Hydronic heaters are mechanical systems or components that warm spaces by primarily using hot steam or water. Some examples include radiators, hot water radiant floor heating systems, hot water baseboard heaters, steam boilers, and hot water boilers. Hydronic heating techniques have existed since at least the time of ancient Rome, when the Romans used clay pipes filled with water, heated by fires, to warm their bathhouses.
The most prevalent heating system of this kind is typically a gas or oil-fired boiler that heats water or steam. The water or steam then travels through piping to various components of the heating system, such as baseboard heaters, freestanding radiators, or special tubing or pipes in radiant floors. Other alternative hydronic heaters include hydronic electric baseboard heaters, solar water heaters, and wood-fired boiler systems.
The advantages of using hydronic heaters are numerous. Hot water radiant heating tends to be more efficient than electric or forced air heating. Systems that use hot water or steam are also apt to not dry a home's air out as much as forced air systems can. Also, since airflow is not going through ducts in hydronic heating systems, dust and particulate matter is less of a problem for those with allergies.
Sometimes hydronic heaters are used in combination with hydronic chillers. In this case, the same mechanical system can be used to heat and cool indoor spaces. This is usually not a cost-effective mechanical setup in home environments, but it can be a sensible approach in larger commercial structures. Additionally, some larger cities use a district heating and cooling system, that offers hydronic heating and cooling to building owners for a fee.
One of the important features of any of these systems is the way in which they handle changing water pressure, and the presence of air in the system. In older freestanding radiators, valves, which can be bled to rid the unit of excess air, are a common feature. In fact, most hydronic heaters have some sort of valve to relieve water pressure and also one to remove unwanted air.
Another important feature that is often necessary for hydronic heaters, since water expands and contracts, is an expansion tank. This tank helps to maintain the proper water pressure in the hydronic heating system. It often uses compressed air. As the water expands into the tank, the air further compresses. As it contracts, the air expands.