Duct Sealing for Volunteers

Here are some common areas you can access for sealing. NOTE: These are all much easier to access BEFORE drywall… And many are completely unnecessary if you do not use returns for cavities (which is no longer legal per MN State Energy Code).

Inside the furnace cabinet on the bottom, notice the foil tape. The tape covers a punch-out for down-draft furnaces. Tape or caulk it up.Furnace box I

This is the front of the punch-out, it’s caulked. The punch-out is a square, be sure to get all sides (you won’t get the back unless you take out the fan OR do it before the cabinet is set). Furnace box II 

This is the outside of the cabinet, on the bottom. Tape the seam.Furnace box III

This is the front of the cabinet, the box where the A/C coil lives. It is a nice gasketed box made for easy access for techs, but if you need to pass the test, sadly you will need to tape this up. Notice also the seams above. Tape all seams! Furnace box IV 

Mastic on all seams. Mastic should be put on in a layer as thick as a nickel. Try to push it into all the seams rather than just brush it on. Mastic I

Here are some pictures of mastic at all elbows, junctions, and terminations. Mastic II Mastic III Mastic IV Mastic V

And here are a couple pictures of the boots sealed to the subfloor, either from below or above. Mastic VI Mastic VII

This one of two larger returns, looking from the bottom up into the cavity. Above the duct itself, you just see a block we made to seal the cavity. Now the duct pulls air just from the living space and not from the wall. Wall return I

Here is an attempt to seal the cavity of an un-ducted return. The cavity should be sealed at each joint. That’s 12… Caulk return I

Up inside the return cavity, the electrician’s run. You can reach up to foam in the hole. But please notice the unsealed gaps along the front and back of the cavity – sadly this duct will never pass the tightness testing.  Foam Return I

Imagine the duct system like a plumbing system. Every crack that water could leak through, air can leak through. Now, just like your plumbing system, the air system is tested for leaks, so please seal up those cracks.

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