In this blog, I'd like to talk about high-efficiency heating systems and what makes them so much more efficient than medium efficiency system like what you probably have in your basement.
First, let's look at the medium efficiency burner. This unit when it sucks combustion air in from its surroundings, usually from the basement, mixes it with the fuel and ignites it forming a flame used to heat the combustion side of a heat exchanger and then is directed through the flue out of the building as exhaust. Air on the house side of the heat exchanger is heated and directed through ducts to different areas of the house as needed. Cool air is drawn in through the intake vents and directed back to the heat exchanger to be heated again. The burner taking combustion air in from its surroundings creates a negative pressure in the entire house which draws air in from the outside through any cracks in doors, windows, attic accesses, outlets etc. causing what you feel as a cold draft.
Now let's look at the high-efficiency burner. These burners not only draw they're combustion air from the outside but also direct it through a heat exchanger that warms it using the exhaust air on its way out, cooling the exhaust air as it does enough for the exhaust air to be able to exit through plastic flue pipes. The warmed combustion air is then mixed with the fuel and ignited and directed through another heat exchanger where it heats the house side air. Then the exhaust runs back outside warming the combustion air and cooling before it exits the building.
So the high-efficiency burner is more efficient because it's using its exhaust air to preheat the incoming combustion air so that less fuel is needed to bring the exhaust up to temperature before entering the heat exchanger. A home inspector can help determine your efficiency.
The other benefit from this method is that because the combustion air is drawn in from the outside directly no negative pressure is created in the house and therefore no cold drafts. This may be more beneficial than the fuel efficiency gained. In fact, houses that have medium efficiency burners could benefit from having the combustion air directly ducted to the burner from the outside. Check with your HVAC professionals.