My house is heated by a condensing natural gas furnace that is rated as 92% efficient. It has the option to draw combustion air directly from outside. I know the main advantage of this is avoiding negative pressure within the house to reduce drafts. However, I thought of a few questions:
- Outside air is colder. Does this decrease the maximum temperature of the flames?
- As the outside air is colder, it is also denser. Does the furnace's performance increase due to increased oxygen content?
- The furnace's exhaust temperature exiting outside is about 43 degrees Celsius, so there is still some heat in the exhaust that is not going towards heating the house. What could be done to utilize more of that heat?