What is the “actual” water temperature in my home really?

The post previous to this was about water heater Deadband.  This post is related in that it shows us another way that deadband affects use of hot water and the safety concerns posed by deadband.

Very high water temperature

Very high water temperature

How difficult can it be to figure out what the water temperature in a home is?

In the State of Washington, Licensed Home Inspectors are required to report when the water temperature is above 120 degrees and then advise the client that the recommended high temperature is 120 degrees Fahrenheit.

What I have found, over and over again, is that if I take the temperature reading at the kitchen—-where I start my inspections—it might read 118 degrees F and falsely be led to think that the temperature is OK.

Because most kitchens have mixing valves, I know that sometimes the temperature might actually be a little higher than that—so I know I am going to check it somewhere else too.

After the kitchen, the next part of the inspection usually moves to the highest level of the home.  The idea is that you want to test all the plumbing from the highest level and then down to the  lowest level so that by the time you get to the crawl space it will be flooded by all the leaking so that you might not even have to do the crawl space.  Of course this is meant tongue-in-cheek—but you get the idea.

Lots of bathrooms—at either the tub or the vanity—may have faucets that are not mixing valves so that it is easier to get an accurate temperature reading at those locations.  That said—lots of newer tub and shower fixtures have mixing valves with anti-scald features which again prevents accurate temperature readings.  Regardless, I usually check the temperatures at this bathroom and the temperatures are usually consistent with the reading (or very close to it) that I got at the kitchen.

By the time I have gone all through the other levels of the home and finally get to the basement (if there is one), I often find the laundry sink which almost always has separate faucets, I know I can get a good temperature reading there.  I take the temperature and all of a sudden it is 130 degrees Fahrenheit.

At first you scratch your head and say, “How can this be?”

The answer is that “time has gone by”—-perhaps an hour or two or three.

When the inspector arrives at the inspection, the water heater has been sitting idle and has been cooling off.  Because there has been no demand for hot water it may have cooled all the way down to its low point—the temperature at which the thermostat would normally kick in and start heating the water.  However, these simple thermostats operate the best with a pronounced change in temperature for them to kick-in.  The temperature of the water might go even below the normal kick-in temperature.  During the normal everyday operation of these thermostats, the temperature differential is likely between 5 and 10 degrees but can vary up to 25 degrees—the difference between whether a baby gets scalded or not.

These swings in temperatures are especially true of vacant homes.

The moral of this story is that it is best protocol to take the water temperature later in the inspection than it is to take it right at the beginning of the inspection—for the most accurate indication of what the temperature actually is.

In the end, it is not difficult to figure out the temperature—but the best protocol must be followed.



Charles Buell, Real Estate Inspections in Seattle


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  1. James Quarello says:

    I would have to say my experience is different. I begin inspecting from the top down, so as I work my way eventually to the kitchen, I find the temperature goes up. This I attribute to be closer to the water heater. The biggest problem I find are with tankless coils installed in boilers. Many, especially if they are older, do not have mixing valves.

    • Charles Buell says:

      Jim, the interior portion of my inspections start in the kitchen and then I go to the highest and furthest locations—and then work my way down. I run enough water at all locations so that temp differences due to distance are not a factor. When I first started fooling around with these temp differences I used to go back and check to see if the temps were higher at the other locations like they were at the end of the inspection—they always were.

  2. What can cause hours or days long reduction of hot temps to tepid from all taps? (Have only indirect access to the tank, in small shared residence, 7 adults total). Live in a very soft water area. Landlord cranked the heater up (natural gas, had been set between A & B), now tap temp is 130°F.

    • Just to clarify, previously the nominal temp was slightly over 120F. I’ve just acquired a meat thermometer, so only now do I have accurate readings. The “tepid” temps were barely over sensible body temperature, so faint warmth could be felt. Had persisted for days. Previous incidents over the last few years had either just lasted hours or “corrected” with a bit of fiddling with the dial, almost as though the thermostat was snoozing and needed to be woken up!

    • PS #2;
      Previously (when I had more access), I was especially worried that the pilot had gone out, but that was never the case. (Visible through inspection window once the cover was removed.) Doubt that “debris draining” has ever been done, and believe the heater is 10+ yrs old. Looks to be in good shape, however.

      • Charles Buell says:

        Brian, I will respond to all of your comments here. Water heater “deadband” may be at play or there may be a faulty thermostat—or other issues. I would see if you can’t get the landlord to have a real plumber take a look at the heater and figure it out. The answer is not to crank up the heater to 130 degrees F unless it is done in conjunction with a tempering valve. See my post about deadband.


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