Thinking outside the box, what about one of these? (just make sure you get a 2 hose model. Single hose models cause excess unconditioned air to be pulled into the space to replace what is exhausted out, making them less efficient)
https://www.amazon.com/dp/B0028AYQD...844c-7d6411346558&ie=UTF8&qid=1527793482&sr=1
We got my Grandpa one of these for his sun room a few years ago. They do work pretty well and he was happy with it. He did plumbing and HVAC work his entire life and still just wanted one of these.