Don't just change out the boiler. Blend in new technology to update that 40- to 60-year-old hydronic system.

Are we doing justice to hydronics? I ask because of what I see our industry doing with the radiant heat business. Although there's great excitement with the re-emergence of this technology and a new wave of installations, new radiant heat and snowmelt systems represent only a portion of our market.

Meanwhile, what's keeping many older, existing hydronic systems alive is the life support we give by plugging in new boilers. But merely installing a new boiler won't do. A new boiler may keep an old system operating, but it's still an old system.

If hydronics is to grow, we must first improve how we handle our core business - the comfort system. Unless we blend in some of the technology the industry has given us since that 40- to 60-year-old system was installed, we are hurting hydronics. Ironically, it's not old gravity piping and column-type radiators that make hydronics obsolete, it's poor comfort.

There are a variety of heating systems that truly need new boilers. Many date back to the days of gravity circulation. Venerable cast-iron radiator installations, for instance, may be on their second or third boiler, but are also likely connected to the original piping. In addition, since the mid-1950s many of the systems that need new boilers are multizoned baseboard installations. What might we do to "remodel" these two systems?

Gravity Two-Pipe Systems

The residential gravity hot water systems were usually two-pipe direct return. Typically the boiler was at one end of the basement; boiler supply and return piping moved both left and right to the other end of the basement. (See Figure 1.) Consider doing the following:

  • Calculate heat loss. The closer the boiler matches the heat loss the more efficiently the boiler will operate day after day, year after year. Use a short method heat calculation form that only looks at the outside envelope of the house. The Hydronics Institute publishes a short form.

  • Count the installed radiation. Then divide the total square footage of installed radiation into the heat loss. This tells you how many Btus each square foot of radiation must supply on the coldest day, and the maximum system water temperature.

  • Change system piping from direct return to reverse return. Piping changes will be minimal. (See Figure 2.) Copper may be used and the new piping reduced to the Btu load. The two-pipe reverse return piping will be hydraulically balanced. Each radiator has the potential to enjoy the same flow and the same temperature. This minimizes a contractor's biggest problem: balancing.

  • Consider constant circulation. The only control of the pump would be a reverse acting aquastat set so low the aquastat will be nothing more than a summer-winter switch. If it's a cold start single-zone system, the owner will have one of the finest heat modulating systems that money can buy.

  • Install nonelectric radiator valves on the radiators that overheat. This is the Midas touch. These valves will modulate the hot water flow to prevent overheating.

If all of the above are done, only a properly installed and delicately controlled radiant system would provide better comfort.

Multizoned Baseboard

In the late-1950s the use of nonferrous baseboard began to increase. It soon became apparent that nonferrous baseboard differed from cast-iron radiators; nonferrous baseboard was more forgiving. Since 90 percent of nonferrous baseboard gently heats the air in the room, heat can be controlled by restricting air flow rather than water flow. Therefore, the need for main piping with branch risers to each room becomes unnecessary. Contractors began interconnecting baseboard radiation from one room into another forming a loop. Since a typical home consists of a living, sleeping and play area, the heating system divided conveniently into three loops. The task of isolating these loops with pumps or electric valves was easy. Zone control became synonymous with baseboard heating.

From the late-1950s to the 1990s, multizoned nonferrous baseboard systems accounted for the majority of hydronic installations. Unfortunately, once the industry established a pattern of piping and control in the 1960s, we became oblivious to progress. Today, baseboard heating systems are just about the same as they were in the 1960s.

For many years we've been installing new boilers to these nonferrous baseboard systems. But could we do more? You bet! Let's tackle two nagging problems:

  • Boilers with short firing cycles.

  • "Pinging" baseboards.

A really successful way to waste fuel is to have a boiler cycling off its high limit. In fact, that's how most multizoned baseboard systems unintentionally operate. A boiler piped to four heating zones will be sized to supply sufficient heat to all zones. What happens when one zone calls for heat? The boiler will create 300 percent more heat than that one zone can dissipate. The unused heat causes the boiler water to become hotter than necessary. On an average winter day - possibly 30 degrees F above outdoor design, with four zones intermittently operating the boiler - the water temperature rises quickly and the boiler begins cycling off the high limit. Apparently, the benefits of zoning are offset by the inefficient operation of the boiler. However, with the help of scientific testing, the Hydronics Institute has given us a solution.

For 30 years, the University of Illinois conducted third-party testing for the Hydronics Institute. One of the last studies (circa 1970) investigated ways to control residential zoned hot water heating. An expensive indoor-outdoor control fared well, but the use of two-stage thermostats fared best. The test involved a three-zone cold start system. The use of two-stage thermostats saved 8 percent more fuel than the indoor-outdoor control and 27 percent more fuel than the single-stage thermostats.

How do the thermostats differ? On a call for heat, the single-stage thermostat simultaneously operates the boiler and the circulator. The two-stage thermostat operates only the circulator. It attempts to move residual heat from the boiler and piping to the radiation. With a conventional boiler, the firing cycles are reduced by 50 percent. When the residual heat is dissipated or becomes insufficient, the thermostat will sense a 1-1/2 degree F drop and then permit the second switch to operate the boiler. With the two-stage thermostat trying to dissipate all the usable heat before making more heat, the circulator runs longer and the system water temperature is 40-50 degrees F cooler. It's a "win-win" situation, offering fuel savings and better comfort.

Now to the annoying and pervasive problem sarcastically referred to as "the sound of comfort." When exposed to a rapid change in temperature, the baseboard element (copper tube and aluminum) expands and causes pinging. Modulating the system water with either indoor-outdoor temperature control, or two-stage thermostats, will minimize the problem but may not entirely eliminate it.

With a temperature variance above 70 degrees F, pinging will occur. Let's say 180 degree F water is circulating through a heating zone consisting of 48 feet of baseboard. When the zone is satisfied, only 10 pounds of water is required to fill the baseboard. For the temperature to drop 100 degrees F, the water has to give off only 1,000 Btus. In less than five minutes it's done.

On successive calls for heat the pinging repeats and repeats. To fully eliminate this pinging, boiler bypass piping should be installed (as shown in the opening page photos). We are using the problem to solve the problem. The relatively cold water from the zone tempers the hot boiler water.

Like the gravity two-pipe systems, the more abundant multizoned, nonferrous baseboard systems also can be upgraded to give better comfort at a lower operating cost.

In sum, if the industry wants to sell more hydronic heat, they'd better be certain that people who already have it are completely satisfied. Don't just give them the best. Talk to them. Tell them why it's the finest heating system available. Tell them how you modernize old technology. Then they'll become hydronic ambassadors, playing a key role in the future of our industry.