I've been looking for effectiveness measures for whirlybird vents for a while and I can't find anything in building codes, and only one empirical claim from askthebuilder.com for a relationship between diameter, windspeed and airflow. I know there are general accepted rules like 1 square foot of ventilation per 300 square feet of roof space, but I'm really looking for a formula for airflow. Am I oversimplifying the problem? Thanks!

  • You want at least minimum airflow/ventilation from the roof at any windspeed even zero. Whirlybirds probably do not increase airflow enough to make them better than other types. You start adding moving parts to a system, you start to add up more failure points. Just wait till the bearings start going out and find out how many neighbours have 12 gauge shotguns.
    – crip659
    Apr 15 at 13:06
  • I mirror crip659's comments. Whirlybirds used to be common in my part of Fla. Too many failed and either bound up, or squealed like 100 6 year old girls. Add to this an area where most homeowners were too old to get on a roof to do anything about it and an entire industry was born to remove these things and replace with ridge vents. I would not install one even if someone paid me handsomely. I know I will be called back because it failed.
    – RMDman
    Apr 15 at 13:29
  • @ Steve, you are not oversimplifying, you are over complicating.
    – RMDman
    Apr 15 at 13:31


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