Although I’ve worked with hydronic heating for four decades and designed systems around just about every possible heat source, I would be hard-pressed to predict what might be available as hydronic heat sources 25 years from now. Fifty years from now, I doubt that I will be predicting anything, and yet, hydronic heating, in some form, will hopefully still exist. If comfort, efficiency and lasting value, rather than only first cost, become established as the market “drivers,” hydronics might even be the dominant method of heat delivery. Imagine that.
By the latter half of the 20th century, the North American hydronics industry got used to the fact that some hydronic heat sources could last for several decades. It was not uncommon for a properly-applied cast-iron boiler to have a useful life of 30-40 years. These boilers usually became technologically obsolete before they were incapable of operating due to some major failure. This was just fine when fuel prices were reasonably cheap and stable, and product development occurred at a somewhat slower pace compared to today. Back then, most North Americans cared little about the “box in the basement,” provided that it responded when the dial on the T-86 got turned up in the fall.
Today, some energy costs are more than four times what they were 20 years ago. Predictably, more consumers are interested in what that box in the basement is consuming. Our industry has responded with a wide spectrum of heat sources from boilers to heat pumps to solar collectors. Still, you won’t find many manufacturers who, in all candor, will tell you that these contemporary heat sources are likely to last more than 20 years.
Balance of system
Although the heat source in most hydronic systems seems to draw most of the attention — probably because it’s the thing that converts dollars into heat, it's certainly not the only part of the system that deserves consideration. A well-designed, correctly installed and properly maintained hydronic distribution system can last for many decades, and, in most cases, well beyond the useful life of its original heat source. This raises an obvious question: “What can designers do today to ensure that the distribution systems they create are compatible with future heat sources?”
The answer should consider the materials used in the system, how the system will be maintained and at what conditions with the system operate.
From the standpoint of materials, most of the present-day polymer tubes, when applied at temperatures and pressures well below their maximum ratings, should last upwards of 100 years. I’ve even read speculation of 200-year lifetimes for PEX tubing. To achieve such lives, these materials should be installed so that they are not abraded due to expansion/contraction movement. They should also be protected from ultraviolet light, and not exposed to hydrocarbon solvents. In my opinion, oxygen barrier tubing should be used on all hydronic system applications.
Copper and copper alloys such as brass should not be exposed to acids such as contained in residual soldering flux or degraded glycol antifreeze. They should also not be exposed to water with high concentrations hydrogen sulfide. Flow velocities in copper tubing should be limited to 4 feet per second. All piping circuits containing soldered copper or threaded iron or steel piping should be internally cleaned with proper hydronic detergents to remove residual solder flux and cutting oils that would otherwise remain in the system, potentially causing corrosion or impaired thermal performance due to fouled heat transfer surfaces. Systems should be operated with demineralized (not softened) water. When glycol-based antifreeze is used, it should be tested annually to verify a pH between 7.5 and 8.0.
Magnetic particle separation should be used to gather up iron oxide and allow it to be periodically flushed from the system. This is especially important for the new generation of circulators using permanent magnet motors, which are likely to become the “new normal” for circulators as efficiency regulations push circulators with permanent split capacity motors into the archives of hydronics technology.
From the standpoint of system design, the dominant concept can be summarized with three words: low water temperature.
A well-designed, correctly installed and properly maintained hydronic distribution system can last for many decades, and, in most cases, well beyond the useful life of its original heat source.
The one prediction that I am willing to make about future hydronic heat sources is that they will operate best at low water temperatures.
So, when you size up radiant panels, panel radiators and even fin-tube baseboard, I recommend that you select and size them so that they can supply design load conditions using water no warmer than 120° F. Even lower supply water temperatures are preferred when possible. This allows those distribution systems to be compatible with a wide range of contemporary hydronic heat sources.
I urge those who design hydronic systems to think carefully about what your systems will look like 25 years, or perhaps 50 years from now. Will those who install the next heat source in these systems see that you considered the long life span of a well-planned and easily maintained distribution system, or will they find it necessary to “shoehorn” in supplemental heat emitters? Will the controls that operate your systems at present still work 20-plus years from now, or will they add to the growing tonnage of electronic waste that we are already producing? Are your present designs for hydronic distribution systems truly “sustainable,” or will they succumb to a “tear out and replace” by the next generation of hydronic pros?
A story worth telling
Well-designed, correctly-installed and properly-maintained hydronic systems are unique in comparison to much of latest hardware currently designed into buildings — especially residential structures. To see why, just visit one of your local home appliance stores and see if the salesperson will, with a straight face, tell you that the refrigerators, dishwashers or clothes washers they currently sell are likely to last for at least 20 years — assuming normal usage. Ask them if the failure of a small component, such as a small proprietary printed circuit board, that might be zapped by a utility power transient, can be replaced at a cost that’s less than 50% of what a brand new appliance costs. Ask them why virtually everything they sell has the option of service agreement. Planned obsolescence is plausibly deniable, but plainly evident, especially to those of us who remember how these appliances were built 40-plus years ago. It’s also something easily veiled from consumers who instead are dazzled by a touchscreen display, a synthesized human voice or IoT connectivity.
This “buy it today, trash it in 10 years or less” status quo presents a backdrop against which our industry can and should promote the long life of hydronic heating and cooling systems. Systems that can last for several decades. Systems that are truly “sustainable,” efficient and compatible with virtually any type of energy source.
Do what you can now to “future proof” the hydronic distributions systems you create. Those who follow will appreciate you forethought.