How To Know if Heating/AC ducts should be replaced?

May 2, 2016 4:43 PM

My place has forced heat. I'm getting quotes to cut in AC. Most reviews I read say the person who quoted the job said they should replace their ducts, and this seems like a typical upsell. Sure enough, at the first quote, the guy suggested replacing my ducts. How do I know if I need to do that or not?

The duct is like a big bag with a plastic shell and insulation wrapped around it. I can see that the insulation around the duct has split, and I'm sure it's not very efficient. I asked if I could just wrap some insulation around it and he said not really because it's just wire and plastic with a little insulation and it's outlived it's usefulness, which sounded a little fishy. For what it's worth, he did say that the size/airflow capacity is good.

I'll be asking the other people who quote too, but I'm guessing I'll be getting the same upsell from all of them, so how can I know if the ducting really needs to be replaced?

posted by willnot to Home & Garden (5 answers total)

Ask them to explain to you WHY. If the ducts are in bad shape, it's cheap enough to replace them, but I'd go with the guy who wants to educate me about it.
posted by Ruthless Bunny at 4:59 PM on May 2, 2016

Insulated flex-duct (the plastic and wire stuff you have) is pretty horrible for airflow - very inefficient. I'd replace it with properly sealed solid metal ducts if you can (sealed with mastic, ideally). If your ducts are running through uninsulated space, you are going to be losing a lot of energy even with that insulation. Better to add thicker insulation to metal duct or to re-route the duct through conditioned space.

If the guy wants to just replace the flex-duct with the same, I'd stay away from him.

The other advantage of solid metal duct is that it lasts for many decades.
posted by ssg at 5:17 PM on May 2, 2016 [1 favorite]

Probably not an up sell. It's really common for air ducts to leak up to 30% of treated air if they aren't in good shape. Buying a new air conditioner without ensuring your ducts are in order is like buying a new set of sprinkler heads without making sure the sprinkler pipes are in good order.
posted by samthemander at 7:50 PM on May 2, 2016

Depending on your location (wink, wink) you may have to pass a leak/pressure test such as California's HERS test. This involves closing off all the vents and seeing if the ductwork is a leaky and/or constricts the air flow enough to keep the furnace / air conditioner from operating at peak efficiency. We have 30-year-old metal ducts, the sales person mentioned that we might need to repair or replace parts, but they ended up just sealing them, so I don't think it's a universal upsell.
posted by wnissen at 8:43 PM on May 2, 2016

If you don't have solid metal ducts, then yes replacing them seems pretty standard.
posted by saradarlin at 2:16 AM on May 4, 2016