Hydronic heating systems use steam or hot water that is heated by a boiler and distributed via pipes to radiators or baseboard convectors, or to tubes for radiant floor heating. The hot water can also be used to heat air via a coil and blower. The boiler may burn oil, gas, propane, or wood or use electricity to heat the water. The water may be preheated using a solar thermal system or ground-source heat pump. Steam is distributed via pipes to steam radiators. Hot water can be distributed via baseboard radiators, wall radiators, or radiant floor systems; or, the hot water can be used to heat air via a coil and blower. Steam boilers operate at a higher temperature than hot water boilers and are inherently less efficient, but high-efficiency versions of both types of boilers (up to 95%) are currently available.
The minimum federal rating for a fossil-fueled boiler is 80%. For more on boiler efficiency and considerations on replacing your existing boiler, see Section 2.1 above. Also see “Furnaces and Boilers” at www.energysavers.gov.
Hydronic heating systems can provide energy and cost savings by being zoned to only provide heating to areas of the house that are in use. Zoning can be done by installing separate circulating lines, using zone valves controlled by separate thermostats, or using a central electronic controller and emitters with controls on them.
Steam and Hot Water Radiators
Steam heating is one of the oldest heating technologies. Steam moves itself through piping without the use of pumps. Older, high-mass boilers are less efficient and there is also a significant lag time from when the boiler turns on to when the heat arrives in the radiators.
Hot-water systems pipe the hot water to the different rooms of the house where heat is distributed through baseboard convectors or upright wall radiators (similar in design to steam radiators) or through radiant floor heating loops.
Radiant Floor Heating
Hydronic radiant floor systems pump heated water through tubing, which is laid in a pattern underneath the floor. The cost of installing a hydronic radiant floor system varies by location and also depends on the size of the home, the type of installation, the floor covering, and the cost of labor. Because radiant floor heating requires lower temperature water than radiator heating, the water for hydronic floor heating can be heated or preheated with a solar thermal heating system or a ground-source heat pump.
When the heat source is a ground-source heat pump, the cycling can be reversed in the summer to provide cooling. Radiant floor cooling works best in dry climates; it is not recommended in humid climates because of the potential for condensation to form on the floor surface.
The tubing can be installed in traditional concrete slabs, a thin layer of concrete, or pre-grooved wood panels. The slab under the radiant tubing must be insulated. Some flooring types such as thick carpet can diminish the heat transfer ability of radiant flooring.
Radiant heat wall and ceiling panels that distribute hot water through tubing installed in wall- or ceiling-mounted panels are also available.
Repair or Replace?
If you have an existing hydronic system that you are not ready to replace, talk to your contractor about what can be done to improve its efficiency. Hydronic systems can have problems with corrosion that clogs components. Some annual maintenance is required by homeowners and HVAC technicians. See the sidebar on this page for tune-up recommendations.