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Need advice on ductwork in Florida condo: flex or ductboard?

Elizabeth Hilder | Posted in Energy Efficiency and Durability on

I own a condo unit located near Sarasota Florida that was built in 1974. It is currently being remodeled and as part of that process (which involves removing drywall ceilings where the ducts are located) I want to improve on the current HVAC system, including reconfiguring and replacing ductwork.. To my surprise, I have found that the companies down here only offer flex duct (or if I really do not want flex then ductboard), but not sheet metal ducts (what I have in my home in Washington DC). When pressed, they say they do not recommend sheet metal because of the humidity – which makes no sense to me since I live in a place with very hot and humid summers.
My question is: if I am stuck with choosing between flex and ductboard, which is the better choice? What are the pros and cons of each?
Here are further details – It is a 1500+ square foot unit on the third floor of a six story building, with concrete slab floor and ceiling. Existing 10 year old system is 2.5 ton single stage. There is no return duct, just a return register in the air handler that is located in a small utility room with a louvered door. If possible I would like to run a return duct to the 2 bedrooms or else put a return in the hallway outside the the utility room. The current ducts are sheet metal with insulation on the inside – and from what I saw on a recent visit where a wall was removed, the insulation inside the ducts is pretty dirty.
I would be grateful for any advice.

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Replies

  1. Steve Knapp CZ 3A Georgia | | #1

    I imagine most of the contractors don't install metal ducts because flex goes in so much more quickly. Flex duct can be fine if it is properly installed, which it often isn't the case. See this article for some things to consider if you decide to use this material: https://www.greenbuildingadvisor.com/blogs/dept/building-science/how-install-flex-duct-properly

  2. GBA Editor
    Martin Holladay | | #2

    Elizabeth,
    I would accept insulated flex duct if I were you. Specify duct with R-8 insulation, not R-6. Make sure that the duct seams are sealed properly, that the flex duct is properly stretched and supported by hangers, and that there are no unnecessary loops and sags.

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