For instance this duct plus elbow https://www.supplyhouse.com/Lambro-Industries-1020L-3-1-4-x-10-90-Galvanized-Elbow

https://www.supplyhouse.com/Lambro-Industries-126L-3-25-x-10-Galvanized-Duct-24-Length

Delete if not allowed. Thx

In short: There's a very good chance that this is a return, given what you've posted, everything is normal, nothing to do here.

So, a return only needs to suck air from the house. That's it, nothing scientific. Sometimes we wish there were more to it, but, no, that's it.

As such, returns aren't ducted, per se, and are allowed, by code, to simply use the hollows made by interior walls.

You could enclose the channel with sheet metal if you really want to and have nothing better to do with your money and time, but there's really no reason to do so.

To set your mind at ease, find where this comes out, furnace wise, and see if it's a return or supply. (returning to the furnace or supplied by the furnace)

Hm, good point. I have a much larger return inlet in the hallway, but I'll check tomorrow if I have suction at that duct as well. Is it normal to have more than 1 inlet? I certainly have better things to do if it's not needed.

I don't actually know the math here, but for the best performance, a furnace wants more (less restriction) return than its supply capability.

So, yes, more than one is normal. One per room, then a central one is completely within the realm of possibility.

Returns are ducted, they just aren't insulated.

It's not uncommon to have one or two returns, but not one per room. You only see multiple in larger homes, as the return also directs air flow throughout the house.

I would not want a return in a wall cavity. Returns are typically where the filters are installed, although it's also not uncommon for that filter to be next to the unit, but you are trying to pull air from a cavity that has limited capacity. The whole idea of Returns is to allow for enouhh cfm back to the unit, you'd never restrict a return like this.

In the context of this thread, "ducted" is meant to be "encased in sheet metal".

Returns are not expected to be ducted within standard, American, code. Other codes exist, we aren't talking about them.

All, I checked with a sheet of paper, and there's no draft either way when the furnace is on. Meanwhile it's clearly sucking air at the big return (not pictured), and pushing at all the registers. Maybe this in-wall thing was capped off at some point!?

I've heard of one return per room, but never seen it.

Hard to tell for sure from the photo but it looks like an old floor register. If there is no air flow coming from it then my guess is that the previous owners at some point renovated and moved some walls around and rerouted the supply line elsewhere and instead of removing the old line just decided to leave it since it was inside of the wall. As for return air, usually it is done with one large duct but sometimes it is done with multiple if there is more than one floor or the furnace/heat pump supplies multiple units in a house but it is not usually in every room. As long as the air can transfer out of the rooms (ie. most doors have a gap underneath them) and make it to the return air duct that’s fine.

Yeah, that would make sense I think, thanks.