I would recommend you stay away from the hot water heater thermostats... This is the heart of any bator. The wafer type is as cheap as you want to go, there like 20 buck or so. But a nice digital unit with a probe is really the kitty's nipples. Your likely going to have 35 -40 dollars in a home made bator by the time your said and done... I made and use one still as a hatcher. If I built another, It would have a 250 watt heat element, you can get them on ebay. A puter fan that is wired separately so it can be unplugged at lock down to prevent shrink wrapping eggs. And in a ply wood box instead of the foam. But I dont ever think you could build the perfect bator. Always something to modify... Bill
Absolute truth! You want that temperature range to be as minimal as possible. WH thermostats are made to cut your water heating element on and off with a wide temperature differential window.......much too wide to try to hold 99.5 degrees. Go here - https://www.backyardchickens.com/forum/viewforum.php?id=5 ... and read all the testimonies from people who fight temp problems by going the cheap route and using a WH thermostat. Like Bill said, at least get a wafer style, as a lot of the big-name manufacturers use this as a "backup" in the event their real-mccoy fails.