In Which Joist Bays Are Panned (Properly-ish) and The Author Goes a Little Crazy
During basement demolition, my friend and I discovered that whoever installed the first HVAC system in the house used panned joist bays for the air return from the parlor and front door entryway. I assume that the original was completely panned with sheet metal (to match the panning made inaccessible by the staircase) but at some point, the portion that was exposed in the basement was replaced with cellulose ceiling tile. Subsequent HVAC installers (latest was in 1992) just tied into the cellulose bays without replacing the panned bays with actual ducting. When the addition was added in 1958, they ran an additional air return with ducting that they also tied into the cellulose panned bay.
By accidentally ripping out the cellulose tiles that covered the two panned joist bays, I destroyed the negative air pressure in the "return" (whatever the word for the opposite of a plenum is) and kinda screwed up the HVAC system. Technically, I could probably run the system with the return air coming solely from the basement, but I would worry about air quality and air infiltration through the basement windows and furnace flue. Clearly, it had to be repaired before the next cold snap: even though it was mid April, we were still having some nights reaching the mid 40s (Fahrenheit, for you metric types).
There was no way I was going to be able to properly run ductwork from the return registers all the way to the HVAC unit without some serious time and house surgery, so I decided to re-pan the joist bays and tie it into the remaining cellulose panning as best as I could. I bought some sheet metal sized specifically for panning joists from the BORG as well as some thrice-cursed sheet-metal screws and duct mastic: I already had HVAC sealing tape from repairing the flex-duct in my other house. Before doing anything else, I thoroughly vacuumed as far into the bays as I could reach from both the basement and register ends: it was really gross so I'm going to stop thinking about it now.
The panning process should have been a simple process, how hard could slapping some sheet metal onto the ceiling be? Well, let me tell you, if you do it the way I did, without the proper hex driver bit with a magnet in it, you'll run out of curse words about 40 minutes in. Trying to hold up a floppy piece of sheet metal with one hand and your head, while fighting to keep a tiny sheet metal screw in the bit was bad enough, but because the bit didn't have any retention, the screws kept flying out of the bit instead of biting into the sheet metal. After running through my entire pocket of screws to drive a single screw, I had a choice, wait until I got the correct bit, or predrill every single hole and hope they all lined up. I was on a deadline and had no car, so I started pre-drilling, effectively doubling the time it should have took. The problem i then had was that a hole big enough to retain the sheet metal screw caused the wood portion of the hole to loose most of its holding power. So back to driving the screws without pilot holes. Every five or six screws I managed to get in, I would climb down from the ladder and collect all the dropped screws to refill my pocket. By then end of it, I was hot, sweaty, and frothing at the mouth.
This is what it looked like before taping:
To seal up the panning, I first applied a liberal coating of mastic to all the exposed edges of the cellulose tiles we tore out and to the area where the cellulose and sheet metal would meet. After the panning was in place, I went back and sealed all the joints with UL listed foil tape. The hardest part was where the panning met the HVAC trunk since the flange was positioned for the thickness of cellulose and not sheet metal. I ended up making another flange out of spare sheet metal to interface the junction and then covered it in a few layers of tape.
Mission accomplished.
By accidentally ripping out the cellulose tiles that covered the two panned joist bays, I destroyed the negative air pressure in the "return" (whatever the word for the opposite of a plenum is) and kinda screwed up the HVAC system. Technically, I could probably run the system with the return air coming solely from the basement, but I would worry about air quality and air infiltration through the basement windows and furnace flue. Clearly, it had to be repaired before the next cold snap: even though it was mid April, we were still having some nights reaching the mid 40s (Fahrenheit, for you metric types).
There was no way I was going to be able to properly run ductwork from the return registers all the way to the HVAC unit without some serious time and house surgery, so I decided to re-pan the joist bays and tie it into the remaining cellulose panning as best as I could. I bought some sheet metal sized specifically for panning joists from the BORG as well as some thrice-cursed sheet-metal screws and duct mastic: I already had HVAC sealing tape from repairing the flex-duct in my other house. Before doing anything else, I thoroughly vacuumed as far into the bays as I could reach from both the basement and register ends: it was really gross so I'm going to stop thinking about it now.
The panning process should have been a simple process, how hard could slapping some sheet metal onto the ceiling be? Well, let me tell you, if you do it the way I did, without the proper hex driver bit with a magnet in it, you'll run out of curse words about 40 minutes in. Trying to hold up a floppy piece of sheet metal with one hand and your head, while fighting to keep a tiny sheet metal screw in the bit was bad enough, but because the bit didn't have any retention, the screws kept flying out of the bit instead of biting into the sheet metal. After running through my entire pocket of screws to drive a single screw, I had a choice, wait until I got the correct bit, or predrill every single hole and hope they all lined up. I was on a deadline and had no car, so I started pre-drilling, effectively doubling the time it should have took. The problem i then had was that a hole big enough to retain the sheet metal screw caused the wood portion of the hole to loose most of its holding power. So back to driving the screws without pilot holes. Every five or six screws I managed to get in, I would climb down from the ladder and collect all the dropped screws to refill my pocket. By then end of it, I was hot, sweaty, and frothing at the mouth.
This is what it looked like before taping:
To seal up the panning, I first applied a liberal coating of mastic to all the exposed edges of the cellulose tiles we tore out and to the area where the cellulose and sheet metal would meet. After the panning was in place, I went back and sealed all the joints with UL listed foil tape. The hardest part was where the panning met the HVAC trunk since the flange was positioned for the thickness of cellulose and not sheet metal. I ended up making another flange out of spare sheet metal to interface the junction and then covered it in a few layers of tape.
Mission accomplished.
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The next day I went and bought the correct driver bit.
My favourite parts of this blog are the parts where I have no clue about what's being discussed (panned joist bays), and then I get to the end of the post and there's a picture, and then I get to reread the whole thing again reimagining it without the brown horses.
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