I think you're both right that it's some kind of fiber/particle board. Managed to pull some of it back and that's what it looks like. I'll also test for asbestos I guess.

You're right but to me the particles don't look fine enough. OP should definitely make sure though.

Note that a half-tripped breaker won’t be easy to spot. They often look like they’re on. You have to flip them all the way off and then back on.

Spray with anti microbial and close it up

Just close it up.

If the motor were engaging, you should get a hum. You checked both the circuit breaker on the device and the circuit breaker in the breaker box?

No sound at all

Looks like it has an asbestos type colour to it.

Were there any 3 way switches involved with what you changed? Did you put any "smart" devices in? When you measure 12V is it 12VAC or 12VDC?

Some smart devices (particularly dimmers) use digital signals, or other internally generated voltages on the traveler wire between the switches. If this traveler is tied back into one of the other AC lines this could cause problems.

If you vent out the soffit, consider using rigid ducting instead of a flexible hose. It's harder for a fan to push air through a flexible duct, so the fan will work better. It also allows you to put a small drop from the bathroom fan to the soffit exhaust vent. Doing so will allow any condensation that forms to drip out the soffit exhaust vent.

Stickyback plastic

From the texture it looks more like you have some kind of particle board instead of drywall.

Personally I'd unscrew a smaller piece, that'd allow to look for insulation, as well as closer inspection of the "drywall". I also don't think that you'll get a very nice finish on it if this is your first time, at least not for any reasonable effort. Filling the gaps is one thing but getting the whole area flat is a whole other ordeal. Not doing it would leave you with clear filler lines everywhere in contrast to the texture of the wall.

Dude said he didn't want to run a vent pipe out his roof. Insulation will not solve the problem of attic condensation dripping down his pipe. I suggest a solution, I've heard no alternative solution. Maybe a flapper at the top? That would have been a productive comment.

Did u check the hot water pipe feeding the shower to make sure it was open?

Can't quite tell but I do not think that is drywall, looks like it may be fibreboard? If so you can't really mud that, may want to consider installing some type of durable panelling (there are products made for this type of thing, or even mdf or plywood) and use that as the finished wall. Or could put new drywall over top and mud that. But Mudding and taping is a lot of work if you're new to it, and drywall is easily damaged in a garage, although it does look great when new.

As for insulation, guess it may depend where you live. If you have cold winters and ever want to hear the garage it's a must.

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Yep, did each rad by closing them all and opening one at a time, starting downstairs and moving up. Defo fully cleared the entire system.

Top point is the towel rad in the bathroom, but air seems to find its way to one rad in the master bedroom over the others.

There is an auto air valve on the HW tank, if that helps

Just sand it lightly. This is not a big deal. Mold needs water to grow and there's precious little of that in kiln dried lumber.

You 100% have to plan. If you don't you can either wind up with a machine that bottlenecks itself or mismatched parts. Everything should be complementary and more than capable of what you plan use it for. I also like to leave plenty of room for expansion and good ventilation.

Not that interested.

I'll let it run while taking a shower and for 10-15 minutes afterwards. The moisture is just collecting on the ceiling excessively and completely (not partially) fogging over the mirrors. I've never lived anywhere where turning on the fan didn't have some impact, and I genuinely do not notice a difference from when there was no fan. We're not taking excessively hot showers for extended periods of time either.

No.

Color match, then paint from corner to corner. Prep work is everything.

SketchUp. It doesn't take many test drawings to get down the ones you'll use most.

Last time I looked, there was still a free desktop install from 2017. It's all online now.

Or even just moving to nicer or better switches/receptables.

My house had a bunch of the old shitty dual-rounded style outlets. When I got kids, I swapped most of those for the square outlets that also have protections against somebody jamming something in one side (plug needs to evenly push on both hot+neutral for it to "open").

Later also replaced many of the stick switches for cosmetic reasons (the old ones had cracked/dirty covers and deco looks a bit nicer).

I believe the cap diameter is 8" and the vent ducting is 4" diameter. Any way to test to confirm your suspicion?