Like he said, and call the hood mfg and ask the tec support to size you a new EF. Failing that get the size of the hood, type of equipment under it, and M and S of any MAU, and take this info to your supply house and ask the in house HVAC engineer. Be sure that you check with the inspector befor you go touching any duct, cause most cases as soon as you touch that hood to make any type of modification, all bets are off, and you have to bring the whole thing up to code. Don't take chances, one grease fire and the place will go up and they will be asking "Who worked on this last, and how much can we get out of his insurance!"
That is a very nice advice,now considering Energy Conservations(sorry to add a new question here) since a change-out of whole fixtures here.Any suggestion on timers,switches or enhancing its operational cycle via tapping exhaust fans with EMS?