Moving air through a pipe doesn't really car if if it (the Pipe) is going up, down or sideways. Sure up is always better because you gain the natural rising of heated air, but plenty of setups flow down. Where do you think the air in ALL downdraft hoods and JennAir's flows??? Re: remote vs. internal- either type will work AS LONG AS the selected unit pushes/pulls enough air (cfm's) to overcome the static pressure of your pipe and all the bends. Remote or inline ones are generally quieter than hood mounted ones.

We recently bought a house with an ADU and are getting ready to rent it. The range hood in the kitchen is both ducted and ductless. For some reason, the installer (or previous owner/tenant?) installed the range hood so that it both ducts to the outdoors as well as back into the unit. Trying to understand how to convert this to the ducted-only configuration. Can I just block the holes to the ductless part? Is it more complicated than that? Looked at the manual quickly and didn't seen an obvious fix (or set-up to reverse). Any thoughts appreciated. Thanks.

Sorry if I was unclear, but the silencer removes noise that is beyond the silencer relative to the listener. So, not that it would matter, but hood baffle noise would be partially silenced when listening on the roof. Relative to the cook in the kitchen, the silencer removes noise beyond it. So, hood baffle noise and local duct noise and local hood interior transition noise won't be affected by the silencer when listening at the cooktop, but duct noise on the roof side of the silencer and most importantly blade tip turbulence noise from the roof blower or the in-line blower that is past the silencer (relative to the hood) will be attenuated when listening at the cooktop. The blower noise is typically the loudest, so the silencer is important to minimizing noise. (It is worth pointing out as I think I did sometime in the past that blade tip turbulence noise dominates baffle noise given well designed baffles. I only have personal experience with my Wolf/Independent hood, so it is possible that a particular baffle design could be noisier than a particular blower design.) So the silencer should be as near as feasible to the hood (past any dampers), and the motor closer to the roof or on the roof. A duct that passes heated rooms should be insulated from the rooms passed, and possibly partially coated with damping material (I use automotive sheet metal dampener sheets). A damper is needed at the hood (probably part of the hood) and another should be at the roof. The Wolf/Broan low profile blower I have has its own damper which opens upon flow. Abbaka and Broan blowers look similar and appear to use the same approach. An upblast or downblast quasi-commercial blower and housing design may need a conventional damper just below it. Dampers should be checked for function without hanging up on errant screws before workmen can escape the project. A straight run will have minimal duct bend turbulence noise (caused by flow separation, perhaps). It may or may not make adding a silencer inconvenient, architecturally. kas

^^^^ that! Ductless range hoods are usually installed where there is NO WAY to put in real ducted hood. They are definitely inferior for removing the heat, humidity and odors from a kitchen.