Replacing 40 Year Old Exterior Blower

I need your collective wisdom here. My house has a range hood venting system that vents directly out through the flat roof above. The motor and fan have died and the original piece is a Kitchen-Aire blower from a company that is now out of business. We need to replace this fan with something that will fit in an 8 inch round. The old fan was 60 cycles (which I guess is 3600 RPM), but I'm pretty sure (correct me if I'm wrong), that the number I should look at isn't really RPMs, but CFMs. The venting system ducts turn at least once and maybe twice to reach the roof, so it's definitely not ever going to be the most efficient system. I've found two different kinds of models that I think will work; one is a Fan-Tech Exterior Mounted fan that looks a lot like the one I'm replacing as it's round and mounts on the roof (and it's 401 CFM) while the other one is a Prestige FRB 1000 Flat Roof Blower, rated at 1000 CFMs. The price difference is about $500, so I want to make sure I get this right.

Here's my question: would a new fan, even at 401 CFMs be so much better than a 40 year-old one that I should go with this? OR does the other one rated at 1000 CFMs promise to make that much of a difference? We do not cook with gas, so exhaust might not be that important. How do I compare the old technology with today's? And if neither of these types of choices is right, where do I get other ideas?


Thanks so much!
SargassoC

 

The 60 cycles is a charecteristic of the US power system. It has nothing to due with the RPM's of the fan.

Most likely the 1000 cfm exhaust fan will need a dedicated circuit just for its usage and possibly an externally mounted blower motor. I do not think this is what you want. These are more for large or commercial kitchens.

Yes, you want an efficient fan, but remember that for every cfm exhausted out there needs to be make-up air from somewhere. Most of the time it comes in through poorly sealed weatherstripping and windows.

I looked on the Nutone and Broan websites but did not see the thru the wall fans they used to carry.

 

And remember, too, all the air you are venting is either air conditioned or heated air, so the more you evacuate, the more your hvac system will have to work. I'd go for the 400 cfm.