It hasn't. It gets a lot of birds to full term but then they die most before they even pip. This is the first time using it with a fan. The temp has been steady this time.FeatheredFreind,,that decision is up to you.If you've had your bator a long time and never had any probles with it maintaining correct temps,why temp fate with a broody? In my opinion which isn't worth 2cents,,the best broody I have ever witnessed year after year was the old White Rock breed.My grandmother had 200 laying leghorns for decades and each year she would go to our neighbors and borrow 4-5 broody White Rock hens. They were then brought home,straw was placed inside a clothes basket,30 eggs was put in the nest,then the hen with a piece of plywood and a brick on top.21 days later 30 chicks was hatching just like clockwork and once the hens and chicks was removed from the clothes basket,noone better get within 25 feet of those chicks.I wonder if that breed of chicken is still available and not from hatcheries? Sorry to get off topic,but if your bator has proven reliable,stick with it.