Where to locate secondary air handler
Hi All,
We’re building a 4400 sq ft house in CT and awaiting HVAC proposals from a few vendors. Builder’s preferred vendor is proposing two Mitsu heat pumps + 2 ERVs, with the finished basement and first floor getting one pair and the second floor getting the second pair.
Now, nobody’s run a Manual J yet, so maybe we will just have a larger single heat pump that’s got a bunch of zones, but in the event we need a second air handler, do people have strong opinions on putting the unit itself on the second floor?
We were going to go w/ foam on the exterior of the roof which would have allowed for any 2FL units to go up there, but when we got quotes it was going to cost an arm and a leg so we’re just doing a vented attic with R-60 of loose fill on the floor. We’ll be burying insulated ductwork in the attic, but we didn’t build a mechanical chase from the basement up through the house into the plans and there isn’t a great place to put one. We could place the second air handler on the second floor tucked into a well-insulated closet, but I’m not sure if the noise will be too much to deal with.
Appreciate any advice – thank you!
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Replies
How large is your attic space? I guess you would not consider an unvented attic.
Per my post, no, we're not doing an unvented attic.
Since it is a new build, you can spec floor trusses with a duct chase. You can put a downflow air handler in a 2nd floor closet delivering air a supply trunk in this chase and from there run takeoff to feed the rooms on the 2nd floor. No need for any ducting in the attic or moving all this to the basement. The bonus of the downflow air handler is it puts the return at the top near the ceiling which is where you want it for best cooling performance. Most multi position air handlers can be configured for downflow operation.
The modern ECM air handlers are very quiet especially at lower flow rates, no issues with it near a bedroom. As a bit of extra insurance, I would insulate the walls of the utility room and go with 5/8 drywall there.
Thank you for the advice, Akos! We've got floor truss plans printed up, but I'll talk with the engineer about making sure they include a duct chase - I frankly can't tell if they do by looking at them.
Also appreciate the tip on downflow vs. upflow for the air handler.
EDIT: So my designer tells me that we've got 24" open web floor trusses, which should have plenty of room to run HVAC as-is. Sound right?
Ask them to lay out the trusses and the 2nd floor utility room. The trusses do have openings but not all of it can fit something like an 8x14" trunk. You want the trunk preferably directly under the air handler or a couple of feet over where an easy 90deg bend can connect it.
The takeoffs to feed the rooms should be no problem in most cases with trusses. Usually the thing that will get in the way are any larger pocketed beams, don't know if you plan has any of those.
For a rough layout (you can do it even on paper), you generally want a supply trunk running a good part across the house with supply feeds from there to under each outside window. If you can make this work with the existing trusses, it should be easy install.