Ventilation Fan Replacement - Size Problem

[golfer99]

I am looking at replacing the NuTone 667RN (http://www.nutone.com/PDF/InstallGuides/667RNins87574.pdf) currently installed in our shower. I removed the grill to see what size hole was already in our ceiling and found it to be massive compared to other fans I have looked at. The inside housing for the fan is 9x9, but the circular hole cut in the ceiling is a full 13 1/8 inches in diameter. Most of the replacement fans I had been looking at are square or rectangular holes and they are several inches smaller than what is already cut. What are my options here? If I find a fan motor that would fit inside the current housing, can I stick it in there and leave the existing grill to cover the hole in the ceiling? If not, are my only choices to either find a huge fan that would also cover this hole or to patch the ceiling around a smaller fan?

Thanks in advance.

 

[Jimbo]

Here is your parts diagram:
http://parts.broan-nutone.com/nuton...xtype=7&keyword=667RN&Search.x=10&Search.y=23

Here are some similar models
http://nutone.com/product-detail.asp?ProductID=11237