Vermont Casting BHDT36 - Manual (Page 18)

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The maximum number of 90 degree elbows per side wall
installation is three (3).
The maximum number of 45 degree elbows permitted per
side wall installation is two (2). These elbows can be
installed in either the vertical or horizontal run.
The maximum horizontal vent length is 36" (914mm) when
90º elbow is installed directly onto fireplace.
Fig. 36
For each 45 degree elbow installed in the
horizontal run (while maintaining a constant
horizontal plane), the length of the horizontal
run MUST be reduced by 18" (457mm). This
does not apply if the 45 degree elbows are
installed on the vertical part of the vent sys-
tem.
If a 90 degree elbow is used in the horizontal
vent run (level height maintained) the maxi-
mum horizontal vent length is reduced by 36
inches. Fig. 36. This does not apply if the 90
degree elbows are used to increase or redi-
rect a vertical rise.
The maximum number of elbow degrees in a system is
270º.
Sample: 1 - 90º
2 - 45º
3 - 45º
4 - 90º
Total 270º
Example: According to the vent chart the maximum
horizontal vent length is 20' when the vertical height is 7.5'
from fireplace base height. If one 90 degree elbow is
required in the horizontal vent it must be reduced to 17'.
Fig. 38
Fig. 37
3 FT
(92cm)
90"
2286mm
84"
2134mm
120"
3048mm
90 º elbow=3'