Desuperheater Buffer Tank Bacteria

[rjkobbeman]

I have an Envision setup with factory desuperheater and have plumbed it using a two tank setup. Plumbed per Waterfurnace, I have a holding tank that is not energized and have a gas water heater plumbed in series downline from the holding tank.

During winter and summer the holding tank temperature seems perfect. Under heavy heating/AC use, the desuperheater turns off because of it reaching the high water temp limit.

However, now that I am paying more attention to my system, I noticed that in spirng and fall the holding tank water temp is room temp because the desuperheater is not running -- obviously because the main system is not running.

My question is, is there a risk of bacteria -- specifically Legionnaires' disease bacteria due the holding tank being cold. After reading about this bacteria it seems that water in tanks should always be at 140 degrees F. Should I energize my holding tank during the spring/fall? What does everyone else do?

[hje]

I do not energize my holding tank during the spring/fall. The regular electric water heater I keep at 120*F.

[idahohvac]

You are adding fresh water every time you open a hot water valve, as long as it is piped like WaterFurnace recommends. I do not believe you should have any problems.

[jongig]

I have an Envision setup with factory desuperheater and have plumbed it using a two tank setup. Plumbed per Waterfurnace, I have a holding tank that is not energized and have a gas water heater plumbed in series downline from the holding tank.

During winter and summer the holding tank temperature seems perfect. Under heavy heating/AC use, the desuperheater turns off because of it reaching the high water temp limit.

However, now that I am paying more attention to my system, I noticed that in spirng and fall the holding tank water temp is room temp because the desuperheater is not running -- obviously because the main system is not running.

My question is, is there a risk of bacteria -- specifically Legionnaires' disease bacteria due the holding tank being cold. After reading about this bacteria it seems that water in tanks should always be at 140 degrees F. Should I energize my holding tank during the spring/fall? What does everyone else do?

If your water comes from a CWS or PWS, Community or Public Water System you’ll have a residual disinfectant, probably chlorine. This chlorine will kill most harmful bacteria if not all. Some bacteria can grow in a water heater such as iron reducing bacteria but it’s not harmful. It just looks and smells bad. However, if the water in the heater goes over 120/130 in the year the higher temperature will kill it off, it grows very slow. If your water comes from a well that’s a whole different problem. Many wells may have contamination and you’d never know unless you check the water.

John
PA, Licensed Water Operator

[rjkobbeman]

I'm on city water... so I feel confident that the quality is good. This is something I never thought about... until I was selling my old house (not the house with geo). The realtor said to leave my water heater on so bacteria did not grow. This got me thinking and one internet search led to another...

I ended up turning off my desuperheater (new house) now that my system is not running very much. My theory was that the holding tank would be cold and not warm. (During winter/summer it heat the water hot.) I will probably turn it back on now that you explained this to me.

Thanks for the help everyone.

[watercop]

If bacteria is in fact a problem in unheated water tanks, why isn't it a concern in cold water lines, well tanks, etc.

While I would avoid having potable water stagnate for weeks or more at a time, so long as water is actively flowing through a particular system component (supply pipe, buffer tank, whatever) I wouldn't worry about bacteria arising from failure to heat the water.

[Comfortwave H&A]

100 to 120 degrees F is that best temp for Legionella to flourish.
If you turn up your electric or gas "final" tank to about 140 - 150 you will kill off the bateria. I think you need 6-8 hours at 140 for a complete kill.

Next problem is you need an anti-scald valve at the final tank to ensure no one gets burned.

There are a ton of online resources that discuss Legionella, and how to kill it off.