A few weeks ago, I took a day off work to work on things. I bought rolls of insulation, and some spray foam. I put the insulation in the attic (a 25 foot roll went from end to end--the inside dimension of the room is about 31 feet, but the attic space is very short so you can't get a second layer of insulation across the joists). This was hard work--crawling around on joists, insulation, heat, nasty. Good exercise. I was smart too this time--I bought a special pair of rubber gloves and a disposable bunny suit to protect myself from the fiberglass. It was a very good idea and really kept me comfortable. Tape the gloves and suit together, so fibers dont' get in the way. I also was able to put some serious insulation over the closet and garage door which should help. It does seem the heat doesn't run out of the room as quickly now.
I upgraded the door into the attic space. I made one out of 3/8" plywood, and new weather stripping, and a new latching mechanism (the old one was wallboard and screws and was falling apart). I put some rigid foam behind the door (cut to fit the opening) and sealed the hole where small cables came through (phone, network, and CATV cables, I'm only using the phone and network at this point.) Again, this mks things much better
I then used the spray foam to fill gaps around the foam I stuck in the vents in the fireplace brick. That has made a big difference. I then used the rest to fill some gaps in the joists under one of the crawl spaces.
I've also put plastic film on the windows. I still have a bay window that's leaky--I have film for it, and may use some board insulation to insulate the deck of the window.
So, finally, I feel like I'm making progress, but there's still some cold coming in. Most of it at this point seems to be from the floor. I have been in the long crawl space and determined some of the insulation has fallen and needs to be reinserted--I can in fact feel the cold spots where the insulation is sagging. I also have another crawl area that I get to from the basement--this is where they found termites on our home--and there's clearly some insulation deficiencies there. I thought about ripping out and replacing all of it but I think I can fill in gaps and get a small amount of new insulation to fix the really bad spots.
One last thing is I need to re-weatherstrip the door to the garage. It sits in the jamb oddly, and there's a gasket on the bottom of the door that is broken.
And, still, you can feel a draft through the sliding dimmer switches. I've sealed around the light switches, but you can't easily seal through them.
I can't imagine what the previous owners did. Clearly they ran the gas fireplace at full tilt, prices be dammed. We'd easily have over $500/mo gas bills if we did that.
I'm hoping to do the insulation work on the rest of the holiday weekend. We shall see.