Hydronic is a heating system for a building in which the medium for carrying heat throughout the structure is circulating water, especially when the circulation is aided by a pump.

A boiler is a pressure vessel that heats water for various purposes. Even though they are called boilers, only steam boilers actually boil the water. It is a “a closed vessel or arrangement of vessels and tubes, together with a furnace or other heat source, in which steam or other vapor is generated from water to drive turbines or engines, supply heat, process certain materials, etc.


  • Cast Iron: High temperature, high mass for steam or hot water
  • Copper Tube: High temperature water boiler
  • Steel Fire Tube: High temp product of combustion pass through tubes to heat water around the tubes to hot water or steam
  • Steel Water Tube: High temperature products of combustion pass around tubes which water is pumped through to be heated
  • High Efficiency: Either water tube or fire tube which heat either high temp or low temp water and remove extra latent heat from the products of combustion


  • Radiant Floor: Water is circulated at a lower temperature through tubing in or under the floor. Low temperature, high efficiency
  • Hydronic Baseboard: Can be either copper tube or cast iron. High temperature, low efficiency
  • Panel Radiators: Medium to low temperature, high efficiency
  • Cast Iron Radiators: High temperature, low efficiency or low and medium temperature, high efficiency
  • Fan Coil Unit: High temperature water circulated through a coil which air is blown over. High temperature, low efficiency

Water flow through the boiler and out to the system is created by what is commonly called a pump but is properly referred to as a circulator in a sealed system. Circulators are sized and specified based on the gallons per minute (GPM) of flow required and the resistance (Ft-Head) to that flow created in the piping system.

Many types of circulator and mixing controls are used to control hydronic heating systems to improve comfort and efficiency by zoning and controlling water temperatures to increase the boiler efficiency.

When deciding on a boiler it is important to understand the required system operating temperature. A boiler with a high Annual Fuel Utilization Efficiency (AFUE) will always operate at a lower efficiency than labeled when system water temperatures are higher than AFUE tests. It is all about the system.

Call Ambrose Mechanical now and we can help you understand the benefits of a professionally designed system. 585-663-7826

Boilers and Hydronic Alternatives refers to how the various boilers can be used to heat water and numerous types of equipment can be used to remove heat from the water to transfer it to the air or other materials to be heated and the control components, circulators and mixing valves that increase comfort and efficiency.

Combi Boiler with high temp convectors & low temp radiation.
(Image created by Ambrose Mechanical Services):