My house is 112 years old. I was in my attic and soaking my shirt because it was 120° in there (I live in Florida). I thought how nice it’d be to get some fresh air in there. I thought it’d be even better if I could get that air from the (somewhat) cooler air in my crawlspace. Then I noticed the 4" cast iron pipe that was used to be the drain pipe for the house from 1915 through about 2000. The vent for that pipe runs through my attic and straight down to my crawlspace…unused and forgotten. So I cut the pipe and disconnected it from the roof and cut off and closed up any branches it had. I cut it and slapped a screen on it in the crawlspace. In the attic I put on an inline fan (6 watts) and a bit of duct to vaguely direct it around the attic. Early tests say my attic is about 7° cooler. Am I crazy?
The roofers may be able to do the vents for a small up charge. I wanted the gutter people to do mine but the gutter price alone was well beyond what my inexperienced DIY ass wanted to pay. I’d recommend adding a ridge vent with the roof though, as that’s a very related task.
When I did one corner of the house with soffit vents, I couldn’t feel anything in the attic, but I could see cobwebs dancing in the draft above the vents. Nothing in the other corners. So I have to trust they work. I started on the side with the most frequent breeze