Best Water Heater Temp

David_16 · January 30

Finally had my new Weil McLain EcoTEC boiler and indirect installed today. I'm very happy with the install, it looks like they did a nice job.

My old 40 gallon indirect didn't have a mixing valve and was probably set around 125. New 45 gallon indirect has a mixing valve set to 120.

What should I set the tank to? Is there a range that's safe/ideal?

EdTheHeaterMan · January 30

According to some herein, to kill bacteria that may grow in a water heater at 120°F, you should store your water at 140° and mix cold to get it to the desired temperature. My wife would kill me if I provided ONLY 120° at the shower.God rest her soul I set my mixing valve to 125°F but I could not ever use only HOT in the shower. I had to add cold to get the water to 118° where I liked it.

You got to make the women happy!

pecmsg · January 30

ASHRAE recommends 140*f for 1 hour to kill legionnaires disease.

Point of use no more then 120*f.

EdTheHeaterMan · January 31

pecmsg said:
ASHRAE recommends 140*f for 1 hour to kill legionnaires disease.
Point of use no more then 120*f.

I agree but I didn't have to live with ASHRAE. I had to live with PAT. and she was the higher authority having jurisdiction back then. ...and that was before the NEST thermostat came out.

jumper · January 31

Hot enough to hurt but not hot enough to scald. Difficult to achieve such precision.

EdTheHeaterMan · January 31

jumper said:
Hot enough to hurt but not hot enough to scald. Difficult to achieve such precision.

That temperature is actually different for each person. I think that teenagers have the greatest tolerance for hot water. They can stay in the shower for over 40 minutes if the hot water lasts that long. That is why i have a valve on the water heater that would slowly close the water to the tank after 15 minutes. I don't think my 42 year old daughter ever found out about it. My son figured it out when he started to work for me in the business. It is disconnected now.

EBEBRATT-Ed · January 31

@EdTheHeaterMan My boys would take 45 min showers if you let them. More than once after a knock on the door and a warning I would go downstairs and shut the hot off.

David_16 · January 31

So 140? The installer wanted to set it at 155 but that sounded very high to me.

Jamie Hall · January 31

Short answer -- water heater at not less than 140/ Mixing valve to taste -- but it really shouldn't be more than 120, even if you have temperature controlled mixing faucets.

David_16 · January 31

I know he set the mixing valve at 120. My question is what to set the water heater at. "Not less than 140", means 140, 145, 150? 155 definitely would be too hot? Since there's a mixing valve in place, I'd think there would be a pretty tight ideal range to use.

EdTheHeaterMan · January 31

140°. the hotter the tank the more it costs to heat and store it.

Jamie Hall · January 31

Most modern hot water heaters can't be set much above 140 anyway.

ChrisJ · January 31

Jamie Hall said:

Most modern hot water heaters can't be set much above 140 anyway.

Its funny you say that because the last two Bradford White heaters I've bought ran 140 almost set on "normal". I have no idea why this is or how hot the higher settings go as 140 was the target anyway.

HVACNUT · January 31

Is it a WM indirect or standard coil HX indirect? If it's a reverse indirect, tank temperature gets set 5° lower than boiler setpoint for the indirect. In your case, Priority 1 (DHW) 180° setpoint. Tank temperature 175°.

Whats the temperature rating on the tank? Higher tank temperature acts as higher capacity when using a mixing valve.

yellowdog · January 31

Setting any domestic tank temp at 175° sounds like risky, bad advice to me.

ChrisJ · January 31

yellowdog said:
Setting any domestic tank temp at 175° sounds like risky, bad advice to me.

Why is that?

ethicalpaul · January 31

Scalding risk in case of mixing system failure would be my thinking.

I believe my water heater came set to 120 from the factory. I have it at 130. I think the legionella risk in residential water systems is greatly exaggerated. Aren't most cases from cooling towers or fountains throwing tons of warm water mist into the air? Are there any cases known from showers?

Apparently a main cause is the inhalation (aspiration) of water or ice while in the hospital (I assume from people who have difficulty eating/drinking due to various illnesses/age)

Intplm. · January 31

@David_16

Set the water heater temp anywhere between 120 and 130 degrees and you should be fine.
I have seen code requirements and department of public health rightings offering these temps.
Find your comfort level there and don't get scolding water on you.
120 deg is what mine is set to and that's plenty.

David_16 · January 31

120-130 sounds low if I've got a mixing valve at 120. Right now, it's 145 and i want to see how long of a shower that gives me. If a long shower is no problem, I'll drop to 140 as that seems to be the "right" answer here.

Intplm. · January 31

David_16 said:
120-130 sounds low if I've got a mixing valve at 120. Right now, it's 145 and i want to see how long of a shower that gives me. If a long shower is no problem, I'll drop to 140 as that seems to be the "right" answer here.

It really isn't. The temp you are leaning toward is scalding hot and could hurt some one.

hot_rod · January 31

If you have a mixing valve installed, the tank needs to be about 20 degrees hotter than the mix valve setting. So 140- 145 is adequate, with a 120 setting on the valve. Unless you need more drawdown, no need to go above 140 or so.
You could set to 110 or 115 actually, that is plenty warm for showers.

I like the dishwasher to run hot so I'd use the temperature boost function if you go down to 110F.

Keep in mind tank life decreases with higher temperature operation, and more mineral precipitation. Hot, hard water will require you descale the mix valve occasionally. It comes down to how much water flows through it as far as maintenance intervals.

Some brands and models of thermostatic mixing valves fail safe, that is is cold is interrupted the valve closes to a dribble. A scald protection feature.

HVACNUT · January 31

yellowdog said:

Setting any domestic tank temp at 175° sounds like risky, bad advice to me.

Read the Turbomax manual and you shall be enlightened.

jumper · January 31

How bad can bacteria be? After a few seconds hot water is diluted.

yellowdog · January 31

Just because something says you can, does not mean you should. I will personally not set anyone's tank higher then 140° and i am not a fan of the tank in tank type of indirects. If you need more tank temp than that, you are band-aiding some other problem. Raising tank temps that high is the same to me as putting a tigerloop on an oil line that's been in place for 20 years.

RollCNY · January 31

yellowdog said:
If you need more tank temp than that, you are band-aiding some other problem.

When I had my indirect set at 140 to 142° (inexact measuring location), I would find that the first shower of the morning would have a spot, about 2 minutes in, that you would feel the water cool (not cold, but noticeable change) that would last maybe 15 seconds, and then go away. It only happened when the boiler was starting from full cold, but not if it was in mid heating cycle. This cooling didn't bother me, but it displeased the mrs.

I assumed this was just how long it took to open zone valve, open damper, light burner, heat water to higher than my 120° mixing valve setting, so I incrementally raised my storage water tank temp to something like 147 to 150°. At that temp, in no circumstance do I (or more importantly she) feel the cool spell, and I feel I have essentially infinite hot water for my use case.

Not to be daft, but since this is a band aid, what was the correct fix?

WMno57 · January 31

jumper said:
How bad can bacteria be? After a few seconds hot water is diluted.

It's Legionella, it causes Legionnaires' disease. Old people and people with compromised immune systems are at risk.

It is usually spread by breathing in mist that contains the bacteria

I.e. taking a shower.

At 60 °C (140 °F) – 90% die in 2 minutes (Decimal reduction time (D) = 2 minutes)
At 50 °C (122 °F) – 90% die in 80–124 minutes, depending on strain (D = 80–124 minutes)
48 to 50 °C (118 to 122 °F) – can survive but do not multiply
32 to 42 °C (90 to 108 °F) – ideal growth range

https://en.wikipedia.org/wiki/Legionella
Not all water has Legionella in it. Even if the water has it, if you are young and healthy, not as big a deal.

People of any age may develop Legionnaires' disease, but the illness most often affects middle-aged and older people, particularly those who smoke cigarettes or have chronic lung disease. Immunocompromised people are also at higher risk. Pontiac fever most commonly occurs in those who are otherwise healthy.

https://en.wikipedia.org/wiki/Legionnaires'_disease#Diagnosis

hot_rod · January 31

It is more of a personal choice as opposed to right or wrong DHW temperature. If legionella or bacteria frightens you, elevated temperature handles that. More capacity from a smaller tank with higher temperature.

Keep in mind the control is near the bottom of DHW tanks. A 140 reading there will give you 150 or more at the top of the tank due to stratification.
Unless a recir pump is stirring up the tank.

The free Lochinvar online simulator lets you play DHW temperature and capacity games.

MarkC · January 31

I have an indirect with a mixing valve. I target 140 tank temp and mix down to 120. However, I have found the 140 tank target temp elusive because the heater seems a little slow to turn off once 140 is reached in the tank plus the after-run feature in the heater further boosts the tank temp after the heater has turned off. So, my tank temp SETTING in the heater control is about 125 in order to achieve actual tank temp of 140.

Intplm. · January 31

No! It is a very serious safety concern.

140 degree water is not acceptable for bathing as it is proven to burn within seconds of contact.
Never set a persons water to that high and dangerous temperature.
Burns from scalding hot water can cause serious injury in the most dangerous room in a building, that being the bathroom.
If a owner wants to set the water temp differently then that's on them. But do not do it otherwise.

The title of this post is "Best water heater temp"

Those who are most susceptible to injury are the young, old and those who have illnesses are the most vulnerable to this as well as legionella exposure.

jpsr · February 1

My NTI boiler has a legionella setting that periodically raises the indirect water temperature to 140f. The frequency of this is user selectable. I believe this is more of a issue in stagnant systems, or branches that are seldom used. Most systems turn over the contents of the tank in a day or two, so unless there is a significant contamination in the supply I believe this shouldn’t be a problem.

Intplm. · February 1

jpsr said:
My NTI boiler has a legionella setting that periodically raises the indirect water temperature to 140f. The frequency of this is user selectable. I believe this is more of a issue in stagnant systems, or branches that are seldom used. Most systems turn over the contents of the tank in a day or two, so unless there is a significant contamination in the supply I believe this shouldn’t be a problem.

I agree, as long as the water temp of 140 deg does not reach the discharge point of use.

This sounds like a very good feature in helping prevent legionella.

Best Water Heater Temp

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