Proper temperature of boiler water going into Super Stor

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David W.

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I just had a massively oversized Burnham Alpine 105 installed by my landlord whose plumber obviously didn't know what he was doing. It replaced an antique oil forced hot water 130mbh boiler. Haven't used the heat yet but the hot water is amazing. I watched the boiler kick on to fire the tank after a shower and observed a constant 170 degree burn of roughly 6 or 7 minutes straight and then it was satisfied. Is that set up right? The water set temp is probably 140 (I like it hot!)
 

Dana

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That wouldn't be out of the question for a in indirect that was being kept at 150F, a bit high (but not super high) for 140F. Priority hot water calls are typically at max fire until the call for heat is satisfied. The boiler has it's own internal high-limit. For heat to get across the heat exchanger into the potable water at a reasonable rate there has to be a double-digit delta between the return water to the boiler and the potable water. If the bottom of the tank drops to 120F the water coming back from the heat exchanger to the boiler is something between 130-140F. As the tank temp rises it will eventually modulate back a bit when the output of the boiler hit's the boilers high-temp limit.

To be legal in MA there must be a tempering valve or mixing valve at the output of the hot water heater, and that has to be set to 110F by the installer (though you can bump it up if you like.) The temperature of the tank has no effect on the temperature of the hot water you see at the tap, until/unless the tank temp drops below the tempering valve's adjusted output. Even if you like it hot, a 125F setpoint on the tank is plenty high enough.

At 140F storage temps even large active legionella colonies will be killed off over time, but at 125F not so much. Still, storage temps above 120F is enough to keep legionella colonies from growing- it's not super-dangerous. At 110F, it's in the high-growth zone, where they can grow quite rapidly. From an energy use point of view you save a bit by dropping the storage temp from 140F to 125F, which is still screaming hot if you crank up the tempering valves setpoint to where it isn't mixing in any cold water.
 

David W.

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Sounds like it's working fine then. He initially set the DHW circulator pump at "2" instead of "3" and the boiler was short cycling like crazy when calling for hot water. I bumped it to "3" and it seems to have calmed everything down. Just checked and he omitted the tempering valve but there aren't any kids here so I'm not worried.
 

Dana

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Sounds like it's working fine then. He initially set the DHW circulator pump at "2" instead of "3" and the boiler was short cycling like crazy when calling for hot water. I bumped it to "3" and it seems to have calmed everything down. Just checked and he omitted the tempering valve but there aren't any kids here so I'm not worried.

Maybe you're not worried, but both the landlord and plumber could be held liable if some later tenant got scalded. This is a code violation- did an inspector sign off on it, or was it bootlegged in on the cheap by an unlicensed unbonded type of plumbing hack?
 
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