I need to route some round metal ductwork through the truss space between my basement and 1st floor. The duct needs to run perpendicular to the trusses. The photo below shows the area including existing 4-in waste drain plumbing that's obstructing passage. My options seem to be 1) re-positioning the plumbing to allow a 6-in round metal duct to be installed; 2) somehow route duct around the existing drain line, or 3) some combination of both. 1) I may be able to drop the drain to gain clearance by installing some 22.5 degree elbows to lower the drain under the duct and then rising again to reconnect to the nearby vertical drain/vent, effectively creating somewhat of a trap. This concerns me though as it may lead to clogging, stagnation, etc. It doesn't seem like good practice and may violate code, but I'm not sure. The drain serves a 1/2 bath and kitchen sink. 2) I may be able to pass the duct by the drain using some duct boots to transition from a round to a rectangular cross-section that can run either above or below the drain pipe. I'd want to transition back to round duct after passing the drain. The concern there is excess flow restriction. Use of flex duct is not an option. I'm a fairly capable DIYer but drain/vent plumbing seems a little like voodoo to me sometimes. Thoughts?
Exactly. That's a no go. Where does the heat originate and what is it.....round or rectangle? If rectangle, you can try to find some that will fit that space, then go to round. Just not a great idea to reduce, then increase. What size round did you plan to use? Adjustable elbows are your friend if they'll fit. You could possibly use an oval stack duct that's normally used in stud cavities, then you'd need the oval to round pieces to make those transitions.
pics of other end of plumbing??? just lower the whole line to the point of exit????? PVC 2 cuts 2 couplers done???? PVC plumbing exposed in a garage?? a few more pics should help. 12" trusses should be lots of room to make it work.. being above garage I am guessing the room is cold and you are adding a heat/cooling run?? Insulation might be more betterer as Papadave would say.
The air handler is about 12 ft. away. I'd like to use 8" round duct to feed two registers but will have to separate into 2, 6" round ducts for because of this drain pipe. A 6" elbow is too large. My thought of transitioning to duct boots is similar to what you're suggesting with the stack duct. If I go from 6" round duct to something rectangular like the duct boot below, then back to round with another duct boot. The 4x10 duct boot has a cross sectional area of 40 sq. in. while the 6' duct is about 30 sq. in. so I don't think flow restriction would be an issue. I'll look into stack duct too.
The exit point is shown in the photo at the lower left. It's a drain/vent in a wall and would be tough to lower the tee. Any lowering without moving that tee would probably flatten the slope too much for good pipe flow/clearing. Yeah, its PVC above a garage and I plan to insulate.
The 4x10 transition will work fine. You also may be able to offset two elbows to get under the waste pipe. You can drop down an additional 1 1/2"of the bottom cord of the truss and still stay above the ceiling You will get better airflow from each register if you run separate 6" round duct to each one. May cost a bit more but it will work better.
Leave the plumbing alone. Don't touch it. For getting past the drain line (which form the pics I see no probs at all) you can use round to oval fittings. Yes, the 4 X 10 boot idea will work also but for better air flow, use the round to oval fittings. A couple of straights should get you past that drain line and then back to your round pipe. The 6" round re-sizes down to about 2 3/4 inches on the oval end of it. 6" round to oval fitting image - Google Search Hope I'm not too late to this party.
