Duct shape and material

[Arcadis]

Anybody got some experience in duct design for residential HVAC? I'm trying to find an answer whether I should prefer metal pipes (aluminium) or polymer ductboards. Any objections concerning material, optimal fluid dynamics etc.?

Thanx in advance!

 

[Golestan]

Here are my thoughts:

Friction coefficient is lower for round ducts.

Metal round ducts and externally wrapped insulation will be easier to clean for future duct cleaning.

Keep any round flex duct to min. 5-6 ft. long.

For lower pressure drop, use smooth bends and transitions.

For low noise levels keep the fpm low (500-900).

Regards,

 

[VinceNY]

Were is the duct line going, in the attic or in the basement?

I try to use round duct first, then square duct(aka 8x8, 10x10, etc.), and so on with a maximum ratio of 4:1. Use galvinized sheet metal. If it's ran in the attic, wrap the outside rather then linning the inside. The liner tends to come off with age. I'd stay away from ductboard, I wouldn't use it in my house.

If your running down walls with runouts use oval rather than
sqaured.

 

[Arcadis]

Partially it will be placed subsurface, but also in the basement. I 'll have to choose between aluminum pipes externally insulated with rockwool or PIR ductboard two sides coated with aluminium sheet. Both can be installed with smooth bends. Difficult choice...