Recirculating can be a better-than-nothing option where there is no possibility of exhausting outside. In this forum, the only recirculating hood that has been well described is the Vent-a-Hood ARS. Others may well be suitable, but to answer the question: The chimney is likely the only place where the series of filters can be placed to remove the smoke, grease, and odor. The baffles or mesh at the entry to the hood only removes grease particles on the large end of the spectrum; the rest are usually exhausted outdoors, and this component, along with odor needs to be further filtered with auxiliary means. Further, the filters need to last for a while for the system to be practical, so their volume should be expected to be significant.

https://www.houzz.com/discussions/2347276/vent-a-hood-ductless-ars-range-hood-update#n=65

kaseki--

I was hoping you'd comment here. Thanks. Also thanks for explaining the difference between size of grease particle closer to the range and higher up.

I read all about the Ventahood, and it's too pricey for my particular remodel.

I'll keep on looking at chimney models and also try to learn re from Faber what it means when it says the hood I am contemplating, "includes charcoal filters and a diverter to send the air thru the side grates on the upper chimney."

One more quick question regarding recirculating: I believe I read that baffles are preferable to mesh for most hoods. Is this also the case for ductless, or doesn't it make a difference?

Baffles have the advantage for standard residential and commercial hoods of having the same pressure loss whether clean or oily. If the air flow is high enough through the ductless (the velocity at the baffles is high enough) then baffles will work. Under-powered hoods with low air flow may be better served by mesh filters so long as they are kept clean. If the hood has a stack of charcoal filters and whatever else is deemed appropriate, either the flow will be low or a higher pressure blower with an appropriate fan curve will have to be used. I don't have a recirculating hood, so I can't be specific.

Broan and Wolf may sell recirculating hoods. Broan reportedly answers the phone so you can ask. Wolf also answer their phone.

In the extreme of low budget, the most that can be said is that pushing the effluent through a mediocre charcoal filter will still be better than through no filter. In that case, however, comments in various threads here by @opaone on air quality should be noted and one might consider cost of adequate filtering vs. cost of health hazards from poor filtering.

Kaseki--Thanks again.

I know this is pretty much theoretical, but I am trying to get a general feel for what is considered sufficient and insufficient flow through a charcoal filter. The Faber I am considering has baffles (or they can be replaced with mesh) and four CFM levels depending on which button is pushed--150, 295, 395 & 560. With CFMs like this should there be mesh rather than baffles? In my greatly underinformed knowledge, my guess would be that the 150 and 295 levels would be considered insufficient airflow while the 395 and 560 might be considered sufficient. Should I be looking for a chimney hood with higher CFMs, or would something like this be adequate in my situation?

It isn't the CFM at the baffles, as this varies with the baffle area for a given blower. It is the velocity at the hood aperture that becomes a higher velocity at the baffles (inversely proportional to their gap area) that determines entrainment. And your CFM values are blower ratings, not actual flow rates. While baffles perform centrifugal extraction, for which higher velocities are more extractive, a given baffle design will likely have a lower velocity limit for adequate performance.

Charcoal filters, on the other hand, might perform best if the flow rate were low per unit area. Charcoal works by adsorption, and I expect gentle contact to be the most effective, but I have never read anything related to that issue.

In any case, as I'm sure you would have noticed reading enough hood threads here, for hot oil cooking a hood entry velocity of 90 ft/min is deemed (by me) to be adequate for residential hoods with low reservoir volumes. It may be understood that lesser cooking conditions can be addressed by lower velocities, and boiling eggs by the hood being off.

Adequacy really depends on hood reservoir volume, and percentage of the hood entry aperture that the baffle gaps equal. Without computational fluid dynamics analysis of the entire configuration, starting at the pan, or use of a test kitchen, it is difficult to make unqualified pronouncements.

Look for a hood that can do 90 CFM per square foot of entry aperture when at full power accounting for the pressure losses vs. the hood blower's fan curve. You probably won't find a recirculating one, or won't find the data. Residential hood manufacturers do not in general (some exceptions such as Wolf) provide blower fan curves, and I do not believe that the ARS even meets the worst case plume velocity suggested actual flow rate. You are in compromise heaven with the most expensive solution, and more affordable units will be even more compromised. Accept your fate, or move. [humor attempt]