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mos87 OP t1_iwy6us7 wrote

Reply to comment by kittenrice in Diying forced air duct termination by mos87

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.

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kittenrice t1_iwy7gyq wrote

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.

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DragonsBane80 t1_iwya5wz wrote

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.

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kittenrice t1_iwydn26 wrote

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.

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mos87 OP t1_ix19ncr wrote

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!?

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deviantbono t1_ix1o9nx wrote

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

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