Codes accept 'cross connections' as an acceptable design practice

The last code development cycle for the International Codes brought about a code change that was submitted to the model codes by a manufacturer of a unique product that has filled an aftermarket niche. An entrepreneur decided to address the problem of dumping water down the drain while waiting for hot water to arrive at a fixture. His solution to the problem was simply to add a small circulating pump under the lavatory or sink and connect it to both the hot and cold water lines to the fixture and circulate hot water to the fixture through the hot water pipe and utilize the cold water pipes as a hot eater return path back to the water heater.

When I first heard of the concept of circulating hot water back through the cold water piping, I was slightly amused and I was well aware of the fact that it was an obvious code violation along with a serious health and safety issue. The hot water in the cold water piping can create a scalding hazard and if it is hot or warm water it can lead to accelerated water treatment chemical dissipation and there will be an increase in the growth of bacteria and other organic pathogens in the water which creates a biological and potentially a legionella hazard. When I first saw the proposal, I was pretty sure that the plumbing industry was not going to accept circulating hot water in the cold water piping because that is a direct cross-connection and the code prohibits cross-connections. I thought the backflow prevention folks would surely see this and step up to address the issue at the code hearings.

Unfortunately, during the code hearing testimony, there was little or no opposing testimony from the backflow industry on this issue and the proposed code change was promoted as a “water saving” and “energy saving” measure to reduce the waste of water poured down the drain and to reduce the energy used to heat that water. It seems like green marketing hype had an effect on code development. They bought it and the code change passed. It seems you can call something green and people seem to think green is good so they blindly support it. Anyone can propose a code change and sometimes they don’t understand all of the consequences of their proposals. This sometimes leads to code change proposals that are well intentioned, yet unsanitary and unsafe. If a presentation is done well, it is possible to convince enough code committee members to support a code change that is in conflict with other sections of the code because it sounded good at the time.

The code change to recirculate hot water through the cold water pipes was presented in the name of energy and water conservation. I’m the No. 1 advocate for energy conservation and water conservation, but only if it does not create a health and safety issue. It appears the code change for circulating hot water back to the water heater passed because many of the code committee members were thinking of their personal experiences of waiting for hot water in their home and they were not presented with facts about the potential health and safety consequences to the public in larger buildings. I think this system is great for an individual homeowner who knowingly chooses to install this system in a private home and live with the health and safety consequences of such a decision. However, I do not believe we should allow it as a design option for all building types. We already have a way for hot water to be maintained at the fixture by installing a dedicated hot water return piping system. The codes have accepted cross-connections as an acceptable design practice.

With this code language, we have gone back in time about 50 years to the days of two handle faucets with crossover flow. I’m hoping there will be some comments and some common sense employed to correct this terrible mistake by well-intentioned individuals that has created a serious health and safety issue.

The following are reasons why we should not circulate hot or tempered water through the cold water distribution pipes:

Circulating hot water in the cold water pipes can scald someone who will not expect to find hot water in the cold water pipes. This is a form of cross connection that backflow protection language in the codes was specifically intended to prevent. The proponent has indicated there can be a thermostat that shuts-off the circulator when the water temperature gets to a given temperature, but that is a manufacturing option in their catalog and there is no language in the code change that mandates thermostats or even a maximum or minimum temperature. As the code change is written, there is no temperature limit for hot water that can be circulated through the cold water piping.

If someone in a high rise apartment building has a bathroom located a considerable distance from the circulated main decides to install one of these circulator pumps under a lavatory or sink, then everyone else in the building will have hot water return water flowing through their cold water piping. This is why we have code language prohibiting cross-connections between plumbing systems. If circulating hot water though the cold water pipes is allowed people in all other floors of the building will be drinking and brushing their teeth with hot or warm water.

Recirculating hot or warm water in the cold water piping will increase bacteria growth and biofilm formation in the cold water piping.

Hot water in the cold water piping system will promote accelerated dissipation of water treatment chemicals. The act of recirculating the hot water back into the cold water system is actually holding the water and circulating it in the piping system longer than it normally would have been. With the increase in low-flow and ultra-low-flow fixtures associated with water conservation measure, the water treatment chemicals will dissipate at the same rate while the flow rate goes down.

Reducing the water flowing out of and into the water system promotes stagnation. Lack of flushing water flow causes the water to remain in the piping system for longer periods of time. This contributes to water treatment dissipation and will lead to an increase in bacteria levels in the domestic water system and will contribute to legionella bacteria and other organic pathogen growth in the domestic water systems.

This allows the water treatment chemicals to dissipate over time and when the water is circulated though the water heater, the heat accelerates the dissipation rate of the water treatment chemicals. The water is held in the plumbing system for longer periods of time contributing to stagnation and loss of water treatment chemicals and less water in the drain to contribute to drain line transport.

If someone in any commercial building installs one of these circulating pumps that circulate through the cold water pipes, the people in other areas of the building that want or expect cold water will be receiving hot or warm water when the draw water from a tap for drinking or cooking. I would not be happy if the electric water cooler or drinking fountain in my office was receiving hot or warm water that is injected into the cold water pipes from a circulation pump under a sink in a tenant space down the hall. I will be drinking hot or warm water from the drinking fountain and if I have an electric water cooler, my electric bill is going to go up because now the refrigeration unit on my electric water cooler will be cooling hot or warm water instead of cold water.

The hot water in the cold water pipes will have dissolved metals in the hot water. This is because all tank type water heaters have magnesium or aluminum sacrificial anode rods in the tank that corrode and dissolve metals into the water to protect the tank from corrosion. These dissolved metals are present in hot water tanks, but typically not in the cold water piping. This is why all cooking shows recommend you fill your cooking kettles with cold water. It is for this same reason I don’t want the tenant on another floor in a condo building being allowed to circulate hot water with dissolved metals into my cold water piping on another floor for drinking and cooking water.

If you are as concerned about this, consider writing a comment opposing this code change on the International Code Council’s Cdp Access website. You can also attend the International Plumbing Code commentary hearings September 30 through October 7, in Long Beach, Calif. n

Ron George, CPD, is president of Plumb-Tech Design & Consulting Services LLC. The offices of Ron George, CPD, have relocated to 303 N. Monroe Street, Monroe, Mich., 48162. The phone numbers and website will remain the same: Office 734-322-0225; Cell Phone: 755-1908; and Website:

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