Galvanized or Aluminum duct for O.A.K.

[Detector$]

Is there any advantage or disadvantage of Galvanized vs. Aluminum ductwork for an outside air kit? Mine will penetrate the floor in the center of the house and go down into the vented crawlspace. It does get hot and humid in NC in the summer.... I assume you don't have to work about galvanized rusting???

 

[fossil]

Either one's fine, including flexible. Your choice. Rick

 

[Highbeam]

The flexible aluminum "semi-rigid" stuff from HD in 8 foot lengths is what I used. It allowed easy installation and made very tight bends. This stuff won't get hot so it is simply a matter of choosing the easiest one. I would skip the galvanized on the off chance that it may rust some day. Where this pipe runs in your living space it will be cold to the touch since it is passing cold crawlspace/outside air. It might be cold enough to allow for some condensation in the perfect storm so go for aluminum. It is cheap.

 

[fossil]

C'mon, Highbeam, either show him or point him to the pics of your install, including the critter screen...it's pretty dang cool, and might give him some more specific ideas. Rick

 

[LLigetfa]

In the furnace duct business, the rigid guys really poo poo the flex duct kings as a bunch of lazy asses doing a disservice to the industry. They say that air flows much better in rigid.

I say, don't use flex unless you need to.

 

[fossil]

This isn't exactly a finely tuned system here. A ~3" diameter duct to provide air to a woodstove is probably well more than double the required cross-sectional area, and it's a gravity fed system...fairly lazy airflow. The head loss because of the corrugations in flexible ducting aren't even in the equation, in my opinion. I'd say flex is just fine for this application. Rick

 

[Highbeam]

Okay okay, here's my OAK duct photos with the aluminum semi-rigid duct.

https://www.hearth.com/talk/threads/26567/

This ain't a furnace duct and the flex that the HVAC folks are talking about is a weird plastic/fiberglass stuck that does not maintain a constant cross section. The problems it causes are flow restrictions and most importantly joint pull apart since it is easy to sloppily attach it to the registers with loose hose clamps. The standard hangers for HVAC ducts tend to squish the flex and do not support it well enough. I also would prefer rigid for HVAC.

Couldn't have done this without using flex.