I am reading these posts with great interest as we moved into a house in September that has an island with Jenn-Air 4 burner gas cooktop and downdraft vent. We've always had electric but wanted gas in an island with an open floor plan so I could interact with our guests while cooking. The Jenn-Air system has many drawbacks. 1. I want/need 6 burners 2. Only one larger burner, two medium and one tiny. 3. Fan is LOUD on high and ineffective, even on high. 4. Fan IS EFFECTIVE at drawing the gas flame away from the pots/pans, thus greatly increasing cooking time. I want to replace this with a 6 burner gas cooktop that has enough space between the burners to use a couple of 12" saute pans plus a couple of 6-16qt pots and a couple of smaller pots. Based on the discussion above and the fact that I installed an 800CFM Broan under cabinet hood that barely kept up with the fumes in the old house, I think I'll want a 1200 or 1600 CFM blower (mounted in the attic to reduce noise in the kitchen). Problem is the master bath and walk-in closet is above the kitchen so I will have to shoehorn the ducting in the walk-in closet. I assume the extra run will eat some of the CFM. Does anyone have recommendations for a cooktop and vent/blower for this application, or links to sites with good product selection and design planning info? What about so-called "stacked" burners that are supposed to allow low simmering without compromising high output? If this post belongs in another category please let me know. I did a search but this seemed to be the discussion that most accurately covers my concerns. Thanks, Don

First, a warning -- I have never lived in a house that needed make-up air. Not even close. Double-pane glass makes little sense for us since all the heat goes around the sashes in our Victorian. My experience with MUA is related to commercial systems. What follows is an opinion about the kinds of things that would make me consider MUA. Unless you have a Code requirement for make-up air, you have a fireplace you use when cooking (I seem to remember that you are South Bay?), have a "naturally" vented gas appliance in "connected space" (no always-closed doors between the hood and the appliance), or have a "tight" house (recent, energy-efficient construction, most likely), I would skip MUA. Even if you do need MUA, the difference in the maximum hood flow probably wouldn't significantly influence the the cost of the MUA system, which I would think was primarily labor driven. If not significantly more expensive, and you can run at least an 8" duct (preferably a 10"), I'd go with 900 CFM for two reasons: * You have it when you need it -- guests over, and the kitchen fills with smoke... * A 900 CFM blower at 600 CFM may be noticeably quieter than a 600 CFM blower at 600 CFM The 24" will serve you well. Enjoy your new range!

Pro cooking requires pro ventilation. Please review the many hood topics in this forum for an idea of the requirements that apply to hoods. If your purpose in buying a "Pro" cooktop is "Pro" cooking, or for that matter any cooking that yields hot oil or grease vapor, or excess moisture with or without entrained odors, your hood has to capture and contain the cooking plumes from the cooktop pans as well as the burner combustion products that pass around them. This requires a hood that extends beyond the cooktop in width, and beyond it in front-to-back depth. One would need a rather high (and loud) airflow rate to achieve even mediocre capture with a 15-inch depth hood because the hood flow would have to bend the rising (meter per second) and expanding front-burner cooking plumes toward the narrow hood aperture. Hood flow is very ineffective at changing air direction well away from the hood; rather a hood functions by keeping plumes that make it to its aperture from escaping into the kitchen. Wolf should be embarrassed by their poser kitchen imagery on the linked page. A 15-inch depth hood will limit you to heavy cooking on the rear burners (assuming a wall mount), and even then the hood has to be wide enough. If the hood metallic structure is to be hidden, then hood inserts are used in bump-out cabinetry in order to achieve a 24-plus-inch depth (as determined by cooktop size and placement), and in this case a desirable 42-inch width to overlap a 36-inch cooktop. For a powerful cooktop in action, baffle filters are more suitable than mesh filters as shown in the Broan link. Mesh filters will loose effectiveness unless rigorously kept clean. They also have higher pressure loss if effective, and thus reduced flow rate for a given blower. No air flows through the hood to the outside that hasn't been allowed into the house, and this inflowing air is called make-up air. Supplying it at low pressure loss, and conditioned where necessary, is an integral part of hood selection and integration into the kitchen when capture and containment require significant air flow. Once the scope of the kitchen ventilation task is understood, we can support determination of the details. kas

It is worth pointing out, I think, that the pressure differential across the blower, called pressure loss, is essentially the same whether the blower is in the hood, at the end of the duct outside, or in a door blowing into an otherwise sealed house. The pressure loss is the sum of all the losses due to friction and turbulence in the duct, duct cap where present, hood transitions, baffles, make-up air system restrictions, etc. Any slight differences in pressure loss with blower position will be due to local transitions where the blower is mounted versus the blower's air flow uniformity at the blower exit. The resulting flow rate will be that which applies to that pressure loss on the fan curve plot. Front of hood deposited grease is due to insufficient overlap and/or insufficient air velocity at the hood aperture. Hoods are generally poor at drawing air from the vicinity of the burners. Most plume capture depends on the plume's upward velocity, mainly driven by the buoyancy of hot grease and water vapor and air. The plume naturally expands as it rises, hence hood aperture overlap is desirable.