from Wiktionary, Creative Commons Attribution/Share-Alike License

  • n. A device that automatically responds to changes in temperature of a liquid, typically water in a domestic hot water heating system, by activating a heating or cooling system to maintain the temperature of the liquid at a desired setting.


aqua- + -stat (Wiktionary)


  • - On the hot water return pipe that the water continues to flow through there is an aquastat which is set to 130 degrees, once the aquastat senses that the water has reached 130 degrees it will break the current to the pump and therefore there will won't be any flow of water over the flow sensor.

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  • For cast iron boilers in multi-zone hot water systems, reset controls (lower control in Figure 2) that directly vary water temperature as a function of outdoor temperature can outperform systems that operate on a constant temperature aquastat.

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  • A lot of residential heaters have an aquastat labeled cold, normal, hot, these normally refer to 100°F, 120/130°F and 140°F.

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  • The 'knob' you're turning up is an aquastat that controls in the water temperature in your tank.

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  • However, give this a thought: Put the aquastat just after the circulating hot water line passes the last usage point, at the beginning of the return loop.

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  • For best operation the deadband (differential) of the aquastat probably should be around

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  • If you're complaining about tepid water when you come home from being away for a few hours, this is the cool water in the pipes your feeling, the aquastat controls the temperature in the tank only, and without circulation (opening a tap or running a pump) the water in the pipes cool down and won't heat up until you open a tap and flush the cool water and replace it with warmer water from the tank.

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  • As I mentioned, this aquastat controls the water temp in the tank, if it drops below your set point, it will call for the heating source to power (either oil, gas, electric or an indirect source like a boiler), if you keep the temp too high it will constantly be calling for this source to keep the tank up to temperature and you can expect a dramatic increase in your utility bill (and your carbon footprint).

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