Did more work over the weekend on the furnace build. Saturday I finished up the back wall ducting. Had to do about 6 feet of length to finish up the 23' run and then did a shorter 6.5' run. The last section of the long run is still removable. What you see sticking up is the foil tape. I cut the white protecting paper and stuck the foil tap on the sides of the duct. When I put the vent into the room I'll peel the paper and seal the duct.
Here it is in the ceiling in the hallway below
Then I had to push more crap around so I could pull up more floor to put the return ducting in.
Unfortunately I neglected to account for the runs under the hallway so I ran short of the 1/2" isoboard so I couldn't finish the runs. Probably going to need 3 more sheets. Too bad no one has it currently.
So on Sunday I moved on to the next thing. I picked up nipples and fittings so I could properly locate where the furnace would actually go. I made it work out so the supply side duct would be 16' long which works out well with the 8' long sheets.
I thought I would start on the supply duct but decided to go to electrical. I had to do this before the return ducts were permanent as the wiring needed to go in the same areas. So back up to the box store for electrical and some aluminum.
Originally when I put the sprayroom in I ran a 3 phase circuit for my fan and 3 more hots for the room. I used one line for lights and another for outlets. The 3rd was unused, until now. I tapped off that leg and used MC to run to the switch I had on the furnace.
Then I decided to run the wire for the thermostat. That was fun

. I had to fish it through an insulated wall. Couldn't find my fish tape so I had a roll of 12-2 which I thought was stiff enough to stay true. I drilled a 3/4x2" hole in the sheetrock for the 5 wire cable and the thermostat. I drilled a 3/4" hole in the double plate right next to the wall so I'd be in between the insulation and the sheetrock. 6 tries with no success. I cut a Poplar board 3/32" thick and 5/8" wide. I put a hole near the end and marked a line at 49" which was where the hole should be. Put the "fish board" down the hole and amazingly I nailed it 1st try. Woo Hoo.
Ran the wire up to the furnace. I took the copper wire out of the remaining MC shield and inserted the thermostat wire into it for protection on the exposed part of the run. I wired it to the control board in the furnace. On Monday morning wired the other end to the thermostat board.
At the end of the day today I used the 1 1/2" wide aluminum to extend the flange on the supply side of the furnace so I would have more flange to hold the ducting since it's not going to be connected to a metal duct that can just be screwed to it.