How much water does burning propane produce?

How much water does burning propane produce?

Moisture buildup can be a big problem in tiny spaces during the Winter.  Without regular ventilation, water from cooking, showers, and breathing can build up and condense on cold walls and windows.  In severe cases, moisture can create mold growth.

If you're using an un-vented or "vent-free" propane appliance like a catalytic heater, "blue flame" heater, or certain instant water heaters, your appliance is adding 1.6 pounds of moisture into your space for every pound of propane burned.

heating with a wood stove in cold and moist climates

Why does burning propane produce so much water?

It doesn't seem possible, does it?  How could one pound of propane contain more than one pound of water?  Let's take a look at the chemistry.

C3H8 (propane) + 5O2 (oxygen) → 3CO2 (carbon dioxide) 4H2O (water)

For each molecule of propane burned on the left, 4 molecules of water are released on the right.  The molar mass of propane is about 44 grams/mol.  The molar mass of water is about 18 grams/mol.  So:

44 g Propane + Oxygen → Carbon Dioxide + 4*18 g Water
44 g Propane + Oxygen → Carbon Dioxide + 72 g Water
1 g Propane + Oxygen → Carbon Dioxide + 1.64 g Water

So, where is all that extra weight coming from?  In fact, very little of the weight of the water produced comes from the propane itself.  By weight, water is mostly oxygen, and the oxygen comes from the air.  If we add the molar mass of the remaining molecules, the equation balances nicely:

44 g Propane + 5 * 32 g Oxygen → 3 * 44 g Carbon Dioxide + 4 * 18 g Water
44 g Propane + 160 g Oxygen → 132 g Carbon Dioxide + 72 g Water
204 g Reactants → 204 g Products

Be careful using non-vented propane appliances in a tiny home

Even if the appliance isn't burning inefficiently and creating carbon monoxide or using up the oxygen in the room, it's dumping a ton of water in your living space.

To avoid moisture problems, either use vented appliances, or arrange for adequate ventilation to get rid of the moisture in your space.

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