I recently had my old, broken furnace replaced with a high-efficiency condensing furnace. One function of this furnace is that it extracts enough heat from the exhaust gases to condense them into liquid ("condensate"), which is sent out of the furnace and down the drain.

My understanding is that this liquid is mostly water. I'd like to use this to reduce my water usage, rather than letting it go down the drain. Is furnace condensate safe to use on my houseplants? If not, is there something else I could safely use the condensate for?


1 Answer 1


Yes. This would be absolutely fine for plants. It would be almost pure water - not dissimilar to distilled water.

  • has there been any study to back this up?
    – anurag
    Jan 11, 2021 at 8:50
  • 1
    I've not looked for one, and don't see why one would he needed. Incomplete (or imperfect) burning of LPG/propane/butane results in water, carbon dioxide and carbon monoxide. The later 2 are gasses, so even if they weren't gasses they would not hurt plants. (Indeed they would likely benefit plants)
    – davidgo
    Jan 11, 2021 at 9:08
  • Well, @davidgo, I came across this 2015 article which says that the condensate water output is corrosive. That might be harmful to the plants/trees!
    – anurag
    Jan 11, 2021 at 9:21
  • Further, I came across this article with information about what should be the pH value of the growing medium of some of the plants/trees!
    – anurag
    Jan 11, 2021 at 9:29
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    On the other hand , if you want to believe the net story ; you are getting free fertilizer in the water ( the "N" of NPK ).. Jan 12, 2021 at 18:31

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