I decided to do a few things to quiet down my exhaust fan today, and thought I should take some measurements to see the difference it made. I’m sharing this information in case it will help others choose how to spend their money or time.
This is a 4’x4’x6.5’ grow tent in my basement with a 400CFM fan, hung outside the tent, screwed to the floor joists above. Downstairs readings were taken in front of the outlet side of the fan, 4’ away and 5’ above the floor. Upstairs readings were taken directly above the fan in a room with a hardwood floor, 4’ above the floor.
The three changes I made were: Add 6" insulated flexible exhaust ducting(I left the full 25 foot length), hang the fan with zip strips and surround the fan with a cardboard box.
Here are my observations:
FAN WITH INSULATED EXHAUST DUCTING
Downstairs: Reduced 5 decibels
Upstairs: Reduced 5 decibels
FAN WITH INSULATED EXHAUST DUCTING, SUSPENDED INSTEAD OF DIRECTLY ATTACHED
Downstairs: Reduced 10 decibels
Upstairs: Reduced 5 decibels
FAN WITH INSULATED DUCTING, SUSPENDED AND SURROUNDED WITH CARDBOARD BOX
Downstairs: No difference
Upstairs: No difference
Based on my amateur observations, I would say that suspending the fan made the biggest difference and cost only pennies.
Some caveats, however: If this were a proper scientific measurement, I would have measured each modification individually as well as together but in different orders of application. Since this equipment was already in place, I didn’t want to take it apart multiple times to do that. It’s quite possible that the cardboard box might make a couple of decibels difference by itself but that the sound being created by the vibration of the fan had already been absorbed by the other two modifications. If you have no money to spend at all, the cardboard box (assuming you have one) costs nothing just to give it a try.
