Many plumbers, at the behest of their local plumbing/heating wholesalers, have given in to the notion of dabbling in hydronics because, "after all, it is just piping isn't it?"

Plumbing vs. Hydronics. What do these two trades have in common? They both use piping and tubing to transport fluids from one point to another. And in most cases, they both require a certain skill and knowledge of how to solder. Beyond these few similarities, however, there are many major differences that do not seem readily apparent on the surface. Let's examine some of them:

Figure 1


Although both trades commonly deal with the same types and sizes of piping and tubing, their end results are quite different.

In plumbing applications, water is generally driven through the system by water pressure in the water mains. This pressure is typically 30-150 psi. This substantial pressure allows a large quantity of water to move through a very small pipe in a very big hurry at the flick of a wrist.

But in hydronics, although the piping may be pressurized by city water pressure, the actual movement of the fluid is accomplished by relatively small pumps, whose pressure-generating capabilities are typically less than 10 psi. Minor details, such as not reaming the pipe to full bore, can and usually do have a severe negative impact on the operation of a closed loop hydronic heating system. Although mandatory under the codes governing both trades that "the pipes shall be reamed to full bore," most plumbers don't take the time to ream their pipes because there is no perceived "negative impact" to the operation of their plumbing systems. In the case of most potable water distribution systems, this is true. This is due in part to the fact that their systems are not flowing constantly, and the flow is being driven by a force three to 15 times greater than the forces found in a typical closed loop hydronic heating system.

Knowing this adds new meaning to the path of least resistance and the need for the proper reaming of all pipes. Most good hydronic technicians know this for a fact. Those who don't are typically plumbers working in a "hydronician's" world.

Figure 2


Both trades use the same fittings, but hydronicians use fittings to balance out the subtle flows in their heating systems. The plumber on the other hand, just has to run pipes from point A to point B and let the city water pressure take care of getting it there.

A good hydronician would never consider using a "bull head" tee in his distribution system, but plumbers do it all the time. Hydronicians are required to use as few fittings as possible due to the potential hydraulic resistance to flow, and correct flow is critical to the operation of the heating system.

Plumbers could actually learn a lot from a good hydronician. Let's take for example the piping of three 3-port hot water storage tanks being heated by a low mass copper fin tube boiler. A good hydronician would pipe the tanks in parallel reverse return to keep the pressure drops through all three tanks equal. A conscientious plumber would probably pipe the tanks in pyramidic parallel to even out the flow. An unknowledgeable plumber would pipe them in parallel direct return because "it looks better and uses less pipe." Let's look at the physical differences between these three methods.

In Figure 1, the tanks are piped in pyramidic parallel, just like it shows in many manufacturers' installation manuals. The correct balanced flow is dependent on the installer's ability to guarantee the perfect center to center positioning of all header tees. If he can't center the tees perfectly, the flow through the tanks will not be balanced. This system is quite cumbersome to install and maintain and is quite labor and material intensive. A typical installation will require a minimum of 15 elbows, 13 tees and around 75 soldered joints. The labor necessary to install a system of this type would depend on the skill level of the installer and tools used. A person of my experience and skill level could probably perform this installation in six to eight hours using conventional tools.

In Figure 2, the tanks are piped in parallel direct return. Piping in this manner will cause Tank #1 tank to see the majority of the flow, Tank #2 to see slightly less flow and Tank #3 tank to see very little flow. During draw down and pumped circulation, the water is going to follow the "path of least resistance," which will be Tank #1 and #2. Tank #3 becomes under used and will create shortages of hot water during peak load periods. The only way to balance this system out is to install balancing valves at the outlets of the tanks and the return tappings of the tank. Even with this, the balance will only be correct for the same flow that was imparted upon the tanks at the time of balancing. Flows less than design at the time of balancing will not be balanced through the tanks.

Although pretty in appearance, this method of installation should be avoided at all times. A typical installation of this type would require seven tees, six elbows, approximately 40 soldered joints and could be performed in four to six hours using conventional equipment. Balancing would require the addition of at least two to three additional hours.

Figure 3
In Figure 3, the tanks are piped parallel reverse return. The flow path and pressure drop through all three tanks would be equal during draw down as well as during pump-forced circulation. There would be no balancing required. This method of piping is preferred among knowledgeable piping professionals and is typically practiced by a good hydronician. The installation would require seven tees, six elbows, around 40 soldered joints and about three hours of "smart" labor. I emphasize "smart" because as a hydronician I don't use conventional tubing cutters, scratch cloth and 3/8-inch flux brushes anymore. Now that I am a hydronician, I use a carbide-bladed high speed chop saw, a 1-inch upright belt sander, flux sponges and I get the work done in less than half the time it used to take using traditional tools.

Based on what you've seen and read, which way do you think is the preferred way to do this job? Example 3 of course!


Prior to the introduction of the ball valve, the choice of valves was limited to gate valves and globe valves.

Gate valves look great until you have to use them. In most cases, they haven't been used for the 20 or so years that they've been installed. Consequently, over the years, an accumulation of scale and other deposits have built up on the gate glides and stem assembly. The first time you have to close it is usually the last time it will open.

CRUNCH SNAP! I don't know of many other plumbing sounds that will give a plumber a sick feeling than that noise will. If the plumber happens to be so lucky as to have another valve in place up stream, the replacement of the valve is not too bad. If the plumber is unlucky, he may have to shut off the whole street just to replace one valve.

Globe valves, on the other hand, depend on a washer and seat assembly for positive shut off and are inherently more reliable than their gated counterparts. The major disadvantage of globe valves is their inherently high pressure drop. Remember, a good hydronician avoids the use of high pressure drop items in the installation of his system. A good hydronician prefers the use of full port ball valves.


Other than a domestic hot water heating system circulation return pump, or possibly a sewage ejection pump, that's as close as most plumbers ever get to a pump. Hydronicians, on the other hand, depend on pumps to make their systems work. A good hydronician knows how to read a pump manufacturer's performance chart and knows how to interpret what he reads.

As you can see, installing a good hydronic heating system is not as simple as connecting pipes from a boiler to some baseboard and throwing a pump and a few other things in for good measure.

So stop and think about these differences the next time you have the opportunity to install a hydronic heating system. It will make a world of difference in the operation of your system. And by the way, the next time you decide to take on a hydronic project, think like a hydronician, not like a plumber. And I know what plumbers think like. I am one!

Applying Hydronic Principles
To Basic Plumbing Systems

Having been in the plumbing and hot water heating business for more than 20 years, I've had the opportunity to see some pretty wild and crazy pump installations done by plumbers on domestic hot water circulation return systems.

I have seen more pumps die an early death from being run dry than I care to count. In fact, if I had a dollar for every pump that was run dry, I'd probably be a very wealthy man!

With these untimely pump deaths still fresh on my mind, I find it necessary to write this article in an attempt to educate and "hydronicize" all those plumbers out there who don't understand what it is that they're doing to cause the deaths of these young pumps.

First, let's cover some basic rules that apply:

  • Never install a ferrous-bodied system. Rust never sleeps.

  • Always size the pump correctly. Don't assume! If in doubt, contact your local wholesaler and tell them how long the longest main is, how large it is, how long the return is, what size it is, what type of check valve is being used, how many and what size elbows are in the circuit and how many gpm you desire to move through the circuit. (Typically not more than a few gallons per minute.) Bigger is not better, and one size does not fit all.

  • Always install a check valve on the circulation return to prevent cold water from back charging through the return. Your customers will love you forever. Has a customer ever complained to you about fluctuating hot water temperatures while they're trying to shower?

  • If it is necessary to install a check valve on the cold water supply system, make sure you install a properly sized expansion tank on the outlet of the storage tank. I intentionally over emphasized "if" because in 90 percent of the cases where I see a check valve installed, it's not necessary. How many leaking T&P relief valves did you say you've had to replace?

  • Always install a timer and an aquastat on the domestic hot water circulation return pump. I have never seen a situation in a residential setting that the DHW circulation return needed to be run 24 hours per day. In most cases, turning the pump on one hour before first hot water usage in the morning, and turning it off 1/2 hour after the last daily usage in the evening is more than adequate.

    With the new programmable time clocks available from the pump manufacturers, it's even possible to run the pump for every other half hour when it is between starting and ending uses. With the aquastat installed, when the water comes back adequately hot during a preprogrammed "on" period, the pump is turned off, saving unnecessary wear and tear on not only the pump, but also the piping system. Hydraulic Erosion Corrosion is not a pretty thing.

  • Always insulate the circulation return lines and the hot water mains. The typical perception is that the heat losses from the pipe are occurring within the heated envelope, and are, therefore, not considered an "unrecoverable" loss. This is true. However, most houses are not in a heating mode 365 days a year.

  • Always, always, always install a purge cock on the end of the circulation return, downstream of the pump, and make sure the pump is full of water PRIOR to turning the pump on. Again, if I had a dollar for every ...

  • Never ever, ever install two or more returns into a common return without providing some means of balance and/or isolation. How else are you going to make sure that each individual return has been thoroughly purged and properly balanced?

  • Always install isolation valves around any components that you know will eventually need to be repaired or replaced. Do you know how to use a scuba suit?

    I have included a drawing showing the perfect circulation return system for a typical domestic hot water heating system.

    The plan is quite simple. Cut this article out and paste it to the inside of your lunch box. Then the next time you're in the field installing a circulation return pump on a DHW system, take a lunch break before you install the pump. (To hell with your boss, you can take your lunch when you feel like it. Right?) Then, while you're eating your lunch (or breakfast), study the drawing and when you're done with your break, install the pump the way you saw it done in this article. Pretty simple, eh? And maybe when your boss sees what you've done, he'll offer to take you out to lunch. Not a bad deal!

    And think of all the young pumps whose lives you will save. Better yet, think of all the mother pumps out there who you'll have made happy.

    In all honesty, if you do it this way, I guarantee you'll have done it right.