My first exposure to the word manifold had to do with cars, hot rods really. Names like Edelbrock, Weiand and Offenhauser were stickered across the rod’s windshields. Performance was the game back then. Allowing the engine to breathe easier or add additional carburetor size. Now-a-day’s manifolds, for me, are more work related, mostly in the hydronic industry.

Basically, manifolds serve as a distribution point for the fluids that carry heat energy in a hydronic system. Most commonly, we think radiant when we hear manifold. It’s the gathering point for the pex tubing used in hydronic radiant systems. They come in a large array of sizes, shapes, and materials. Copper and brass continue to be most common. Plain and stainless steel, various plastics and composites, really any material that can handle pressure and temperature can be formed into a manifold.

Some hydroncians built their own manifolds from copper tube, either with fittings or a tee-pulling tool. If you can lay down a waterproof bead, a welded steel manifold can be fabricated with basic hand tools. I have used welded steel manifolds from Earthlee that border on works of art. Lee will custom build a manifold for you, to any size and dimension you can imagine. I like a welded steel version for commercial shops, where they may see some abuse.

The sky is the limit for added features. Balancing valves, flowmeters, electric actuators, pressure bypass valves, air vents, temperature gauges, and even delta P circulators can be assembled onto manifolds. Custom sized wall cabinets are available for many radiant manifolds to allow a nice clean, easy access to remote manifold installations.

But consider manifolds for other fluid moving tasks, hot or cold.

Manifolds are ideal for distribution to panel radiators or hot water (HW) baseboard. For example, manifolds make for a great “homerun” distribution center. Manifold distribution is also used on the potable waterside for hot and cold home run systems. Vanguard, now Viega, pioneered that potable water manifold concept.

High flow manifolds with large diameter trunks, and larger branch ports are available for snowmelt or larger BTU moving job.

High flow manifolds are common in ground source loop fields. Here, too, the manifold can be loaded with options to ease installation, allow flow adjustments, and facilitate troubleshooting. GEO manifolds are often plastic or composite, from a simple group of PVC fittings, to the highly asserozied composites with all the features of a top quality radiant manifold, even an insulation jacketing package and mounting brackets.

The task assigned to manifolds is fairly straightforward. Evenly distribute the thermal energy - via water, glycol or other heat transfer fluid - to the heat emitters. The manifold is the final gathering point in the journey before the fluid marches off into service as the carrier of BTUs.

Most often we equate manifolds with radiant floor heat systems. This is a fair analogy as the radiant market is certainly one of the main drivers of innovation into manifold design.

I’ve actually site-built copper manifolds the length of the building. Lengths of copper tube and a tee-pulling machine is all that is required to accomplish this. It was a fun challenge, but fairly time consuming, and lacking of that factory look and finish.

On the high-end side you will see manifolds machined, assembled and built with the fit and finish of a quality watch. I have seen polished manifolds proudly displayed behind a glass front on a custom home.

Manifolds are available to accept all of the various PEX and hybrid PE tubes. Some manufacturers offer segmented “olives” (ferrules) to accommodate minor OD tolerance issues with the tube. Look for PAP specific connectors with isolation washers to keep the PAP’s aluminum layer from touching the manifold. This addresses any dielectric issues with the dissimilar metal corrosion potential.

I think we will see a resurgence in manifolds to accommodate ¾- or 1-inch zone valves for baseboard supply. With the emergence of delta p circulators into the U.S. market, I think we will see more systems zoned with motorized or thermal zone valves. Manifolds built to accept ¾- or 1-foot zone valve equipment may be back in Vogue soon. Deja vu all over again. Some may remember the early Sparco ¾ branch zoned manifolds.

Always flush your hydronic systems, use a cleaner if required to protect the manifolds and all the components of your systems. Chose a manifold compatible with the tube. I remember the early non-barrier radiant tube installations that used with steel manifolds. These rusted through in a few years time. If you use non-barrier tube in hydronics installations select the manifold material accordingly. If you use chemicals or glycols be sure the manifold is compatible. Be aware of temperature limitations. Check with the manufacturer about chilled water applications or limitations.

I’d venture to say the selection in manifolds is as large as the boiler offerings. Try the various styles and type to see which fit your style and applications best. Let the manufacturers know of any ideas or improvements you may have.

It’s time to pull manifolds out of the dark and into the spotlight. Man, oh man…I love a nice manifold!

Bob “Hot Rod” Rohr has been a plumbing, radiant heat and solar contractor and installer for 30 years. Rohr is a longtime RPA member and Plumbing Engineer and Phc News columnist. Bob joined Caleffi North America as manager of training and education.