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4. Outside Weatherhoods and Ducting to the outside.
The outside weather hoods must have built in bird screens to prevent birds and
rodents from entering the duct system. Minimum mesh size of 1/4” must be
used. Smaller mesh size will result in restricted air flows with increased potential
for the development of blockages.
Vent hoods with gravity dampers must not be used.
Weather hoods should be installed:
a) A minimum of 6 ft. apart from each other.
b) At least 18” above ground level
c) Away from sources of contaminates such as automobile exhaust
fumes, gas meters, garbage cans.
d) Locate away from prevailing winds whenever possible.
The size and design of the weather hoods shall be selected to ensure adequate
free area to minimize air flow restrictions.
It is recommended that 6” insulated ducting with a integral single piece vapour
barrier be provided. Due to the high air flow restrictions in insulated flex duct
it is recommended that run lengths be kept to a minimum, stretched tightly and
with as few elbows as possible, if length greater 25 ft. use 7” insulated duct.
Minimum RSI value of 0.75 (R4) is required.
Weather hood collar should be screwed to inner surface of sill plate and sealed
with high quality caulking or aluminum faced tape. Both the inner and outer
liners of flexible ducting should be securely attached to the weather hood
tubing and collar and to the HRV collar. A good bead of high quality caulking
(preferably acoustical sealant) should be used prior to clamping the liners. It is
very important to ensure that the fresh air intake line is well sealed and that the
vapour barrier is sealed.
Insulation
Inner Liner
Collar
Clamp
Vapour Barrier
Weatherhood