Best Way to Insulate Ductwork

[El_Viajero]

I want to insulate my old, hard-pipe, non-insulated air ducts. They are in the crawlspace. My options seem to be...

1. "Classic" fiberglass duct wrap. You wrap it around, tape it together, and try not to compress it too much. Yeah? Downside: Fiberglass is yucky to work with.

2. Bubble wrap insulation. Not yucky to work with, but you have to keep airspace between the duct and the bubble wrap by using spacers. It might be tricky to install properly.

Does anyone have preferences? I'm particularly interested to know whether anyone has installed bubble wrap insulation (with the airspace, obviously) and been successful. I know it's common for people to install the stuff improperly.

One other issue: My ductwork rests on concrete blocks on the floor of the crawlspace. I guess I'll need to insulate around those blocks as well since I can't actually insulate the part of the ductwork that's resting on those blocks?

[lthenderson]

They do make cotton duct insulation if you are truly worried about working with fiberglass. Personally, if I am doing lots of work in a crawlspace, I already have on pants, long sleeved shirt, facemask and gloves, which are what you need when working with fiberglass. I usually put on a hat to keep it out of my hair for good measure and then take a shower and throw the clothes in the clothes washer when I'm done. No problems with itching afterwards.

[bigdoug03]

The "best" way is also the most expensive: closed cell spray foam.

The problem I see with aftermarket fiberglass duct insulation is that you have to be very meticulous about sealing the vapor barrier, else warm humid air from the crawlspace will get to the surface of the cold duct and you will have condensation. Wet fiberglass insulation no longer works as an insulator, and even worse it provides a warm, wet place for mold and all kinds of other things to grow.

[405programmer]

I also have a crawlspace with old ducts. I would look into not insulating your ducts and just insulating and encapsulating your crawlspace. That will improve your home's efficiency all the time not just when the air is blowing and will drastically improve the air quality in your home as far as mold spores and moisture is concerned. I am currently saving up the money and willpower to DIY this job myself.

If you really want to have insulated ducts the easiest thing would probably be to just cut the old ones off and reinstall flexible ducts with insulation. The downside is that would be more expensive than just insulating the ducts.