Posted 05 December 2011 - 06:59 AM
umeshr,
Paul has submitted valuable points regarding your query as always he had done, but i want to add one point:
If in an area where there would be the risk of heavy snowing such that the snow weight would increase the set pressure of the vent opening it should certainly be prevented. In one case i have heard the vent cover was equipped with heat tracing that activated, automatically based on specified temperature or manually by operator, in cold weather to prevent accumulation of the snow on vent cover.
Fallah