Radiant Heating System Explained: Heaters and Circulators

PEX tubing has become a very popular material in radiant heating installations due to its low cost and efficiency. While tubing is the product that does the actual distribution of heat, there are other components in the system that are equally as important. Aside from PEX tubing, the system must have a circulator and a heating source in order to function.

A hot water circulator is considered to be the "engine" of any radiant heating system. Its responsibility is to keep the water flowing from the boiler, into the PEX tubing and back to the boiler to be reheated. Contrary to popular belief, a circulator and a pump are not the same, as they perform different functions. The purpose of a pump is to carry liquids from one point to another, while circulator simply re-circulates water through a circuit.

Circulators on the market today are significantly more advanced than their predecessors. Taco circulators are available with various speed options.

When choosing a circulator, flow rate and pressure drop must be considered to ensure that the circulator will fit specifications of a particular radiant heating system.

The flow rate is measured in gallons per minute (GPM) and it varies depending on how much heat is lost during circulation. Lower return temperature would generally result in increased flow rate. Pressure drop, measured in pounds per square inch (psi) is also referred to as loss of head. It is caused by friction as water moves within tubing and by elevating the water mass. Once the flow rate and pressure drop rates are calculated, a special chart is used to match the data to a circulator that’s the best fit.

In order for a radiant heating system to operate, it needs to have a viable heating source. Although there are a number of heating sources that are suitable for radiant heating, boilers and tankless water heaters are among the most popular options.

A boiler is a device that is used to heat water. It consists of a tank that holds water and a gas or oil powered burner that heats the water inside. In a radiant heating system, the water from the boiler is circulated through PEX tubing loops, where it transfers some of its heat to the surrounding areas and is then returned to the boiler to be heated again.

For many years, a boiler has been the most trusted and effective way of heating water. Depending on the region and available heating resources, most boilers are either gas or oil powered. They have a long life cycle and can provide hot water in high quantities, with temperatures reaching up to 200 degrees Fahrenheit. Boilers, however, are bulky and often require to be housed in a special boiler room.

A tankless water heater was first introduced in the middle of last century. The system behind it is drastically different from a boiler, with the main differences being that it heats water instantly and only as needed and that it doesn’t have a tank. Heating on-demand reduces energy consumption as well as energy bills (gas or electric, depending on the model). Considering that a tankless heater is rather expensive, it will take a few years for the savings to pay off. Tankless water heaters, such as the ones manufactured by Takagi and Stiebel Eltron are compact and take significantly less space than other heat producing sources.