Once you decide on a cfm requirement (I won't address that in this message), you need to determine the pressure losses from the hood transitions in and out, its baffles, the ducting AND the residual negative pressure that you will have in the house with the intended MUA. These pressure losses are then used to look up on the fan curve the actual cfm. For this you need to choose candidate fans and get their fan curves (from Broan's website, Wolf's customer service, Fantech's web site, etc.). Hood and baffles may be worth a tenth of an inch of water by itself. The house may be a half a tenth negative. The duct losses will vary with length and bends. For example, achieving 1260 cfm will likely require a fan that, at zero static pressure, is rated somewhere between 1500 and 2000 cfm. As you add MUA (accounting for house leakage when there is residual negative pressure), the pressure loss in the ventilation fan decreases raising the cfm exhausted. This is clearly a recursive analysis unless you separate the functions by establishing a specific household pressure you are aiming for. At a specific pressure and outward flow rate, and given an estimate or measurement of the house leakage at that pressure, the MUA can be separately engineered. Don't forget the effects of any other household exhaust fans, dryers, furnaces, etc. As I recall noting before, household MUA is more difficult to engineer than restaurant MUA, and is more like large building MUA where the inlet and outlet flow rates, and even wind flow pressure effects, are always changing. Likely points of control are the MUA motor or a bypass flow path motorized damper. If the furnace has a separate (passive) MUA and is installed in a sealed room, then a passive MUA system for the rest of the house may be acceptable. Unlike a building, you probably won't have a problem opening a large exterior door against a negative pressure. kas

In San Jose, the link below applies. See C.1. Edit: Also, this link http://resaveguide.lbl.gov/step-1-assess-the-home Here is a link that might be useful: SJ ventilation requirements This post was edited by attofarad on Mon, Apr 22, 13 at 18:30

The downdraft blower is integral to a Jennair range, not a separate piece. You will need an overhead vent hood. There is no physical place for any separate downdraft with a range. Plus, why would you want to go with something that works so poorly?

No. Downdrafts vent behind the range. For an overhead hood, you will need a new vent penetration through the wall behind the hood. Look at the installation instructions for some hoods that you're considering to get an idea of where the vent duct work needs to be.