Open "Air return"

I was at house today for a meeting. Before leaving she asked if I could look at there furnace. I said sure, love to. It’s a newer high efficiency Lennox, had camera took some photos. The air return duct had the top open about 5 to 6 inches. I said I’ve never seen that before. It’s a 1920 house that got new furnace before they moved in. I could only see two return registers in house both on main floor, were they trying to get more air by lifting top of return vent? The pipes and vents are all over, I think because of age of house they had a hard time adding duct work, there a combination of steel, flexible and plastic. You can see the Service Plus sticker on return air vent, so someone must have thought this was ok. The basement is about 15 X 15 area not alot of sq ft. I told her I would run it by you guys before recommending what she shoud do.

I would think that is a sloppy install at the very least.
In the 3rd picture it appears as if the flex duct is dropped onto top of the HWH.Is that the case here?

You are correct, one of many things.

The newer furnaces will shut themselves off if they do not get enough return air, let alone used gas like crazy.

If those are 6 inch flex returns it is seriously undersized for return duct work. In my opinion all that duct work supply and return needs to be removed and installed with the correct size ducting.

Knowing Minnesota, this has the feel of a converted **gravity system **(poor attempt), possibly installed by Harry and his cousin Olaf!

(Starting on page 40).