Finally stopped the drafts in my glass sunroom extension

I had a nearly identical issue with my 10x12 sunroom last winter. The floor was the biggest culprit for me beacuse it's built on a crawlspace with zero insulation underneath. I ended up crawling under there with some R-30 fiberglass batts and stapling them between the joists, then sealing it all off with a vapor barrier. It made a massive difference in how the room felt on my feet, even more than the window film I tried first. Regarding those sliding doors, I found that the adhesive weather stripping from Frost King held up alot better than the generic stuff I bought at the big box store. I also used some 3M window insulator kit film over the glass panels that we don't open during the winter. It’s a bit of a pain to shrink-wrap with a hairdryer, but it creates that extra dead-air space that keeps the frost from forming on the inside of the glass when it drops below twenty degrees.

That trough-the-wall AC unit is definatly a heat sink. I acutally bought a quilted interior cover for mine after sealing the gaps with Great Stuff foam like you did. It stops the drafts that blow right through the vents when the wind kicks up from the north. It’s those little $20 fixes that realy add up when the utility bill arrives.

My sunroom has a vaulted ceiling that was radiating heat right out through the shingles. Since I didn't want to tear down the drywall, I actually went up into the tiny attic space and blew in about 12 inches of cellulose insulation. I used a rental blower from Home Depot and it took maybe four hours. The difference in the summer is actually more noticible than the winter; the room doesn't turn into an oven by noon anymore. On the glass side, I found that even with decent shades, the aluminum frames of the sliding doors were still freezing to the touch. I applied some 3M Window Insulator Kit film directly to the frames to create an extra dead-air space. It looks a bit like plastic wrap if you don't heat-shrink it perfectly, but it stopped that localized downdraft that happens when the warm indoor air hits the cold glass surface. Between the blown-in insulation and the film, my space heater barely has to kick on anymore.

Glad you found some relief, but have you ruled out the header above those sliding doors? In alot of these extensions, the framing above the glass is basially a hollow box that lets cold air dump right down into the wall cavity. Even with the cellular shades, you might still have a convection current happening behind the fabric. I'd also be curious if you checked the actual seals on the AC unit's internal damper. Foam around the casing helps with the rough opening, but those units are notorious for leaking air directly thru the vents regardless of how well the trim is sealed.

This is so helpful! I'm just starting to fix up my own place and I'm totally geeking out over these DIY fixes. I never even thougth about the AC unit being such a huge heat sink, but it makes so much sense. Does anyone know if using that same spray foam works for soundproofing too? My neighbor's dog barks constantly and I'm wondering if beefing up the insulation around my windows whould finally give me some peace and quiet!

If you realy want to kill the draft from those sliding doors, check out the Duck Brand Large Sliding Glass Door Insulation Kit. It’s a lot more durable than the standard window film and actually fits the dimensions of a sunroom door without having to piece two sheets togehter. Since you already did the weather stripping, adding that extra layer of crystal clear film creates a much better thermal break. It’s cheap but way more effective than just the shades alone for stopping that ‘falling’ cold air sensation.