Custom return filter box
rondeaunotrondo
| Posted in Green Building Techniques on
I had a vetted HVAC company install a mid static ducted 9K mini split for me using third-party duct design. They spec’d a 20 x 10 x 2 return filter thus they had to build a custom filter box. The work does not look the best, unfortunately, and they put screws in the face of where the filter would go. He did leave me enough room to put a gasket in which I was doing when I realized that the Filter does not sit perfectly flat because of the screws, allowing bypass. Should I just remove these and seal and then gasket?
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Replies
I would say they have done a pretty good job with the install.
Air filters never seal perfectly out of the box, you need to add some weather stripping.
I would add a thin layer of foam against the back side and a V shaped vinyl one around the perimeter.
The easiest solution is probably just to put some foam weatherstripping around the perimeter of that interior side over the entirety of the sealed/screwed area. Make sure that the door puts a bit of pressure on the filter when it closes so that the filter seats well against the weather stripping. This isn't a super critical application here, you just want to minimize any air bypassing the filter.
Bill
Thanks Bill and Akos. I always value your opinions. I have both 1/4 inch thick and 1/8 inch thick 3M close cell weatherstripping which I’ll use as a gasket. I cannot lay the foam flat because of the screws. Are you saying making a thin strip inside the screws? My thought was just to remove the screws and that way I can have a nice flat surface to lay the weatherstripping down.
Use open cell foam strip since that is squishier. You can cut a small hole where the screws are in the foam so it lays flat.
This doesn't have to be perfectly air tight, mostly air tight is good enough as air will want to flow through the filter not around these very small gaps.
You can use a hollow "leather punch" and a piece of wood to cut very clean holes in the foam weatherstripping. Just make sure there is foam on at least one side of the screw that is thick/wide enough to still function. It's not super critical, but you do want it to lay as flat as possible.
I agree with Akos too, you want to use the softer open cell foam (usually this stuff is gray and not black). The filter frame is only a lightweight cardboard, and you don't want to deform it too much with excessively firm weatherstripping.
Bill
Ask the contractor if it would be possible to replace the hex head screws with countersunk flat head screws. Of course it is total possible he can hardly say no.
Please be very nice when you make the request and offer to pay reasonable costs for the change. It is clear that they have done much better work than one would normally see for return ducting.
Then put some foam strips in place so when the fan comes on it will pull the filter tight into your weatherstripping.
Walta
Countersunk screws don't usually work in very thin materials like the sheet steel ductwork is made from. I don't think that will be an option here. Button head screws would probably be the next best thing, but it's easier to just punch out some holes in weatherstripping wide enough to still have material around the screw after punching a clearance hole.
Bill