Your city may have CFM regulations, please check this in this link: Municode Codification
Title BUILDINGS AND CONSTRUCTION - HOUSING CODE

To fit 30"

Compatible with all machines for an opening of 26.75W x 10.75D - IKTCH IKB01-30-A (Recommended Home depot) -HERMITLUX 30 TB1370G-AC-11 -COSMOS COS30IRHP -HOME BEYOND H70-27 -FIREGAS FGS-USB21G70AC -EALLMALL EL11-30 -STREAMLINE T-4015-1-DL -VEVOR E70-27

To fit 36"

If your cabinet space is 36", your total width would be 35.75" and your range hood machine could be 34" wide.
The standard overall depth of our hoods is 19". We can make them larger, please remember that it will cost an additional $80.
We can also make it 36" or 35-15/16"

If you purchased your machine and it's too large, don't worry. We have a special model to fit your machine. The Wider model is only for carpenters. It's difficult to assemble. You can see the difference between a standard model and the Wider model at this Link.

We recommend these models: