ALTHOUGH I ENJOY working with copper pipe, and I really like a good design challenge, I've come to the conclusion that a wellengineered low-loss header, out of the box, makes a lot of sense. Modern high-head condensing boilers pretty much dictate their need and use.
Just before this heating season's first cold front closed in around our home in southwestern Missouri, I was in the midst of a hydronic overhaul; only the radiant loops would stay. I had ripped out the system's primary loop, and the tangle of copper thrown on my porch — with many of the parts still intact — hinted at the complexity of the primary/secondary piping arrangement that I was replacing.
As I wrangled that piping network from my mechanical room wall, an idea struck me. Why not inventory what's here, and estimate the time it takes me to design and construct what a pre-assembled low-loss header provides?
What lay in ruins on my porch floor was this: 10 ft. 11/4-in. copper; eight 11/4-in. reducing tees; six 11/4-in. elbows; air purger; unistrut channel; unistrut clamps; loop hangers; miscellaneous fasteners; solder and flux; and the time to design, cut and torch the loop and assemble all the components.
The approximate cost? I figure $ 1,000 to $ 1,500. Probably more, especially considering the volatility of copper costs!
My new, improved hydronic heating system includes several Grundfos three-speed SuperBrute circulators, a selection of Watts Radiant gear, a Lochinvar Knight wall-hung condensing boiler and a Caleffi HydroLink low-loss header.
Low-loss hydronic headers are available from Caleffi, Viessmann and Buderus in pre-assembled packages that perform the function of a parallel primary loop. The key detail is a pair of closely spaced tees or a hydraulic separator between the boiler or heat source and the load circuits. Their purpose is to connect the secondary circuit to the primary loop in such a way that neutralizes any tendency to influence flow in the secondary circuit.
Many regard the installation of a parallel primary loop or low-loss header as fundamental to the optimal performance of low-temperature, multi-zone hydronic systems of almost any size or configuration. Some, however, caution against overusing low-loss headers.
A P/S primer
Hydronics expert John Siegenthaler says that primary/secondary piping has been used in the hydronic heating industry for decades. He adds that the essential design detail has always been a pair of closely spaced tees that couple each secondary circuit to a common primary. This detail "uncouples" the primary and secondary circuits, allowing several circulators of different pumping abilities to "coexist" within the same system without interfering with one another.
Whether a parallel primary loop is built on site, or the function is performed with a purchased, preassembled low-loss header, it's the closely spaced tees — or their equivalent, closely spaced ports — that allow each circuit to function as a singular circuit with no real connection to other circuits.
With P/S piping, the ability to isolate system circuits makes it relatively easy to design sophisticated multi-load systems without concern over how flow rates and pressure drops will change as various circulators turn on and off, Siegenthaler says. This is a huge advantage because, otherwise, circuits compete with one another for water pressure and greatly complicate the mission of heat distribution.
Most important, Siegenthaler says, is the ever-broadening understanding of how to apply the technology. Clearly, this will result in greater numbers of high-performance systems. And it's interesting to note, too, that these systems aren't necessarily large or complex. While P/S piping is best suited for more complex, multi-load, multi-temperature systems, their applicability can extend into the arena of simpler hydronic systems. P/S piping can be used for small, three-and four-zone radiant heat systems.
Series primary loops are best suited to situations where two or more secondary loads will operate with different supply temperatures, Siegenthaler says. He adds that the basic principle is to connect the higher-temperature secondary circuits near the beginning of the primary loop and the lowertemperature secondary circuits near the end.
This arrangement tends to increase the temperature drop along the primary loop, reducing flow rate. An added benefit is that it may permit a reduction of the size of the primary loop's piping and circulator(s).
Sensible modifications to this basic design will accommodate any number of secondary circuits, permitting them to operate at similar supply temperatures.
A different view
As I mentioned earlier, some hydronics experts caution against the idea that every job can be designed this way. This group includes CONTRACTOR's own hydronics columnist, Mark Eatherton. He suggests a more judicious approach to applying these design techniques because he believes that it's possible to overuse low-loss headers.
"I'm aware that Viessmann recommends their use with the Vitodens boilers to ensure no more than a 30° delta on the boiler side," Eatherton says. "The same thing can be accomplished through primary/secondary piping, but many contractors unfortunately don't understand the proper design and use of a primary/secondary configuration. They lack attention to detail regarding distance between elbows and first tees and elbows and last tees, causing unwanted flow through the secondary."
Eatherton notes that when we first started doing primary/secondary piping, things were much different. He adds that times have changed, and many contractors have learned waysto do the piping that allow all branches of the system to see the highest temperatures available with the boiler enjoying the lowest temperatures possible. Hence, he notes, we have the best of all worlds.
"There are times when the prefabricated manifold makes sense, but it's not in every case, and because we typically do large systems, a four-port unit just doesn't have enough ports to satisfy our needs," Eatherton says.
He adds that he does agree with me that low-loss headers can save a lot of time and money, if they fit the need.
With the advent of low-mass, modulating, condensing boilers, Eatherton says, many of have figured out a way to eliminate the need for the circle circulatoron snow-melt systems. The circle circulator is still necessary if numerous output temperatures are required, and if there are numerous heat sources in one system, he says.
"I just can't yet see the prefabricated units satisfying that need, but it's never too late to teach an old dog new tricks," Eatherton says. "I'm always open to better and faster ways to get'er done."
Bob "Hot Rod" Rohr owns and operates Show Me Radiant Heat, a division of MAXROHR Inc., a contracting firm in Rogersville, Mo. A past president of the Radiant Panel Association, he holds Master's licenses in plumbing, mechanical and gas fitting. He can be reached via e-mail at [email protected] or by calling 417/753-3998.