That is a long run for ductwork. I would consider upgrading the blower and possibly moving to a 12" duct. I would consult an HVAC contractor to get the proper flow rates...

In my view, losing only 300 cfm given the duct pressure loss, the hood transition losses, and filter losses, is pretty good for a fan curve. However, I would suggest using a larger 1500 cfm fan to improve chances of successfully capturing and containing the effluent that is possible from such a large and powerful cooktop. Given the hood size that is needed, a large flow rate is needed to keep the air velocity high enough at the hood aperture.

It is essential that the hood overlap the cooking surfaces by enough to capture the rising expanding effluent. Assume from each cooking surface an expansion half angle of 22.5 degrees, and determine for the intended hood height whether the expanding cone stays within the hood aperture.

Don't ignore that when Broan or others assert a flow rate, they are assuming that the cooking area pressure equals the outside pressure. This would require an outdoor kitchen or near perfect make-up air system. Any house negative pressure will cause the maximum flow rate to drop per the relevant fan curve, another reason for increasing the fan capability.

Broan publishes their fan curves so the effects of pressure loss can be clearly quantified.

kas

What are his reasons for not putting the blower on the back of the house? Just curious.

Courtesy?

If you're already considering a Broan blower then you should definitely step up to the 1500 cfm model. I have the Best version. The $200 price difference would be worth every penny. In the grand scheme of things it's actually a relatively small percentage. I know every penny counts, I went through that myself. But in this case $200 for some assurance and peace-of-mind is well worth it.

@ jscout:
I am more concerned about the additional noise from the 1500 cfm fan than the additional cost (hehe, this range+hood setup is going to cost more than the cabinetry and only slightly less than a space rocket). Do you think your fan is much noisier than a 1200 cfm model would have been?

@ weedmeister:
This is a narrow rowhouse, so the back of the house = precisely underneath the bedroom windows and over the sitting area in the back yard :(

@ kaseki:
thanks for such a detailed, technical answer!

When you say noise, are you referring to inside noise or outside noise? If inside, it's a non-issue. The only thing I hear from my 1500 is the airflow across the baffles and the faint humming of the motor. And that's only on high. On medium it's so quiet I sometimes forget it's on.

I doubt the noise outside would be significantly higher. I don't have decibel ratings, but you can probably call Broan/Best and see if they have that. Physically, the outside dimensions are the same, so I think they both use the same frame, chassis and duct size. My guess is it's just a different motor size since the 1500 is rated at higher amps.

For what it's worth, I just wanted to add that in my case, the A/C condenser situated beneath the external blower is much louder.

You need a HVAC professional involved. You will also need makeup air and that needs to be coordinated with your heating and cooling systems.