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OT: high-flow return grille for home AC system

specfab

Titanium
Joined
May 28, 2005
Location
AZ
Does anyone know of a good source for high-flow return grilles for residential/commercial AC systems? These are sometimes also known as fixed-bar return grilles. I have done a bit of internet searching, and have a very few possibilities, but I just want to canvass others to see what I might be missing.

Background: Replaced home AC system with a more efficient, higher-capacity variable-speed system a couple of years ago, and existing return grille (roughly 24 x 28, open area about 19 x 23) is a stamped steel louver unit that makes a huge amount of airflow noise when closed as designed. I would like to find an off-the-shelf fix before I feel compelled to make my own.
 

MwTech Inc

Titanium
Joined
Feb 6, 2005
Location
Fishersville VA
Have no idea the size of your system and all the details of how it is installed, but noise in a return usually means inadequate return duct sizing for the system.
 
Is it just the noise, or the look that you want to change?
Went through this last year when i took out a wall, moved a bunch of ductwork, and fixed the poorly adapted/poorly sized air-return the furnace guys had cobbed in when the furnace was replaced a 1/2 dozen years ago to get tri-fuel option.

My solution was the local community based architectural salvage co. for antique cast iron grilles.
It's irrelevant to the Q, but the one i selected for return was actually originally a coal heating vent with adjustable dampers. OTOH the size and open space is good, at least 4x the size of the bad job it replaces. I will either disable the throttle (Internal louvres), or placard it.

smt
 

deltap

Cast Iron
Joined
Sep 3, 2004
Location
Wisconsin, USA
Return air grilles don't have dampers. Noise is too much velocity or too short a duct run. Most residential duct is way undersized. Design return air for 300 ft/min velocity.
 
Return air grilles don't have dampers.

Well aware of that.
However, the casting was the correct size, much less restrictive than most modern returns, and fit the "look" my wife wants in her billiard room. So, you just leave them open (placard) or remove or disable the dampers.

My main point was that if looks were any part of the issue, local salvage can be an interesting resource, though more especially for the heat vents.

smt
 

specfab

Titanium
Joined
May 28, 2005
Location
AZ
Thanks for the inputs. The Shoemaker link looks like a possibility to add to the short list.

Re: noise vs. appearance, I'm simply looking for a return grille that I can secure against the return duct opening in the hallway ceiling that doesn't restrict air flow very much. The current stamped-steel louver assembly has to remain cracked open about 3" on the non-hinged side, hanging by wires, in order to get the noise down to a simple low-frequency rushing of air sound. With the grille closed and screw-locked in place, the air velocity creates a lot of higher-frequency sound that is obviously an indication of restricting air flow to the blower. Everything I've read points to installation of a high-flow grille as a likely solution. The appearance will be different for sure, where the grille has much larger openings, and uses round rods and smooth-edge profiles on any grille member to create less restriction and smoother air flow, and will indeed be damper-less.

The AC company that installed the system didn't engineer the intake side of this very well, in terms of informing us that we might need to consider the intake/return air duct sizing. I gave them some crap about it after this noise issue became appraent but never got any response from the management. The specs for the system (Carrier Infinity) I think show that an 18" duct is recommended for return side, which I would have thought would engender some offering of information from the installer, as we have a 14" duct. Replacing the return duct is pretty much a non-starter based on the construction of attic space in the immediate area. It would be a major project in my estimation. I have found that eliminating airflow restriction at the entry point helps a lot, though, which is what brings up my question.
 
What Bill said.
Is the current grille in the side of the duct, or is there an L down to it?

Reason i ask, if it is directly into the (under) side of the duct itself, you could lengthen the opening (presumably between trusses or joists?) and add a longer grill. If it Ell's down to it or you don't have length in that part of the ceiling, you can add another near it.

It almost sounds like my system, where it was "installed" instead of *designed* for efficiency and comfort. In your case it sounds like putting the optimal capacity duct would have been inconvenient to the installers, or possibly compromise structure (less likely, but that is what they will tell you the problem was). If it was designed, even loosely, it might not be ideal to add return air to another part of the house if it creates dead zones somewhere. OTOH if it was not designed, you might have those anyway?

I'd certainly complain to the installer company, if you paid to have a new installation and they spec'd either correctly adapting your existing duct system, or putting new in, so far as necessary to meet the new unit's manufacturer specs.

Mine was installed by "friends of a friend" at an advantageous price. They are professional installation company, but they are not designers or engineers. They installed my shop, too; & I know how they work. I did not really want them messing with the structure in my old house nor pay what it would cost for someone who did not completely understand it, so got the heat on, and modded myself over time to improve when doing other house renovations.

smt
 

Bill D

Diamond
Joined
Apr 1, 2004
Location
Modesto, CA USA
Something like this but in wood was what I meant. Looks like a vent for a floor furnace to me.
Bill D
 

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Gordon Heaton

Stainless
Joined
Feb 19, 2007
Location
St. George, Utah
. . .uses round rods and smooth-edge profiles on any grille member to create less restriction and smoother air flow. . .
From experience: round rods do not provide smooth air flow at higher velocities. In fact, they induce a lot of turbulence on the backside which causes excessive vibration or rumble. They will work at low velocity.
 

Bill D

Diamond
Joined
Apr 1, 2004
Location
Modesto, CA USA
The strut wires for biplanes are not round. They are teardrop shaped in cross section to reduce air friction and drag. I suppose they make it quieter as well. You could buy some and weld up a grille to match.
Bill D

 
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bosleyjr

Diamond
Joined
Sep 30, 2006
Location
SE PA, Philly
I would strongly suggest having the volumetric flow checked. I had a new system put in when I moved to this house in 1998 and the idiots who installed it had the flow set to default (way too high). Net net was that the coolling cycle in summer never ran long enough to knock down humidity. So poor comfort. Flow rate optimization is something to check...
 








 
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