Wednesday, February 2, 2022

Heat Exchanger for Home Furnace Exhaust?

I was watching steam furiously rising from the roofexhaust pipe of my neighbor's furnace this morning and I suddenly thought: a heat exchanger catching that heat and putting it back into the house.

The only time it is producing heat is when it is running but that is likely when you could use more heat in the house anyway.  Yes, it needs to be offset so that condensation does not run back to the furnace but draining to the lawn?

The more extreme the temperature contrast the more benefit you get.  In Los Angeles or Honolulu there is no need.  In Boise or Anchorage or the South Pole?  Lots of advantages. 


  1. Modern High-Efficiency Condensing furnaces and water-heaters extract enough of the combustion heat that PVC can be used for the vent out the side of the house.
    They do exactly as you suggest, an additional heat exchanger to remove what would be wasted heat, but they also require blowers to force the exhaust.

  2. Most modern furnaces cool the exhaust and condense the moisture. I doubt you'd want to do more. Perhaps your neighbor has an old furnace?

  3. I guess others have already figured this out. Thanks to all.