I recently attended a program where the presenter (a good friend of mine) discussed how hot water recirculating is “green” and should be mandated by the plumbing codes. We often think of hot water recirculating systems being installed in commercial buildings. But he emphasized residential construction.

Until this presentation, I often thought of a recirculating system as being somewhat anti-green. In the good old days, environmentalists spoke of the waste of energy to maintain the temperature of hot water in a recirculating system. I could not disagree with these environmentalists; installing a hot water recirculating system does use more energy to heat the water and run the pump for circulating.

As was pointed out in this presentation, though, this old-school thinking was shortsighted. When going green, you must consider all of the energy use, not just the local use in the building.

Without a hot water recirculating system, there is a tremendous waste of water when a remote fixture is first used. A person turns on the faucet and waits for the hot water, resulting in water waste. That water was once heated, which means there is a waste of heated water, and use of the water heater. The water had to be treated at the water treatment plant and transported through the public mains. That used energy. Finally, the water is discharged down the drain and must be treated at the sewage treatment plant.

When you take everything into consideration, it is easy to see that hot water recirculating is green.

Why Wait?

The plumbing codes only require temperature maintenance when the source of hot water is more than 100 feet to the last fixture. A fixture that is 99 feet away will have to wait a long time for hot water.

I recently did the plumbing in my older brother’s house. His water heater was less than 100 feet to the furthest fixture, but the house was still big. I returned the hot water line just short of the last room having plumbing fixtures. There was about 15 feet of additional piping that was not on the recirculating line.

Before he moved in, I asked my brother to conduct a test. First, I wanted to see how long it would take to get hot water to the most remote fixture without the recirculating pump operating. With just the hot water faucet turned on, it took three and a half minutes to get hot water. At a discharge rate of 2.2 gpm, that amounts to 7.7 gallons of wasted water.

After allowing the hot water piping to cool down, the recirculating pump was turned on. Hot water arrived at the same faucet in 10 seconds. When comparing three and a half minutes to 10 seconds, that is considerable.

In my own home, where the remote fixture is much closer to the water heater, it still takes a minute and a half every morning to get hot water. Still a considerable waste of water every day.

As you can see, the 100-foot distance specified in the plumbing codes is not a green-friendly number. You should start to consider hot water recirculating for almost all plumbing systems.

Hot Water Maintenance

The green debate continues with the various ways of maintaining hot water in the piping system. The heat tracing manufacturers claim they are more green-friendly since they use less energy to maintain the temperature of hot water. Self-limiting heat tracing tapes only supply energy when the water temperature drops below a certain temperature, typically 110 degrees F. Additionally, the heat tracing tapes can extend further down the piping to limit the amount of hot water piping that does not have temperature maintenance. Finally, they claim that there is no cost of operating a pump.

Pump manufacturers are providing ways of controlling the use of the pump to save energy in the operation of the pump and the reheating of the water. The simplest form of control is a timer clock on the pump. The common complaint about a timer clock is that once there is a power failure, the clock is out of whack and no one remembers to reset it.

Other systems turn on the recirculating pump by sensing the temperature of the hot water. When the temperature drops, the pump starts to circulate the hot water until the temperature setting is satisfied - another good green method of limiting the use of the pump.

Some engineers prefer a small constant operating pump for a recirculating system. You don’t have to move much water, and the pump likes to operate 24/7. The thought is that the smaller pump will use much less power. Plus, the life of the pump is greatly extended.

Another concept is to provide many instantaneous water heaters throughout the building. This avoids long runs of piping, and minimizes the temperature loss in the hot water piping system. This type of design is gaining popularity in certain commercial buildings. I also have seen the concept used in a large “McMansion”: Three gas-fired water heaters were located throughout this huge house.

The beauty of a hot water recirculating system is that you can sell it as green and convenient. The owner can be proud of helping the environment, while not having to wait long for her hot water.

When analyzing a hot water distribution system, forget about the 100-foot distance for hot water recirculating. Start thinking that you should always include a hot water recirculating system. Sell it as a green feature for the building. Then remind the owner of the convenience of having hot water instantly.

This is an easy sell, and everyone is happy. Just remember, go green.

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