These look real similar to the inline fans used on boats. I just had to get some inlines for my boat I grabbed on ebay, by the way was agreat deal as its a 23 foot lund with traile 5 sleep cabin with motor for $3000, and I find them on ebay for about $0 they are anywhere from 250cfm to 1200 cfm depending on the model just have to hardwire a plug to the sires...Also watch out for Texas Hydro for some reason alot of chatter about them online and from word of mouth that they also report to police on thier buyers which makes no sense to me but when you start to see dozen of people saying the same you keep an eye open