Rigid duct has less restriction to the airflow. This is particularly true if the flex duct isn't installed properly. Some contractors will run miles of flex. A few feet of it is okay.

 

Depends on the installation: if it is in a crawl often insulated metal will sweat. Metal will last longer but you may want to make sure it is a little oversized because it is definitely noisier than flex. Insulated metal will usually cost more to install these days. It was the standard when I first got into HVAC but now flex is the standard and it is easier to run.

If you are in the country metal would be better because it is less susceptible to rats and mice.

With flex you better hope that proper procedure is followed or your flex will be falling off the boots and collars.

But really, both are viable options. It is the installer that will make the difference.

 

Rigid IMO if you can swing it- however a properly designed installed and commissioned flex job can perform quite well.

 

Thanks... all ducts are within conditioned spaces, and no issue with wildlife! I was worried that long runs of flex would impede airflow?

 

If not sized are run correctly flex will impede airflow but installed correctly it works well. The trunk line (main duct) is going to be metal right with the branches flex?

 

Yep... main trunk is metal with flex for branches. Good to know that this is legit, as I like this contractor and the quote is good.

 

conditioned space? inside the living space?
or in foam sealed semi conditioned attic?

whats your location?

 

Mostly in soffits/chases within the living space. Philadelphia is the location.

 

that is excellent!

I'd use flex, you don't have to worry about critters, like in attic or crawlspace.
fur down will hold duct straight & level the only other thing is to keep it tight.
less cost, faster install, only leaks at either end..so mastic seal.

in older homes it isn't uncommon to see hallways furred down & no
ducts run..hallway ceiling is supply plenum & air exits through holes
with supply grills. hopefully they sealed fur down well!! if they
did, it works very well.

running duct gives you the chance to size the duct for the
room it serves, which is better all the way around.

be nice to see pics...if you'd like to share.

wish I'd have taken pics as we built the furdowns around
the ducts inside my house. I really regret that!

best of luck

 

Metal leaks more than flex if not carefully sealed, but flex is more restrictive if not carefully installed.