Vents provide a hole for air to be pushed out of the house or cottage. They can also allow unwanted critters to come-on-in...
There are a few tips on selecting a vent to avoid unwanted guests:
1) A self closing flapper
Pick a vent that has a 'flapper' that open when you vent is on but closes when the 'air' is off.
To add to the critter protection get a vent with a screen, but a screen of the right gauge to keep out the critters but also let out the unwanted lint that may collect on a fine mesh screen.
Plus there are a few attributes that just make a better vent
3) Rust Resistant
May sure the vent has either a powder-coated paint or is made of rust resistant material like stainless steel or plastic. I would avoid galvanized and eventually these always seem the rust eventually.
4) Large Opening
The whole idea is to vent your moist air as fast and efficiently as possible. a small opening impedes this.
5) Strong Materials
Being on the exterior the vent is likely to take abuse. Weather it be the weather or branches or humans, it will be hit. make sure it is of a materials that will withstand some abuse. That is why I like metal vents over plastic - plastic gets brittle, especially in the winter
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