Flexible Duct in code noncompliant plenum?
A guy that works for me installed a plenum to distribute hot air from an electric furnace, to the rooms adjacent to a hallway. After he got done, I double checked, and it turns out that the plenum doesn’t meet code.
So, I now have two options: One is to run rigid ducting up into the attic. This will take it outside the conditioned space. The other option is to run flex duct inside the plenum.
The plenum was made by dropping the ceiling a foot, so I have approximately 8-inches of depth to work with to run the ducts.
I’m hoping that we can pull flexible ducting through the plenum, (every point we need to reach for an outlet is in line of site from where the manifold on the furnace needs to be), without having to rip things up. All five of the rooms served are 10X8-feet.
So, does anyone have recommendations for flexible duct brands or products to install in the plenum? Or general advise that might help?
Replies
I doubt that you could stuff enough flex duct into the 8" furred space to adequately carry the flow needed.
Could you install 8" high duct in the furred space, and bridge side-to-side with the drywall tight to the underside of the supply duct?
Bummer
I'm wondering if you had a problem finding the couple answers to the original question about the legality of the plenum that were posted within an hour of your post.
Would it be not beneficial to pull down that sheetrock so it can be done easier?
Best of luck.
You can't slip a rigid duct down the plenum? (maybe that had to be done AS you were doing the plenum ceiling?). You can't remove the drywall? I'm thinking you will have just as much difficulty snaking flex as installing rigid. And you don't get near the performance out of flex that you do w/ rigid. In hind sight your man was a bit hasty. Did he already finish the drywall? Even so, maybe in the grand scheme of things it would be worth removing and redoing. You might be able to do some reasonable surgery w/out completely tearing down the ceiling and framing. The mudding/taping I've seen lately on a repair has been pretty amazing. It depends on how right you'd like it done (in addition to all the other factors affecting you that we posters can't see or be aware of).
To tight of access for rigid.
The access is too tight for any length of rigid to get in there. So, the options are:
1.) Remove the plywood, and most of the framing; install rigid, and install a suspended ceiling, (what I orignally intended, before I was misinformed that a plenum would meet code).
2.) Snake flex into the existing plenum.
I know that rigid is the more efficient solution. But the facility is normally not used during the winter, and the heating system will normally be operated only 6 to 12-weeks a year. So, efficiency isn't the concern it normally would be.
Money is tight. I have about $125,000, to try and maintain over 400 buildings, works out to about $300 per building. So, frequently near term cheapest wins. And, since Congress still hasn't passed a budget, I don't really know if I have any money yet.
These are pretty short runs, correct? If so, I would suggest running a larger flex duct than is called for, with the knowledge it will be mashed down. Basichy you are running oval lex instead of round.
Duct efficiencey matters more on long runs and with cooled air.
As always ... the specifics of the poster's situation can trump the logic of the ideal. Decisions aren't always just about the science of the situation. You have economics and practicality to deal with as well. Pay your money, take your choice I always say. Would most people install a suspended ceiling grid in your situation (vs. a 'hard' ceiling)? If so, seems like that is a reasonable option w/ hard duct ... leaves things accessible for future changes, too.
If you are the one to pay for utilities or even if you are just trying to have good rentable space, there is value in more efficient air distribution in terms of either energy or comfort ... and people are beginning to realize the true value of comfort. My (and other's) analysis of comfort shows huge dollar savings in high levels of comfort since the cost of labor is often 10x+ higher than that of energy. This can translate into rentability and tenant satisfaction.
This started as a simple, rehab of a bathroom.
Back ground: I am the Facilities Engineer for a National Forest. I took on the job two years ago. And, have hired two seasonal, (half year appointments), guys to help me in the field since then. One of them is a semiretired guy, who twenty years ago ran his own HVAC company, the other used to build and restore log cabins. It had been ten years since there was even a seasonal facilities maintenance tech on the Forest before I hired my two guys.
The buildings had virtually no skilled maintenance for about a decade. The buildings were mostly built by the CCC's in the 1930's and are therefore historical which compounds my problems, because nothing on the exterior can be changed, and very few irreversible changes can be made to the interiors. Dual pane windows aren't allowed. I have to scrape of lead paint, and repaint cedar siding that is original to the buildings. Pulling the old siding, of which 80% of the wood is damaged, and replacing it with new siding isn't allowed, even though that would be less expensive.
In the decade where there wasn't anyone to do maintenance, the guys took it upon themselves to fix things since there wasn't anyone to do the work. We are constantly finding things that are scarey.
Electrical receptacles in bathrooms that aren't gfci protected. We started to replace one of those last summer, and found out that it had been wired for 240. Someone had landed both the white and black conductors to adjacent breakers. Copper water lines that have been closed off by crimping a lead bullet in the end. Rube Goldberg plumbing configurations that run in circles, and change diameters three times while transitioning from copper to galvanized, to pvc, and then back to copper. Water heaters with the temperature and pressure discharge valves replaced by plugs.
On this "remodel" We originally intended to replace an old sheet metal single stall shower, with an new fiberglass unit.
Then the fire kids ripped out the entire bathroom floor, because the floor was soft under the old shower where it leaked. Then they decided that there was mold in the walls of the bathroom, and ripped those down. It is nice to have the help, but they are pretty gung-ho types, with little or no experience. So, things sometimes go sideways.
We weren't going to have central heat, but since we had an electric furnace, (that got pulled form another facility), we decided to install that.
So, I now have a fifty year old building that has a completely remodeled bathroom, that is now ADA compliant, complete with a nice tile floor, (only because we found the tile in one of our storage buildings and didn't have to spend too much to add tile backer to the new subfloor we had to build).
New pergo floors through out the rest of the building, only becuase we found a great deal on pergo if we bought five pallets of a close-out line. (less than 80-cents a square foot, which makes it the least expensive flooring option we have), and it actually holds up to kids in fire boots better than sheet vinyl.
And, an electric furnace we can't use, because the ducting isn't right.
I am constantly trying to figure out how to get things up to code, when I don't have hardly anything to spend. It was a battle to get approval to buy new code books for my guys to carry in their trucks, and for me to have on my desk.
We had a near miss accident last year with a portable table saw. There was a great ruckus because it was my personal saw. Then we fianlly got money to buy a new portable tablesaw, and a miter saw with stand. But only after I took the approver over the the shop, so they could understand why the tablesaw we had, (a 1940's 3-hp, 3-phase, Delta Unisaw), wasn't suitable for portable use, and driving 100+plus miles to make trim cuts on flooring wasn't practicle.
...and I thought I had troubles.
Your HVAC guy is not entirely off base. Although what he suggest won't meet code, there is probably no real danger from using a drywall chase to convey air from an electric furnace--just don't try to add an A/C coil into the system; that would create too much moisture for the drywall to handle. Hopefully, the furnace is new enough to have a high limit cutout that prevents excessively hot air from entering the plenum. The code requires controls to prevent operating temps above 200 degrees and a cutout to shut the unit off if the temp goes above 250 degrees.
But I see your dilema--if anything goes wrong in the future, or if anybody comes behind you and starts nitpicking your work, you wouldn't have much of a defense.
I know none of this helps you a bit--sorry.