The process of ventilating and exhausting the composting toilet also sends heat out of your composter. Toilet flush water also cools it. Evaporating leachate can cool the process, too, through evaporative cooling. So do not overdo the exhaust system. To minimize the heat loss, install a fan speed controller to keep the fan speed at levels just adequate for odor control, but not high enough to cool and dry the compost too much. Turn down the fan speed until you smell odor in the bathroom. Then turn up the fan just a little until the odor goes away. This should be sufficient.

Or, place a lit incense stick inside the toilet, if you see smoke coming out of the bowl, then there is not enough ventilation or exhaust. A rate of 1 to 5 cfm (cubic feet per minute) should control odors and provide sufficient oxygen to the process.

This heat loss also underlines the value of using warm air sources:

• Insulate the vent pipe, if it passes through cold unheated spaces, to prevent condensation — the vapor from evaporated water and urine, which will run back into the toilet. Keeping the exhaust chimney warm encourages throughput of the vapors.
• Or paint the un-insulated vent stack black and put it in its own window or a greenhouse facing south. Solar chimneys help maintain a draft. (This is a little complicated and heats only the pipe on sunny days.)