Let me know how the FAN works out for you David. I'm interested if they're anywhere as powerful as the listed ratings.
Will do.
I'm actually checking them out on Amazon right this very moment. I'm looking at dual and single options; Reading reviews; etc...
I'm coming closer to making a decision. I believe I found the right brand [Flex-a-lite] that is made in the USA. I'm trying to decide which model of theirs to purchase.
I actually bought a couple of the different radiator fans a while back on Amazon - completely worthless. The CFM values are definitely not even remotely close to what they claim. They also have about zero static pressure (probably because they're intended to be in situations where air is basically forced in most of the time), so are terrible in any restrictive setting.
The only consumer-y thing I've bought that's worth anything are these:
http://amzn.to/1Ok7W8aYou can get similar ones from Home Depot and Lowes, and they definitely move a fair bit of air. I usually set these up in tandem, with the auto-close grates. The thing you have to consider with smaller fans is that if they stop working, and you have a channel that is restrictive in any way, they're going to short circuit (meaning the fans adjacent to the failed fan will just suck air back in from the exhaust side).
I also would recommend just finding multi-speed fans, instead of trying to use a motor controller to control speed. It just adds cost and heat, with very little upside IMO. Depending on where you're located, you could also look into buying used swamp coolers - they generally have a decent belt-drive squirrel cage blower that will be in the 3k-4k CFM range. In Arizona they're cheap as hell, typically only a couple hundred bucks used, and have great static pressure.
The other thing to consider doing if noise is an issue is just make sure the air channels are not straight - make sure you have larger than necessary ducting, and then put two 90 degree turns in it - and if you're doing ducting, get the kind with internal insulation (looks similar to heavy duty bubble wrap), this will also diffuse the sound. I have 2 of those fans linked above exhausting in a similar setup, and you can barely hear the sound on the vents outside (similar to what you'd expect from a laundry machine).
Anyway, hopefully that helps save you wasting money on those radiator fans.