I love it when I come up with yet another way to make Barbara and Leslie go scurrying off to check their water heaters. Well beaten paths are easy to follow. Water heaters should be cool to the touch. Now if you put insulation around them, the tank will feel warm between the tank and the insulation after a while. If you hold your hand against the side of the tank long enough it will also feel warm---after a while.
So what does it mean if the water heater feels warm to the touch? (And no, the sun isn't shining on it and the cat is not sleeping on it)
Between the outer metal shell of the heater and the inner hot tank there is insulation that shows down the rate of heat transfer. If that insulation gets wet it will conduct the heat from the tank and warm the outer shell. This picture shows the surface temperature of the water heater---definitely warm to the touch.
This tank had a very slow leak at the connections at the top of the tank and had been leaking long enough to saturate the insulation and damage the wall next to the heater as well as in the adjacent room. Note the rusting at the connection at the top of the tank as well as at the access panel under the thermometer.
PS, for those of you that are new to my blog (or for some other "unexplained" reason have never noticed) all pictures and smiley-face inserts (emoticons) have messages that show up when you point at them with your cursor.
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WA State, Home Inspector Advisory Licensing Board