re: more ? on btu/h to heat structure
17 nov 2000
charles stoyer wrote:
>why isn't the floor considered? what is the heat loss through an uninsulated
i seem to recall an old ashrae estimate of r10 to the deep ground temp
(average annual air temp, eg 55 f near phila) under a basement floor.
heat conducts upwards better than downwards in ground with some moisture
and evaporation below and condensation above, and warm air rises, and
still air has about r0.3 per inch for downwards heatflow, so i tend to
ignore floors on grade away from the walls and crawlspaces that are
well-sealed around the edges.
>what is the r-value of logs? i have a cabin with 6" d-logs
d as in half a log? ashrae says wood has about 1 per inch, about 1/6/12
= 0.0139 btu/h-f for the 1" horizontal slice below the center of a round
log with average thickness of about 6", 1/5/12 = 0.0167 for the next lower
inch with average thickness of about 5", 1/4/12 = 0.0208 for the next lower
inch with average thickness of about 4", and 1/0.8/12 = 0.1042 for a 1"x4"
thick slice of r0.2 masonry chinking. that's a total of 0.156 btu/h-f for
4"x12" wall section, or u0.467 (r2.14) for a 1'x1' section.
>what r-values are available for windows and do heavy curtains help?
us r4 (u0.25) seems economical. last i looked, r8 was about $40/ft^2,
and those windows blocked more solar heat in the winter. heavy curtains
don't help much unless they are very well sealed against air leaks.
>if i put, say, r-13 insulation in my walls, what is the effective
>r-value of the wall, considering there are studs every 16" and
>there is paneling/siding/sheetrock?
hard to say. the paneling and siding might add r1. the sheetrock might
act as a heat collecting fin for the studs to lower the r-value. as a
rough estimate, a 16" x 8' wall section has a thermal conductance of
10'x1.5"/12/r6 = 0.208 btu/h-f for the studs plus 9.42ft^2/r13 = 0.724
for the insulation, a total of 0.932 btu/h-f for 10.67 ft^2 of wall,
which makes the overall r-value 10.67/0.932 = 11.4.
>what efficiency to be expected from a convective rv propane heater? if
>it is rated at 22,000 btu/h, do i lose 30% to the outside and retain 70%
sounds ok, if it's vented to the outdoors.