[Tell It Right]

The problem is the water *IN* the hot water tank that you use in the house. The hot water tank never gets warm enough to kill the legionella bacteria just like in the cooling towers at the hotel where legionella got its name.

I honestly don't understand how this can be. See posts # 11 and 29 for two FReepers with experience with heat pump water heaters keeping the water thank at 135F or 140F like we would with a "normal" water tank.

[Don W]

I’m speaking as an operating engineer that worked large cooling and heating systems for over 30 years. I attended numerous courses on the prevention and mitigation of these and other biological, chemical treatment, and contaminant problems.

Yes, the heat transfer fluid does not normally enter the domestic water system, but it’s the hot water temperature that poses the risk.

Water can have legionella and not affect people if the concentration is low enough, but keeping your hot water below 140* is dancing with the devil.

I keep my DHWT at 160*f. Yes, that’s a bit hot and perhaps a bit wasteful, but that’s my preference.