Abstract: Apportioning energy costs among units by sensing a heat exchange for at least one heat exchanger in each unit. In response to this sensing, a value corresponding to an amount of heat provided by the heat exchanger is determined for each unit. Each value is transmitted to a central location, and they are processed to apportion energy cost for each unit as a function of the respective value. Total values for each heat exchanger can be summed to provide a summation value corresponding to a total amount of heat provided to the unit over time, and energy costs can be apportioned as a function of this summation value for each unit. A probe that includes a probe body and an electrical heat sensing element mounted in the probe body. A tamper detecting mechanism responds to forces applied to the probe and interacts with a conductive lead of the probe to provide an electrical tampering indication.