This is an instance that you get what you pay for. The higher cost make up air system will be automated to engage WHEN your hood is running and not when not and will balance the air flow. It will also be designed to bring the make up air close to the exhaust so that as you suck out your heated or cooled home air you are bypassing most of THAT air and getting new air direct from outside sucked near your appliance so as your appliance sucks out air, it is getting make up air from very close by and is NOT sucking out conditioned home air for the most part. So there is dual ducting system to the appliance, one in, one out. (Note: for the purposes of this discussion "appliance" means the UNIT of range/cooktop AND its accompanying vent hood.) Often the in air is brought up under the appliance and vented from under the appliance up the front of the appliance and then sucked out the top of the appliance. The energy savings from this approach versus some generically located damper are significant. You will also bring less fluctuation in humidity levels into the home with the engineered system, also saving energy and wood surfaces in the home. In addition to the integrated parts (i.e. the automated damper), you are paying for the secondary ducting system for input air, and the design and parts to install it to an optimal location.

The caveats here are that the worth of the engineered system are increased in harsher climates where you are paying to make home air either hotter or colder than outdoor air or where maintaining constant humidity levels in the home is important, and increased as the CFM the system is run at increases. And then there are issues of code.

So you'd have to take into account these in your cost benefit analysis, especially in a mild climate and using a relatively low CFM air flow.

This post was edited by beautybutdebtfree on Thu, Jun 26, 14 at 9:44

@beautybutdebtfree, indeed, you get what you pay for. But generally the makeup air system is not designed for kitchen exhaust fan, it's for the whole HVAC ventilation. I ended up buying a 600CFM hood after the closing of the house and hired contractor to install a simple passive make up air damper.