Ventilation system registers – wall, ceiling, or floor?
We’re going to do a walk through with our HVAC contractor next week to determine endpoint locations and duct layout for our ERV-based ventilation system. Most of what I’ve read indicates that both the fresh air supply vents and the return grilles should be located high up on the wall or on the ceiling. But some preliminary back and forth has me thinking that my HVAC contractor would like to put the supplies on the floor. Simpler for them I guess. From a comfort perspective, seems like the high wall or ceiling location would be preferable. But this will also increase total duct length and the static pressure in the system, which we’re trying to minimize due to the fact we’re using a pretty small unit (Renewaire EV90P).
So if the HVAC contractor pushes for the floor locations for the fresh air supplies, should I push back and insist for a wall or ceiling location?
Background info: will try to keep as much of the system in solid duct as possible, but would probably prefer flex duct for the final several feet of the run, just to keep noise down.
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The "noise" of an HRV is pretty low, even when fully hard-piped. We're talking really tiny air flows compared to those used for heating & cooling.
I'm not sure what the perceived advantage is for ceiling-mounted registers. In a heating dominated climate that might promote somewhat better air mixing due to the cooler HRV output convecting downward. With the registers floor mounted the motion of the air will be across the floor level, with less mixing. But as long as the input as exhaust registers are reasonably well separated and the register grilles are designed for direct rather than lateral throw I'm not convinced it really matters.
I can't respond directly to your questions but want to offer a couple of considerations to keep in mind during this stage of the installation process. I would avoid locations where the supply might blow directly on you since any draft affect comfort. I'd also avoid registers and grills that overly resist airflow since they can create quite a bit of noise if the fan is running at high speed.
For a high-performing house, with low ACH50, and for ventilation only, the supply can be either floor, high-wall or ceiling as long as the right ducts and diffusers are used, and verify the supply CFM per each terminal. High-wall and ceiling provides better directional flow for air movement. On the floor you need to make sure you are not placing some furniture on top of the terminals EVER… hard to make sure! My 20+ year experience with high-performing houses, is that the simpler the better. There are very few HVAC contractors that know how to correctly perform all manuals (J, D, S & T), design, install and commission properly any system. IMO, a good HVAC contractor or experienced Designer/Architect should be telling you what you need, not asking you.
We design and build Zero Energy Ready Homes only, and as an alternative, I prefer to use spot-ERVs, like Panasonic WisperComfort (20-40 CFM) for small houses or WhisperGreen for larger houses (50-80-110 or 110-130-150 CFM units) where they are ceiling mounted in an open hallway with minimal all-metal ducts, and along with synchronization with the HVAC system and passive return vents from other rooms, we get better results. Much simpler and economical.
William,
Here's the advice given by David Hansen, an experienced ventilation contractor, in his JLC article, Installing a Heat-Recovery Ventilator:
"We try to locate bedroom registers away from the bed. When we rough-in our duct drops, we always work from the top floor down. We locate both the fresh-air and the stale-air registers high on a wall or in the ceiling. After choosing tentative locations for the registers, we follow the intended duct routes down to the basement, to be sure there are no unworkable obstacles. In most cases, all the fresh- and stale-air registers are wall-mounted 6x10 registers, and each gets its own separate duct down to the basement. To keep airflows as high as possible, we use 6-inch duct for stale-air pickups. For fresh-air supplies into bedrooms, 4-inch ducts are usually adequate. We use mainly 30-gauge galvanized ductwork."
I agree with Armando that floor registers are a bad idea.
Thanks to all for advice, been away from screens for a few days. Feel like I'm in a bit over my head here, and too far down the road to make any major changes, too many pressures from the construction schedule (want to get this all in before other trades come and do rough ins.). Also, having some doubts about skills of HVAC contractor, but would be very difficult to change horses at this point. So I'm just trying to do my best with this, with big assists from the always helpful GBA community.
Having never been in a house with an ERV based ventilation system, I'm wary of comfort issues with the air blowing cold in winter. Hopefully, as Dana suggests, these concerns are overblown. General idea here is to run a trunk line of 6 inch galvanized duct for both supply and return. This will run through trusses of 2nd floor, and so ceiling registers for at least the 1st floor seems like a good idea. Floor registers would be easiest for 2nd floor, but I'm going to see if I can get them in the walls without adding a lot of static pressure to the system.
Martin, I've read that article by David Hansen in detail and it was very helpful. Interesting that he doesn't mention any method for controlling total airflow or airflow at endpoints. This is another conundrum for us that I thought our HVAC contractor had considered more carefully ...
And Armando, I will definitely keep your recommendations for spot ERV in mind when we get around to finishing part of the basement. For the two main floors of the house, just want to be able to close doors in bedrooms and offices (both very helpful with young kids in the house.) The passive connections between rooms ... I assume you're talking about transfer grilles or the like. We considered this, but again, noise and privacy considerations prevailed. And we can't much rely on our heating/cooling system (heat pump, forced air) to distribute air - hopefully with solar gain and woodstove use, there will be many times where windows will be closed and there will be no forced air.
One more question. Dana, if I'm understanding your terms, on a floor register we'd want a register that throws the air upwards (direct), not out into room (lateral). Did I get that right?
I am in 4a and would like to have my ductwork run through the bottom plates of partition walls so that the register is a foot or so off the ground. However, my reason for this is solely to prevent significant dust, dirt, dander, hair, etc. from falling into the ductwork if it is laid flat on the floor (common from what I see in homes here). I feel that the register being on a wall significantly mitigates this concern.
Since the top plate would not be cut, I am not concerned with the partition wall "hinging" out. I suppose I could add a couple blocks between the studs as well to bridge the two wall sections.
Thoughts?
Keeping the supply and return diffusers within arm's reach on the walls means not getting out a ladder when the grilles or filters need to be cleaned.
Worry about collecting dust and dirt ruled out placing ours on the floor.
Ceilings would've been fine, but, in our case, it would've added time to the install.
It was only after moving in that we appreciated how much having them on the walls makes routine cleaning a lot easier.
https://kimchiandkraut.net/2019/02/21/hvac-for-passive-house/
Thanks for the link. I think ceiling is fine as well, but that would require also me cutting through the top plate.
Bringing the ductwork 12-18" off the ground satisfies my interest in keeping it directly off the floor to facilitate brooming or mopping. -Cheers.
You're probably somewhat more likely to have issues with furniture blocking the registers if they're up off the floor that much. I don't think I'd worry too much though, there will be tradeoffs no matter what you do.
Funny thing for me is I just renovated my home office, and the previous owners had both floored over (with new hardwood flooring) the two supply registers in the floor (which I located and reopened the first year I had the house), and also the return that was high on the opposite wall. I'd always suspected that there was a return, but I didn't find it until I had all the walls open (I replaced all the old drywall due to wallpaper). What's really strange is this is a corner room with two exterior walls, and a previously VERY poorly air sealed and almost uninsulated bay window too so it used to be a cold room. It's lots more comfy now that I have all those issues fixed :-)
Bill
I like high-wall. Floor registers fill up with crap. Busy ceilings are more visually obtrusive than busy walls.
I have my registers at 12 inches below the ceiling on interior walls. They point upward toward the ceiling. The registers are painted to blend into the wall.
I wonder if there are code differences depending on climate zone.
Example - In cold weather zones, registers are designed near the floor since heat rises, and in warm weather zones the registers are near the ceiling since cold air falls.
This is more of physics than code. A register is used to distribute air along the ceiling where it can mix through out the room. I think manual T has a good discussion of the Coanda effect. You use the manufacturing data to confirm the throw and velocity. The end goal is a comfortable room for the occupants.