One would have expected Prestige to provide some advice, but without it, I recommend you match six-inch vents with six-inch ducts. Larger ducting reduces resistance but also slows down the air velocity. Commercial ducting requires 2000 ft per min air velocity to limit the amount of grease that will condense. According to some sources I've read, residential velocities should aim for the 1000 to 2000 ft per min range. The two six-inch vents can be merged into a duct with the same cross-section, around 8-inches, but only if both power packs are powered at the same time. Otherwise, keeping the velocity up requires individual ducts. A call to Prestige may be desirable. kas

"They said the hood vent was probably getting too much power and thats why it got messed up." No. That makes no sense. I'd do the following: Pull the cable out of the hole at the bottom of the cabinet Obtain a surface-mount electrical box (example) and remove one of the knockouts. Attach the electrical box to the back of the cabinet. Route the cable into the electrical box and clamp (example) it in place. Wire up an outlet (example) and attach it to the box. Attach a cover (example) to the box. Run the cable from the microwave through the existing hole and plug it into the new outlet. -- amateur

Does this hood have an internal blower? (A) If not, I would recommend you purchase a 1000 CFM or greater nominal (zero static pressure) flow rate blower and decide whether to put it on an outside wall or on the roof, with a 10-inch duct between the hood and blower. The longer roof path may allow adding a silencer from Fantech. Selection will depend on house architecture and allocated cost. (B) If supplied with blower, duct either path as described above without the external blower or silencer. I am only guessing here, but suspect your existing wall vent will be too small for the blower you need to use so if you choose that direct option, some carpentry will be required. Please dredge through the many hood threads here to gain insight into what your goals are and what the requirements are for good ventilation. Also note that a make-up air (MUA) system will be needed in most locations.

We don't have the option right now to duct to the exterior. Technically a recirculating vent hood is supposed to filter the air and send out clean air. So wouldn't it be clean air?