Fixing Toilet Tank Condensation

MOTHER EARTH NEWS readers receive guidance on condensation in a toilet tank, including tests to make on toilet parts and room temperature changes.

| January/February 1987

I have a problem with condensation from my toilet tank. We want to put an oak floor in the bathroom, but we're afraid the toilet tank condensation will ruin it in no time. Meanwhile, we keep a long pan on the floor to catch the drippings. Any suggestions?  

Fixing Toilet Tank Condensation

First, make certain the toilet tank condensation isn't coming from a hairline crack in the tank — or from a damaged ballcock valve or seat, which could spray water onto the lid and down the outside of the tank.

If you've determined that the tank is indeed sweating, try lowering the temperature of the bathroom and the surrounding area and reducing the humidity of the room with a dehumidifier or a ventilating fan. In addition, you could install a plastic tank liner to insulate the tank walls from the cold water.

Richard Freudenberger, research coordinator 

Paul Myers
6/30/2012 2:46:03 PM

Another solution is to place an adjustable mixing valve between the toilet and the water supply. This valve has inputs for both hot and cold lines, and can be set to a temperature that is above the dewpoint in the house. 70 degrees is usually good enough to prevent condensation unless your house is REALLY hot and humid. This will work better than running straight hot water, which wastes energy, and heats your house, and is simpler than adding another tank, which will probably spring a leak someday.

6/27/2012 8:42:17 PM

Wrap the tank with a thick towel.

Poodle Mikey
6/27/2012 1:24:22 PM

The old solution for this problem was to pipe the toilet supply to the hot water line. This will still work - but at the cost of using slighting more hot water. Air conditioning and elevated public water tanks has largely eliminated the issue by reducing indoor air RH and by raising the temperature of the cold water. Of course a well-water supplied system still gets cold water. The best energy conservation solution that I can think of it to make the supply line to the toilet either very long (run the line from one end of the house to the other before it goes to the toilet) or pipe the toilet water supply water feed through a small uninsulated water tank. A very nice way to kill two birds with this stone is to strip an old water heater and use it an an ambient storage tank pre-heater in-line with your existing water heater. The cold water comes into the pre-heat tank first and comes up to ambient temperature there Before getting to the actual how water heater. So the hot water heater has less work to do and costs less to operate. The other benefit of course (to close this circle ) is that the toilet supply can be piped from the ambient-pre-heat tank - rather than from actual "cold water".

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