Duct Work and Ventilation Q and A

Metal ductwork
  • 1-40 hours
  • Intermediate
  • 0-2,000

Q. I have read that return air vents should be left unblocked, but the one in our dining room is in the worst spot! Is there a minimum recommended space between furniture and air returns when leaving them completely unblocked isn't ideal?

A. Just enough space so it can get the air to it, like the same square inches of air that the face of it has.

Q. I've read that I can install my Aprilaire 600 anywhere on the return duct. Does this include over a joint? Obviously, a nice, flat part of the return would be ideal, but because of the placement of my water heater, that's not an option.

Just to be extra clear, the joint is nothing special - it's just where the installer joined together two pieces of ducting. One piece fits inside the other, and the sheet metal on the "outside" duct is doubled back over on itself to form a 1-inch band with a 1/2-inch lip that sticks out perpendicular to the duct itself. The return duct is 25" wide. I would cut the hole so that this joint would be roughly in the middle half of the hole above the joint, half below.

I'm assuming that the function of that lip is to give the duct some lateral stiffness - in other words, it reinforces the side and keeps it from being able to flex in and out too much. Am I risking anything by placing my humidifier in this spot and removing part of the joint?

A. Don’t do it. That’s what is called a T bar or T slip. It's to help hold that 25" so the duct doesn’t go in and out when the blower comes on. If you do cut it, put a new one above and below the humidifier across the duct.

Q. 1. I want to build a soffit around the plenum. Is there anything special I should take into consideration? It seems like a straightforward task. 2. I want to insulate the middle wall to damper noise. This is a weird question, but how much heat does the average plenum give off? I am using unfaced insulation, but will there be too much heat buildup in the studs themselves? The plenum rests right on the wall. I guess I am worried about fire risk.

A. Some codes call for the hot air duct to be 1" down from the joist. But yours is already in, so I take it it's OK. Don't put any paper next to the duct for sure, and keep the filter clean all the time. This will keep the temperature in the duct lower.

Q. What is the best way to reduce dust in my home? I can upgrade the filters in my forced air system, but are there other methods that will do a better job?

A. Number one would be to remove any carpeting in your home. You can introduce outside air and make your building a positive pressure instead of a negative pressure. There are air filters and cleaners. All are installed to do certain things according to the application.

Q. I have two gable fans and would like to know if they can be moved to the roof. I've been looking for dome covers large enough to fit on the outside of the roof, and this is considerably cheaper than just buying new roof fans. If this is possible or feasible, is there any retrofitting that needs to be done or can I just put them on the roof and install a cover on the topside?

A. Just make sure to cover over them, and don’t let any rain water in. You could also build a small cuppola up there on the ridge and put them into it. Lots of people do that.

Q. I would like to know if this practice is okay, and if there is any special Y adapter I could buy, that could connect to the 4" ductwork I am using. I also understand that I would need some sort of flap dampener in the adapter to reduce and back flow.

A. No, I would never tie two exhaust type systems together. The dryer makes a lot of lint, and if you tie into your bath fan, it will plug up.

Q. I'm finishing my basement office and wondering if it is okay to come off of existing duct lines (that go to the first floor living room) for heat and cold air return, or do I have to come off the main duct?

A. No, tap into the main trunk line. Don’t cut into any room runs. It just don’t work right. You can’t balance it out.

Q. I have a one-story house with a basement, and was looking to put a return air vent in the basement. I have two upstairs. My basement has a barroom that does not have any heat running or return running to it. The room is about 13 x 25. I wanted to add two ceiling heat vents to heat the room and wanted to add a return vent as well. What size should the heat vents, return air vent and ductwork be? Should I go larger than 6" or stay with 6" sizing since the rest of the house uses 6"? As for the return, what size should it be and where should it be placed in the room? Should I use the flex pipe for the return and heat vents or just the heat vents?

A. Use just the 6" metal pipe for this. Run the heat runs to just off the outside wall and use a 2 x 12 register on the boot blowing down. On the cold air, you don’t say just how you have duct there. Can you cut in say a 6 x 14 grill in the cold airdrop low or sleeve out from the drop to a wall there and put the grill on the wall low? You can cut the cold air in just about anywhere. You do want to make sure that the air from it will still go through a filter before it gets to the furnace and A/C coil.

Q. I am thinking of having UV light air cleaners installed in my system, possibly along with a larger 4 or 5-inch air cleaner. Do these UV cleaners work, or are they "snake oil?"

A. Yes they do work.

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