What Duct Size Does the AlorAir Sentinel HD55 Use?
The AlorAir Sentinel HD55 manual specifies 6-inch flex ducting on the supply/outlet side. The part that needs more care is duct length: the manual says a maximum of 6 feet, while AlorAir currently sells an 11.5-foot 6-inch outlet duct and lists the HD55 as compatible.
Because those two current manufacturer-controlled sources do not line up neatly, we would not silently choose one and pretend the discrepancy does not exist.
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Quick Answer
- Supply/outlet duct diameter: 6 inches
- Manual’s stated maximum duct length: 6 feet
- Current AlorAir accessory: 6-inch diameter, 11.5 feet long, listed as compatible with HD55/HD90/HDi90
What the HD55 Manual Says
The Sentinel HD55 user manual says the supply grille is designed for 6-inch flex ducting. It also says the supply duct adapter is standard on the unit and gives a maximum ducting length of 6 feet.
So the clearest documented answer to “what diameter duct does the HD55 use?” is 6 inches.
Why the Length Is Less Clear
AlorAir’s current accessory catalog sells a 6-inch aluminum-foil outlet duct that is 11.5 feet long and specifically names the Sentinel HD55 as compatible.
That creates a real documentation mismatch. The older HD55 manual says 6 feet maximum, while the current accessory is nearly twice that length.
We do not think the safe interpretation is “therefore 11.5 feet is definitely an approved maximum run.” A compatible accessory can be sold in a length that users trim, and the manual may also predate the current accessory. Without a current HD55 instruction explicitly changing the maximum, the discrepancy should remain visible.
What About the Intake Side?
The user manual section is specifically written around the supply duct adapter. Older AlorAir installation material also illustrates supply-and-return configurations, but the current HD55 manual excerpt does not provide a simple second round-duct dimension for the intake side in the same way it does for the 6-inch supply connection.
If your plan requires a fully ducted return as well as a supply run, verify the current return-kit configuration for your exact HD55 version rather than assuming both sides use the same collar.
Bottom Line
The Sentinel HD55 uses a 6-inch supply/outlet duct. For duct length, the manual’s 6-foot maximum conflicts with AlorAir’s current 11.5-foot compatible outlet accessory, so a run longer than 6 feet is something to verify rather than infer.
Check current Sentinel HD55 availability
See the current HD55-compatible 6-inch outlet duct
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