You need a 42” hood, with an 10” duct, and 900-1200 CFM fan. You need MUA. It isn’t optional.

Or you need the 30” consumer grade range with the 12,000 max BTU burners.

Thanks - can you give me a little more reasoning behind it. We've talked with sales professionals who have tried to sell pro ranges that have 100k+ btu's to go with a 400 cfm. Clearly they are trying to push the sale rather than what is best for a kitchen.

Those sales people probably don't even cook! They would rather close a deal...make it easy for you to skip MUA, than help you create a healthy environment. You should choose the appropriate hood, and install the required MUA. We did a passive one (not connected to our hvac) and it wasn't too expensive.

First, for scaling hood volumetric flow rate vs. whatever, it may be helpful to read the Greenheck Guide, at least to page 12, available at: https://www.tagengineering.ca/wp-content/uploads/2015/02/KVSApplDesign_catalog.pdf.

Second, my view is that the Greenheck method best represents addressing the actual physical phenomena, because the BTU method only has an indirect relationship with the plume to be captured and contained.

So, with that noted, for capture, your hood should overlap the locus of cooking pan surfaces by enough that at the height of the hood aperture, the plume is mostly captured. Most of the higher velocity portions of the plume are contained within a 10 degree angle from vertical for each point on the pans. A three-inch margin relative to the appliance width is usually sufficient, at least to 36 inches height. A maximum front-to-back distance is recommended, where maximum applies to the sizes of potential candidate hoods available for sale.

For containment, the air velocity into the hood aperture has to be sufficient to ensure that all captured plume components are entrained into the air entering the baffles, and none reflects out of the hood (spillage). This depends on the shape of the hood, baffle area, temperature of the pan, and whether hot gas combustion products are also being collected. Because this is mainly affected by the velocity of the plume, and because one cannot shut closed various "unused" parts of the hood, the maximally hot cooking hood flow rate has to be the same whether only one burner is used or all burners are used. (This may not apply to large reservoir commercial hoods.) Hence, we multiply the required containment velocity by the entry aperture area to find CFM. Viz., 90 ft/min desired velocity x 7 sq. ft. area = 630 CFM. This is the actual required volumetric flow for hot cooking conditions on gas such as wok cooking or searing.

For valid reasons, not actually requiring cynicism, blowers are rated for zero static pressure conditions and have a corresponding 'fan curve' to define performance when there is a pressure drop across the blower circuit. For kitchens, this circuit pressure drop comprises the pressure loss getting the replacement air into the kitchen -- ameliorated by a MUA system, the pressure loss passing the baffles, pressure losses in hood and duct transitions, and in the exit cap. If the blower is built into the exit cap, then that is usually included in the blower data.

When all the parameters of the circuit are not known, it is usually sufficient to acquire a blower with a zero static pressure flow rate of 1.5 times the required flow rate. For the example above, this is approximately 1000 CFM.

With the pressure loss of well filtered passive MUA, one might want to go higher to 1200 CFM. With active pressure balanced MUA, 900 might do. It depends on many factors.

In any case, for blowers rated for over 400 CFM, MUA is required in most municipalities. A passive duct with damper and perhaps a nice pleated furnace filter may be adequate in temperate conditions. For cold environments, a means of heating the MUA in the duct, or in an intermediate room into which it is first introduced, is needed. MUA should not be introduced into the kitchen in a way that causes turbulence between the cooktop and the hood entry aperture.