Aquastat
Encyclopedia
An aquastat is a device used in hydronic heating systems
for controlling water temperature. To prevent the boiler
from firing too often, aquastats have a high limit temperature and a low limit. If the thermostat
is calling for heat, the boiler will fire until the high limit is reached, then shut off (even if the thermostat is still calling for heat). The boiler will re-fire if the boiler water temperature drops below a range around the high limit. The high limit exists for the sake of efficiency and safety. The boiler will also fire (regardless of thermostat state) when the boiler water temperature goes below a range around the low limit, ensuring that the boiler water temperature remains above a certain point. The low limit is intended for tankless domestic hot water---it ensures that boiler water is always warm enough to heat the domestic hot water. Many aquastats also have a "diff" control which determines the size of the range around the "low" and/or "high" controls.
Aquastat is a registered Trademark of Honeywell International Inc.
Hydronics
Hydronics is the use of water as the heat-transfer medium in heating and cooling systems.Some of the oldest and most common examples are steam and hot-water radiators. Historically, in large-scale commercial buildings such as high-rise and campus facilities, a hydronic system may include both a...
for controlling water temperature. To prevent the boiler
Boiler
A boiler is a closed vessel in which water or other fluid is heated. The heated or vaporized fluid exits the boiler for use in various processes or heating applications.-Materials:...
from firing too often, aquastats have a high limit temperature and a low limit. If the thermostat
Thermostat
A thermostat is the component of a control system which regulates the temperature of a system so that the system's temperature is maintained near a desired setpoint temperature. The thermostat does this by switching heating or cooling devices on or off, or regulating the flow of a heat transfer...
is calling for heat, the boiler will fire until the high limit is reached, then shut off (even if the thermostat is still calling for heat). The boiler will re-fire if the boiler water temperature drops below a range around the high limit. The high limit exists for the sake of efficiency and safety. The boiler will also fire (regardless of thermostat state) when the boiler water temperature goes below a range around the low limit, ensuring that the boiler water temperature remains above a certain point. The low limit is intended for tankless domestic hot water---it ensures that boiler water is always warm enough to heat the domestic hot water. Many aquastats also have a "diff" control which determines the size of the range around the "low" and/or "high" controls.
Aquastat is a registered Trademark of Honeywell International Inc.