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re: ceiling mounted furnace question
4 jun 1999
bill78 wrote:
>i am in the process of having a 30 x 46 workshop built for
>woodworking-woodturning mostly.
>
>it will be 2x6 construction with r19 walls and r30 ceiling with a slab
>floor. some windows, some skylights...10 ft walls. seattle area.
with some perimeter insulation for the slab, and 2x6s on 2' centers, each
2'x10' 2x6 cavity with 24' of 2x6s might have a thermal conductance of
24'x1.5"/12/(5.5"xr1) = 0.54 btu/h-f for the wood and 118.5/12x23.5"/12/r19
= 1.02 for the insulation, a total of 1.56 btu/h-f per 20 ft^2 of wall, for
an overall r-value of 20/1.56 = 12.8 ft^2-f-h/btu, including stud thermal
bridging (the fairly low parallel thermal resistance of the wood.)
the thermal conductance of the walls would be 2(30+46)10/12.8 = 119 btu/h-f,
plus another 30x46/r30 = 46 for the ceiling. making 4% of the floorspace r4
windows adds 14 btu/h-f, and a low air leakage rate of 0.5 air volumes per
hour adds an effective thermal conductance of 0.5x30x46x10/55 = 125, making
the total thermal conductance 304 btu/h-f.
>the county will only allow a furnace of 24 btus per sq ft in a non
>residential building, so about a maximum of 33,000 btus in my case.
that should keep the workshop 70 f until the outdoor temperature reaches
70-33k/304 = -39 f...
>i am concerned that i will want a bit more heat to raise the temp on a
>extra cold day. ( my permit calls out a ceiling mounted ng furnace. )
you may have additional heat from the machines and people inside...
nick
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