When it’s cold outside, growers may want to heat the air and/or soil inside a tunnel, and this can be done using permanent heating systems, or emergency systems for coping with unusual conditions. Whatever system is used, a temperature warning system is important to provide notification when heating (or cooling) is urgently needed. To determine what size heater is needed, one must calculate the heat loss when a certain minimum temperature is desired inside the tunnel when there is a certain outside temperature. More information on heating, ventilation, and other engineering issues can be found at the University of Massachusetts greenhouse and floriculture web site and on the University of Vermont Extension agricultural engineering blog.