degrees better than thermal board, but that difference diminishes under low R floor coverings (tile) and especially under low load conditions (very well insulated for your climate).

I have no idea why anyone would put the aluminum under the plywood. We always put aluminum plates on top of the infill when we do sandwiches. It should make a difference in water temperatures. Sandwich, incidentally, should roughly split the difference between thermalboard and warmboard. that's rough of course, but a decent approximation.

sandwich plates are not typically continuous.

Most manufacturers have output charts for their products. Some lie. Some methods, like sandwich, don't really have easy charts available and so it is a bit "murky", as you say. But even with exact output given... then define what the efficiency difference is, running your system 30 degrees cooler (to take a very big example). Go ahead, I'll wait ;)

There is a lot more that is "murky" than just output at a given water temperature, for sure. You can be sure running much cooler is potentially more efficient, but how much is always hard to say. OK,
I will try to reply,
Yes it does seam backwards to place the plates as we do, and yes we live in a democracy so as some of our customers do they place the plates grove exposed. to do this is easy and certainly accptable, we prefer the protection the plates offer to the pipe.
In our application it is quite fast these are the steps.

Detail;
1st. place turns first according to lay out, turns have a slight bevel so the pipe is captured.
2nd lay in 4 or 5 lengths of pipe(turn to turn) and cover with plates (1/2"x24"x5" Heat Transfer Plates single 'U' style .019" thickness)
3rd use site manufactured 3/4 ply wood strips ripped 6 3/4 inches fasten down with nail gun, screws, hand nail ring shank, what happens in this process is that the plates, pipe and plywood are smooth to the floor and the straight edge of the 3/4 plywood straightens out the floor.

If you chose to do the top down approach you follow similar steps,
1st Place turns
2nd place 3/4 X6 inch plywood infill strips,
3rd place heat transfer plates grove up, secure with your favorite (hand nail, nail gun,screw).
4th place pipe

Both systems work great,

Our average system temperatures run in the 100-120 degree range, less is better. the plywood becomes saturated with heat and works like a thermal mass.
We have had zero complaints with this system.

We do not have and charts, we just know it works. it is a tremendous improvement over staple up, system temps can stay quite low. the saturation of heat is held with in the envelope.
This brings to question how much heat in the warmboard system is saturation in to the wood, It certainly does not all radiate up....I think we have a thermal mass issue here, though not as prefered as concrete,

On another design note worth mentioning, a clever woman in up state NY applied this system using our 12 1/2 inch wide plates over a uneven barn floor, I think this is a great think out a the box design;
not level uninsulated slab,
She took long 2x4"S pressure treated, laid them out on a 12 inch pattern, shimmed to level and fastened to the concrete placed Bubble foil bubble ( I know smoke and mirror) between the 2x4"s . she was working on a slab error of like 2-3 inches over 60 feet and did not want more cement and foam, we went there with her.
Next using the 1/2"x24"x12.5" Heat Transfer Plates double 'UU' style .024" thickness she stitched the 2X4"s together, snapped in the pipe, 8 inch pattern, and captured the whole thing with a ply wood top.

Dan


I agree wood has an insulation property, R-1 per inch. At least that is what I am told when looking at R value of say a log building.
Closed cell foam similar to DOW board is R 5.5 per inch and has little ability to hold heat as mass. Wood on the other hand does. Further we also see that in the sandwich application there is surface exposure of the top 1 inch of the heat plate, or on an 8 inch pattern 15% of the surface of the plate is exposed on the upper layer.
I whole heartily agree that if you want more surface area place the plates top side rather than captured.
Point is it works both ways at low temp, I can only assume that there is a heat saturation effect.
More specific is the RHT Floor Panel system has its place. It is a direct substitute for a large number of the conventional systems offered by the cooperate giants at less than 1/2 the cost. By relying on the ability to rip plywood in the field using local lumber we present a some what greener alternative than shipping an entire above sub-floor system across country.
We have a large project coming up locally in the next couple months, I will suggest to the installer on site to place one zone plates up, we will photo documenting the project anyway and this may be a good start. The whole house will be heated with a condensing boiler (LAARS Neo Therm, Nice boiler I might add).
The Design temp is set at 110 degrees. Perhaps a side by side study of 2 zones will be of use. The only real difference I would expect is speed of recovery.
Dan





You don't want more than a few inches between plates if you are on top to avoid heat striping. but continuous is not necessary. We use a 5-3/4" wide plate 9" o.c., or a 4" wide extrusion for high output at 7" o.c. (both picked to minimize plywood waste as much as anything.. 1" gap between strips).

Dan: you know there is more to expect than just slower response. What affect does throwing another 1-R down on top of your floor have? That's the difference between "wood" floors and "carpet". It's almost the difference between underfloor and overfloor systems. It makes a difference. If you're going to put the plates under the infill, save the cost, expense, and resource usage of your extra layer of plywood entirely and stick to the joist bay.

And the plywood was likely shipped just as far as Warmboard.

And you're really missing the boat if you are counting on the wood to act as a thermal mass. Pound for Pound it holds half the heat of concrete, and you have a lot less pounds per square foot than you would with concrete. "not as ideal" as concrete is a bit of an understatement: it's useless as a thermal mass. Utterly useless. OK,
First pipe pattern, If using the RHT floor panel system, turns are on 8 inch pattern, the 5 inch plates are easier to line up and work fine.

Ok, Thermal Mass, first agreed wood is not ideal and pales in comparison to concert.
Post form another green builder, solar section;
Concrete has a specific heat of .156 Btu/lb/°F and a density of 144 lb/cu ft. Pine is .45 & 34. That means it would take roughly 3 times the pounds of wood to store a thousand Btus as concrete, and since it weighs only about 1/4 as much the volume would be about 4 times as much per pound. It would take roughly 50" of pine thickness to store the same amount of heat as 4" of concrete. Oak is .57 & 50 so it would take only about 30" of oak!

My point was that there is stored thermal mass.

Next Wikipedia, search Thermal mass;

Properties required for good thermal mass
Ideal materials for thermal mass are those materials that have:

* high specific heat capacity,
* high density

Any solid, liquid, or gas that has mass will have some thermal mass. A common misconception is that only concrete or earth soil has thermal mass; even air has thermal mass (although very little.)

Again this is no substitute to concrete. We are in full agreement here.

Last, movement of plywood vs specialty items made of wood.
Plywood is a huge commodity,made in mass production runs at maximum efficiency vs waste. If not manufactured locally/regionally it is most often transported by rail. Rail is the most cost effective mode of transportation short of sea container.
So if the stars line right your ply is made regionally, or second best moved geographically closer by rail. These are the contributing factors on why I can buy 3/4 ply 4x8 sheet for 25-30 dollars in anywhere USA. Am I fooling myself?
Done for the day, best to all.
Dan







Dan, obviously wood has some mass. while all is pure energy, you can pick up wood and feel that it has weight. Kudos for noticing this ;)

even though it technically has mass, it's not enough to be useful for any purpose we are discussing. That is why we don't build wood passive solar walls or collectors or tell people to add layers of wood to their floor if they are short cycling their boilers. Because it doesn't help and it only serves to confuse the issue to talk about the "mass" of the wood floor. Why not also talk about the "mass" of PEX pipe or the aluminum plates themselves? Because it too would be silly.

Mass collects and stores heat. Wood does not do this to any level that is worth considering. You are using wood as a conductor, which it is not good at doing, and that is all. The only benefit mass brings to the table anyway is either collection of passive solar energy, time-shifting your heat generation (say,to off-peak times), or cycling control on a low mass heat source: wood won't help with any of this. so practically speaking, it is not a thermal mass. Which isn't a big deal, because mass itself is only useful for those three things anyway, but acting like "wood has thermal mass" isn't much more useful than throwing down a carpet and claiming it too is thermal mass.

Point taken on rail shipping.