If the function of the hood were to air out the house, then the number of burners running at once might determine the desired flow rate. But that is not how hoods are intended to be used when cooking. The hood is intended to immediately capture the rising and expanding effluent (from any burners) and then contain the effluent using sufficient air velocity at every point under the baffles to both contain and partially degrease the rising effluent as it winds past the baffles.

To do this the air velocity generated by the hood blower has to be high enough that smoke not "reflect" out of the hood aperture when it reaches it and finds a restriction. Uprising velocity can be 3 ft/s. At the very least the baffle gaps need this flow rate to assure containment.

My rule of thumb is to take the capture aperture area in square feet and multiply by 90 cfm/sq.ft. This will be the desired actual achievable flow rate. No blower system will achieve its rated flow rate in a real environment. Even if we give VAH credit for an actual flow rate of an entire hood and blower assembly (in this case 600 cfm or 1200 cfm), once the ducts and make-up air (MUA) restrictions are included the actual flow rate reduces. And no information has ever crossed my attention horizon that specifies how VAH measure their purported flow rates, so we can't be sure that they are anything other than magic numbers.

If I were to use a VAH in this context, I would buy the 1200 cfm rated unit and hope that I could run it at less than full speed for reduced noise and still achieve capture and containment of hot rising effluent from pans, griddles, or whatever. Boiling eggs will not require this level of flow rate (or any for that matter). But unless the 48-inch range is purely a poser installation, at some point you will use it to cook something that generates grease and smoke. Even capturing much of the oven output when it is opened will require a decent flow rate.

Don't forget that for either blower there has to be a source of MUA. The actual flow rate out of the hood is always matched by the flow rate into the house, and if the latter is small, then so will the former. But worse, while that is happening the house pressure falls, and combustion appliances can back-draft, potentially inducing CO into the house. This is hazardous. So plan ahead how you intend to provide low pressure drop MUA.

kas

Thanks for great information! Can you clear up what kind of system I need for proper MUA. Is this something that sits in the blower or the liner. Or is it vented separate...? What kind of MUA system is best for my size vent/range.
the MUSIC is something new to me, want to make sure Im venting correctly. Thx

Not music....mua

Open windows are MUA sources, but ideally a ducted path to a ceiling or floor diffuser with a damper that opens when the pressure is low, or when the blower is on, is desirable. If the path is to be filtered, then there will be some pressure drop in the house and any combustion appliances need their own (unfiltered) MUA. In some climates the path has to be heated also. Complexity soars. I suggest reading the many messages here on the topic. Also, for background, the references noted in My Clippings will be useful.

When one embraces the pro kitchen look, including a large stove requiring an even larger hood, other aspects of commercial kitchen operation start to intrude. The most complex and most expensive to run system for a commercial kitchen or restaurant is the ventilation system. Hence, in a kitchen reno the costs don't stop at the visible appliances; the relatively hidden ventilation-out and ventilation-in components have to be planned, integrated, and paid for.

Long ago, big wood powered cast iron stoves, often much larger than 48 inches, graced farm kitchens. The grease went wherever it wanted, and MUA for the fire leaked through the walls. Often these kitchens were closed off from the living quarters, or in quasi separate rooms. With modern open living spaces, deliberate ventilation of grease, smoke, water vapor, and odor is much more critical.

kas