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One subtle path of heat loss is radiant energy, and can go in non-intuitive
directions.
If a warm object and a cool object face each other across a gap, heat will
move from warm to cool.
Such is evidently the case between the bottom of a first floor and a
basement slab below, even when separated by considerable distance.
The edges of the slab are under foam but the middle is still open and largely
connected to the earth, so it still runs a little chilly in the winter.
This can "sink" a little more heat out of the structure by absorbing more
*downward* radiation from above than we want to permit.
This is why products like Reflectix are made. Typically used in hot Florida attics to try and cut the roof heat gain a little bit, it also made my very effective window shades and now I was going to put a lot of it to work to try and warm up the first floor some, the literal floor, as yet another experiment. |
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| Cutting 16" strips |
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The idea is to string it across the joist bays, wherever they're accessible,
and staple it in along the edges. A 48" roll cuts nicely into three 16"
wide strips, and if the joists are 16" on center but have some thickness of
their own, there will be just enough hanging out to staple through.
In attics there's less in the way, and the edges could just be face-stapled to most of the joist edges. That might give a little better coverage, but I need access to the joist space itself to deal with various infrastructure, so I'd take that mild hit. Making the funny downward bend along the edges wasn't difficult. |
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| 1" air gap clear of subfloor |
| The idea is *not* to nail it up tight against the flooring. If you do that, now you've turned it into a direct conduction situation. The barrier needs to just block the *radiation* [and maybe a little air convection along with], so it needs to sit clear of the warm object and try to reflect that heat back up into it. So having this one or two inch gap everywhere does make it a little fiddly to install uniformly, and work around various objects in the bays. |
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| Working around the X-braces, with minimal contact |
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As long as most of it isn't in direct contact, it should help.
Obviously the open edges of the joists are still a radiant surface, but
a much lower percentage.
When I shot the IR camera in past where I still had an open edge under
the subflooring, I could easily see after temps stabilized, that the wood
behind the Reflectix was warmer than the exposed wood over the floor.
I forget how many rolls of the stuff I needed -- three or four, but working in stages (including having to clean out underneath each area) didn't take all that long. And it really does feel like the basement space has gotten even closer to being "seasonal storage". It seems to try its best to stay at mid-fifties temps most of the year, and now with less influence from overhead. As cold weather arrives in the Fall, it almost feels like the basement is staying *warm* for the next month or two as the soil temp slowly changes. |