fireplaces

[Les C]

Having had a direct vent heater, I can tell you that it vents directly to the outside (ooh, that's useful!). Kidding aside, the heater sits next to an outside wall and a double-walled, "two transport" pipe goes horizontally out. One carries exhaust out and the other carries fresh air in for the combustion in the heater. It's efficient because you don't lose a lot of heat out the exhaust. I imagine that a natural vent is like a chimney, where the heat rises up, carrying the exhaust gases out. Fireplaces are generally inefficient; I think the heat loss is something like 50-60%. Direct vent heaters are something like 98% efficient, retaining most of the heat.

Unless you live in Volcano, I don't see how all of this efficiency would matter.