"A few years ago a contractor installed ceiling grills typically used on the floor for forced air heating in the ceilings of my bathroom and living room. The grills are connected with a "Y" insulated conduit in the attic leading to a 20 liter pail connected to a turbine vent installed on the roof. The pail has an additional hole on the side to also draw warm air out from the attic.
I will be replacing the shingles on the roof this spring and was going to replace the turbine vent with a Maximum model 303 vent with no moving parts.
Do you think this set-up is actually drawing stale air and humidity from my living space with the doors and windows closed and if so, would the Maximum vent do as good a job as the turbine?
The roofing contractor is prepare to replace the turbine with the Maximum vent however he wants to block the hole on the pail used to help exhaust air from the attic. According to him that hole must be blocked to allow the other two Maximum vents to work correctly drawing warm air out from the attic." ---- Kaz (Montreal)
Hello Kaz
From my experience and study of building science, ideally there will be no connection at all between air inside your house and air inside your attic. In fact we spend a great deal of time and effort totally sealing the barrier between these two parts of the home. The house is warm and humid, the attic in the winter is freezing cold and if you add any moisture at all, it will turn to ice, not exhaust to the outdoors. You might want to read up on the function of an attic: Overview: Attic Moisture. These two zones of the house were often mixed in grandpa's house and it worked, but his attic wasn't very cold because he didn't have any or much insulation -- hence the frosting problem of humid air was not the same as in today's house, where the temperature difference between the two zones is extreme. And grandpa didn't pay the same for heating fuel as you do.
Those "passive" vents of yours have been costing you a fortune in heating bills, and when the wind was not blowing to cause the turbine to draw all the air out of those ducts, I am sure that those holes in the pail were simply escape routes for household moisture to get into your attic, not out of it. Turbines work, but unfortunately they only work when the wind blows and then they work too well, exhausting far more air than you want to exhaust. You may have noticed that turbines are being taken down from most roofs in Canada, and in snow country, they are being replaced with the MaxiVents , passive vents that never get covered by snow.
It is true that those ceiling grills have probably kept the humidity levels down in your house, but they have done that at great heating cost and potential damage to your attic. I would not simply close those holes in the bucket, but I would totally remove the ceiling grills and close the ceiling with a vapour barrier and a drywall patch -- or at least seal up the holes from the attic if you want to leave the gills as decoration inside. Then if you find that you are getting too much humidity in the house, consider the installation of an HRV: To HRV or not to HRV. The old Turbine octopus was a bad idea and should not be left in place.
jon