Ceiling exhaust fan is vented through the roof
LANGYEL
| Posted in General Questions on
My ceiling fan over the stove is vented through the roof. I live in Wisconsin . There apparently is NO back- draft panel that flips open and closed when the fan is on or off. Is one necessary because of our winters etc.
Roofing contractor said that is the way that vent has always been. Am I losing an exorbitant amount of heat in the winter? In the summer months WITHOUT AIR CONDITIONING My house has always stayed 15 to 20 degrees F cooler then outside. Apparently the warm air doesn’t come in. But does my heating air escape toooo Much?
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Replies
Langyel,
I'm not sure what you mean by a "ceiling fan over the stove," but I'm going to assume that you are talking about the exhaust fan on your range hood.
If my guess is correct, you want to install a backdraft damper designed for a range hood fan. Here is one from Kenmore:
http://www.sears.com/kenmore-backdraft-damper-kit-for-range-hoods/p-02259102000P
I'm not sure whether this product requires a length of horizontal duct -- but it may. If so, that may require you to reconfigure your duct.
Colder air is denser than warmer air, so in summer the direction of the stack effect is reversed- the cooler air stays in the house rather than rising up the open hole in the ceiling. In the winter the warmer air of the house will rise, escaping out of that hole in the ceiling.
What's worse, in Wisconsin the temperature differences that drive the stack effect infiltration pressures are more than twice as high in the winter than in the summer:
75F indoors, 95F outdoors on a hotter day of the summer is only 20F temperature difference.
70F indoors and -10F on a cooler than average winter night is an 80F difference.
That's 4x the temperature difference, yielding a MUCH greater stack-effect drive!
Sorry. I have a stove/ oven free standing. No hood. Above is an exhaust fan in the ceiling venting through the roof outside. No baffle or back-draft panel in the piping to the roof or on the fan. Does there have to be one? In summer will the cool air stay in the house and in winter will just minimal warm are escape? Is there a shield I can just add to the vent cap inside the house to block the warm air from escaping?
The effect in the summer is somewhat negligible, but still not great.
But a six inch diameter (or even a 4 inch) hole in the ceiling with a stack-effect drive is a fairly significant heat loss. There are houses that don't have that many square inches cumulative air leakage in the whole house, let alone a hole configured in such a way that stack effects alone will move a significant amount of air! It definitely needs a damper!
A butterfly damper placed anywhere on the vent piping makes a real difference. Stack effect pressures aren't enough to cause it to open up, but the fan will. Putting it somewhere that is easy to inspect, test & service may be useful. For a visual on the type of damper I'm talking about, see this:
https://www.youtube.com/watch?v=AD2uGZYdg54
The big box stores will have them for under $20, or you can order them from web-stores once you've figured out what you need.
How old and tight is the house? There is a possibility that hole is currently saving you from condensation issues in the winter.
To: Anopn3 - The home is very air tight. New 40R insulation, new roof, basement window covers, All windows and doors triple pane glass with krypton gas. When we had a summer here in Wisconsin and it hit 110 degrees Fehr, our house (closed up) with the stove ceiling vent as it is now, had an inside temperature of 80. The house is 49 years old and all brick veneer.
If I were you I wouldn't do anything right now. This winter, measure your indoor humidity dew temperature, and see if things are significantly colder near that hole. If no humidity issue, then do what Dana suggests. If there is, then you have to take care of that first.
Doesn't anyone make a simple 8" diameter center hole plate that I could just attach to the plate cover opening to close it off in the winter? Seems the easiest.
Maybe I could just stuff it with some insulator in winter.
I'm having trouble visualizing your exhaust setup. Can you post a picture?
I am sorry, but I can not post. It is a fan in the kitchen ceiling similar to ones you see in a bath room.