As I write this the Toronto area is enjoying a brief winter warm spell – it’s only freezing! Two weeks ago we saw temperatures around 20 degrees celsius below freezing.
My house, like most newer homes in Canada, is heated with a high-efficiency, or condensing furnace. High-efficiency furnaces can achieve from 89% to 98% fuel efficiency.
These modern furnaces have a sealed combustion chamber, a combustion draft inducer and a secondary heat exchanger.
Combustion
The combination of a sealed combustion chamber and a combustion draft inducer (a fan to propel outside air through a PVC pipe into the combustion chamber) are both more efficient and prevent unsafe backdrafts (Principle 1 – Segmentation).
Secondary heat exchanger
It’s this last bit which which wrings almost all of the residual heat from the combustion gasses, including the latent heat of evaporation (Principle 36 – Phase Transition), reducing the exhaust to below the boiling point.
