Instruction: Given a question and the related document, and generate the answer to the question based on the information provided in the document.

Input:
Question: What size hole is needed in the ceiling?
Document: Just perfect...needed to replace an existing fan that was too small....bought this one...Broan 676 110-CFM 4.0-Sones Ceiling Mount Ventilation Fan!~ It made a world of difference!~
It only gets 4 stars because I cannot say I love it, and the reason for that is it's a ceiling fan.I was able to remove the motor and the fan and put them into an older 684 model housing. This was the main reason why I got this. Purchasing the motor alone would have been about the same price, so I figured I'd get the whole thing and have spare parts if needed.
Came with all the parts needed. Installed it in our bathroom and worked well for what we needed it for.
It was challening to install, but not anything to do with this fan. The old fan I was replacing was very different in size and method of mounting. It took quite a bit of altering to get it to work. Other than that, it is relatively quiet and is effective.
Ordered two fan units for different bathrooms. One room is twice the size so I increased slightly the air replacement capabilities from the older units (1974 installed). This fan is more noisy in either setting then the original product. Next time I will purchase the Panasonic whisper version.
Ordered to replace same model but mounting box was bigger so I used the motor and ceiling cover works perfect
We had the same fan in our bathroom, just in an 80cfm fan instead of 110cfm. We were getting some mold growth so decided we needed more airflow. Got this one to minimize extra work. It uses the exact same housing and power supply so it was super easy to just change out the fan part I needed. 15 minutes tops, once I figured out how to get it apart(15 minutes for that ;) didn't want to break it! First time doing anything with a fan like this).
I bought this to replace an old fan that the builders had installed (my old one was only rated at 50cfm). I needed a new one because I was getting condensation on the bathroom walls since the old one was not moving enough air. I was able to install this in about 20 minutes from below and it works great. Perfect sound level to wash out any unwanted bathroom noises but not to loud so it's not annoying. It certianly moves a lot more air than the old fan.
I bought this model because the price was right for a spare bath, and it was the right size to replace the old one. I didn't care that it was 4.0 sones. How loud could it be for the length of time it runs.? But the first fan received vibrated on the spindle and my electrician suggested I get a replacement. I did. Amazon was amazingly fast with the replacement and sent it out before they received the old one. The second one was fine and suits my needs.
When replacing bathroom fans, the duct size can be extremely important.I have found the higher CFM products usually have a 4" duct.However, older homes often have 3" ducting.Ducting in two story homes often can not be replaced with new ducting, particularly when the fans are crammed into small spaces.Most hard ware stores do not sell 3 to 4 inch duct converters.Further, Amazon does not indicate the duct size for this fan.
Answer: I just measured the hole in ceiling drywall and it was 8 1/2" x 8 1/2" for this model I have installed. Hope that helps!