PM columnist John Siegenthaler is an industry authority on designing and installing hydronic systems. He’s been writing “Hydronics Workshop” since July 1996 for the magazine.

In May, at the Radiant Panel Association annual meeting, John will release “PM’s Hydronics Toolbox” — a compilation of his PM columns, along with a new “Hydronics 101” section. The book promises to be a powerful tool for contractors looking to better understand hydronic fundamentals.

The following excerpt, Chapter 1, describes the benefits of hydronic heating. This chapter is most useful for hydronic heating contractors having a difficult time marketing their product.

What is Hyronic Heating?

Hydronic heating systems use water, transported through piping, to move heat from a heat source where it’s produced, to heat emitters where it’s released. Within this broad description are hundreds of possible system configurations. With proper design each is capable of meeting the exact comfort needs of its owner. Some systems are as simple as a tank-type water heater connected to a loop of flexible plastic tubing that warms a bathroom floor. Others may use two or more boilers operated in stages, releasing their heat through an assortment of heat emitters like fin-tube baseboard, panel radiators or radiant ceiling panels. These same boilers can also provide the building’s domestic hot water. They might even heat the swimming pool, or melt snow as it falls on the driveway.

The advantages of hydronic heating

There are many advantages of hydronic heating that your customers should know about. They include:
  • Superior Comfort: Hydronic heating has long been respected for its ability to provide excellent thermal comfort. The better systems achieve this by not only maintaining the desired air temperature in each room, but by warming objects in the room and the room surfaces themselves. Superior comfort is without a doubt the single biggest reason discriminating owners choose hydronic heating.
  • Unobtrusive Installation: Another big advantage of hydronic heating is the ability to install it without having to drill, saw, or otherwise hack out major pieces of a building’s structure. Because water is more than 3,400 times more “thermally concentrated” than air, a hydronic system only has to move about 1/3,400 of the volume of fluid that a forced-air system does to convey the same amount of heat. This means that small tubing can replace large cumbersome ducting. For example, a 3/4-inch diameter tube can deliver the same amount of heat as an 8-inch by 14- inch duct when both systems are operated under typical conditions. When necessary, a tube this size is easily routed through the building’s framing without having to drill large holes that could significantly weaken the structure. The entire distribution system is easily concealed within the building’s structure. Accommodating an 8-inch by 14-inch duct in a similar situation is an entirely different matter. With the possible exception of wooden “I-joist” framing, or specially designed floor trusses, a duct this size simply can’t be run laterally through the floor deck. This forces compromises like suspending the ducting from the bottom of floor framing and thus reducing basement head room. Or concealing the ducting by building valences or soffits around it within living spaces. Should the aesthetics of an otherwise meticulously planned building have to be compromised just to “shoe-horn” in the heating system? Aesthetic issues aside, there are countless buildings in North America with poor air distribution (resulting in poor comfort) all because their duct systems were compromised by the lack of routing options.
  • Design Flexibility: Hydronic heating offers almost unlimited possibilities to accommodate the comfort needs, usage, aesthetic tastes and budget constraints of just about any building. A single hydronic heat source can supply hot water to several different kinds of heat emitters, provide the building with domestic hot water, and heat ancillary loads like a swimming pool or spa.

    Here’s an example: A few years ago I designed a hydronic system for an upstate New York home that uses radiant floor heating on the slab-on-grade first floor. The second floor is served by individually controlled panel radiators in each of the three bathrooms and baseboards in the bedrooms. The system also supplies on-demand garage floor heating, as well as the home’s domestic hot water. It even heats the indoor pool and the tile floor surrounding it. All these loads are supplied from a single oil-fired boiler. Try doing that with forced air!

  • Clean Operation: One of the chief complaints from owners of forced-air heating systems is the amount of dust and other airborne pollutants their systems distribute through the house. Although often the result of poorly maintained filters, this complaint also demonstrates one of the pitfalls of whole-house air circulation.

    Most heat emitters used in hydronic systems induce very gentle air circulation relative to that created by a forced-air system. Those that do use fans or blowers typically create room air circulation rather than whole-house air circulation. People with allergies will appreciate the reduced air movement offered by hydronic systems year after year. How can you put a dollar sign on this benefit?

  • Quiet Operation: A properly installed hydronic system can operate with virtually undetectable sound levels in the occupied areas of a home. The loudest sound will often be the fuel burner on the boiler, which is usually in the basement or an isolated mechanical room. Modern hydronic systems using constant water circulation, in combination with variable water temperature controls, can all but eliminate the expansion noises of piping that are associated with some older, high temperature hydronic systems.
  • Zonability: A heating system designed to maintain all areas of a building at the same temperature, at the same time, doesn’t give its owner much flexibility. The heating system in most homes should provide the option of dividing the house into two or more independently-controlled comfort zones. Such systems can reduce energy consumption by allowing for lower air temperatures in unoccupied areas. They also allow the comfort level of rooms to be adjusted to suit individual tastes and activity levels.

    Imagine a heating system that automatically adjusts itself as sunlight pours into some rooms, but not others. One that automatically reduces heat output when several people gather in the living room, while at the same time creates a toasty, warm bathroom for another person to shower in. This type of “room-by-room” zoning is easy to accomplish with hydronics without resorting to elaborate or expensive hardware. Accurate temperature control to within +/- 1 degree F of the setpoint temperature is possible.

  • Energy Efficiency: Hydronic systems reduce energy consumption in several ways. To begin with, the small size of hydronic tubing compared to forced-air ducting of equivalent heat carrying ability greatly reduces undesirable heat loss from the heat distribution system. For example, the 8-inch by 14-inch duct previously mentioned has about 16 times more surface area than the 3/4-inch pipe. This means its heat loss will also be about 16 times greater when operated at the same temperature and surrounding conditions. Think about situations where piping or ducting has to be routed through crawl spaces or attics. Heat loss to such spaces is truly heat lost! Heat you paid for. That is heat needed in the rooms at the far end of the distribution system to maintain comfort. Even if you insulated the tubing and ducting with the same material, heat loss from the ducting would remain much higher than that of the tubing. It would also cost more to insulate the ducting because of its greater surface area.

    The electrical energy needed to circulate water through a well designed hydronic system is usually a fraction of that used to move air in a similarly sized forced-air system. For example: The cost of operating a typical 90 watt hydronic circulator for 2,000 hours per heating season in an area where electricity costs $.10 per kilowatt-hour is about $18. By comparison, a small furnace using a 400-watt blower motor would have an operating cost of about $80 over that same period. While the difference of $62 per year doesn’t seem overwhelming, the total difference in operating costs over the life of the systems could be several thousand dollars.

    Some types of hydronic systems, particularly those heating floors of rooms with high ceilings, reduce energy consumption by reducing air temperature stratification. Because air isn’t directly heated to high temperatures, it doesn’t carry heat up to the ceiling where it does little more than increase heat lost to the attic. Instead, the heat remains in the “occupied zone” of the room where it best meets the comfort needs of the occupants. Because radiant floor heating offsets radiant heat loss from the body, it also allows most people to feel perfectly comfortable at air temperatures several degrees lower than would be possible with non-radiant systems. Lower room air temperatures mean less heat loss and lower fuel consumption.

    Finally, as previously mentioned, zoned hydronic systems also provide the potential for unoccupied rooms to be kept at lower temperatures, which also lowers heat loss and reduces fuel consumption.

    Go to to order copies of the book.