A minor nit: Burning gas for heating is not 100% efficient, unless you really want to die of carbon monoxide poisoning. Combustion gasses are exhausted to the a

A minor nit: Burning gas for heating is not 100% efficient, unless you really want to die of carbon monoxide poisoning. Combustion gasses are exhausted to the atmosphere. Heat is transferred via a heat exchanger into the recirculated internal air of the house. [1] https://en.wikipedia.org/wiki/Central_heating https://en.wikipedia.org/wiki/Central_heating