Hydronic heating systems, also referred to as radiant heating, circulate heated water throughout a space to provide comfort heating to an entire home. In this type of system, a boiler heats water and circulates it through pipes or tubing to a heat distributor such as radiators, finned-tube baseboard, radiant tubing, towel warmers, and kick space heaters. In addition, the boiler can be used to indirectly heat domestic water and whirlpool baths, or to melt ice and snow on sidewalks and driveways.
Recent advances in cooling technology also allow for the successful operation of air conditioning with a hydronic heating installation. Hydronic heating is highly energy efficient because it is delivered through completely sealed systems with a minimal loss of heat.
Hot water from a boiler or water heater is the medium for heat transfer in a hydronic system. Radiators and finned tube baseboard are the most common source of heat transfer, but radiant loops are gaining popularity.
Hydronic Heating — How It Works
Modern hydronic heating is an energy efficient home heating system that enables heat to be delivered precisely when and where it is needed.
Hydronic heating is ideal for any residential home or building. The system has become popular with homeowners who seek a quiet, clean, efficient, and comfortable space.
To understand hydronic heating, it is important to first review how radiant heating works using these heat transfer processes:
- Conduction is the transmission of heat through a medium without perceptible motion of the medium itself. Put your hand on the hood of your car after it has been out in the sun for a while. Your hand gets hot from direct contact with the hot metal. Density plays a major role in an object’s conductivity.
- Radiation is the emission or propagation of energy in the form of invisible rays, waves, or particles that are absorbed by a person or object. On a clear day in mid-winter, step out from the shadow of a building into the bright sunlight. Feels good, doesn’t it? You are being warmed by solar radiation. Radiation is a very effective means of transferring heat as it can’t be disturbed by wind or moved.
Hydronic heating systems are effective because the boiler uses conduction to efficiently and quickly heat the water. Hot liquid is circulated throughout piping in the home via conduction and heats concrete, tile, and other types of flooring. The heat from the liquid radiates warmth into the room at a comfortable and consistent temperature. Thus, a radiator is a good example of conduction.
Elements of Hydronic Heating Systems
It’s important to review the various types of hydronic systems to determine the ideal unit for an application. Hydronic designs can be customized to meet most residential needs, whether it is a new home or a remodel. The flexibility of this type of advanced home heating system, as well as the high levels of energy efficiency, have made hydronic heat an increasingly popular choice for both contractors and homeowners.
The following basic elements are required for hydronic heating in a home:
- Boiler — The device used to heat the liquid.
- Liquid — The common form used is water although some also utilize a mixture of water and antifreeze.
- Tubing — PEX or another type of small, flexible plastic tubing is commonly used to circulate water.
- Manifold/Thermostat — The manifold directs water flow and room temperatures and is connected to the thermostat.
- Heat Emitter — The radiator, finned-tube baseboard, radiant tubing, towel warmer, kick-space heater or other heat distribution element.
- Pump — Used to keep the heated liquid moving throughout the tubing so that the warmth is consistent.
Hydronic Heating Options
A variety of hydronic heating options exist to heat water. These include a natural gas or propane water heater or boiler, electric boiler, wood boiler, heat pump, solar water heater, or a geothermal heat pump.
Condensing boilers achieve very high efficiencies by capturing and using heat from the combustion process that would otherwise be wasted. The boiler’s heat exchanger uses the exhaust gases from the combustion process to preheat water as it enters the boiler. In addition, the water vapor produced in the combustion process condenses back into the water and releases heat that is then re-used. Together, these two processes create the high efficiencies associated with condensing boilers.
Several options can be used in conjunction with a boiler to improve output and efficiency. These include a tankless hydronic water heater, combined hot water and heating systems boiler, solar water heater, and a geothermal heat pump.
- Tankless water heaters are designed to provide on demand, energy efficient hot water for domestic uses, such as showers, faucets, and dishwashing.
- The combined hot water and heating systems boiler — often called a combi-boiler — is growing in popularity for installations in homes and commercial buildings. These units are relatively new to the industry and can be designed for use with water tanks and tankless water heating. The unit is a high-efficiency water heater and a central heating boiler, combined within one compact unit. Therefore, no separate hot water tank is required, offering space savings within the property.
- A solar water heater will not provide enough heated water by itself, but it can increase the energy efficiency of the system and work in tandem with a boiler.
- Geothermal heat pumps use the natural warmth of the ground several feet below the soil to preheat water. This method can reduce the amount of natural gas, electricity, or oil that a boiler uses to save energy.
Hydronic Heating Emitters/Applications
Heat emitters include underfloor radiant loops (sometimes also in walls and ceilings), baseboard heaters, and radiators.
The most common system is often called "hot water base board heat" because most of the hydronic heating systems installed in the United States use hot water running through base board heating units to heat the living spaces of the home.
Other hydronic systems use cast iron radiators or tubing in the floors, ceilings, or walls to circulate heated water and radiate the heat to the living space.
Radiant flooring is a popular option for new home construction as it can be easily added into the concrete floor or joist system during construction. Tubing for a hydronic system may be installed in a conventional concrete slab or in a lightweight, gypsum-cement slab. Or it can be stapled to the undersides of subflooring.
For home remodels, hydronic baseboard units and radiators are easier to install because they require less tubing below the floor. They are often placed along the walls of a room in areas that make them less conspicuous.
Radiant panels for walls and ceilings can heat a broad area. These panels are most often used with electric radiant heat versus hydronic due to the possibility of water damage.
There also are several outdoor radiant heating systems that can be a helpful addition to one’s home. Options include the ability to melt snow on sidewalks and driveways in areas that receive significant snow fall or ice. Radiant roof heating can help protect a home’s roof from future leaks due to snow and ice buildup.
Radiant heating loops can be placed beneath pool walls to allow for an energy efficient way to keep the pool warm and lengthen the swimming season.
A variety of applications and system configurations are capable of meeting the exact heating requirements of the owner. A simple design might be a tank-type water heater connected to a loop of flexible plastic tubing for warming a bathroom floor. A more complex application would include the use of two or more boilers operated in stages that distribute heat through an assortment of heat emitters.
A well designed and properly installed hydronic system will provide comfort and fuel efficiency for the life of the building.