Homemade incubator water heater temp varance


7 Years
May 15, 2012
I made two home made incubator the same size as the Little Giant, I used the water heater thermo but I'm getting a temp of on at 91.5 and off at 109.0. on one and the other one turns on at 87.2 and off at 104.5. Is there any way to set them so there isn't a big varance temp?


8 Years
Jul 4, 2011
Midland Ont. Canada
How close to the heat source do you have the thermostat?
Water heater thermostats work off of radiant heat and need the heat source to heat them up to cycle properly.

It should be wafer side towards the heat source [light bulb?] and be not more than 1.5" from it.
You can also drill extra holes in it to make it more stable.

Here is a link to a site for drilling the extra holes in the thermostat

Here is a picture of how I have mine set up and the temp doesn't vary much more than 1/2 a degree.
Also add a heat sink to the incubator if you have room - I just use a couple of water bottles.

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In the Brooder
7 Years
Apr 18, 2012
cover bulb with foil or when they lit temp will increase immediately which can harm eggs... until ur temp meter detect ur temp can rise and chicks can die.. eggs must be heated by warm air not direct bulb light source.

MI chickens

In the Brooder
8 Years
Apr 21, 2011
Zeeland, Michigan
I've used a double layer of foil as a loose "tent" that's open at the ends. It blocks the direct light from the bulb and I think it helps the thermostat operate more evenly. I have a water heater thermostat that I modded and it stays within + or - 1/2 degree with the foil tent.

Maybe you might want to try lower wattage bulbs.

P.S. My thermostat shares the tent with the bulb, the foil doesn't come between the two.
Also when I modified the thermostat, I removed the metal cover (drilling out the rivets). Then I drilled out the 1/4" hole in the metal cover to about 1/2". This exposed the bi-metallic disk to more of the bulbs heat. I then reassembled it using appropriate size screws and nuts. Drilling this was easier with a drill press, if you try this be careful taking it apart and putting it together, it easy to mess up.
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9 Years
Oct 22, 2010
Southern Oklahoma
I have a cooler incubator, you can see it here. It is controlled with a modified water heater thermostat. Before you try to modify the thermostat, you need to know why, and how it works.

A water heater thermostat, for water heaters, detects radiant heat, NOT ambient temperatures. In order for the thermostat to work even better, holes can be drilled into the thermostat to help it to react faster to temperature change.

A regular central heat/air thermostat detects ambient temperature.

Here's a video explaining radiant and ambient temperatures, within a home made incubator.

This is RebelRooster's vid.

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