Quote:
Originally Posted by jeff5may
I believe you're missing the point here. Even though the fiberglass batting does conduct a miniscule amount of heat, it offers a surface for your floor to radiate its heat into. Once the radiated heat is spent on the top surface of the batting, the underlying batting prevents this heat from travelling anywhere. It merely compresses the stratification effect to near the source. At the bottom of the batting, the surface temperature is much closer to ambient, preventing much of the radiant heat from heating the air below.
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Jeff, You have a point, being that inasmuch as that the upward facing 'visable surface' of the bat will absorb downward radiant energy from the subfloor and, because of its low mass, will quickly rise in temperature approaching that of the radiating subfloor, thus reducing radiant heat transfer (being the difference of the 4th power of the absolute temps of the radiating bodies) from the subfloor. But the black poly film on the crawl space floor sees the radiating subfloor much the same and may introduce convection currents heating the crawl space air.
You say that "the underlying batting prevents this heat from travelling anywhere". Not so! The conductivity of the batting is higher than that of the
crawl space air. Again, batting, bulk insulation's only purpose is to prevent
natural convection heat transfer! And we we have agreed that there is no natural convection heat transfer process in the downward direction.
Radiant energy passing thru air does not heat the air!