Some facts about bubble wrap duct insulation, its R value and usage.
By Glenn Hooper January 22, 2015
Turning a profit these days get harder and harder. Many small companies and the people they employ have to consistently fine tune and tweak to improve bottom line. Its hardly any surprise that when a product hits the market that has all the virtues of a NASA spin off, low cost, offering very impressive specifications that tradesmen will flock to it. The old saying, if it looks like a duck, walks like a duck … Aside from the virtues of this product, it installs considerably easier and is very cost effective. The foil face bubble wrap manufacturers may have a fantastic product, but they unfortunately market their product to an industry that is unaware of codes that restrict its use.
Heat moves by 3 methods
- Convection (mass air transport)
- Conduction (By touch)
Insulation’s R value is a measurement how much resistance against conduction a product has. Most if not all insulation is designed to fight heat loss (and gain) from conduction only.
Insulation earns its R value by the results of whats called a “Hot Box Test”.
Without getting into great detail, a sealed box of known size is completely insulated with the test product. The people who perform these tests are usually engineers wearing lab coats, and they can take hours fitting the insulation in, with not even a strand left untouched, massaged and carefully put in place…
The interior of the box is heated. Exterior surface temperature measurements are taken at various times. Knowing the exterior surface temperature and how many watts of power was used to create the heat and a little math gives the R Value.
Its a test that measures conductive resistance only.
Heat loss and gain by radiation (line of sight) more importantly, resisting it, is a much trickier concept. keeping it simple, metallic or shiny surfaces have a low emissivity or poor ability to emit radiation (Heat). That/s why when manufacturer’s add a heat sink, or metal plate to help remove heat from something, they almost always paint it flat black. A flat black finish can emit heat well, it has a high emissivity.
Ok, so shiny metallic finishes resist the transfer of heat and flat black can absorb it (and give off), got it ? Good!
Insulation companies who make metallic bubble wrap (or their distributors) like to boast about their products attributes, and often add the equivalent reflective R values to the conductive values, giving an overall equivalent R-value. Some products say R4, R6 or R8. Some of the better manufactures state in fine print (When you can find it) the conductive R value of their products. Most metallic bubble wraps are about an R-1.
Worth mentioning, to get the equivalent R value to what the manufactures claim on the packaging, the installer has to use spacers under the insulation to keep the prescribed air gap between the ducts and the foil.
I have heard some say that the insulation could be installed loosely to maintain the gap. Under certain circumstances this may be a cost effective solution. Current codes don’t require insulation when the duct’s are in conditioned space. I worry about uninsulated ducts in conditioned spaced sweating during certain conditions and think the bubble wrap may be a fine choice.
Now the nitty gritty, The 2010 mechanical code of New York State says,
The 2015 International Energy Conservation Code which NYS is now following says;
“R402.1.3 R-value computation…
Computed R-values shall not include an R-value for other building materials or air films…”
Ultimately, bubble wrap should NOT be used where the code prescribes a required R value for ducts. However, there are no restrictions if the ducts are in a conditioned space!