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

How complicated can it be to take a temperature reading?

In the State of Washington, when a Licensed Home Inspector tests the temperature of the water, they 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.

hot water

Water temperature way too hot!

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 lead me 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 highest to lowest 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.  Not really–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.  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 temperature at this bathroom and usually it agrees with the reading (or very close to it) that I got at the kitchen.  In Washington State, limiting water temperature to less than 120 degrees F has been required at tubs/showers since 2003, so it is a good idea to check the tub and shower hot water temperatures of these newer homes.

By the time I have gone all through the other levels of the home and finally get to the basement, 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.

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 you get to the inspection, the water heater has been sitting idle and cooling off.  Because there has been no demand for hot water it has 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 need 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 every day 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.

And it is not just a concern for babies.  As our population is aging, the elderly and infirm are also vulnerable to scalding.

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.

While taking an accurate temperature reading in the context of a home inspection, proper adjustment of the temperature can be even more difficult–but that may be the topic of another post.



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.


  1. […] how water heaters sometimes run out of hot water faster than they should, and another on the different temperatures that will be produced by a water heater during different stages of the heating […]

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