OK, let me make an observation; if one had a displacement blower (like the Rootes blower on an unlimited dragster) one might be able to pull 1200 CFM against a significant back pressure, or even possibly lower house internal pressure to the point that a window would break. For normal kitchen hood blowers, however, slight pressure differences across the blower cause a reduction in flow rate. At some point modest back pressure will kill all flow and the window is out of danger. How modest is modest? For example, in the case of a Broan-NuTone 801642, (used by Wolf), its rated 1200 CFM at zero static pressure air flow rate drops to 700 CFM at 1 inch of water column differential pressure. (Approximately 407 inches of water column equal one atmosphere, so one inch is 0.0025 atmospheres.) The blower flow rate approaches zero CFM when the pressure difference is 2 inches, w.c. As noted above, one important purpose of MUA is to avoid back-drafting of combustion appliances, which for some appliances occurs above 0.03 inches, w.c. A second purpose of MUA is to allow the blower to move a good fraction of its rated flow rate. Even with windows wide open and no screens, the pressure difference across the blower will be significant due to: pressure loss across the baffles, pressure loss passing hood transitions, duct turbulence, and exterior cap pressure loss. With MUA supplied by other means than screenless windows, there will be some further pressure loss moving air through the MUA ducting, possible screening, and in colder climes, past the heat exchanger or heater. To look at it another way, when the blower is running the pressure loss will be just that which limits the flow rate to that which the blower's fan curve shows matches the pressure loss. There is always MUA, and it always equals the flow rate that the hood can expel air at to the outside. If this is inadequate for containment of captured effluent by the hood, then the MUA has to be improved to allow more flow. The VaH blower fan curves, data from which has been seen on VaH's web site in the past, shows an even more steep decline in performance with pressure loss than comparable Broan blowers. However, VaH's scheme of using a squirrel cage fan as both a blower and a grease vapor expeller eliminates the bafflepressure loss, so VaH can compete so long as the ducting is short and the MUA is adequate. kas

kaseki I know SZ answers their phones and normally their customer service is beyond reproach. this time I was underwhelmed by the response. It's not as if I've had this ventilations system for years. I said the spring is broken, can you please send me a new spring.. She said "send me a picture" then told me it's not broken just bent. The baffles she told me are very easy to take out. I had a couple of men friends help me as I figured I must be missing something. They did not have to stand on the ladder but ultimately had just as difficult a time to get them out and in. So it's not a "girl" thing :)) Normally they want you to fill out a survey on how they did. She did not, as most likely she realized her service was not that great. Maybe she was having a bad day. Happens! Drilling holes is doable. I have all of the equipment and a myriad of drill bits but have not had much training in the way of drilling into stainless steel. Do you drill a pilot hole? If I go to the "leaf Spring" store and buy a few, I could practice drilling holes before tackling stainless. :)) For now I guess I'll live with it. So many other things that are more urgent. This only becomes an issue every few months. Ingeborg

@TxMomma really appreciate the insight. I will have a 36” wide Wolf range, so I need the 42” wide vent insert and that one has the 1200 CFM capability. But I doubt I’ll ever need to use it on that setting and my contractor assured me that my space is large enough with sufficient ventilation so that makeup air wouldn’t be an issue for me. I also found vent-a-hood much more expensive and my appliance person highly recommended the Zephyr brand and the Monsoon II in particular because of its depth and also the LED lighting in the front and back of the insert. Sounds like such a nice practical feature. Would love to hear how it sounds/works once you have the chance to test it out. Thanks

@kaseki I try to research everything before I post a question. Actually spend a day or two trying to research things when I have free time to get my answers. However the comparison of these two brands I only found one post, and most things are old and outdated. Newer features come out every couple years so I think it’s good to refresh the question. Also, unless you have time to read everybody’s responses in between the lines sometimes it’s hard to get a straightforward answer. Some of the stuff is confusing to me Your answer right there just probably saved me another three hours of reading posts so I appreciate it very much! Honestly, though this may sound like a dumb question, I thought the hood is wider for aesthetics and the liner could be the size of the cooktop. However, it sounds like you want the liner and the insert to be wider than the cooktop. I also cook a lot and Want to be covered for a lot of smoke. I am also surprised that both of these brands don’t seem to come deeper than 12 inches. Wolf only comes on 30” also. I wonder why they would even suggest a 30 inch when I have a 36 inch cooktop! Can you suggest another brand?