Heat meter
A heat meter, thermal energy meter, or BTU meter is a device that measures thermal energy provided by a source, such as a central heating system, by measuring the flow rate of the heat transfer fluid and the change in its temperature (ΔT) between the outflow and return legs of the system. Heat meters are used in district heating systems and other shared heating systems to measure heat delivered to residential and commercial tenants, which enables consumption-based billing (submetering).