If you block old floor registers, you will be heating/cooling your crawl space. The conditioned air would flow out the .large holes.

I must not have been clear. Complete new systems with R-6 flex ducting in the attic. Old ducting fed into crawl space from package unit outside. Crawl space ducting will be abandoned.

Well patching them with flooring which gets expensive fast. There are no easy solutions that look intentional. Hopefully r8 ducting not r6. Is your attic insulated?

I like the ceiling registers, but, I would never want my units in my attic. It took many years for the old ducting to rust, and be unusable, I would replace it, and keep the registers that you have. Makes no sense to have patches all over your floors.

If the clearance in the crawl space limits access for removing and replacing the existing duct work, then installing new duct work there is likely to be problematic, too. You'll likely end up with poorly sealed, poorly insulated duct work due to the poor access. There's no reason ductwork can't be installed in an attic, and properly sealed and insulated. The old duct work can be abandoned in place. If you don't want to include the cost to patch, refinish or replace existing floor finishes, you can afix some insulation to the underside of the floor registers to air seal them and reinstall them.

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The crawl space has very limited clearance of 18-24 inches. It is an "army crawl". The H&A company gave an estimate of $18K to remove and replace the ducting. It was only an estimate. The job would be time and materials, so it could go higher.

The real "rub" with the new attic units is that I will have 2 year old and 5 year old, 3-ton package units that will be abandoned.

When we purchased the house 2 1/2 years ago, the inspector (aka dufus) missed the ducting issue and another major electrical panel issue. Arrrggghhh!!!!

Find a new company. $18k to replace ductwork, even in a challenging location, suggests they don't do this regularly and don't really know what they are getting into.

I agree, check with other heating companies and make sure you get reputable ones. A friend, just had all hers replaced (2000 sq ft house), and cost was 4000.00

Live in a small town, population 5,000 (65 miles from larger city). Only other H&A company that would respond said they would not even consider replacing ducting. They bid $41K for two units in the attic. The other company (The only one that got 4 star reviews. All others got 2.5 stars or less.) bid $23K for two units in attic.

Current trunks are formed metal and ducts are fiberglass wrapped metal. Both main trunks also have to be replaced/rebuilt. That will require a good sheet metal man. I think that rises above the skill of a handyman. The humidity has been running in the 92-95%. I have been told flex ducts may not be suitable for that environment.

Have you had an estimate about leaving your two units on the ground, and running the lines up and through a closet or two to get to the attic, and then the lines run through the attic, but, leaving those heavy units down on the ground where they belong. My last house, had the ducting ran under the house just about 4 feet to a linen closet, where they then went up inside the linen closet to the attic, and then to to the new round heat vents in the ceilings. It was all done by a heat and AC man. Small town here too. Actually smaller than your town. It would still mean you had vents to cover up, but, at least, wouldnt need to replace your units, which, are fairly new

We have been dealing/investigating/talking about this issue since Nov. 2022. Recently spent over an hour with the H&A's install manager trying to find a way to get the output and return trunks into the attic. Simply is not possible due to where the units are located.