Hydronic Heating Systems

Hydronic heating systems are hot water heating systems that use water as a medium for conveying and transmitting the heat to the various rooms and spaces within a structure. Hydronic heating systems are based either on gravity flow principle or forced circulation. Hydronic heating or forced-hot-water heating is widely used in residential and commercial structures.

In a typical hot-water-heating system, the water is heated in a boiler or water heater and circulated through pipes to baseboard convectors or radiators located in various rooms. The energy source used to heat water may be oil, natural gas, propane, electricity, or a solid fuel, depending on the heating unit type.

The hot water is circulated through pipes to baseboard convectors or radiators located along the walls of the rooms, or through radiant panels installed in the floors or ceilings. A centrally located thermostat controls rooms’ temperatures in small residential and commercial buildings. When the thermostat call for heat, the boiler or hot water heater heats the water heats the water and sends it to the room convectors or radiant heating panels where it released and distributed through the rooms by natural convection.

In larger houses and commercial buildings, the heating systems are zoned with individual thermostats controlling the temperatures in each zone.


Classification of Hot-Water Heating Systems

Hot-water heating systems can be classified in a number of different ways, depending on the criteria used. Generally recognized the following classification categories:

  • Type of water circulation;
  • Piping arrangement;
  • Supply water temperature.

In all hot-water heating systems, water is circulated either by allowing it to flow naturally or by forcing it through the line. The first one is referred to as a gravity hot-water heating system because circulation results from the difference in weight of the water caused by temperature differences (heavy when cold, light when hot).

In a forced-hot-water heating system, the accelerated circulation of the water can result from:

  • Using high pressures;
  • Heating the circulating water and condensing the steam;
  • Introducing steam or air into the main riser pipe;
  • Using combination of pumps and local boosters;
  • Using pumps alone.

If a hot-water heating system uses supply water temperatures above 250 deg. F, it is classified as high-temperature system. High-temperature heating systems are widely used in large heating installations such as commercial or industrial buildings.

A low-temperature heating system is the one, having a supply water temperature below 250 deg. F and is typically used in residential and small commercial buildings.


Advantages of Hydronic Heating Systems

There are several advantages to using hot-water heating system as opposed to steam and forced-warm-air heating systems. Some of those advantages are:

  • Hot-water heating is more flexible than low-pressure steam systems because temperatures can be widely varied.
  • Due to the low working temperatures of the water, the heat from a hot-water heating system is relatively mild, and the air does not become too dry.
  • Function as a reservoir for storing heat, as radiators remain warm for some time after the fire in the boiler is extinguished.
  • Hot-water heating systems deliver uniform and comfortable heat without problems of air stratification and cold pockets.
  • Comfortable humidity levels.
  • Less energy is used to circulate water than blow air through the ducts.
  • Quiet operation.
  • Easy zoning.


Disadvantages of Hydronic Heating Systems

The main disadvantage of a hot-water (hydronic) heating systems is the initial installation cost, which appears to be higher compared to forced-warm-air (FWA) heating systems. Other commonly known disadvantages are:

  • Slower heat response;
  • Stagnant air caused by lack of ventilation;
  • Baseboard convectors may interfere with furniture placement;
  • Condensation in some Hydronic cooling systems.