I've got a church with a few old "Nun's Cap" type roof gravity vents. In my opinion they were remnants from the days of natural ventilation during cooling season. The church now has A/C. The arrangement, I am told, (the ceiling it is above is over 20 feet in the air and I have not seen above it) is that the space above the dropped ceiling is an RA plenum and that there is no insulation and that the openings to these nun's caps are open to that plenum. The building has gas fired hot water baseboard heating and split system DX A/C with no outside air to the units.
My question is, are these gravity vents even necessary? In my opinion they are not, but am I missing some reason to keep them?
If these vents are the only outside air inlets for this system, then yes they are required to stay. If you block off these vents, my concern would be co2 levels during services. Just my opinion.
That is a concern with me too. Without inspecting them, I'm not sure that they don't have a backdraft damper in them. If that is the case, then they won't allow in OA, except by relieving air to make room for infiltration. The room is fairly large in cubic feet approximately 80x30x18(avg hgt) =43,200 ft cu. with lots of windows and doors and a Sunday Service averages 150 people.
The vents are not connected to anything any longer? if the space it that big with lots of windows and it sounds like an old structure the building probably has enough leakage to copensate for co2. what about an hrv?
I believe the gravity vents were never connected to anything and were there just to vent the roof space and or aid in natural ventilation of the building. I agree that CO2 is probably not too much of an issue. It is an over 150 year old building lots of old wooden windows, even some wooden doors.
An HRV is not in the budget unless a problem rises.
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