I CAN'T TELL YOU how many times someone has asked me, and just about any wholesale supplier worth his salt, "What is the best insulation for below-slab application in snow-melt systems?"
And the only correct answer is that one correct answer for any hydronic question, and that is, "It depends!"
Of course, you already knew that.
I too ask myself those questions on a regular basis, and I'd often wondered what the answer was.
I also ask myself why none of the nonprofit organizations have ever really delved into this question. I guess the answer to that question lies in the hands of the people running the nonprofit organizations. With so many of the manufacturers being paying associate members of trade associations, it is not wise to nip at the hands that feed you.
But still, one has to wonder why it is that the subject has not been researched in depth to create a ratings and applications chart to help people like you, me and the public in general make some reasonable decisions. A lot of different materials are being used for below-slab insulation and, in some cases, no insulation at all is being used or specified.
And I'm supposing that somewhere, someplace, probably in a mismanaged documents vault for the federal government, someone has tested all these insulations. The data just needs to be cleaned up and put into a common and comparable form. And a person could probably spend the rest of his life looking for that data.
So, I set out to do my own unscientific survey and research. I call it unscientific to let everyone understand that this was not a controlled, scientific experiment. In reality, it is nothing more than a comparison of products under much the same scenarios of exposure and application. I'm pretty sure it doesn't include every possible or currently marketed piece of insulation. It wasn't meant to. I don't have the money for the data-logging equipment.
To get sidetracked for a minute, I have to let hydronic contractors know that if their slab is un-insulated, they are not doing themselves, the owners or the environment any favors. I also find it nearly impossible to guarantee performance of anything without insulation. I can and will spend more time on those topics at a later date. Now, back to the subject at hand.
The candidates
To avoid appearing biased toward any one product, I asked my local suppliers if they would be interested in donating or somehow acquiring the needed patches of insulation for our comparison. My suppliers, Matt Carr from Dahl Plumbing Supply and the omnipresent Dennis Bellanti from Ferguson Enterprises, came up with most of the off-the-shelf technologies.
The samples included 1-in. thick extruded polystyrene (XPS); bubble foil bubble ( BFB) one layer thick; 1/2-in. thick expanded polystyrene (EPS) with aluminum on one side; BFB glued to 3/4-in. EPS; Insul-Tarp and The Barrier.
I almost wish I had left one section completely un-insulated, but these comparisons were done on an active system in a customer's driveway (with theirs and the general contractor's acknowledgement and acceptance), and I didn't want to chance having an icy spot in the middle of a steep, curvy driveway.
The application
The "samples" were laid out in 4-ft.by-4 ft. patches, end to end, on a part of the driveway that rarely sees any winter sunshine. This was intentional to avoid the possibility of unexpected solar influence. Which brings to mind a quick question: Why don't people consider using solar to do the work of boilers on these snow-melt systems? I've seen it done and I know for a fact that it works. Ever so slowly, but it works. More on that in a future column as well.
The sections of insulation were laid out near the center of a 12- ft. wide driveway in an effort to minimize side edge loss influences. The primary choice of below-slab insulation is and has been 1-in. thick XPS insulation. That has been the standard in our company for as long as I have been here.
The hydronic grid serving this section of the snow-melt system was piped in an unusual way as well. One manifold was at the top of the 400-ft. run and another manifold at the other end of the 400-ft. run. In other words, we didn't have to loop back on ourselves in the slab. We ran straight shots from one manifold to the other.
I can already hear the cries of the Dead Men reading this saying, " You can't do that! You'll run out of heat before you get to the end of the run, or cause the one end to melt long before the other end gets up to melting speed," but we used some mechanical magic on this project. Four-way reversible flow valves change the direction of the fluid flow every 10 minutes or so. It's much easier to install the tubing that way, and the performance can outdo reverse return counter flow tubing installations.
Finally, here's an application for the flow reversal valve that is not crisis management but rather done by design. I have used flow reversal valves in situations that I wish that I had not been dragged into, such as rescuing do-it-yourselfers and when somebody encased a 1,000-ft. loop length in the slab. This is the first time I've used it in a new construction situation.
Tune in next month as we continue our experiment and testing of below slab insulation products. Until then, Happy 4th of July hydronicing!