I’m assuming he’s referring to installations where the return air duct in rooms has a high and low grill so you pull the hot air off the ceiling in Summer and the cold air off the floor in Winter. I had my house in Maryland retrofitted like this. When they built the house they put the sheet metal supply ducts for the upstairs in the outside walls in lieu of insulation. The return for the upstairs was a 20″ x 20″ grill going to two 2″ x 3″ (1.5″ x 2.5″) wall cavities with the sole plate cut open about 12″ in each cavity which ran through the floor joist to the same thing on the first floor. I gave up my pantry and some hall space to have supply and return ducts run to the upstairs with high and low returns in each bedroom. Finally had cool bedrooms in the Summer and warm bedrooms in the Winter. The house was built in 1982 and the old 3 ton York heat pump was still working in 2007 when I had everything redone with an Infinity 5 ton system with zoning. Also had a SunPure SP-200 air purifier (4″ MERV 13 filter, catalytic converter and UV lamps) installed and a Skuttle humidifier. When we sold the house in 2014, the air handler still looked like new inside.

Grill sizing and or tapping the edge of the filter is important. My mother had return grill filters which were not taped. Every time the system turned on it would suck/pull the filter up against the frame and then dropped it once the air handler turned off. The drop would make a “dong” sound and wake me up. Annoying as hell.

@Paul, since Allison didn’t reply, I’ll bite. Checking the specs for lattice and regular stamped filter grilles (re: Hart & Cooley catalog), the pressure drops, even at 400 FPM face velocity, are on the order of 0.02 IWC for stamped and 0.01 IWC for lattice. At the preferred 200 FPM face velocity, pressure drops are off the chart, but extrapolating, they’d be on the order of 0.005 and 0.003, respectively. So no, it would be silly to spend extra money on aluminum lattice grilles chasing efficiency! OTOH, you might prefer the look of lattice grilles. I personally don’t care for that look.

@Roy wrote: “I am guessing the payback on lower lifetime filter costs would be quite good.”

Absolutely! Not to mention reduced blower energy, assuming proper setup for as-built external static. In new construction, the additional first-cost to size filter grilles to achieve < 200 FPM face velocity is minimal.

Thank you, Allison!

Yes,it does eliminate the need for a filter at the air handler unit. Make sure the return ducts and filter grill is sealed as well to ensure that all return air is filtered.

Danny: Yes, thanks for mentioning that. It’s a good idea for the supply-only ventilation system that’s popular here in the Southeast (central fan integrated supply) to have its own filtration anyway because it can bring in a lot of stuff – wasps, pollen, gnats…

Absolutely true, Danny! (I put that in the footnote.)