Repairs to cold air returns-natural gas heat

I'm planing on repairing/cleaning my furnaces cold air returns. They are built using a couple of the houses floor joist, with a sheet of drywall at the bottom of the "box". I'd like to paint the inside of the ducts, and use a mildew inhibitor. I'd also like to use an aluminium backed insultation sheet in place of the guypsum board that was previously used.
Any suggestions? Should I paint the inside of the ducts, and what type of material should I use replace the drywall material with?
Thanks,
Steve
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Are you indicating that you are getting mildew in the ducts? This really should not be happening. The air should not be that damp, unless what we have here is an unheated space that relatively warm moist air from the house passes thru. If moisture is condensing, then of course that drywall is a terrible choice for boxing in the joists.
If you already have mildew, you need to chlorox the whole space and then painting it would probably be good. Then either use the insulation board (which I personally think is too flimsy and fragile), or sheet metal, which you then insulate from the outside with insulation board (glue it on).

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The house I bought was a bank repo. It sat for about a year with out electric power or heat. The house doesn't have rain gutters, and one of the basement walls has a crack that runs horizontal half way up. It has a very damp basement, but no visable standing water. There is so much himidity in the basment, that the gas pipes, and heat ducts have rusted and I believe they should be replaced. I bought the place about three weeks ago. It smells a little better, but still has that old house musty smell. (It was built in 1972). I have hired a mason to come in and dig up the basement wall and re-block the cracked portion, but he hasn't started yet. Once I get it aired out/cleaned, and get the walls some what water proofed I should be o.k. I also need to put up rain gutters and grade the property so I hopefully won't have the water problem anymore.
After that I'll fix the three rafters that the squirrels chewed in half, and replace the cellulose insulation that they pee'd on, fix the holes that the squirrels chewed in the soffets, and maybe in a couple of years replace the 30+ year old shingles.
I'm a young single guy, so why did I buy this house rather than keep renting? LOL. Home ownership, is this all worth it?...I just got my summer tax bill, ouch!
Steve
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If you had one squirrel there are probably more up there, a family. Get moth balls and throw in attic. Does you air system have a supply and return in basement, get a dehumidifier for the basement. Rust will happen ,your pipes are probably ok, you can wire brush and paint them. You probably have alot of mold down there, get a garden sprayer and bleach, spray dark areas, if they lighten up it is mold , spray till you get rid of it. Mold grows at 65 to 70% humidity, use a dehumidifier..My basement was like that , I got 6 gallons of bleach sprayed, and left for a few days. Squirels and rodents will get back in if you dont seal all entrances, and even then It is Their Home they were there first, they will eat through wood and thin aluminum to be warm this winter,
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NO! FOR THE LOVE OF GOD, DON'T DO THAT! The house I bought has aluminum backed insulation boards instead of metal for all of the ducting. There is an air return duct in the crawl space (dirt floor) that wasn't air tight or even close to it. Because of the air gaps, nasty musty odors were rising up into the next floor. Also, the insulation had black mold on it. I got a HVAC contractor to replace the insulation board with metal. All the odors from the vent are gone.
Then I found that there was insulation board for the ducting right next to the A/C condensing unit. It's covered in mold on the inside. That will be replaced in the next week or two.

Use metal. More expensive but maintenance free and will last you for the rest of your life.

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Did the HVAC contractor make a complete box out of metal, or just nail metal where the insulation board used to be? From what you discribed my houses' musty smell might be coming from the cold air return ducts (in the basement). Back in my high school metal shop days, they taught us how to make air ducts using a metal brake, and a bead roller. I wonder if I could make my own ducts, or if they sell them already made? I've been warned not to use duct tape to seal them...ironically enough the experts say it's the worst product to use for sealing air ducts...
Steve
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