Lydia Segal is planning a 2,000-square foot house in Colorado (Climate Zone 6B), and aiming for “Pretty Good House” performance. Among the many questions she’s trying to answer is whether electricity or natural gas is the best choice for heating, domestic hot water, and cooking.
She’s lucky enough to have both a reliable electricity grid and easy access to natural gas in the small community where she lives. So the practicalities of delivery are not really a concern.
“We are weighing the pros and cons of gas powered vs. electric powered system for DHW [domestic hot water] and for in-floor radiant heating,” she writes in a Q&A post at Green Building Advisor. “If we set aside the issue of fossil fuel use, what are the pros and cons of each?”
That question is the topic for this Q&A Spotlight.
[Lydia Segal’s name appears as “User-6885857” in her original post. For instructions on how to change screen names, see How the GBA Site Displays Readers’ Names.]
Burning fossil fuels is always a concern
It’s not really possible to set aside the environmental issues raised by the use of fossil fuels, replies GBA senior editor Martin Holladay. Burning fossil fuels “happens to be the greatest environmental threat to life on our planet,” Holladay writes.
“Most green builders design all-electric houses,” he adds. “If their local electric company offers a program for the purchase of wind-powered electricity, they sign up with the program. If possible, they install an on-site photovoltaic (PV) system to balance their annual energy use.”
That said, natural gas has one advantage over electricity when used for heat, Holladay says. It’s often cheaper on a BTU basis.
But there are a number of disadvantages to using gas. Not only does it contribute to global warming, but natural gas pipelines also leak methane, a powerful global warming gas. Gas utilities charge a minimum monthly fee, even when no gas is being used. And, Holladay says, gas-burning appliances installed inside a home’s thermal envelope may raise concerns about backdrafting and indoor air quality.
It’s not that cut and dried, Segal says: “It seems to me, there are pro and cons besides the obvious environmental, those being the efficiency, the economics and maybe the logistics. By logistics I mean simplicity and local availability of install and maintenance (should my spouse go before me, I am in trouble!) and the ability to lock and leave allowing us to go on vacation etc.”
A plus for natural gas
Although there are good reasons not to choose natural gas, there’s also a good argument in its favor, says Andrew Bater.
“In times of disaster, perhaps with the exception of earthquakes and extreme flooding, natural gas infrastructure may be up and running while other above-ground electric utilities are out of service,” Bater writes. “For example, after Hurricane Sandy where we used to live in New Jersey we had no electricity for a number of days, except what we provided with our own small generator. However, we had town-provided water and natural gas. Our old pilot-driven water heater kept on cranking along; it was pretty nice.”
With that in mind, Bater installed a propane range when he built an energy-efficient home a few years ago. The cooks in Bater’s family preferred gas, and they know the range will work when the power goes out.
“Comforting to know that we can make a bowl of soup if all else fails,” he said.
Think twice about radiant-floor heat
Segal has specifically mentioned in-floor radiant heat, but rather than supply the system with hot water from a gas or electric boiler, Dana Dorsett suggests investing that money in photovoltaic (PV) panels.
“A 2,000-[square foot] Pretty Good House in sunny high-altitude Zone 6B Colorado can probably hit net zero energy with a PV array that fits on the house if the heating system is a combination of inexpensive electric mesh radiant floor (for maximal cush-factor) running off a floor thermostat, and a cold climate minisplit or two for maintaining the room temperature(s),” Dorsett says.
Even if Segal doesn’t think she’ll need mechanical cooling in a house built at an altitude of 7,000 feet, any minisplit that heats also can cool. “Whether you need to run it in that mode or not, it’s there,” he says.
“In a well-designed, solar-tempered Pretty Good House, you may find there will be days when some amount of active cooling is useful, though nighttime ventilation strategies usually work just fine in your area,” Dorsett adds.
“Cheap low-voltage mesh radiant floors can still be a nice comfort feature in places that might matter (say, in bathrooms). When used judiciously it won’t impinge heavily on the average heating efficiency of a house heated with minisplits.”
Dorsett suggests that Segal start with accurate heat load calculations from an engineer or RESNET rater (not your average heating contractor) so the minisplit can be sized properly, adding, “Then, at 7,000 feet it’s important to do the homework on capacity derating for altitude on the minisplits. Some minisplit installers understand it, but (sadly) most won’t have more than a clue (assuming they’re even aware of the issue at all.)”
Heating demands can be very low
If Segal’s new house is designed with passive solar principles in mind, and is well insulated and air-sealed, she might not need an elaborate heating system, says Robert Opaluch.
“It is possible that the amount of heat you will need even during the coldest ‘design temperature’ days or overcast days will be fairly small,” he says. “You may not be able to cost-justify a central heating system. The inexpensive electric mesh radiant floor or minisplits noted by Dana are likely to be all you need.”
Opaluch built a passive solar home in Boulder, Colorado, and installed electric radiant panels in the ceiling on the first floor and used in once in five years. Upstairs, radiant electric heat is needed on only about a third of the nights in mid-winter.
“This 1980s house might barely meet today’s ‘Pretty Good House’ level of insulation and air-sealing, but was passive solar,” he adds. “You can calculate the wintertime solar heat gains and heat losses to design a passive solar home that works well in Colorado, an ideal cold sunny climate for passive solar wintertime space heating.”
Assessing renewable energy
One potential problem Segal sees with electricity is the proportion of non-renewables in the mix.
“Your suggestion about going all-electric is a good one,” she writes, “though it leaves me in a conundrum as the local energy company Xcel, states on their web page for Colorado, 45% from coal and 25% energy derived from natural gas. So no escaping non-renewables. Local ordinances mandate grid connection.”
That’s not necessarily true, says Holladay. Xcel offers its customers a program called Windsource, which allows them to buy power that’s generated by wind turbines.
In addition to buying “lo-carb” electricity from the utility, using PV to generate her own power offers a number of advantages, Dorsett says. PV will help lower both peak and average loads on the grid, and is cost-effective when net-metering is in effect.
“Being connected to the grid, when your PV output exceeds your load and you are exporting electricity to the grid, your power exports are offsetting fossil-fuel use and lowering the amount of power being transferred on the local grid and transmission grid,” Dorsett writes. “Your power is effectively going from your house to your neighbor’s house. When buying wind power from a remote wind farm, it is putting power onto a transmission grid that’s offloaded at a substation to your local distribution, which is quite a bit more infrastructure use.”
The rate at which renewables are being added to the grid is increasing, Dorsett adds, with wind power now cheaper than combined-cycle natural gas, and with utility-scale solar not too far behind. “So even if it’s a heavy fossil-fired grid in September 2017, within the life cycle of your heating system that is likely to change dramatically.”
Our expert’s opinion
Here’s what Peter Yost, GBA’s technical director, has to say:
I get pretty nervous when I hear about folks using unvented gas appliances inside an airtight or “pretty airtight” home during emergencies when there is no electricity. We make three things when we burn fossil fuels, if we are lucky enough to combust them perfectly: heat, CO2, and moisture. The latter two byproducts can be pollutants if we don’t have ventilation to dilute them or exhaust them.
And given the efficiency limitations of atmospherically vented gas water heaters, it’s hard for me to imagine their fit in a “Pretty Good House.” So if you are using a gas DHW appliance, it is either power-vented, direct-vent, or sealed combustion, each of which needs electricity to work in an emergency. [Editor’s note: See further discussion of this issue in Comments #4 and #7, below.]
I think one of the greatest leaps forward in the last ten years has been how PV has moved residential high performance largely to a single integrated power source for all loads and introducing us to a “net” thinking about total load: electricity.