Reuben's Home Inspection Blog


There is no perfect temperature for your water heater

What's the best temperature to set your water heater to?  There's no single great answer.  The American Society of Sanitary Engineering Scald Awareness Task Group recently released a white paper on this topic, which essentially says that there is no perfect temperature to set you water heater to.

What's a safe temperature for water?

On the side of most water heaters you'll find a warning that says water temperatures of 125 degrees Fahrenheit can cause burns or death.  To be safe, the water coming out of the plumbing fixtures in a home shouldn't be any hotter than 120 degrees.   The handy photo below (courtesy of Charles Buell)  shows how fast second and third degree burns can happen at temperatures that any new water heater is capable of producing.

Water Temperatures

Just turning down the temperature at your water heater until you're at a safe 120 degrees isn't enough to solve potential scald hazards because the thermostat on a water heater isn't designed to keep the water at a constant temperature; it's just designed to keep the water within a certain range of temperatures.  Seattle home inspector Charles Buell has posted a couple different blogs explaining how this works - one explaining 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 cycle.

During a recent inspection of a large home that was heated with two high-efficiency water heaters, I found quite a range in temperatures.  When I first turned the hot water on at a fixture, the water temperature started out cool; this was because the water in the hot water pipe had cooled down to room temperature.  As the hot water from the top of the tank arrived at the plumbing fixtures, the water temperature rapidly jumped up to nearly 154 degrees - this was hot enough to cause first degree burns instantaneously, and second degree burns within one second.

Dangerously hot water

The water only stayed at this temperature for a few seconds; it quickly dropped back down to about 135.  While there was a tempering valve installed to mix cold water in with the hot water right at the water heater outlet, it wasn't enough to completely control the water temperature at the fixtures.

Minnesota has no requirements for residential water temperatures.  Anti-scald devices are required in all new or remodeled showers or shower-bath combos in Minnesota (4715.1380 Subp. 5), but this does nothing to address the final temperature of the water coming out of a fixture.   Anti-scald devices only help to prevent people from getting scalded by a sudden swing in temperature while taking a shower.  With old shower valves that didn't have the anti-scald feature, if a toilet would flush while someone was taking a shower the pressure on the cold water line would drop, quickly increasing the water temperature at the shower.

Lower Temperatures Allow Bacteria Growth

It seems as though the solution to help prevent accidental scalding would be to turn down the temperature at the water heater to say, 115 degrees, but lower temperatures actually create other problems.

At temperatures below 135 to 140, Legionellae bacteria, which is responsible for Legionnaires' Disease, can survive and even multiply in the water heater tank.  Estimates by say that up to 600,000 cases of Legionnaires' Disease are misdiagnosed as pnemonia each year, because this is something that isn't tested for in hospitals.   The diagram below shows the time it takes to kill Legionellae Bacteria at different temperatures.

To help prevent bacteria growth, the ASSE recommends keeping the water in your water heater tank at about 135 - 140 degrees Fahrenheit.

Water Temp Effects on Legionellae

Of course, this creates a scalding hazard.

So What's the Answer?

To help prevent bacteria growth and to lower the risk of scalding, have a plumber install a tempering valve and crank up the temperature at your water heater to about 135 - 140, as ASSE recommends.  Last year I wrote about how I installed a tempering valve on the hot water outlet at my own house in order to get more water out of my water heater.  These valves would be a good thing to install in every home.  A tempering valve allows you to keep the water at a dangerously high, Legionellae-killing-temperature inside the water heater tank, yet it mixes cold water in with the hot water right at the outlet, making it so you don't get this hot water at the rest of the fixtures in your home.

Tempering valve function

As I mentioned in my story about the recent inspection with dangerously hot water, a tempering valve won't guarantee safe water temperatures, but it will get you a lot closer.

Reuben Saltzman, Structure Tech Home Inspections


Comment balloon 55 commentsReuben Saltzman • April 17 2012 03:32AM


Reuben- Thanks for the very informative post. We all need a reminder to check our water heater temps and the tempering valve sounds like a great precaution and investment.

Posted by Christin Mahrlig (The Allen Tate Company) almost 7 years ago

Christin - thanks.  Ever since I installed one of those tempering valves, I haven't run out of hot water.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) almost 7 years ago

Rueben, congratulations on you FEATURED post. It is  a great information everyone can use.

Posted by Kwee Huset, Venice Florida Homes For Sale (Kwee Huset Realty) almost 7 years ago

Great post, but who uses water tanks anymore.

By the way, legionella is far more likely to occur in the moisture of the air conditioning system then from a hot water tank. Standing water in those systems is a problem. 

Posted by Erv Fleishman, Luxury Prop Specialist Realty Associates (Realty Associates) almost 7 years ago

Hi Rueben,

I will have to look into this device.

Good news for home owners with a large brood.

Have a great day.

Best, Clint mckie

Posted by Clint Mckie, Desert Sun Home, Comm. Inspection 1-575-706-5586 (Desert Sun Home, commercial Inspections) almost 7 years ago
Great blog and great job. Keep up the good work and good luck to you this year. Thanks.
Posted by JOSH EVANS *JoshEvansHomes 516-655-5000 (Village Properties of Mineola, LLC) almost 7 years ago

Kwee - thanks.

Erv - your link takes me here - .  Interesting take on AC systems.  That makes sense, but I haven't heard about it.

Clint - I think we're going to start seeing more and more of these.

Josh - thanks, same to you.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) almost 7 years ago

I will bookmark this post and read it again and also share it with others.

Posted by Gita Bantwal, REALTOR,ABR,CRS,SRES,GRI - Bucks County & Philadel (RE/MAX Centre Realtors) almost 7 years ago

Thanks, Gita.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) almost 7 years ago

My father had legionnaire's disease. It almost killed him. My problem with leaving the water heater temperature high is wasting energy. I suppose I could set it high for a week or so every now and again to disinfect the tank. 

Posted by James Quarello, Connecticut Home Inspector (JRV Home Inspection Services, LLC) almost 7 years ago

Over hot also means the burner is likely shortening the life of the tank itself, Interesting graph too. Thanks

Posted by Scott Seaton Jr. Bourbonnais Kankakee IL Home Inspector, The Home Inspector With a Heart! (SLS Home Inspections-Bradley Bourbonnais Kankakee Manteno) almost 7 years ago

Reuben pepole will find this to be a real helpful blog post.

Posted by Carl Winters almost 7 years ago

Reuben, what is the right solution? To save energy, you turn it down but to kill off bacteria you should turn it up. Is there a happy medium?

Posted by Michael Setunsky, Your Commercial Real Estate Link to Northern VA almost 7 years ago

Best thing to have is a tankless water heater. For a whole house use it needs to be gas though.

Posted by Than Maynard, Broker - Licensed to List & Sell - 405-990-8862 (Coldwell Banker Heart of Oklahoma) almost 7 years ago

Thanks Reuben.  Very informative.  Always wondered why the water temperature sometimes fluxuates during a shower.  I will be looking to install a tempering valve.

Posted by Paula McDonald, Magnolia Realty ~ Granbury, TX 936-203-0279 (Magnolia Realty ~ Granbury) almost 7 years ago

I have had this on my radar for a few years now. My beef was that the water was too hot for instant use and I had to find that mixture of cold/hot until I could use it. I did not need scalding water on stand-by all the time. I finally found the right temperature for hot water with very little mix...I had to experiment a while. Good post

Posted by Richie Alan Naggar, agent & author (people first...then business Ran Right Realty ) almost 7 years ago

James - first off, thanks for sharing about your father.  I guess the Legionella thing must really hit home for you.

Secondly, quit your whining about hot water costs.  I haven't forgotten about what you have in your house to heat your water and keep it warm.  What do you pay, two bucks a month ;) ?   I calculated my monthly water heating costs to be about $12 - $15 per month.  I've heard that every 10 degrees will be about another 10% more expensive.  So lets say I spend an extra $3/month to crank my water heater up from 120 to 140... big deal.  

Scott - yeah, I'm sure you're right about that.

Carl & Ceil - thanks.

Michael- I guess you can't have the best of both worlds.  Personally, I think it's worth the extra money in water heating costs.

Than- tankless water heaters have pros and cons.  Google 'cold water sandwich'.

Paula - I think that's the way to go. 


Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) almost 7 years ago

Richie - I have that problem too.  Before I had kids, I never had to worry about this and I just kept scalding water stored in my water heater without any problems.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) almost 7 years ago

Wow Reuben, very insightful. Thanks for sharing this knowledge.

Posted by Dominique Britton, Experience the Difference in Real Estate Services ( Realty LLC - 678.250.5022) almost 7 years ago

Excellent post and reblogged!  I think I'll even link this one to my FB page since it is excellent safety information that could prevent a serious burns to young children (and adults too for that matter).

Posted by Kate McQueen, Tailored service for your real estate needs! (CB&A Realtors) almost 7 years ago

Reuben, thanks for all the nods.  The tempering valves do get us a lot closer to the solution.  I would like to see tanks coming from the store with a LOT more insulation around them---especially the electric ones.  As long as gas has a vent they will be basically impossible to adequately insulate---although the direct vent ones would be better.  I would like to see tanks with a minimum of 4" of spray foam around them.

Posted by Charles Buell, Seattle Home Inspector (Charles Buell Inspections Inc.) almost 7 years ago

Very informative! I would like to re-blog this for my readers - great safety tips. Thanks Rueben.

Posted by Carla Harbert, RE/MAX Omega, Brunswick Ohio (Full Time REALTOR in Ohio) almost 7 years ago

I did not know what temps were dangerous. Thanks for the info.

Posted by Tim Lorenz, 949 874-2247 (TIM LORENZ - Elite Home Sales Team) almost 7 years ago

Properly insulated lines and a max temp of 120 degrees at least helps save you some $$$.

Good post, thanks for sharing it.

Posted by Anthony Daniels, SF Bay Area REO Specialist (Coldwell Banker) almost 7 years ago

Hi Reuben, great post and you are right, there is no right answer. Keeping it that hot would waste energy and casue high billes, but then there is the matter of safety.

Posted by Sandy Acevedo, RE/MAX Masters, Inland Empire Homes for Sale (951-290-8588) almost 7 years ago

Reuben, Very nice post.

This is the great crux of hot water systems. Too hot for safety versus the bacterial lagoon.

I actually discuss this very topic with my clients and then let them make a decision. We have to report temperatures over 120 in Wa. St. and they know why. 

Posted by Donald Hester, NCW Home Inspections, LLC (NCW Home Inspections, LLC) almost 7 years ago

This is great information and I will reblog it to family and friends.

Posted by Debbie Reynolds, Your Dedicated Clarksville TN Real Estate Agent (Platinum Properties) almost 7 years ago

Nice article on hot water Reuben.

There are wide ranges of hot water systems in homes.  You have some nice photographs of clean modern appliances and fixtures.

Not too long ago I was at a house with separate (non-mixed) hot water faucet and cold water faucet at the bathroom sink.  The hot water was heated from a steam boiler.  I observed 203F at the hot water faucet.

I guess the good news is that they can eliminate all legionellae in all the pipes and faucets.

Another interesting study is the bacteria growth in the various distribution pipes (CPVC, PEX, Copper).

Posted by Jim Mushinsky (Centsable Inspection) almost 7 years ago

I despise that feeling in your hands that lasts three to four seconds when you've put your hands under water that's too hot and you're waiting for them to go back to normal. I don't believe that it has ever happened to me where it didn't make me think for a moment about those who've suffered severe burns to their entire bodies. I just cannot imagine...

Posted by Margie Kopp Sorrell, Lake Oconee Real Estate (Coldwell Banker Lake Oconee Realty and Lake Country) almost 7 years ago

I've got a question for you, Reuben.  Does a water heater wear out faster when it's kept at the hottest temperature all the time?  Is there a risk?  My brother keeps his at the max all the time, and that's scarey to me.


Posted by Raymond Denton, Simple Man (Academy Mortgage Corporation) almost 7 years ago

Making a call to a plumber tomorrow morning. I never knew that about Legionnaire's disease.  This was a great post!

Posted by Kathryn Maguire, Serving Chesapeake, Norfolk, VA Beach ( (757) 560-0881) almost 7 years ago

I don't think in PA we have rules about temp, but this is good info to know.

Posted by Erica Ramus, MRE, Schuylkill County PA Real Estate (Erica Ramus - Ramus Realty Group - Pottsville, PA ) almost 7 years ago

Dominique - thanks for reading.

Kate - Thanks.  I know this wouldn't be nearly as much of a focus for me if I didn't have two little ones at home.

Charles - yeah, I've heard you beating that drum before :).  Good chatting today.

Carla - thanks for the reblog.

Tim - my pleasure.


Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) almost 7 years ago

Anthony - Insulated water lines... some day.

Sandy - yes, this will certainly cost a little more in energy, but I think it's worth it.

Donald - after writing this, my discussions about water temperatures will certainly be a little longer :)

Debbie - Thank you.

Jim - thank you, sir.  203 degrees?  Yikes!  No worry about bacteria there.


Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) almost 7 years ago

Margie - me too!  I once accidentally stuck my arm in a vat of boiling water my accident; boy was my hand red.

Raymond - yes, keeping the water at a hotter temperature will surely wear things out faster.  The water heater in my home has a 12 year warranty, and the one before it was replaced after 11 years.  If the water heater I have now last the full 12 years, I'll be happy.

Kathryn - thanks!

Erica - definitely; it's all about safety.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) almost 7 years ago

Often when houses are vacant for a period of time, the water in the tank smells bad.  Particularly so on well water-fed heaters.  This is great info!  I tell people about 130F and that a tempering valve is always a good thing.  Few listen.

Great blog Reubs!

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) almost 7 years ago

Jay - I know exactly the smell you're talking about.  Yucky.

Shesh - you make a very convincing argument, and you bring up many valid points - especially the first one (stupid!!!!).  I'll have to let those folks over at ASSE know that they got this one all wrong, and there's probably no such thing as Legionella.

Perhaps you're right, and we're becoming a "sociaty of dumbies."

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) almost 7 years ago

I resisted the temptation Reubs to say anything about that last comment, since it is your post.  As tongue in cheek and sarcastic as you know I like to be on some posts, even I would have had a hard time coming up with a comment that, um, creative!

There are so many grammatical and spelling errors it would make the NEA proud (the true NEA goal - dumb them down...).

I was in a house the other day that was obviously kid central.  It appeared that must be why the people were selling - no room!  The water temp at the kitchen sink was 187F!  I had to leave the sellers a note.  Perhaps not my purview to do that, but I was concerned for everyone there. 

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) almost 7 years ago

Oh, where did you get that chart?  Is it copyrighted or can I swipe it and use it?  It's got a good credit, so the author probably wouldn't be too upset if I was to include it in my reports, or a link to it.

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) almost 7 years ago

Jay - It's hard not to leave a creative comment when you get an anonymous comment like that, isn't it?  For future reference, I'm definitely not 'touchy'.  Comment away :)

I heisted that chart off the white paper from the ASSE that I linked to - .  

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) almost 7 years ago

I know you're not touchy!  I tease you as much as I do anybody.  I just thought you deserved the opportunity to comment on it first!

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) almost 7 years ago

Reubs, I have a new Burnham high efficiency boiler with an indirect water heater. My gas bill, I just converted, all winter was around $115 a month. Still have to wait and see how much just hot water will be during the warm months. And for the record I wasn't whining, I'm just being cheap ;)

Posted by James Quarello, Connecticut Home Inspector (JRV Home Inspection Services, LLC) almost 7 years ago

Always informative! I knew about the scald hazard but the Legionnaires' Disease aspect I don't think I had ever encountered before.

Is it cowardliness that makes most flamers anonymous?

Posted by Marshall Brown, BSEE, CHI (Mid America Inspection Services, LLC) almost 7 years ago

Thanks Jay :)

James - yeah, I figured :).  I'll stay tuned to hear what your water heating costs are.

Marshall - Thanks.  As for the flamers, it's either cowardliness or they're a part of the sociaty (sic) of dumbies (sic) ;).


Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) almost 7 years ago

Great tips. Thanks!

Posted by Bill Fields (Bill Fields Learning Systems) almost 7 years ago

What an informative and well written blog. Thanks for the education!

Posted by Elisa Uribe Realtor #01427070, California Homes for Sale in the East Bay (Golden Gate Sotheby's International) almost 7 years ago

Wow, you always hit such interesting topics! I never thought about the temperature of a water heater, but will now!

Posted by Sylvie Stuart, Home Buying, Home Selling and Investment - Flagsta (Realty One Group Mountain Desert 928-600-2765) almost 7 years ago

GREAT info. I just got a new heter a few months ago and need to chck it out, and put the temepring valve on it!


Posted by Travis "the SOLD man" Parker; Associate Broker, email: / cell: 334-494-7846 (Team Linda Simmons, Enterprise, AL 36330) almost 7 years ago

Hi Reuben, excellent post and really enjoyed the graphics.  Thanks for sharing.

Posted by Bob Miller, The Ocala Dream Team (Keller Williams Cornerstone Realty) almost 7 years ago

Reuben, thank you for the valuable information, one more thing to watch for in my rentals.

Posted by Bob Crane, Forestland Experts! 715-204-9671 (Woodland Management Service / Woodland Real Estate, Keller Williams fox cities) almost 7 years ago

Reuben - great information, thank you for sharing, got a temperature valve at my new unit.

Posted by Peter Michelbach, i Sell Real Estate almost 7 years ago

Wow, never knew about the Legionaire's stuff & temperature. Thanks for the helpful info.

Posted by Lyn Sims, Schaumburg IL Real Estate (RE/MAX Suburban) almost 7 years ago

I just learned a lot. thank you.

Posted by Nan Herring almost 7 years ago

Great information.  Didn't know this.  Thanks so much for sharing.

Posted by Marsha Cash (RE/MAX Advantage) almost 7 years ago

Great Post! Another area of concern is old gate valves on tankless coils or lack of mixing valve on tankless coils. We also stress insulating all of the hot water piping. When this is done, the temperatures need to be re-measured as several degrees can be gained from the insulation!

Posted by Hank Richter (HomePro Inspections of RI) almost 7 years ago