Furnaces have been around for a very long time, and have been one of the most popular heating systems available for most of that time. This has led homeowners to gain at least a little bit of basic knowledge about the various parts of the furnace and their roles. Hydronic systems, however, are only recently becoming popular among homeowners. This means that much of their inner workings are not common knowledge quite yet. In an effort to educate homeowners about some of the ways in which hydronic systems operate, let’s examine the aquastat.
An aquastat is a device installed in hydronic water systems for the purpose of controlling temperature within the boiler. An aquastat is similar to the furnace limit switch in operation, maintaining a safe operating temperature for the central heating unit. There are two settings in every aquastat, a high setting and a low setting.
Despite the name, most boilers are not actually meant to boil water. Doing so would result in steam, and a dangerous buildup of pressure in a system that is not designed for it. For this reason, the aquastat shuts off the boiler when it reaches the high temperature limit. This keeps the water hot, but below boiling temperature.
The low temperature limit is meant to keep the water supply temperature from dropping too low. When the boiler shuts off after reaching the high limit, the system will continue to circulate water for as long as the thermostat is asking for heat. Eventually, however, the water will begin to cool. When the water temperature reaches the low limit, the aquastat starts the boiler up again to raise the water temperature.
These two limits allow the aquastat to keep a tight control over the water temperature in the system, making sure that it is neither too hot nor too cold. Without the aquastat, the boiler would run the risk of overheating or not heating enough to meet the home’s needs.