On 12/31/2015 3:53 PM, dpb wrote:
On 12/30/2015 4:03 PM, TomR wrote:
...

Heat transfer is faster where the delta T is higher. The larger the
difference in temperature, the faster the heat transfer.

"...for a given overall heat transfer coefficient across the media per
unit area".

For conduction/convection it's Q=U A dT

I suspect that the greatest delta T is between the inside of the
crawlspace
and the outside air through the uninsulated side walls of the crawlspace;
and not so much between the floor above and the floor of the crawlspace
below.

That is why I think that insulating the now-uninsulated side walls of the
crawlspace would be the best (and easiest, and least expensive) first
option. I think that is where the most significant heat loss is located.

That may be true but need more than just which is the larger dT to
really say where the main heat loss actually would be.

That said, it makes sense from a physical standpoint to tighten up the
exterior wall closing up any leaks and taking care of old single-pane
windows w/ no storms, etc., etc., etc., ...

Whether you get more bang for the buck from further insulation there or
the floor probably has more to do with what the air leakage from that
area into the living space is than anything else, though.

--

If the ground is not an insulated slab there will still be loss from the
floor. I'd start with the underside of the floor first. Just do
between a couple of joists and you'll feel the difference in a short time.