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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?

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

davidgo
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  • has there been any study to back this up? – anurag Jan 11 '21 at 08:50
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    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 '21 at 09:08
  • 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 '21 at 09:21
  • 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 '21 at 09:29
  • So the questions then would be - what is the effect of nitric acid on your particular plants and how concentrated is it? – davidgo Jan 11 '21 at 09:38
  • Well, all I am saying is, before a practice is adopted by a large populace, its short and long term effects should be studied in controlled environments. – anurag Jan 11 '21 at 10:16
  • Corrosive has nothing to do with plants. Basically it is distilled water saturated with CO2 ; so it is acidic but neutralized as soon as it contacts soil ( by limestone , etc.) – blacksmith37 Jan 11 '21 at 19:04
  • @blacksmith37 As per the 2015 article link I have shared above, the condensate also has Nitric Acid, which may not be good! – anurag Jan 12 '21 at 05:56
  • Don't believe something just because because it is printed on the net . What makes this condensate acidic is the CO2 ,not a ppm of nitrate. – blacksmith37 Jan 12 '21 at 17:23
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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 ).. – blacksmith37 Jan 12 '21 at 18:31