You are not drilling where you think you're drilling.

As you now know, that's tile backer/cement board, which is underneath the tiles in your picture.

I mean, maybe your goal is to run cat 6 up through the middle of the floor, idk, I prefer it being in the the wall myself. Or maybe the 'target' wall was built on top of the tile? Crazier things have happened.

You need to make some sanity checks here and measure out where to drill 3 or 4 more times. Or open the wall where you want the wires and drill down.

It's a fairly simple thing to do, if you're comfortable working with electricity and have basic tools (like a multimeter).

I would install it at the boiler and use the existing wires, making sure to label them as 24V on the stat end.

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.

For the love of god, colloquially, if you think your backpack is what makes you stink, bathe more often. Fuck.

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.

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)

Keep the WD-40 well away from the fan if you want to have any hope of fixing it. WD will attack any remaining lube in the bushings and prevent you from adding new. Someone suggested light oil, do that. You should be able to find "Zoom Spout" turbine oil at most hardware stores, it's an oil for lubricating motors, unlike some other Water Displacement products that like to cosplay as lube. This paragraph brought to you by Water Displacement products, for when you absolutely, positively have to kill an electric motor.

The likelihood of disassembling a small motor like this, replacing the bushings, (which you're going to source...where?) then getting it back together aligned well enough to spin, as a home gamer, is pretty close to nil. Sorry, that's just how it is. I've rebuilt larger motors successfully, but the little ones just aren't made to be worked on.

Your best bet is to try to source and replace the motor or just bite the bullet and replace the unit. Get it at Menard's if you can, at least you'll get some store credit for other stuff, provided you remember to send in the rebate.

You can't tie it back?

How are you getting in?

Just tie back the opening and put a fan in it.

Do you have any other bi folds you can compare it to?