Water heater temperature setting with blanket

Hemlock

According to the Dept of Energy: "Don't set the thermostat above 130ºF on electric water heater with an insulating jacket or blanket – the wiring may overheat."
Elsewhere the government and scientific studies say that 140 degrees is needed to kill Legionnella bacteria.
How to reconcile those two statements?

Jamie Hall

You can't, obviously. But is that so odd? The essence of modern government is the ability to hold two totally contradictory things together as true...

Larry Weingarten

Hi, When you add a wrap to your heater, do it in a way that does not cover up the element hatch covers. (Also leave access to the drain valve and T&P valve.) By not covering the hatch covers, you mostly will not be exposing wiring to higher temps. Also, generally the top of a heater is better insulated than the sides, so no additional insulation is needed there. This is good, because you don't want to cover the electrical box on top of the heater. FYI, both hot and cold lines attached to the heater on average lose as much heat as the tank itself, so go crazy doing a wonderful and magnificent job of insulating those pipes with "too much" insulation, that's also as air tight as you an make it. About Legionnaires, 131F prevents growth of the bacteria and takes roughly six seconds to burn, so seems a good balance point if a mixing valve is not used. If you have any old, young or immune compromised people in the house, a mixing valve is the right thing to do.

Yours, Larry

Hemlock

Thank you, Larry. So you think I can insulate my heater and set it to 140 as long as I follow your caveats? In my case, 140 is the safest temperature for health.

Larry Weingarten

Yes. There may be an abundance of caution going on as well. Residential heaters used to be allowed to get up to 160F and commercial heaters still can go to 180F. A question though, is scalding not an issue? Installing a tempering valve would probably make things less risky.

Yours, Larry

Hemlock

Scalding is not an issue (mixing valve). I've researched the Legionella question thoroughly (read all the major scientific studies and noted how the knowledge based developed over time) and am confident about my choice of temperature. CDC: "Store hot water at temperatures above 140°F." The most recent studies validate that.

pecmsg

Legionaries bacteria is killed @ 140*f after 1 hour. 
Point of use max temperature is 120*f   

My mixing valve is set for 115*

EBEBRATT-Ed

Most water heater mfgs do not recommend using insulation blankets