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Tankless water heaters make net zero achievable

A modular builder designed his own home to achieve California's ambitious zero net energy goals with a combination of solar power and propane water heating.

By Jeffrey Lee

California wants all new residential construction in the state to be zero net energy (ZNE) by 2020. Steve Lefler wants to prove it's affordable to achieve ZNE — today. 

ZNE homes produce as much energy as they consume, usually through a mix of energy-efficient building techniques and onsite power generation. As architects and builders throughout California gear up to meet the upcoming standards, Lefler, vice president of Modular Lifestyles, a modular home dealer and builder, decided to take on the challenge with his own modular home.

Using a combination of solar photovoltaic power and an efficient propane tankless water heater, he achieved the ambitious goal, and he has the energy bill savings to prove it.

The net zero challenge

Lefler constructed his 1,939-square-foot home in Paso Robles, California, where the unforgiving climate would provide a true test. "I'm very competitive to prove a point that I'm not in the middle of Irvine or San Diego, where it's very temperate climates," he says. "This climate is very difficult. It has 125 days of 100 degrees and 45 days of below 30."

Click to enlarge   
Click to enlarge 

The home stands up to those demanding temperatures with a well-insulated building envelope, achieving an R-value of 38 in the attic, 23 in the exterior walls, and 22 in the floor. A 3-kW photovoltaic system provides nearly all of the home's energy needs — except for the water heating.

"The worst nut to crack in net zero is heating water," Lefler says. "I have not seen an all-electric house work unless it has $30,000 worth of solar on the roof to run the water heater. You've got to build a whole other array just exclusively for the water heater."

Rather than the huge upfront cost of a larger photovoltaic array, Lefler simply turned to a propane tankless water heater. "I'm not heating 100 gallons a day," he explains. "I'm only heating what the family uses." The unit costs him about $90 per year to operate. "I'd rather spend $90 than build another 16 panels of solar," he says.

Lifestyle luxuries

While propane water heating was key to meeting his ZNE goal, propane also fueled other amenities that appealed to Lefler and his wife, including two sealed-combustion gas fireplaces. "She loves fireplaces," he says of his wife. "It's more ambience and romantic." Since wood-burning fireplaces are banned in new construction in the state, propane was a necessity to achieve that comfort.

Lefler also installed a luxe Bertazzoni propane range, inspired by professional chefs. "Do you watch the cooking shows?" he asks. "Emeril Lagasse, Bobby Flay, do you ever see them cook on electric? Need I say more?"

"It's a commonsense, logical solution to net zero."

Lefler plans to take his commitment to the ZNE goal further by installing a large battery system and a propane generator, taking the house entirely off the grid. "I already have propane, so I might as well use the propane generator to charge the batteries when those lack-of-sun days come for the solar panels," he says.

The results in the first two years of the home's operation have shown that it likely won't require a great deal of additional energy. Lefler spent an average of $611 on electricity and $300 on propane annually, and he says that without a power-hungry hot tub, the house would be close to net zero. He also earned a rebate through the California Advanced Homes Program for exceeding California's "Title 24" Building Energy Efficiency Standards.

With proof of performance in hand, Lefler is pitching a smaller, two-bedroom modular home design to government officials in cities across California. Using a similar combination of solar roof shingles and a propane tankless water heater to reduce energy costs, the homes would be ideal for housing that's affordable both to build and operate, with no natural gas infrastructure needed. "It's a commonsense, logical solution to net zero," he says, "by getting everything onto the electric side and just leaving the hot water to propane."


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