Q. Is there a rule of thumb as to how to size an exhaust fan for a bathroom?
A. It's not that I always want to use larger fans, but depending on the use and size of room, larger fans can be essential to avoiding problems. I have had clients use 50 - 110 CFM units and when the family takes long hot showers, they are having problems. When one installs a steam shower/bath or heated whirlpools, it's even more critical.
The trouble with fan sizing is that many people don't take into account what is actually in the bathroom, like two sinks or one, a three-fixture bath vs. five-fixture bath, and how many people are in the family. These factors are more important than the actual size of the room. Also consider what will happen when you get a house full of company. The other issue is that if a family is taking more showers than baths, more moisture is emitted into the room; again, this is more important than room size.
A bathroom with vaulted ceilings (taller than 8') is also an issue. 9 or 10 ft. ceilings create more need for larger fan size. I do agree though that trying to get a quiet fan is the hard part as they are more expensive, but what is more important?
Q. What are the drawbacks to venting your bathroom out the soffit? I've read where it's not allowed by code in some places.
A. Venting is allowed through side walls or through the roof or soffit. Whatever you do, it must be vented to the exterior.
When possible, venting the fan through the nearest soffit is acceptable. This allows you to make the vent installation under the overhang of the roof, preventing the need for a roof vent. The fan unit can be connected to the soffit vent using flexible plastic duct material with a soffit vent adapter. The duct material is easy to cut and it is expandable, which helps make fitting an easy task. Just clamp one end of the duct to the vent shroud on the fan housing and the other end to the vent. Installing the duct horizontally across the attic reduces the possibility of condensation trickling back down around the fan. Insulating the duct with insulation wrap also reduces the formation of condensation within it. In other words, you cannot just let an exhaust duct lay within the soffit itself. You can call your local inspector to confirm this.
Q. I am redoing my half bath that was originally built in 1983. The exhaust fan cover is very dated, but the motor and enclosure work flawlessly. Is it possible to purchase a new light/cover or do I have to purchase a whole new unit?
A. More than likely but you may want to see who makes yours. If that manufacturer is still in business, get in touch with them.
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