Keeping ductwork out of the attic
Hi All,
I hired Energy Vanguard to do my HVAC system design for a new build, but when my preferred sub came to the site, they pointed out that the design didn’t take into account two LVLs that were part of the house plans.
I uploaded two files – the 1FL floor plan showing the location of the LVLs, and the 2FL duct plan showing where the proposed ducts clash with the LVLs.
In an effort to keep ductwork out of the vented attic, we specified floor trusses big enough to hold ductwork, and we were trying to keep both air handlers in the same utility room in the basement. We do have a utility closet on the 2FL we were planning on using as just a regular closet, but now it’s looking like we might need to put the 2FL air handler there – but I’m still not seeing a great way to run ductwork without at least a small portion of it running through the attic, and I don’t know how that works with a downflow system.
While I’m waiting on Energy Vanguard to get back to me, I appreciate any advice you all can offer. Thanks!
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Replies
The LVL is only in the way of the 145 CFM feed (looks like Bed2).
Move the supply trunk a bit further up (in the drawing) and a bit away from the horizontal LVL so it gets into the trusses again.
For the Bed2 feed, looks like the vertical running LVL is directly bellow the bedroom wall. Extend that bed takeoff all the way up by the windows than come up in a small bulkhead in the corner to feed the bedroom. You can also drop bellow the LVL and run under it in a bulkhead. If you can get the engineer to either move the LVL or the wall a bit, you can come up inside the bedroom wall and avoid any bulkheads.
So I've had three subs come in to the house now, my builder's preference and then two that I like. After seeing the house, everyone upped their quotes, which is frustrating given that they had access the final floor plans and completed duct designs. They all recommend using the 2FL mechanical room for the 2FL system to lower the overall cost of ductwork and make things more efficient, since it reduces a 20-foot vertical run up from the basement. Unfortunately, the 2FL mechanical room isn't in a great location given the presence of the LVLs.
None of the three want to use the floor trusses for the 2FL system - all of them want to bury ducts in the attic. I've done my reading here, and I know that burying ducts historically has not been recommended. I also know it's allowable by code now so long as you bury them properly, and all three builders said the attic ductwork would be R-8 per code, and that they were willing to put flags on the ductwork to ensure it was all buried deeply enough - we're doing R-60 in the vented attic.
If the ducts are really going to buried underneath probably R-30 worth of insulation and wrapped in R-8, is ductwork in the attic so bad?
David,
The primary challenge will be air-sealing, not the amount of insulation.
Malcolm, are you referring to sealing the ducts, or sealing the drywall ceiling? Isn't it true that regardless of where the vents go, I'm going to have to climb into the attic post-drywall and air seal everywhere?
David,
Both.
If the ducts stayed in the floor joists, they wouldn't penetrate the primary air-barrier at the ceiling at all.
Ah, yep - zero confidence my builder could manage to properly install a smart vapor barrier in the attic; plan was always to go up there post-drywall and spend a few hours on my own with a can of foam, sealing everything. We were always going with trusses since it's a wash cost-wise where I am vs. stick building, and I guess at least I have plenty of space for lighting the 1FL now.
You did a design that allows for the ducting to run through the floors, I really don't see any reason to run into the attic.
Around me in the land of 2.5 story + basement houses, air handlers are in the basement and ducting is run up for the upper floors, so running a trunk up is not hard. Ducting for a floor always runs in the floor joists of that floor and never in the attic.
I really don't see why it can't be made to work with your setup. I would talk to your GC and see if they have somebody other than the HVAC company that can install the ducting per plan. From there have the HVAC techs come out and install the air handler.
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