About $40
For a built in unit such as a bathroom ventalation fan, it can cost as little as $40 but you get more air volume and quieter fan operation for more investment. The larger the room the more air should be moved through the room to keep the air from going stale. Venting through a window fan requires little to no additional expense, but venting through walls or ceilings will cost more with additional tubing roof penetration or exterior vent coverage. A good quiet cieling ventalation fan that vents through an exterior wall will cost about $130. Plus $20 for 4 inch flexible ducting and another 20 to 30 for an exterior cover that prevents rodents and exterior air from entering back through a turned off unit.
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