Need help connecting return ducts to HVAC system (with pics)


Old 12-26-13, 11:49 AM
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Need help connecting return ducts to HVAC system (with pics)

Hi all,

So I have discovered that the return on my HVAC isn't connected to the system (whilst getting my thermopump replaced). It looks like a bit of a shoddy job was done adding a filtration/humidification system, and the return pipe is hanging loose. I'm considering adding it, but I need a few thoughts on which approach to take. The pics below are linked to larger versions.

Originally, it looks like the system was missing the entire part 1, which means a 16x24x4" air filter and a humidifier. The air exchanger (pic #2) is functional, and is correctly connected to suck in air from the outside, and to send exhaust to the outside.

Where it gets tricky is this. The "air to building" pipe on the air exchanger identified with #3 on pic2 used to be connected to the input port #4 on pic3 (air comes out when the device is turned on, so clearly it pushes some air out). After the entire assembly #1 was added to the HVAC system, that port was closed, and the air exchanger disconnected, so this pipe lies freely and points at the wall. Currently what happens, is air flows along the green arrow. The return pipe is #5 in the first picture, and it simply hangs above the air intake, so obviously no air is sucked into it. The air is sucked from the general surroundings in the room, under the stairs, etc.

What I'm trying to figure out is this. I want to connect the return pipe, #5, to the system somewhere. I have two choices the way I see it.

1) I could either plumb it to the filtration system, #1,
2) I could connect it to to the air exchanger, #2 (pipe #6, which, when the air exchanger is on, wildly sucks in air). The diameters match, so it seems to clearly have been connected to it in the past.

I feel like choice 1 would be a poor one given the pipe is relatively narrow (the pipe is 6"), so I'm wondering whether it would provide sufficient air flow into the entire system. It *seems* like the more proper way would be to plumb the huge 8" exhaust from the air exchanger (pipe #3) to the air intake #1, but I don't know how to do it - do I need a converter of some sort? The module is 14" x 22", and I can't seem to find any converters between a square filter like that and a 8" pipe.

Any help welcome, and I realise this is rather confusing, so if I can provide more information for this, I'd be more than happy to. Thanks very much for any help!

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Old 01-22-14, 12:11 PM
Join Date: Jan 2014
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Okay so what Iam getting from this is that pipe 5 was originally conected to the return air plenum at pipe 4. I installed a/c ducts for 10 years and have never seen an aluminium flex duct used for a return. All ducts should be insolated unless they are in a controlled air space. But, you will want to have your return pulling air from inside the home itself. You can reconnect to the original inlet or anywhere you can on the return air plenum, But I would recomend using an insolated flex duct. Also you said that the original system didn't have a filter for the unit? If not what is at the other end of #5? If it isn't attached to a return air filter box it needs to be before installing to prevent clogging your coils.

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