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Legionnaires Disease An Issue With Reverse Indirects?
I'd like to verify what I've been told that Legionnaire's bacteria is not an issue with a reverse-indirect like Turbomax. This is supposedly because the domestic water is only within a coil that holds only a gallon or so. I have adjusted the Turbomax's aquastat to cut-out at 150 and cut-in at 135. The aquastat probe is positioned more than halfway down the tank, which likely means when it cuts out at 150, the water temp at the top of the tank could be 160. So assuming the aquastat is calibrated correctly--not a certitude by any means--the tank water fluctuates between 135 and 150 where the probe is, and a bit higher at top of the tank, and transfers X% of that heat to the actual DHW inside the coil. Perhaps the Turbomax engineers put the probe so low in the tank to simulate the actual temp of the water inside the dhw coil.
In order to cut down on the number of DHW calls during the day when there is little or no hot water usage, I'd like to lower the cut-in temp 5-10 degrees. (as long as this wider cut in-cutout spread, like a heating temp setback--does not waste more gas than it saves trying to make up the differential.)
As it is, tank water temp drops enough to force boiler to fire every 5 hours or so for about ten minutes. This and all other gas usage adds up to a therm a day, 3x my prior usage with stand alone hwh. I'm sure temp will drop less after I insulate the 1.25" steel and 3/4" copper pipes.
But if lowering that cut-in temp will increase risk of Legionnaires, I won't do it.