Heh! Like toying with hornets' nests do yah?

VaH salesmen have a long history of what I view as disinformation and partial truth telling, so let me provide my opinion of these assertions.

1) The grease laden cooking effluent has a spectrum of particle sizes. Neither the VaH sling system or baffles (which is a centrifugal sling system also in practice) or meshes remove all of this vapor stream. The goal for filtering is to remove particle sizes likely to accumulate on the duct walls and have the remainder expelled to the atmosphere. All effective filtering schemes do this. While spectrum data are not provided by VaH, or for that matter by residential hood manufacturers, some typical performances can sometimes be found for commercial hoods or special filtering schemes designed for special cases.

2) I have no knowledge of warranty claims.

3) Feh! The capture area is what is designed into the hood configuration, and can be large or small for either type of design. Note that the entrance aperture under a baffle system (with the baffles above the entrance) is the capture area. Capture volume also is important. But it is capture and containment that is the goal. VaH may have better capture area than several poser hoods we all have seen with flush baffles or meshes occupying only a portion of the hood base area.

4) Double feh!! One essential requirement for baffles and mesh filters is to be a fire stop. What if a fire damages the VaH motor wiring and the motor stops? The squirrel cage will not be able to break up flame passage as well as baffles or meshes in that case, I suspect. Anyway I see this as another red herring.

5) As documented here in many cases, a roof mounted blower is perceived to be quieter than one next to the cooks ear, and its noise can be significantly suppressed by an in-line silencer, if space allows. A large roof blower will have lower blade tip speed than the VaH blower for the same CFM, and likely lower sound-causing blade-tip turbulence as a result. In the 2009 era, clinresga, who had both types in two houses, demonstrated by comparable measurement reported in this forum that his VaH was noisier. However, VaH may have improved their design by this point in time.

6) Complaints about VaH motor and box cleaning effort have been made by owners on this forum. Most baffle and mesh filters can be cleaned in a dishwasher, although pre-soaking in a sink with Simple Green may help soften older grease residue.

VaH's claim of higher equivalent performance: What I am willing to charitably assume for VaH when claiming their motor has some higher equivalent performance is that their motor would move more air if it weren't in a hood, whereas most blowers are spec'd in free air. While true, one can't know what another blower will do without knowing its fan curve and all of the pressure losses in the system, many of which are applicable to, BUT NOT COUNTED, by VaH claims.

Worse in this regard, their recently published tabular fan curve data shows worse performance with increasing system pressure loss than equivalent flow rate Broan fans that I have looked at. Hence, a VaH hood system with some make-up air pressure loss and duct loss and sheet metal transition loss may move less air per unit time than a remote blower rated at their equivalent flow rate with the same losses, plus baffle loss. This is likely a limitation of squirrel cage fan designs.

I suggest for conventional fan blowers with baffle hoods that the rated (zero static pressure) air flow rate be 135 CFM per square foot of hood capture aperture. This should yield about 90 CFM/sq.ft. actual flow. Other rules of thumb can be applied. This is mine.

The only air that moves out through the hood to the outside is that matched by the same flow rate of incoming external air made up via deliberate MUA paths or by house leakage. If this is a particularly leaky big house, and there are no combustion appliances connected to your kitchen air, then leakage may work. But I wouldn't bet on it. You likely need a dedicated MUA system. Other than having more leakage potential, the size of the house is irrelevant.

This whole subject is complex, but you may learn a lot by searching this forum for various hood, blower, and MUA threads. If you want to be your own HVAC engineer, then some research is necessary. We can address in future messages the hood size, flow rate, and MUA issues.

kas

Thanks for the detailed explanation. I'm leaning towards the Best/Broan 1200 or 1500 external (rooftop) blower configuration. I don't necessarily need the best of the best, so am hoping if I go this route I won't be disappointed. With a 48" range top I was planning for a 52" hood (2" overhang on each side). I'll have to ask my HVAC guy about MAU issues and see what he recommends. If anyone thinks I'd be going seriously wrong with this setup, I'd like to hear it. I'm growing weary of all the research and was hoping to make a decision soon so I can move on to the hundreds of other tough decisions I need to make!

Thanks again!