HVAC Return Muffler Part 1
I had been putting this off for awhile but it was time to get it done. I really just threw this thing together and I have no idea if it will work for moving the amount of air required and doing so quietly . Fingers crossed!
Basically, I am starting the return at the back of the room and taking it through my stairwell in order to get it into the storage area where it can be tied into my return system. My plan is to see how noisy it is for the rest of the house and if needed I will install a fan and make it into a dead vent. I am doing my best to muffle the return before it gets into the return system aluminum trunk. It goes 4' underneath the stairwell. Then it goes 7' from the floor to the ceiling. It winds a little bit in this last part so it adds at least a foot or two.
So really I am just making two boxes and some transitions. But, it takes longer than you think when the goal is sound isolation.
I used 10'' flex duct throughout along with a few elbows. It is essentially made of two separate muffler boxes. Everything is double 5/8'' dw with gg between. I took care to decouple the return from the stairwell as best I could.
I put a hole in my precious shell. I may eventually make a little box in the back of the room as a transition if I have problems with noise. It can be added later.
And here is the hole under the stairwell. The oversized hole was later patched tight again.
Closeup of cutout.
Installed a collar. Applied duct tape.
This is the decoupling part and a total PITA. It touches the interior decoupled wall but not the other side of it. I used additional pieces of drywall, acoustical caulk, and putty pads.
Put down a base layer of serenity mat and started to build my box from there.
Put up the side walls maintaining a 1/2'' gap to decouple. Also threw in pink fluffy in the space behind the muffler box.
I used acoustical caulk on all of the seams. I had to install a series of cut down 2x4's as the walls went up. It takes awhile to think it through when you cannot put a screw in from the outside!
Here is the flex duct going through the stairwell box. I made the hole on the other side next to the floor to provide a bend in the flex and hopefully make it more difficult for sound to follow to the other side.
Then the cavity was filled with pink fluffy.
All closed up. More insulation will go on top of the box. I am installing shelves in the first 18'' by the door. This box is around 36x36x32.