Hey all, Wanted to share my DIY Duct Muffler project; So my neighbors are very close and naturally I didn't want them to hear a loud fan going 24/7 and raise suspicion. Even though my grow is legal, I still don't want anyone knowing what I'm doing obviously. I wanted to get a duct muffler for my 8" in-line fan but didn't want to spend $100-$150 which is the ballpark range of prices for this size muffler. So I decided to try to build one since they look like super simple construction. Here is what you will need to build this: It will take you about a half hour to build with an additional hour for the adhesive to dry. - (1) 2' or 4' piece of rigid sheet metal ducting. I went for 4' just to increase the sound muffling. Or you could cut a 4' piece down to 3' if that fits your needs better. You can build this muffler for whatever size fan your is. Mine is 8" so I went for a 10" duct with reducers to 8". If your fan is 6" then get a piece of 8" ducting and reducers down to 6"...and so on - (2) Reducers. I have an 8" fan so I got reducers from 10" to 8" - R-15 bat insulation w/ backing. The kind for 2x4 walls. (I needed 8' to cover my piece of 10" ducting) If you want to go a step up you could get soundproofing audio foam but it's kind of expensive. I went for the cheap stuff - Contruction Adhesive - Sheet Metal Shears - HVAC tape -So I started by laying out the piece of ducting flat. Get two heavy object to hold it down. I used a dryer on one side and an old window a/c unit on the other. You need to get it flat to the ground. (see pics) -On the end of the duct that isn't crimped, take your shears and cut about 1 1/2" cuts every 1/2" so that you will be able to fit the reducer on the duct after you put it together (see pics) -Make sure that your pieces of insulation are cut to size. I just needed to cut a few inches off one end. -Put construction adhesive on the inside of the rigid ducting. (see pics) Allow to dry for about an hour. -Lay the insulation down flat (backing against the adhesive, and put weight on it to get a nice bond (I just stepped on the entire surface slowly and carefully). -Strip about half of the insulation off so that when you put the piece of ducting together there will be ample room inside the duct to flow without having too much resistance. For different size ducts, you may have to remove more or less of the insulation. I tried to get it about 1"-2" thick on my 10" duct. -Put the duct together. If you haven't done this before, it can be kind of a pain in the ass. -Put the reducers on the duct. Tape all the seams with HVAC tape. DONE!!
Made a new one that was for a 10" in-line and I lined the inside with a screen to hold the insulation in. Waaay better. The insulation in the old one eventually started expanding/falling from gravity and reducing the diameter thus reducing the max cfm's. Also had the reducer crimped at the metal shop, way easier than cutting slits in the one end...