And you can see from the second pick the bottom part is blocked off. How much air can be really moving through there?
Yes. Romex or coax, you have to try running directly across joist pockets that are cold air returns, never along the length or any other shenanigans. Installing boxes for light/switches in a cold air return is a no-no as well. With romex though, while there might be plenum rated romex somewhere I've never seen any. This really only means that you can't just buy a pricier romex and start running it through plenums, just like you aren't supposed to run romex over commercial suspended ceilings with the "open" cold air returns (can't remember term atm).
Depending on when it was built/wired, that could have easily been par for the course at the time.
Vertically, you mean, up through a cold air return?
He has no central air? When I went back and looked earlier I don't see him say that, anywhere. AFAIK he could have two random grates from a pre-existing heat circulator AND central air. I have no idea. My house has central air AND a heat system built into the fireplace so that isn't an either/or. The only thing I saw when I went back (because I kept reading his posts thinking I was being trolled) was one spot where he talks as if he is planning on installing baseboard heat, and later he then talks as if baseboard heat is already installed. So I have no idea WTF is going on, and even you were addressing the paucity of information earlier yourself so I wouldn't think that would be a leap for you.
Bottom line, worry about plenums if you want; if there are no plenums, then there is no issue. But I can't begin to tell anyone if there are because it isn't my house and I haven't seen it stated yet how the house is heated/cooled to begin with. As far as code goes, I don't want to split hairs over it - I don't care. I brought it up as something to consider, not as an absolute or as something to get into an argument over. If people want to argue and do stuff counter to code, knock yourselves out. I just wanted to bring it up because most homeowners don't know anything about codes or common trade practices, past that I give no fucks.
They do (well I^2*R losses do) but I don't feel like arguing about it, really.
Outside of residential, the NFPA can be a lot more strict and stuff like romex is often never used. Not to mention that they can be hardasses with regards to cables in plenums. Electricians used to run cabling more freely in commercial plenums but it caused a lot of issues so they cracked down on it. And don't labor under the misconception that you only have to worry about a potential fire starting IN a plenum (and that upsizing to a larger gauge will prevent any issue); the nature of plenums means that fire can be drawn into a plenum or provide a path for the fire to spread (thanks, air!), and wiring in a plenum can give a fire looking to spread elsewhere the fuel it needs to spread further. In fact it's pretty unlikely that a fire will start along the length of a cable, but rather that it will start elsewhere (junction box/connections) and then spread TO a plenum (possibly along the length of cable itself). Then it will act like a chimney flue, which when you think about it is a Bad Thing. Deathwing was right in a sense when he touched on the idea that wiring isn't likely to spontaneously burst into flame (possible but unlikely), the true danger is a small fire/flame reaching a plenum and then being fed by copious air and ready fuel (multiple cable sheathing in your case).
Still common in new houses.
