The Knox home has geothermal loops buried under the backyard.

Andrew Know, manager of Naval Facilities Energy Initiatives, decided to go “net zero” on his home in Washington, D.C. What Knox got was a true zero-energy home, done right on a budget.



Andrew Knox wanted to “walk the walk” of energy efficiency, so he and his wife, Elizabeth, had some decisions to make.  To attain zero net annual energy consumption, the home would need solar panels. The lot is only 3,500 square feet, and the surface area of the roof was about 600 square feet plus another few hundred square feet on a detached garage/shed. With its inefficient HVAC (heating, ventilation and air conditioning) systems, the two-story structure with a basement was going to need more square footage of solar panels than the Knoxes had in roof area.

“HVAC contractors repeatedly recommended that I go with a high-efficiency natural gas-fired boiler, and domestic hot water tank, but that wouldn’t have fixed my summertime cooling load,” Knox told me. His existing air conditioner used more than 2,500 kilowatt hours in 2010, well over half of all the electricity consumed in the home.  Andrew needed to get his summertime usage down, and reduce CO2 emissions. Going with a high-efficiency air-source heat pump (heat pumps provide both heating and cooling, unlike the cooling-only air-conditioners) wasn’t going to be enough. In addition, Andrew notes that his boiler was responsible for half of his house’s 15,000 pounds of CO2 emissions, and simply had to be eliminated if they were going to attain true net-zero carbon and energy.

Looking into geothermal heat pumps, Andrew saw that he could go with all electric heating and cooling and achieve better than 30 EER (Energy Efficiency Rating). 30 EER compares favorably to high-efficiency air-source heat pumps, using about half the energy, or in other words, doubling the efficiency.  Under this regimen of all electric—including clothes dryer and cooking—Andrew calculated the loads and saw that he would get close to achieving net-zero energy use.  He selected competent geothermal and solar contractors, signed contracts, and by August 2012, he was making progress toward his geothermal/solar combination net zero home.


The big day came in October, 2013 when the home officially went net zero (DOE link to project).  What’s equally important in this process is that the home is also carbon neutral, producing no net CO2 emissions. Though many don’t necessarily understand the importance of CO2 emissions reduction, Andrew Knox eats, sleeps, and breathes this data in his position as manager of energy initiatives and integration with Naval Facilities Engineering Command.  “It’s critical we get CO2 emissions under control,” Andrew explained. “CO2 emissions have a three-tier scope for reduction: one, CO2 emissions from direct fossil fuel use (like combustion heating), two, CO2 emissions as a result of electrical power consumed (from electrical power plants providing electricity), and three, indirect CO2 for all other purchased items and services, including air travel and food.”  He explained this to me as he was driving to work in his diesel car run on B99 (an affordable blend of 99 percent high-quality, American-made biodiesel—no conversion is required to run B99 in many diesel vehicles).

Since the time the Knoxes started this process, they also started a family, adding Everett (now 23-months old), and his baby brother John Karl (now 3 months). “I had no idea how much laundry was involved in raising children,” Andrew told me. “My energy consumption has gone up for things like laundry, cooking and other appliances. Putting up a clothes line has helped us cut dryer energy use way down until we can get a more efficient clothes dryer.”

Overall, though, house emissions have dropped 30 percent, from about 15,000 pounds a year to 10,000 pounds a year, with the CO2 emissions offset from PV generation at about 11,000 lbs /year.   (The Knox family currently has one electric and one diesel vehicle and is on target to reduce net vehicle greenhouse gas emissions to zero early next year).

Andrew has spent about $80,000 on this project; the remainder of the $110,000 project has come back to him through federal and local tax credits and incentives. There was a premium cost for changing to geothermal, but according to his electrical consumption monitoring equipment, he’s benefited by achieving a 60 to 70 percent


Andrew was perplexed that heating contractors advised against geothermal heating and cooling in favor of air-sourced air-conditioning and natural gas furnace. He was grateful to have found the folks at Harvey Hottel , a Maryland-based HVAC company specializing in geothermal installations. “It’s a tight property, and I was amazed how easily Allied Drilling installed the three vertical geothermal loops. Now they’re a permanent part of the infrastructure of the house, and we never have to worry about them again.”

With geothermal heating and cooling, much of the premium cost is tied up in the ground coupling, or the underground portion of the system. Decades from now, when the time comes for an upgrade to the geothermal heat pump, the cost will be equitable to a standard heat pump.

Mark Hottel didn’t stop with just the geothermal heating and cooling system.  The importance of good insulation can’t be overstated, as Mark said: “We applied spray foam insulation to the underside of the roof and gable ends to bring the attic into conditioned space. There used to be an air handler up there, so we removed the air handler and ran ductwork from the basement to the attic. Now the ductwork will be in conditioned space. Attic temps won’t go over 78 to 82 degrees. We also air sealed the attic and second-floor cavity behind the bathtub.”

Andrew and Elizabeth miss their radiators (the new system is ducted), and prefer radiant heat to forced air heat.  Fortunately that’s an easy option for new construction geothermal owners since geothermal is a water-based technology. In-floor radiant heat is a common upgrade for new and some retrofit applications.  Though the family likes radiant a little better, the Knoxes feel the air is cleaner year-round due to forced-air filtration, a potential benefit to their growing family on a busy D.C. street. No more equipment outside in the weather and elimination of the associated noise factors are other benefits. GHP (Geothermal Heat Pump) owners can enjoy extraordinary longevity of equipment, primarily because it’s protected inside. Still, it’s ultimately up to the homeowner to do their homework and select quality appliances and PV panels.

What words of wisdom does Andrew Knox have for those of us still floundering with utility bills? He says, “Basically, get a good handle on your situation, set your goals, do the low-cost load reductions (energy efficiency) to save money, then do the higher cost efficiency projects—geothermal heat pumps, solar thermal hot water, and the electric car! After that, you can make a much more accurate reading of the required solar panel capacity.  In the meantime, you can sign up for the various local incentives. Then monitor everything (we bought the TED energy monitor) to see where there are places to improve!   In our case, we put in our photovoltaic incentive application before we had done any of the upgrades except the lighting, so we had to make a lot of assumptions, especially about the expected geothermal and EV usage.  We also didn’t figure how many more loads of laundry we would be doing once we had a baby!”

Via National Geographic