If you had to leave som approaches behind at the stroke of midnight this New Year's Eve, what would they be?

As in so many avenues of life, the 20th century has witnessed more advances in hydronic heating technology than all previously recorded history. In their day, the gravity-driven hot water heating systems of the early 1900s were a huge improvement over the standard of tending separate fires in every room. Despite the fact that their efficiency and control characteristics pale in comparison to those available today, these systems and the people who designed them deserve immense respect. They harnessed natural forces using the best tools available at the time to deliver something that greatly improved the quality of life. Perhaps some of you have older relatives who can remember the lavishness associated with having "central" heating systems in the early part of this century.

Today most of these systems, if they still exist, are little more than historical artifacts. Their elegance and utility succumbed to the same incessant market forces that replaced the icebox with the refrigerator, the phonograph with the CD player and the typewriter with the word processor.

The current pace of technological improvement virtually guarantees that many of the strategies we now use as heating professionals will also become artifacts in the not so distant future. As we enter the 21st century, several former icons of hydronic heating are fighting a losing battle with technology and market forces. Those practitioners who refuse to accept the change will fade into obscurity with them. Those who wisely learn to work with their replacements will continue to profit within this industry.

A Final Look Back

The end of this century, a few days from now, will be one of the most anticipated delineations in time ever witnessed. The almost obsessive attention that's been given to Y2K will make midnight 12/31/99 seem like a passage through an imaginary portal in which many will feel compelled to leave certain things behind.

How about you? As a hydronic heating professional, if you had to leave some approaches behind at the stroke of midnight this New Year's Eve, what would they be? I asked myself that question. This month I'll describe five strategies that I feel are best relegated to the hydronics boneyard as we enter the next century.Although one can argue that the size of the heat emitters used with such high water temperatures is significantly smaller than with water at say 170 or 180 degrees F, the associated cost savings seldom tip the scale regarding a purchasing decision. Especially if the prospective customer is aware of the many benefits hydronic heating has to offer.

On the other hand, the "baggage" associated with high temperature system operation can be rather heavy. It includes:

  • Significantly greater heat losses from boilers and distribution piping.

  • Higher surface temperatures that increase the risk of burns.

  • Reduced life expectancy of circulators.

  • Greater potential for circulator cavitation.

  • Incompatibility with most nonmetallic piping materials.

  • Greater potential for steam flashing under low pressure conditions.

  • Heating room air to higher than necessary temperatures, which in turn enhances air temperature stratification and increases air leakage.

  • Greater thermal stresses on system components.

  • Increased likelihood of objectionable expansion/contraction noises.

The increased life cycle cost associated with operating small hydronic systems at high water temperatures makes the saving associated with smaller heat emitters rather trivial. This concept, while probably far from the minds of most American consumers when making purchasing decisions, is now well understood and respected in Europe. Perhaps it's not surprising that the maximum water temperature now used in European panel radiator systems is approximately 140 degrees F. Or that most boilers sold in Europe come with reset control as standard equipment.

My own preference is to use supply temperatures (under design load conditions) of 160 to 180 degrees F (for fin-tube baseboard, panel radiators and other "high" temperature heat emitters). Reset control in one form or another then backs the water temperature down to match part-load conditions. When high recovery rates are needed for indirect domestic water tanks, I'll let the boiler temperature slide up to 200 degrees F (but only during the DHW cycle).

Inevitably higher fuel costs, future efficiency standards and the quest to provide better comfort will drive the American hydronics industry toward lower water temperatures. Get used to it.

2. Tankless Water Heaters: If only I had a dollar for every time I've heard that a tankless water heater coil gave its owner "free" hot water during the heating season. This myth had to have been a sales pitch used during the 1950s and 60s. The reasoning goes something like this: "The boiler is already hot most of the time because the house needs heat, so why not pass some cold water through the coil and steal away a bit of that heat?" Unfortunately Mother Nature is just too smart to let this happen. It takes 1 Btu to raise 1 lb. of water 1 degree F. If that Btu came from your boiler, you paid for it. You might be able to break the speed limit and get away with it, but you won't break the laws of thermodynamics.

Perhaps if the true cost of maintaining a boiler at a minimum temperature of 140 to 160 degrees F year round were known, the owner would realize that Mother Nature is the one doing the stealing. Some studies have cited the efficiencies of boilers with tankless water heaters as low as 35 percent during summer operation solely for domestic water heating.

Energy issues aside, how does the flow-restricting orifice often used in the tankless coil co-exist with some of today's luxury showers that often demand 15+ gallons per minute of water flow? The guy in the opulent body shower advertisement would look a little silly standing there while a couple of gallons per minute drools out of the six-spray heads. Storage within a well-insulated, indirectly heated tank is the answer, and the future.

3. On/Off Control: Would your driving style become a bit more "conspicuous" if your only options for speed control were to either floor the gas pedal or coast? Fortunately the carburetor was married to the internal combustion engine decades ago.

Its equivalent in hydronic systems is a fully modulating heat source and heat delivery system. Several hardware strategies now exist for metering heat input from the heat source into the distribution system and on to the heat emitters. Modulating heat production units, especially in smaller residential capacities, are a bit harder to come by. They do exist in Europe and inevitably will make their way across the pond as loads get smaller and fuel gets more expensive.

How many times do we hear complaints about piping expansion sounds? Or see water temperatures swing back and forth over fairly wide temperature ranges because an aquastat either allows no heat or all available heat to pass a given point in the system? Nature works on a continuum, and seldom tarries at a steady condition for any length of time. Many of us continue to focus heavily on "design load" conditions, while overlooking opportunity to improve system stability during the much more typical part-load conditions.

Some of the more significant future advancements in hydronic heating will involve controls. The concept will be to track nature's gentle but constant variations in heat flow through the system, rather than repeatedly jerking the energy door open and then slamming it shut. Over the next few years, the American hydronic market will see increasing use of variable speed circulators, not just for injection mixing, but for flow control in zoned systems. We'll also see increasing availability of small, fully modulating heat sources. Microprocessor controls will become the norm for managing these variable-speed, variable-capacity systems.

4. "Standard" Expansion Tanks: OK, I admit they still are sold. They still can be installed and will operate fine (at least for a while). But what's the point of installing a tank that's roughly twice the size of the alternative, has to be mounted in a certain overhead location, requires special fittings at both ends of its connecting pipe (which may not even work with some boilers) and almost always costs more to install than the alternative?

Precharged diaphragm or bladder-type expansion tanks began appearing about 40 years ago. They have now captured most of the new system market, and should continue to displace standard tanks in replacement situations.

5. Pumping Toward The Expansion Tank: If there's one technical point that has been emphasized at countless hydronic seminars across the country over the last 10 years it's the concept of pumping away from the system's expansion tank. Still, old habits die hard. Every year I have opportunity to visit newly installed jobs with nicely aligned rows of circulators all pumping into the return header of the boiler. Without fail, the expansion tank is waiting as the point of no pressure changes on the other side of that boiler.

Installing the pumps on the return side of the boiler to take advantage of lower water temperatures had its benefits when pump seals were less reliable. But modern seal technology, as well as lower supply temperatures, make this a moot point today.

Can you still "get away" with setting systems up this way? Sure, under certain forgiving combinations of low head circulators, lower water temperatures, higher system pressures and a good air separator. But it's sort of like "getting away" with building a house from the roof down. Why make air control in hydronic systems any more of a concern than it has to be? So many of the gurgles, whooshes and burps (not to mention the "need to bleed") once accepted as unavoidable simply go away when you pump away.

A Graceful Exit

The technologies I've discussed have served the hydronics industry well during the now fleeting 20th century. Collectively they have allowed hundreds of thousands of homes to enjoy the comfort of hydronic heating. But the curtain is closing, and the next act is waiting in the wings.

How will these former mainstays of hydronic heating technology slip into plumbing history books and out of modern installation practice? Don't rule out code changes. Tankless coils, for example, have already been challenged as some states seek to update their energy codes. However, not being a big believer in the government as the preferred regulator of hydronic heating technology, I would prefer to let competitive market forces combined with professional attitudes toward installing the best systems possible do the inevitable.

The next 10 years will surely see major advances in hydronic heating technology. Keep your eyes peeled for new products and new design tools. Take time each month to stay abreast of what's happening in the field. Learn all you can about it then draw your own conclusions about what's best for your business and your customers. Hydronics is a creative medium, use it to its fullest potential.