Hi All. Still crawling along with our basement reno. I am considering installing a ventilation fan with a humidistat to help keep the moisture level at bay. Am told that is must vent outside so there will be a fairly long run [30 ft. +/-] to a bay cavity with 2, may 3 elbows.

An important thing is that the only air inlet in the entire basement is about the size of a cinder block located at the top of the wall and is adjacent to where the main sewer pipe goes outside. There are 6 hopper windows in the entire basement

I am looking for suggestions on sizing and anything else I may not be aware of. Am Googling now to learn what I can, but here is one of the best place I know of to get straight talk.

Also we plan on getting a dehumidifier that will send the water to a sewer drain.

As always I thank you for your attention

Unless you're planning on somehow conditioning the makeup air that this fan will be bringing in, I think that you'll be disappointed with the results. Instead of spending money on an exhaust fan, I think that you would be better off using a really good dehumidifier such as Santa Fe manufactured by Therma-Stor. I believe that you willfind some useful info on their web site (://thermastor.com/resources/all-about-humidity/)

I’m no expert in basement ventilation, but I know that when encapsulating a crawl space, it’s a cardinal sin to bring outside air IN. It brings in additional humidity that will make your dehu work harder than it should. For these applications, a SMALL 50 cfm fan is installed to exhaust air out of the crawl space to keep it under a negative pressure, which also helps to condition it.

I sometimes have radon gas problems in a crawl space area. This is common when there isn't enough natural air flow.

So I measure the square foot area and calculate the needed crawl space vents needed to circulate enough air per hour.

I can use a carbide hole saw and cut out 3 inch or 4 inch holes then glue into place metal circular grills that will allow the air to flow but not allow bugs into the area. Then I will install a quite vent fan to pull air into the entire crawl space through the vent I've made and out the fan discharge.

Thank you Steve and the rest for your input. Was glad to see my thought on the fresh airwas not unfounded. It seems like extra circulation coupled with a good dehumidifier should do the trick.