Quote:
Originally Posted by Mohawksin
May depend on your style of home. Mine is 4 inches. You can remove the grill and measure. You may not have a duct beyond the fan. For most of the villas the exhaust is to the attic, not to the roof and not ducted to the eaves.. There is no duct. In those cases you can use any size fan you can get in the current opening.
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If the fan exhausts air directly into the attic, it is either a very old house or it was not constructed according to the current building code. An exhaust fan cannot discharge air into the attic space. It must be ducted to the outside.