Asko range hood duct installation is where a lot of otherwise correctly chosen hoods quietly lose most of their rated performance, since the duct run connecting the hood to the outside is just as much a part of the airflow system as the fan and filter, and a poor duct installation can undercut even a well-sized, well-rated hood significantly.
Rigid versus flexible ducting
Rigid metal ducting offers meaningfully less airflow resistance than flexible ducting of the same nominal diameter, because flexible ducting’s ribbed interior surface creates turbulence that rigid smooth-walled ducting does not. Where the physical space allows it, rigid ducting for as much of the run as possible, reserving flexible sections only for tight transitions where rigid ducting genuinely cannot be routed, produces noticeably better real-world performance than an all-flexible run, even with identical hood and fan specifications.
Keeping the run as short and straight as possible
Every foot of duct length and every bend along the way adds resistance that the fan has to work against, so the shortest, most direct path from the hood to an exterior termination point consistently outperforms a longer, more circuitous route, even one built entirely from rigid ducting. Where bends are unavoidable, gentle sweeping bends move air with less resistance than sharp 90-degree elbows, and minimizing the total number of bends matters more than most installers give it credit for during planning.
Correct duct sizing
Undersized ducting is one of the most common installation mistakes, since a duct that is narrower than what the hood’s rated airflow calls for creates a bottleneck no fan can overcome, regardless of motor strength. Confirming the correct duct diameter for your specific hood model against its installation manual, rather than reusing whatever ducting size happens to already be in the wall from a previous installation, avoids this problem from the start.
The exterior termination point
A duct run needs to terminate through a proper wall cap or roof vent fitted with a functioning backdraft damper, which allows exhaust air out while preventing outside air, insects, or debris from working back into the duct when the hood is off. A damper that sticks partially closed from age or grease buildup restricts airflow in exactly the same way a kinked duct does, so it is worth checking as part of a new installation, not just as a later troubleshooting step.
Sealing the joints
Every joint along the duct run should be properly sealed, using foil tape rather than standard fabric duct tape, which tends to dry out and lose adhesion over years of heat cycling. Unsealed or poorly sealed joints leak air, and on a kitchen exhaust run specifically, that leaked air often carries grease residue that accumulates inside wall or ceiling cavities over time.
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