Ventahood can do Magic hence the Magic lung

is there a principle of law "thou shalt not ly" and if so how does one enforce it?

i think the bigger principle is caveat emptor, be careful when "emptying your purse" / disbursing / purchasing. So they can say what they want for ever and ever.

CFMs are CFMs Either the hood moves the air it says it does or it does not. A 600 cfm Ventahood is the same as 600 cfm of most reputable ventilation companies. The general rule of thumb for cfm requirements of a cooktop are: 1 cfm for every 100 btu's of cooktop power. If your cooktop is able to put out 60k of btu's then you would look for a 600cfm capable hood. When you have a griddle or grill in the mix, you would have to bump that requirement up, particularly for a grill.

djh64 - It sounds like you don't understand the basis for Ventahood's claim, and that is that other companies rate their hoods wide open, as in with no baffles or filters in place, whereas on a Ventahood you never end up adding baffles of filters which reduce airflow.

On the surface it sounds plausible; whether it's really a 50% difference I have no idea. My conclusion would be that if you need 900 CFMs then get a 900 CFM hood. If there's any truth to the advertising then you might get better perfomance than with another hood. But don't get a 600 and think it'll perform like a 900, because in my experience Ventahood themselves won't even stand behind that.

This may all change one day, when tougher real life tests get performed on vent fans in standard conditions e.g. X feet of duct with elbows and a backdraft stopper in the duct too. And with the filter if it is designed to have a filter. In one case with unlimited MUA and another with a resistance to MUA, thus a quantity of MUA limited by the fan's very own torque. Then we'll know, more scientifically, whether one setup can pull as much air as another. Today, it's all self-published CFM ratings, thus inaccurate in real world conditions.

Some companies are better than others at backing up their performance claims. For example, Fantech publishes detailed Air Performance Graphs showing the relationship between cfm and static pressure. Without that information, raw cfm claims are meaningless. For example, see page two of this brochure for performance measures of Fantech's FKD line:

FKD product guide

Yes, this is self-published, but I suspect a company willing to put it in black and white is much more likely to stand up to scrutiny than a company that relies exclusively on pronouncements by their marketing firm regarding enhanced performance.

You will not find anywhere (that I've been able to find) comparable specs that back up the mysterious VAH claim of "50% better performance." I agree that the best explanation I've been able to find is lupe's "It's Magic." If you believe that, then go for it.

If we give VAH the benefit of the doubt (and I write from the point of view that any manufacturer who uses the adjective 'magic' is suspect), then we might assume that VAH has put in a blower that moves the specified cubic feet per minute installed in the hood (but without any other restrictions, such as duct length, bends, or transitions to the outside.

If one calls Wolf and digs deep enough into their tech support, one can obtain (Broan) blower data that shows the blower static pressure curves of several blowers (cfm vs. static pressure) with duct length curves imposed. Internal blower flow rates are presented with the (unspecified) hood included, so there is no flow rate loss at zero duct length. External blowers are specified with the zero feet of duct line crossing somewhere up the static pressure curve, which suggests that some (unspecified) hood's pressure loss is being included in the underlying calculation.

Generally, for external blowers, the drop in flow rate due to a hood being attached is less than the ratio of 900 to 600 cfm. However, there may be manufacturers that VAH has in mind who obtain that ratio, and hence VAH can claim that their product is equal to a 900 cfm blower.

I personally think this is a specious way to provide data, but without proper static pressure curves for all hood contenders that one might consider, one is left with guessing.

In any case, unless the hood is large enough in the horizontal plane, and deep enough in the vertical plane, capture and containment may be less than desired, whether on the high or low end of the practical flow rate options.

Another trade in comparing hoods is the ease of cleaning. This is a contentious issue for some, particularly when considering VAH.

kas

PS clinresga: I have my Wolf island hood, Fantech damper, ducting, Fantech muffler, and Wolf (Broan) roof blower hooked up, and will provide some comments when I can.

kas: dying to hear the results. As you know I agonized over the inline Fantech vs roof mounted blower (an Abbaka). It was decided for me when contractor refused to go onto roof to do install. Jeff at Modern Aire has always said that roof mounts are the quietest option of all, though with the silencer, the Fantech is incredibly quiet. I think I recall your Broan is a higher cfm rated unit than the Fantech, which I suspect will outweigh any performance disadvantages of roof vs inline mount. Your setup is pretty much the summit, from what I know.

Ventahoods are the ugliest things out there with what appears to be a similar lack of quality in the fit, finish, and controls. I would never buy one.