Water Heaters - checking water heater temperature

Thermostats on the electrics come set at 120, just for couriosity I thought I would check the temp; using a small dial thermometer with a stainless stem, I ran the hot water in the kitchen sink into a cup for about a minute while the thermometer was in the water and it looks like it was about 115; I can only suspect that water would loose a few degrees from the time it left the tank and found its way to the faucet, correct? Is there a general rule for how many degrees one loses? Is there a better way of checking it like putting a cup under the pressure relieve drip leg and lifting the lever allowing some of the hot water to enter into the cup and take the temp there?
Appreciate any comments.

The setting on the tank is 120 but those thermostats are not very accurate and the printed numbers should just be considered a rough guide.
The temperature at the tap as you have checked it is pretty close to the tank temp.

You also have to consider the accuracy of the thermometer you are using.
Using boiling water and ice water will give you some idea how accurate it is.

As Greg mentioned, the temperature delivered to a tap is not intended to be exactly what the heater is set for several reasons"

1. The set temperature has a range between the minimum and maximum and could be different depending on the location of the thermocouple/sensor. It is really relative and not absolute.

2. I f you draw water until it as hot as you feel in the maximum, you are adding cold water to the tank, which reduces the average temperature of the water in the tank and the resulting discharge water temperature. If you are check for a discharge away from the heater, the dilution will be greater because of the increased distance and amount of heat required to heat the lines to the maximum (don't waste your money on insulation the hoot water lines unless you have a very unique situation).

Do not play with the temperature/pressure valve since this could change the release points (especially on an older installation). A water heater can be a real bomb if that valve malfunctions - The world altitude record for a tank is about 200 feet after going through 2 stories of a house and the roof.

Why are your worried about the exact temperature within a few degrees? Few appliances require specific temperature water and many have interior blending systems.

Dick

120 is incredibly low. I believe 140 is the recommended minimum for water heaters.

Actually, many states have laws (and maybe the federal government has stepped in) to require manufacturers to set the thermostats at 120 degrees. I know my own state Washington) many years ago made it law that water heaters in rental properties and maybe even commercial properties serving public restrooms were to be set no higher than 125 degrees.

However, recent studies have also proven that 120 degrees makes a dandy breeding ground for bacteria, especially Legionella. Because of this some forward-thinking jurisdictions are requiring higher temperatures (140 degrees minimum) in the tank and tempering valves (mixes cold and hot water) immediately beyond the water heater set to no higher than 120 degrees.

Do not play with the temperature/pressure valve since this could change the release points (especially on an older installation). A water heater can be a real bomb if that valve malfunctions - The world altitude record for a tank is about 200 feet after going through 2 stories of a house and the roof.

Dick

While I agree that one should not "play" with the T&P valve that does not mean that it should never be touched. On the contrary, it should be periodically tested by raising the lever to the fully open position and letting it blow for a second or two before releasing the lever. Do not "tease" it by barely opening it for less than a second as it needs a good flow to wash out any scale that may have developed. Testing the T&P valve twice a year at minimum is just good sense but don't test it more often that every three months or you might have problems. It is also a good idea to have a spare valve in case the one installed fails the test.

Glad this issue with the pressure relief valve was cllarified, I was always told to open the valve once a year so as to relieve the working parts of any "stuff" that might accumulate that might prevent the valve from operatiing when it should. I remember a neighbor a couple years ago found that his valve was passing some water and was unable to shut it off just because stuff had built up in the valve and apparantly did not allow the valve to close all the way.

I think what the heater manufacturers are doing (probably pushed by their legal department) is to set all heaters at 120 for the "safety" issue and allowing the end user to then adjust the temp depending on their own personal needs. Sometimes I guess 120 just is not high enough if there is a demand in a short period of time since as that first demand of hot water is used, cold water is bringing brought in reducing them temp a bit......if I understand it correctly. Seems to make sense.

Thanks for the info