I have heard that some people are cutting corrugated boxes the size of the hood area with a cutout for the flow box to make an adapter. When taped in place, the flow can be measured at the cutout. You want to make sure the there is no other leakage within the hood and the adapter is taped all the way around so all of the air flow is through the cutout. The adapter can be reused and you may find that a few of them will work for a majority of range hoods.

There are methods for calculating the needed ventilation that takes into account the existing fans and building tightness. I suggest you look for an upcoming training, there are many available, to learn the best approach to determine the need to add additional ventilation. I think the better your understanding, the easier it will be to implement. The Standard is here to stay. I'm not a fan of continuous ventilation, but 20 cfm to 40 cfm is not much air movement and would take over a week to exchange the air in a small house. The challenge seems to be how to get 20 cfm for less than $600.

PS I also tried to find an online resource, but ACI now charges for access to presentations and everyone else seems to be holding back on the information.

ASHRAE 62.2 Resource

There is an online resource to help with 62.2 and other building analysis questions. http://www.residentialenergydynamics.com/ . I found it easy to use.

Tim