Technology marches onward.

Consider the hardware now available to hydronic heating pros relative to that available 10 years ago. Modulating boilers have become the norm instead of the exception in several markets. Microprocessor-based controllers that communicate with each other are starting to replace stand-alone controls. Computer software now makes it possible to study the performance of “virtual” hydronic systems and make the right design decisions before hardware is installed.

Yes, we've seen significant progress in recent years that has been based on sound application of engineering principles and modern manufacturing technology.

Unfortunately our industry has also seen its share of “bad science” in recent years. Here's one example.

Imagine a new insulation material with a claimed R-value almost six times greater than standard extruded polystyrene. So high, in fact, that no other established insulation product even comes close to offering the same R-value/thickness combination. When installed below a heated slab, this material makes downward heat losses almost nonexistent.

How is such spectacular thermal performance achieved? What have all those scientists at Dow, Certainteed, Owens Corning and the other insulation giants been missing all these years? Well, let's take a look.

Here's how one manufacturer of such a miracle insulation justifies its thermal performance:

  • Step 1: Have a materials testing lab run an ASTM guarded hot box test based on summer conditions (where the average insulation temperature is 85 degrees F) and achieve an R-value (we'll call it R1).

  • Step 2: Have the same testing lab run the same test based on winter conditions (where the average insulation temperature is 45 degrees F) and achieve a resulting R-value (we'll call it R2).

  • Step 3: Assume that since the material is used in both winter and summer, its effective R-value is the sum of its summer and winter R-values (R1 + R2 = Rtotal).

  • Step 4: State the material's R-value without being specific as to the type of installation geometry used during the test (suggesting, perhaps, that it really doesn't matter if an air space is present on one or both sides of the material).
Anybody out there have a problem with this “scientific method”?

I know of one building committee that recently based the future performance of its new multithousand sq. ft. radiant floor heating system on precisely this science. It insisted on the use of this miracle material under the entire heated floor slab, having been assured by its supplier that it would essentially stop all downward loss. Besides, the committee's cost on this revolutionary new insulation was just slightly higher than 2-inch thick extruded polystyrene.

This is all true. It all took place this year. It all happened despite the advice from a seasoned hydronic heating pro that the claimed thermal performance of this material was, let's say, optimistic, for the intended underslab application.

How Hard Is It?

I'm frequently asked my opinion on underslab insulation products for radiant floor heating installations. This usually occurs when I'm standing in a room filled with contractors, wholesalers, reps and manufacturers. There's a pretty good chance that some of these folks have part of their livelihood riding on the sale of such products.

I respond with a few questions of my own. These questions could be applied to any underslab insulation product:

    1. Can the manufacturer show, through complete and unembellished third-party testing, that the product's R-value and load-bearing ability is based on use in an underslab application?
    2. Can the manufacturer show, through accelerated aging tests or actual track records of existing installations, that the product will retain most or all of its claimed thermal/structural performance for 20 to 40 years?
    3. What long-term performance warranty does the manufacture provide to protect the designer from liability should the product not perform as represented in underslab applications? If a warranty is offered, what is the procedure used to establish that the product has indeed failed to perform?
    And my personal favorite -
    4. If the product fails to live up to its claimed performance and needs to be replaced, how hard is it to retrofit underslab insulation?
Once these questions are offered, I usually see a few people ponder them as if it's the first time such things have crossed their mind. I also see a few heads nodding up and down in tacit approval that the questions are at least legitimate.

True, it's a lot easier to roll out a flexible insulation blanket than it is to place rigid foam sheets on a poorly leveled subgrade. True, the shiny foil surfaces on some of these products looks high tech, even “NASA-like.” True, the heating wholesaler, not the local building supply store, gets to sell the underslab insulation. Please reread question No. 4 above and ponder its true answer.

Questionable Miracles

Heating professionals are frequently approached to accept new materials and methods that claim to:
  • Significantly outperform current technology.
  • Make the installation far easier than current practice.
  • Make the installation far faster than current practice.
  • Make the installation less expensive than current practice.
Some of these new materials and methods are legitimate. Manufacturers offering them support their claims with complete and undoctored test results from independent labs. Most are proud to offer up such documentation. This has been the case for years with the thermal performance numbers on IBR-rated finned-tube baseboard.

In contrast, other suppliers simply ask designers to accept what they are being told. This, of course, implies that those designers also accept the liability of using the new product in a multithousand dollar deluxe comfort system.

Any designer who seeks top-shelf quality for his or her client should ask to see the science behind new product offerings. Quality manufacturers should be more than willing to support such requests, realizing the extent to which they expect designers to assume responsibility for its long-term performance.

The hydronic heating industry (especially the radiant panel component of that industry) must remain diligent in protecting the integrity of the systems that have brought it so far, so fast. If you're a heating professional considering the use of a new material or method, I urge you to get credibly established proof of performance from the manufacturer or material supplier. Look for solid science behind the claims. Otherwise, you're tying your finger to Benjamin Franklin's kite string, and there are clouds on the horizon.