Tempering valves(T/V) used with residential water heaters (W/H) - aka ( i believe ) Thermostatic mixing valves.
1. Their main function appears to be to protect from scalding, ( how often do first line of scald defence, residential w/h thermostats fail without isolating the gas/power?)
2. And protect against water borne diseases eg. Legionnaires Disease.
3. Legionnaires apparently thrives in w/h's at 105* to 115*F, and upping the temp to 140*F will kill the disease.
4. At 140* a t/v is required. Note, the cold blending water has not been "treated" at 140*, more likely, it's been warming in the vicinity of the extremely hot w/h . ie. dubious cold water by-passes the w/h and mixes in at the t/v.
5. What about mfr's warranties if the w/h is used at 140*F?
6. What about the extra fuel/power being used to obtain 140*?
7. There are, of course, other methods of disinfecting the system without using high temps.
8. At high temp's, increased scale will accumulate along with the usual, introduced silt and sediment. These particles might possibly disable the functioning of the t/v, even with filters and screens. Perhaps the screens will block with the larger particles and the t/v will req. frequent maintenance?
9. Extra isolators are req'd with a t/v - hence, more sod's law chance of one being left shut and the possible consequences.
Note: Just a few observations; i'm ignorant and curious, and would welcome criticism or further suggestions. Can anyone cite government stats for Legionnaire infections from residential w/h's?