Cooktop vent reducer required from JennAir - does this make sense?

Hi,

First time poster.

I just bought a new gas Jenn-air cook-top (JDG3536WS). This will replace an old electric Jenn-air cook top (22yrs old). The old cook top blower motor has a total of 8' of 5" dia vent pipe (including one 90 elbow), and a 5" wall cap with damper.

The venting requirements for the new unit calls for 6" pipe from blower to outside wall outlet. The strange thing is that the blower on the new cook-top has a 5" dia outlet. I called Jenn-Air and they said I need to first use a 5" to 6" transition piece at the outlet of the blower motor, then run the rest of the piping in 6". They could not explain why 6" piping is required after a 5" blower outlet. Weird.

So, in my case, since I already have 5" dia venting from the cook top to the outside, I really don't want to replace the 5" with 6" unless it will really make a difference in performance and noise.

What do you think? Should I rip out the 5" dia and replace it with 6", or is it reasonable to assume the 5" will work fine? I guess I can try it 1st with 5" and see if it works ok...

I definitely don't want to burn out the new blower motor with too much pressure... any thoughts here?

thanks!

quote; I definitely don't want to burn out the new blower motor with too much pressure

Do you really believe JennAir would use that "good" of a blower? It won't and that short run should not have any repercussions that you would ever notice. It is possible that any "slippage" could create a bit more noise but I doubt that you would notice that either.