I understand that a condensing tankless water heater will recycle that extra heat and only vent the heat that it cannot use; this is why they have a greater efficiency.
But the water that condenses out of the unit, and pumped outside, is that out of the ambient air, like a dehumidifier?
In other words, will the room around the unit become less humid? Or the unit adds this extra water in the first place?
Thank you.
Best Answer
The condensate from natural gas burning comes mainly from the burning. Methane is the primary component of gas, and it is chemically CH4. When burned, you have:
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CH4 + 2 O2 --> CO2 + 2 H2O
The relevant parts here are that 2 "oxygen" molecules from the air are consumed, and (after some chemical shenanigans) 2 water molecules are produced.
This is not simple, since natural gas consists of other things than methane, and the reaction is not a single-step reaction, so carbon monoxide and other things are also by-products. But the majority of the gas is methane, and the majority of the results are dioxide and water.
The water, naturally, is a vapor since it's created in the middle of a burning flame. But the high-efficiency gas appliances really try to capture the waste heat and feed it back into the system, so as a result the water vapor is cooled to "condensate". The condensate is not pure water (a lot of those impurities and by-products mentioned above also condense) and so you should not drink it (seriously, you could die), or even allow it to run through your sewer drain (seriously, it will eat a hole in your poo pipes, and nobody wants an that) without neutralizing it.