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tulanch · Mar 16, 2006, 11:21 AM

I am adding an addition onto my house. The local building inspector has already told me my HVAC unit is more than adequate in size to support the addition. The old duct vents are aluminum. Can or should I use flexi venting in the new part? What are the pros and cons of these two types of vent ducts? And can one vacuum-clean flexi vent ducts?

Thanks for the info

-Terry

labman · Mar 16, 2006, 12:00 PM

The Flexi-Duct should be cheaper and easier to work with. When I installed a new furnace in a new location, I used a length of it for a couple of returns. It went in a tight area needing a few bends. Metal would have been a pain to instal. It is working fine. You may want to go with the metal in any accessible areas where the flimsy plastic might be damaged. Not concerned about that down in my crawl space between a metal duct and a block wall. Should be quieter too.

tulanch · Mar 16, 2006, 12:12 PM

Thanks for the reply! Yep and Yep – it looks a lot easier to work with and it is about 1/3 less expensive...

I wonder if longer runs loose air volume due to the ridges inside the flexi duct when compared to a smooth metal run... maybe I'm thinking too technical... but I have 2 new runs could approach 30ft.

As for cleaning (without ripping the flexi pipe), I would think it can be done because dryer vents get cleaned... I live in Utah and things get very dusty so cleaning the ducts is done frequently.

-T

labman · Mar 16, 2006, 12:58 PM

I have never had my ducts cleaned, so can't say. Likely the most reliable answer would come from whoever you have been having clean your ducts. If they say no problem, no problem.

The air volume is a good question. What you lose from the surface, you may gain from larger radius bends.

ridgid002 · Mar 19, 2006, 12:21 PM

Aside from the obvious differsnces in strength between the two flex duct is certainly much easier to work with and is also insulated which lowers your heat loss somewhat of a downside is that it is not recommended that u have runs of more than 25 feet because it is plastic u do loose cfms on longer runs of flex... also be sure that when u are installing flex duct that u have nice tight runs u do not want the pipe to sag acting as a place for moisture to collect,also make sure that when u install it u zip tie both the inner plastic lining as well as the outer insulation on both ends of the run individually and as far as cleaning goes when u do it just cut the ties drop the flex down and carefully run your vacum through it be sure to have some more titons around to put it back up... lol hope this was helpful