Gary Klein believes in fixing big problems first. “When you solve those, you work on the smaller ones,” he says. More than 30 years ago, when he first started working in sustainable building design, his biggest problem was space heating. However, all of that changed after receiving several phone calls from a determined salesman who always asked the same question: “How long does it take you to get hot water from your fixture?”

After a year of calls, Klein finally decided to find the answer, mostly to get the salesman off his back. The results astonished him—it took 4 gallons and four minutes before he got hot water from his shower. And his home was only 1,600 square feet.

It has been more than 20 years since Klein received that first phone call, and he now spends his days teaching architects, builders, and contractors about hot water design, which he now believes to be a bigger problem than space heating, especially in energy-efficient homes. “If you build a really efficient shell, space conditioning needs go down, but the number of people per household doesn’t change,” he says. “If you still have three people in the average household in a very efficient home as opposed to a very inefficient home, water heating could become as big or bigger than space heating and almost as big or bigger than space conditioning.”

Like many green principles, Klein says the key is to approach hot water systemically. In fact, he says that builders can cut hot water use roughly in half just by “wringing out the wastes behind the walls.”

Klein could do even better than 50%—getting waste down to less than 1 cup versus 4 gallons—but he admits that isn’t practical for most construction projects. However, he does believe that the industry can set a target. “I think that by 2020, all new homes should have hot water distribution systems such that every fixture fitting gets hot water within two to four seconds after people turn on the tap,” he says, an equivalent of 1 to 3 cups of water.

Klein believes that having this type of quantifiable metric is the key to transforming hot water design, a strategy that hasn’t traditionally been used in construction. “Mostly, we sort of pray it works right,” Klein quips.

The problem, he adds, is that no one is really taking responsibility for plumbing performance—a job he feels belongs to builders. “The builder needs to take responsibility for the intent of the plumbing system,” he explains. “They need to specify that performance in terms of what the plumbers bid on, and then they need to inspect to that as they build.”

Klein says his performance metric of 1 to 3 cups is easily achievable, provided that the industry implements what he and his consulting firm Affiliated International Management refer to as “structured plumbing principles.” Some of the key principles are as follows:

• Plumbing should be zoned in each building, such that if there are two wings and they are very different in direction, there is not one large plumbing system. There should be one plumbing system for each zone. There might only be one water heater serving both zones, but there should be two plumbing systems serving the zones.

• Plumbing should be structured such that the trunk line serving a zone of the house is routed so that the branch lines to the fixtures are short-length so you don’t have to fight the diameter question at the code level.

• All hot water pipes should be insulated such that they get greater time between uses for the pipes to cool down, which means more uses will be hot, even without a recirculation loop.

• Each zone, if necessary, should be primed when hot water is needed by using a demand-controlled pump.

• Drain water heat recovery should be used wherever practical.

• Water-use efficient fixtures and appliances should be installed.

According to Klein, most of these principles can be implemented without any major investment. In some cases, he says builders may end up with reduced plumbing costs. “The only extra cost is whether you decide to put in a pump to prime the lines with hot water or not,” he says. “If you are serious about water-use efficiency, you put the pump in. If you are not sure you are serious, you make it ‘retrofit ready.’”

If the industry is ever going to reach his goal, Klein says it will be critical for minimum code to specify maximum volume from sources to uses. And that needs to happen fast. “Even if we get that to be minimum practice by 2015, it still takes a few years for that to get adopted at the local jurisdiction level and might not take wide effect until 2020 or 2021,” he notes. He also thinks that code will have to accommodate smaller diameter tubing.

So far, Klein has been successful in getting many of the structured plumbing principles written into the International Green Construction Code and IAPMO’s Green Plumbing and Mechanical Code Supplement, but more needs to be done. “I’ve been working on this for some time,” he says. “I need help. People have to show up at hearings and say, ‘Yes, this makes sense to us. I am willing to build to it.’”

Parallel to applying these new principles, Klein also thinks that within the next decade, all new construction should be using combination space conditioning and water heating systems, with the emphasis on water heating. This, he says, will be a necessary change as homes get more efficient. For example, according to Klein, the heating system needs for an energy-efficient 2,000-square-foot home in Minneapolis should be about 10 BTU/h per square foot. The same home in Los Angeles would be about 3 BTU/h per square foot. Therefore, the Minneapolis home would only need a 20,000 BTU/h heating system, and the home in Los Angeles would only need a 6,000 BTU/h system. Today, the smallest high-efficiency (92+) gas furnace available is 40,000 to 45,000 BTU/h.

The same holds true for water heaters. “If cut my consumption of water down by 50% to 60% for hot water, I don’t need a really big water heater any more, do I?” Klein says. “The systems are going to be combined so I can afford high-efficiency water heating, and then I can start talking about if I am going to preheat with solar or if I am going to preheat with heat pumps. But we’re unlikely to resolve all of the issues of the heating methodologies until the next decade.”