Hovabators go on and off. It is recommended to keep the eggs away from the heating element, as temps fluctuate the most there. You will need a thermometer and get the temp set well before the eggs are laid (takes me a few days to get the incubator to the right temp).
I made incubators out of styrofoam boxes (hovabators are styrofoam) and placed water on the bottom with a 5 gal aquarium heater. This worked far better than my hovabators, and for about the same price (an adjustable aquarium heater is about the price of the hovabator). I've used cooling racks and egg crate to keep the egg containers above water level.
Also, I don't recommend the air flow model, as I've heard it may dry out the eggs. I used a standard model, had 100% hatch rate while using it for snakes and leopard geckos.
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