Summer ventilation and heat stress
When passive vents stop being enough, how to spot heat stress before it kills, and where a small fan earns its keep.
Heat kills more backyard chickens than predators do, and most of the kills happen above 90°F in coops that ventilate fine in spring.
Standard hens dump heat through panting and through bare skin around the comb and wattles. Both depend on moving air. The summer extension-service target is 5 CFM per bird, which doubles the winter requirement. Most coops cannot hit it through passive vents alone once daytime temperatures cross 85°F.
Three signals say a flock is in trouble before you see a death: wings held away from the body, beaks open with rapid breathing, and birds standing in the shade refusing to come back to the run. By the time a bird is on its side, intervention is hours late.
The cheap fix is one small DC fan, four to six inches, mounted on the outlet side near the ridge to push warm air out. Pulling air out works better than pushing it in. Pair with the inlets fully open and one frozen water bottle per four birds in shade.
Run the calculator at the homepage with the hot-summer climate selection to size the inlet and outlet area you need.