Incubator Thermometer and Hygrometer

Why use a second thermometer

Your incubator’s display shows what its own sensor reads. Sensors can drift over time or sit in a spot that is warmer or cooler than the eggs. A separate thermometer and hygrometer placed among the eggs tells you what the eggs actually feel. If the two disagree by more than about 0.3 °C, find out which one is right before you set eggs.

Where to put it

• Forced air incubator: at egg level, in the middle of a tray, not against the wall or near the heater.
• Still air incubator: at the top of the eggs. See forced air vs still air.
• Leave it in for a few hours before reading, and read it without opening the door if you can (a remote probe helps).

How to check a thermometer

Ice-water test. Fill a glass with crushed ice and top up with cold water. Stir, wait a few minutes, and put the probe in the middle. It should read 0 °C. Note any difference and correct your readings.

For extra certainty, compare it with a medical (clinical) thermometer, which is accurate around body temperature.

How to check a hygrometer

Salt test. Put a few spoons of table salt in a small cap and add a little water to make a damp paste (not a solution). Seal it with the hygrometer in a zip-lock bag and leave it for 8–12 hours at room temperature. It should read 75 %. The difference is your correction.

Wet bulb thermometers are an older, reliable way to measure humidity: a wick keeps one bulb wet, and the wet-bulb temperature converts to humidity with a chart. Then set humidity with the humidity guide.