Thread: Safe maximum temperature for water heaters

Some folks like their hot water heater to be set higher, thinking that they can mix cold water with it thereby increasing the volume of hot water for baths etc. I read a few years ago that setting the temp too high caused a lawsuit for the installing plumber in that the homeowner died from getting into a tub that was too hot for a person with diabetes. It seems that with diabetes, your feet can become numb and you would not be able to feel the danger from the hot water.

With this in mind, I would set the temperature setting to Low and instruct the occupant by disclosing in writing that high water heater temperatures can cause loss of life and to carefully, gradually raise the temperature to their desired setting at their own risk. I would go so far as to have them sign that they understand the disclosure and keep a copy for my records.

Don't you just love lawyers?

Water heaters should be set to 120ºF per the plumbing code. There is more though, the tub and shower valves (if single handle) are supposed to have a temperature limit that is set when the valve is installed. For private residential showers and tubs this setting is 115ºF for public showers it is 110ºF Now if they have a two handle tub and/or shower valve then they will need to have a access installed with a tempering device to set the temperature for the tub and shower.

As for turning up the temperature, the water heater manufactures sell heaters that store the water well above 150ºF, with a tempering valve installed right at the top of the tank. This way the water leaving the tank is still 120ºF meeting the code. These tempering valves must meet the newest standards which is when the tempering valve fails, it fails to cold. This way there is no way the tempering valve can send scalding hot water out. The reason the manufactures are selling units like this, is to come out with a smaller tank that can out perform duel 50 gallon water heaters and even a single 75 gallon heater. Bradford White has a model that will deliver very close to the same amount of hot water in the first hour as a 75 gallon unit which is 155 gallons for the first hour. Their 50 gallon tank that uses this technology delivers 200 gallons of hot water in the first hour.

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Originally Posted by Loren Sanders Sr.

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With this in mind, I would set the temperature setting to Low and instruct the occupant by disclosing in writing that high water heater temperatures can cause loss of life and to carefully, gradually raise the temperature to their desired setting at their own risk. I would go so far as to have them sign that they understand the disclosure and keep a copy for my records.

Don't you just love lawyers?

If I were you I would not touch their water heater settings. I would measure the water temperature at a sink like the kitchen or laundry sink note the set temperature that the water heater is delivering, then measure the temperature at the tub and showers, and note what it is in your reports.

If you make an adjustment on their water heater even if it is to lower it to a safe setting, and the gas control valve fails or thermostat(electric heaters) fails and puts out scalding hot water, you are now liable since you where the last one to touch it.

I provide this pic in my reports. I think I got it from Jerry Peck a number of years ago.

Originally Posted by Gunnar Alquist

I provide this pic in my reports. I think I got it from Jerry Peck a number of years ago.

Thanks Gentlemen, You have answered the question.

Originally Posted by Gunnar Alquist

I provide this pic in my reports. I think I got it from Jerry Peck a number of years ago.

I got that from A. O. Smith.

I don't know if they still do, but they used to give out labels free so you could stick them on their water heaters (or any water heater for that matter).

I used to order those self-adhesive peel-n-stick labels 50 at a time, no charge, not even shipping. Cool.

I like to include this in my reports in the "Water heater" section:

The water heater thermostat should be adjusted so the water temperature doesn't exceed 120 degrees to prevent scalding. Visit the following site: Injury Prevention Policy - Tap Water Scalds

That's a good question. Unfortunately, folk will set water heaters at what ever temperature they think best. When inspecting the water heater, always set the temperature back to its original setting. Indexing the control knob with a pencil mark is not a bad idea.

In one of the counties we service (Frederick MD), new construction rules state that the water heater must be set at 130 degrees. It appears that the move to lower temperatures in water heaters has led to an increase in Legionella bacteria in water tanks. Now what we tell clients is that to avoid issues, set the water heater for 140-145, and install a mixing valve directly at the tank outlet to bring the water supply to the taps down to 120.

Setting the heater to anything less than 150º F will not kill any bacteria. Thing is 150º water will scald instantly. This is one of the reasons the tempering valve must meet a standard that when the mixing/tempering valve fails, it will always fail to cold.

I just did a job that has tankless water heaters set to 150º and they have tempering/mixing valves installed at all the hand sinks. At the time this place was built the fail to cold standard was not in place. The tempering/mixing valve did fail, and it failed to hot. Luckily no one got scalded or hurt. Installed the new mixing valves (replaced all the others) and demonstrated to the owner by turning off the cold supply with the faucet running full hot, the mixing valve shut down the hot supply side almost immediately.

I am not at my shop right now so I can not tell you which standard it is.. If I recall its an ASSE standards 1016, 1017, 1069 and 1070, there are more but those are the most common.

Originally Posted by Welmoed Sisson

In one of the counties we service (Frederick MD), new construction rules state that the water heater must be set at 130 degrees. It appears that the move to lower temperatures in water heaters has led to an increase in Legionella bacteria in water tanks. Now what we tell clients is that to avoid issues, set the water heater for 140-145, and install a mixing valve directly at the tank outlet to bring the water supply to the taps down to 120.

Yes but that's only with electric tanks, manufacturers have a pre setting that doesn't allow the tank to drop to 60 degrees thereby keeping legionella at bay. Just don't turn off your breaker when going on vacation

Originally Posted by Welmoed Sisson

In one of the counties we service (Frederick MD), new construction rules state that the water heater must be set at 130 degrees. It appears that the move to lower temperatures in water heaters has led to an increase in Legionella bacteria in water tanks. Now what we tell clients is that to avoid issues, set the water heater for 140-145, and install a mixing valve directly at the tank outlet to bring the water supply to the taps down to 120.

Welmoed, This seems to me to be the most desirable solution safety wise but probably more costly to keep the WH at that high setting. Figure what a trip to the Doc is and add that to your cost if you keep the temp too low. but beware of scalding because that could cause a high Doctor bill also. All in all, I like this solution best. Thanks for posting.