As a respected remodeler and active leader of the National Association of Home Builders, Bill Owens has been involved with the green building movement for more than two decades. So when it came time for him to remodel his own home, Owens designed it to be zero energy ready (ZER), with a predicted Home Energy Rating System (HERS) Index rating under 30.

While ZER homes currently make up less than 1% of the residential market, the category represents a market opportunity of $33 billion by 2037, according to the Rocky Mountain Institute.¹ A 2020 inventory of ZNE homes from Team Zero counted 28,000 homes, which is a 26% increase from the previous count in 2018, and it’s projected that there are another 30,000 ZNE homes in development.²

Homeowners are increasingly measuring whole-home performance with standards like ZER to differentiate between potential purchases. Another common way to make this assessment is through the HERS Index, which measures a home’s energy performance against a reference model ranging from a Zero Energy Home (0) to a rating of 150 for older existing homes. A standard new home is awarded a rating of 100 while a typical resale home rates 130, according to the U.S. Department of Energy. Moving one point up or down the linear scale is equal to a 1% change in energy performance.

Savvy construction professionals like Owens are implementing mixed-fuel home designs in housing projects to stay ahead of the ZNE housing market and improve their project’s HERS rating. Owens’ 1970s mountain chalet outside Flagstaff, Arizona, is in a dry mountain desert climate. At 7,000 feet of altitude, it experiences extreme temperatures with an average of 100 inches of precipitation annually, mainly as snow. To achieve the comfort, resilience, and efficiency Owens had in mind for his “forever home,” the ideal energy solution was a dual fuel system with the reliability and performance of propane.

Ultra-efficient technologies and materials

Owens’ remodel project included many of the technology and building material hallmarks of modern ultra-efficient homes. He used continuous 2-inch foam insulation on the outside of the house, along with a reflective barrier that reduces heat flow. To remodel a home with existing 2×4 construction, the team used a combination of open-cell and closed-cell spray foam insulation, including 4–5 inches of closed-cell spray foam around the existing crawl space and about 8 inches of spray foam in the attic to achieve close to an R-50 insulation value. Owens paid particular attention to reduce air infiltration around windows and used energy-recovery ventilators to provide efficient ventilation for a home with about 1 1/2 air changes per hour.

With a home that well-insulated, a high-efficiency mini-split heat pump system can handle the heating load in moderately cold conditions. But temperatures on the mountain can drop as low as -30 degrees Fahrenheit, and Owens didn’t want a standby generator substantial enough to run all the heat pumps during an outage. A hybrid heating solution with propane furnaces for the first floor and crawl space was ideal. “I just didn’t want the house freezing up on those cold nights,” he says. The crawl space furnace also heats up the hard floors above the crawl space, which are necessary in the dusty Arizona environment.

With backup propane heating in place, Owens could install a propane standby generator to handle the electrical needs of the furnaces, water pumps, refrigerator, and smart home features such as the smart water valve protecting against leaks. “We’re literally at the end of the grid,” Owens says. “I am the last house on about 2 miles of electric overhead running through a national forest. If a big snowstorm takes down a tree, I could be affected. I’m pretty low on the web to come back and get picked up again.”

Tankless water heating helps achieve green rating

Another feature that supports both the low HERS rating and the lower load on the generator is a propane tankless water heater. Owens calls it “an easy choice just because we were trying to get a robust National Green Building Standard Green rating out of it. There’s no electric unit out there that’ll keep up a whole house. Plus, it’s fairly frequent that we’re out of town, so we just didn’t want any [hot water] storage in there.” The tankless unit includes a programmable recirculation loop to minimize wasted cold water dumped down the drain in a state where water is precious.

In addition to energy-efficiency features, propane fuels several of the home’s most appealing lifestyle amenities. Owens plans to install a propane fire feature on the enclosed porch, which is a safer alternative to open wood fires in a state with frequent fire restrictions and a site bordering a national forest. The home will also have propane cooking, both on an outdoor grill and on the kitchen cooktop. “I like induction, but I don’t like it nearly as much as the propane,” Owens says. “I’ve checked with our energy rater, and he basically said that you get such a clean-burning fuel with propane that that’s not considered a detriment if you have the exhaust hood. It doesn’t work against you on the points for the green rating.”

Building to zero energy standards does come with a higher cost, Owens says, but the payback comes both in long-term energy cost savings and immediate comfort improvements. “This house is so tight that we don’t notice when the wind’s just howling or when we’re getting huge temperature swings out there,” he says.

The experience has also bolstered Owens’ support for dual-fuel homes with both electricity and propane. Trying to run his home purely on solar and battery backup — in a state with disincentives for solar installations — would have been cost-prohibitive. “In a fairly severe environment or environments that are enough away from the grid, there is no perfect panacea with just one energy source,” he says.

The growing market for ZNE

There are many strategies to achieve ZNE, but they all reflect the market’s desire for clean energy strategies that are accountable, equitable, and reliable — without the need for builders like Owens to sacrifice performance or profitability. In fact, a survey by Harris Insights & Analytics for the Propane Education and Research Council (PERC) found that 83% of homebuyers and 89% of builders are likely to consider a ZNE home for their next purchase. Almost the same amount — 81% of homebuyers and 84% of builders — are very or somewhat willing to pay more for a ZNE home. As the ZNE housing market continues to grow to meet this demand, now is the time for builders to educate themselves about ZNE construction and how mixed fuel options can help them achieve more favorable HERS Index ratings.