A certificate on the kitchen counter says this home is 45% more energy-efficient than average, the number printed large, boldfaced, centered on the page. Below it, a HERS score of 55, placing the home impressively close to a scale where zero means net-zero energy. Builder sales materials referenced this score at least three times during the contract process. What they didn't mention: the word "average" on that certificate is measured against a home built to the 2006 International Energy Conservation Code. A neighbor's code-compliant house, built the same year, probably scores around 70.
Efficient? Absolutely, but the distance between what the certificate implies and what the utility bill delivers starts in that 20-year-old baseline.
A Score Frozen in 2006
RESNET's HERS Index, the Home Energy Rating System that underpins virtually every energy-efficiency marketing claim in residential construction, uses the 2006 IECC as its reference point. A score of 100 means a home performs at that code level, and lower scores represent greater efficiency, down to zero for net-zero energy.
Energy codes have improved dramatically since then, with requirements tightening in the 2009 IECC and insulation, air-sealing, and mechanical standards jumping again in 2012, 2015, and 2021. A home built to today's code automatically scores around 70 on the HERS Index, 30% better than the 2006 reference home without any special upgrades, just minimum code compliance.
When a homebuyer sees a certificate saying their home is "45% more efficient than the average home," they're comparing against a standard that hasn't been code-minimum in most jurisdictions for over a decade. Green Builder Media's analysis calls this "a huge over-promise," noting that HERS certificates cite savings "relative to an average U.S. home" without specifying whether that means an average new home, an average existing home, or a blended average of everything standing.
In 2024, 436,000 homes were HERS rated, representing a third of all new single-family construction in the United States, with a national average score of 55. Sounds impressive until you recognize that a builder doing nothing beyond current code lands at 70. Real above-code efficiency, the gap a buyer is actually paying for, is the distance between 70 and 55, not the 45% the certificate proclaims.
“Zero Energy Ready” Meant Ready. Not Zero.
In 2013, the Department of Energy launched the Zero Energy Ready Home program to encourage builders to construct homes efficient enough that a renewable energy system could, in theory, offset most or all annual energy consumption. Over 12,000 homes have been certified under the program, each verified by third-party raters and meeting requirements that include Energy Star qualification, EPA Indoor airPLUS compliance, WaterSense adherence, insulation standards exceeding code, and solar-ready wiring pre-positioned for future panel installation.
Notice the word "ready," because it was doing real work in that name. Certification confirmed that a home could reach net-zero, not that it was net-zero. But "ready" is quiet marketing compared to "zero energy," and builder sales teams leaned on the aspirational term.
Mandalay Homes, a top-200 builder certifying every house under the ZERH program, acknowledged the distinction through its chief technology officer in a Builder magazine profile: "Those houses aren't net zero. That program is just some cool details and resources… that help you build a fundamentally better home."
Meritage Homes, one of the program's flagship builders, delivers 10,000 energy-efficient homes annually. About 1% of their homeowners actually opt for enough solar to reach net-zero on day one. Ninety-nine percent get a genuinely more efficient home, consuming 30% to 50% less energy per square foot than code. But not what most people mean when they hear "zero energy."
Washington Dropped “Zero”
In late 2025, DOE renamed the program. Zero Energy Ready Home became DOE Efficient New Homes. Technical requirements stayed the same. Certification process unchanged. But the aspiration embedded in the name, that these homes stood steps away from zero energy, disappeared.
RESNET's announcement framed the rename as reflecting "DOE's commitment to advancing our nation's housing in ways that are most responsive to current and future market conditions." Neither "zero" nor "energy" as a modifier survived in the new name, replaced by "efficient," a smaller word for a considerably smaller claim.
Timing matters here. Renamed under the same legislative moment as the One Big Beautiful Bill Act (P.L. 119-21), which revised the Internal Revenue Code provisions governing the 45L tax credit for certified homes, the shift may reflect political language management, market realism, or both. Either way, the federal government's most prominent residential energy certification no longer uses the word that once defined it.
Builders who had been marketing "DOE Zero Energy Ready" on their sales sheets now hold a "DOE Efficient New Homes" credential. How many have updated their brochures is anyone's guess.
California’s Net Metering Collapse
If HERS scoring inflates the efficiency gap on one side of the net-zero equation, California's net metering overhaul collapses the energy-credit side. NEM 3.0, enacted April 15, 2023, cut the value of solar export credits by roughly 75% for PG&E, Southern California Edison, and San Diego Gas & Electric customers.
Under NEM 2.0, homeowners received retail-rate credits, about 30 cents per kWh, for excess electricity sent back to the grid. That arithmetic was foundational to the net-zero promise: generate more than you use in summer, bank credits, draw them down in winter, end the year at zero. NEM 3.0 replaced retail credits with "avoided cost" rates, typically around 8 cents per kWh.
Average payback periods for solar-only systems more than doubled, from five to six years under NEM 2.0 to 14 to 15 years under NEM 3.0, according to Wood Mackenzie. California's residential solar market contracted 60% to 80%. More than 17,000 jobs vanished.
For homeowners who bought a "net-zero" home in 2022, designed around NEM 2.0 economics, the math changed under their feet. Solar panels didn't generate less electricity. Walls didn't lose insulation. But the utility's compensation for exported power dropped by three-quarters, and EnergySage calculates that this shift increases the average solar homeowner's electric bill by about $63 per month. Over a 25-year panel lifespan, that's roughly $19,000 in lost savings. Recapturing the net-zero economics the original purchase price assumed may now require battery storage, another $10,000 to $15,000 investment the sales contract never mentioned.
A California Court of Appeal upheld NEM 3.0 in May 2026, rejecting challenges from environmental and solar advocacy groups. In California, at least, solar-only net-zero is effectively over.
What Happens When You Actually Measure
NIST built a Net Zero Energy Residential Test Facility in Gaithersburg, Maryland, and operated it from July 2013 through June 2014 with simulated occupants following standardized activity schedules. In its first configuration, the house produced 4% more energy than it consumed. An optimized second configuration hit 18% surplus.
It worked, but NIST's own technical report found "significant variation between the pre-demonstration phase simulation results and measured demonstration phase performance" across heating, cooling, hot water, and plug loads. Simulation assumptions about equipment efficiency and occupant behavior turned out to be, in NIST's careful language, "incorrect."
A 1996 Lawrence Berkeley National Laboratory study found that one rating system "tended to overestimate the actual energy cost by approximately 50%," and that none of four evaluated systems "showed any clear relationship between the rating score and actual energy cost." Perhaps most usefully for understanding why net-zero homes don't perform as modeled, LBNL identified the rebound effect: "occupants of more energy efficient houses 'takeback' some of their energy savings by using more energy services." Your home uses less energy per square foot. So you set the thermostat a degree lower in summer. Leave the lights on longer. Run the dryer twice. Models can't predict you.
What to Actually Ask
Green Built Alliance, a regional certification body in North Carolina, defines net-zero not as HERS zero but as HERS 15 or below, "recognizing that there is some variability in how people actually use energy in practice that the HERS score doesn't quite account for." That 15-point buffer is an honest acknowledgment that models aren't people.
If you're buying a home marketed as net-zero, zero-energy-ready, or any variation, three questions cut through the marketing:
First, ask what HERS score your home achieves compared to your state's current energy code, not the 2006 reference. A builder quoting HERS 55 in a state that adopted the 2021 IECC is offering roughly 15 points of real above-code efficiency, worth paying for but a long way from the 45% the certificate implies.
Second, in California: ask whether the solar system was sized under NEM 2.0 or NEM 3.0 economics, and if the home was designed before April 2023, rerun the payback calculation with current export rates and budget for batteries.
Third, ask for the modeled annual energy consumption as a number, in kWh, not as a percentage, not as a HERS score, not as a marketing comparison. A number you can hold against your first twelve months of utility data.
DOE dropping "zero" from the program name didn't change the homes. They remain meaningfully, measurably more efficient than code-minimum construction. What changed is the honesty of the label. For 12,000 certified homes and the thousands more marketed under a term they never quite earned, "efficient" was always the accurate word.