Putting this under building code questions, but it could be under a lot of categories. I have read “All About Makeup Air” and “Makeup Air For Range Hoods.”  These articles are both old enough that code updates have changed some of the material questions answered, and neither of them really answer my specific question, so posting it here.  We have a project where the only “combustion” appliance in the home is a gas range.  DHW and space heating/cooling are done by heat pumps.  Dryer is standard electric (not heat pump).  Going by the letter of the current (Ohio) code, we would need makeup air for a 600 CFM exhaust hood.  (The unit chosen by the client actually ranges from 250 to 600 cfm.  We have advised them to use a lower setting, but building department is insisting on MUA because the unit is capable of more than 400- because who knows how the next owner will operate the unit; understandable). However, our real argument against having to supply MUA is that there is really no opportunity to create a backdraft situation, which is, I believe, the true intent of what the code section is trying to avoid.  Since the only appliance in the house that uses gas is the range, and the range hood is “venting” that appliance, is it true that MUA is sort of a moot point from a safety concern for this house?  Yes, the house might experience low pressure with respect to outside, but is that really a safety problem here? 

Code section for reference: 1503.6 Makeup Air Required

Where one or more gas, liquid or solid fuel-burning appliance that is neither direct-vent nor uses a mechanical draft venting system is located within a dwelling unit‘s air barrier, each exhaust system capable of exhausting in excess of 400 cubic feet per minute (0.19 m³/s) shall be mechanically or passively provided with makeup air at a rate approximately equal to the exhaust air rate. Such makeup air systems shall be equipped with not fewer than one damper complying with Section 1503.6.2.

Exceptions:

1. If an exhaust hood system’s manufacturer’s instructions and/or specifications differ from this requirement, the system shall be installed per the manufacturer’s instructions and/or specifications.
2. Makeup air is not required for exhaust systems installed for the exclusive purpose of space cooling and intended to be operated only when windows or other air inlets are open.
3.