Hello all: I have done my best to weed through the complex vent hood/make up air threads, and while I know codes vary by many factors, not the least of which is location, I am hoping for some general guidance here. My advanced apologies if this has been answered in previous threads; if so, I cannot find them or make sense of them :(

I have what I consider to be a relatively simple situation: small kitchen, budget DIY refresh with removal of useless OTR microwave that we want to replace with a vent hood. We have existing 7" venting that routes horizontally approximately 2 feet through the dreaded soffits and then up through the roof on our one story home. All we want to do is put in a vent hood we purchased, rated at 670 cfm's, or at this point, ANY vent hood to meet our meager needs. No wok frying, totally average (47k btu) Bosch gas cooktop with electric oven. One gas fireplace within the "open concept" kitchen/nook/family room combo; gas water heater in garage with simple venting (e.g. opening in garage walls with vents to the outside), furnace in attic, two underpowered bathroom fans. 2300 sq ft home in Northern California built in 1999.

I purchased a chimney style vent hood rated at (670 cfm) via amazon a while back, and did not realize that I could be wading into the mua world. I seriously doubt this hood really moves 670 cfm's, but still want to ensure that it meets code and does not pull co2 into our home. Not willing to get into mua solutions, both from a cost and over-improving standpoint.

I cannot find a single reference to what floor/lowest level cfm fan rating that we would need to avoid mua requirements. As far as i can tell, codes do not list this explicitly, nor was a call to our title 24 energy commission helpful. Apparently, there is some ASHRE calculation one must do for the whole house, but the information is not free and I was advised to consult an HVAC pro.

Willing to consult an HVAC pro, if that is the recommendation here. Or, if any of you GW experts have general guidelines on what the highest CFM rating for a vent hood is in my area, whom to contact, etc, it would be much appreciated. Thanks!