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Dual-Fuel Fits the Bill
Across the country, some states and municipalities are mandating the electrification of homes. This movement likely has (or will) impact you if you are part of a construction business as you plan for future residential home projects (e.g., the 2022 California Building Standards Code). Electric-ready means pre-wiring the residence to accommodate an electric heat pump water heater, electric appliances, EV charging, a battery storage system, and solar panels. But a fully electric home is a bit of a misnomer, as these regulations leave the door open for other fuel opportunities such as natural gas and propane. These fuels are still allowed and frequently used if builders meet ventilation and efficiency requirements.
Meet the dual-fuel home. Dual-fuel homes can help contractors and homeowners meet resilience and sustainability goals while offering a more comfortable living environment for homeowners. A dual-fuel home is one powered by propane and grid electricity, and sometimes renewables such as solar. Dual-fuel systems use propane for tankless water heating and as a backup for electric air source heat pumps, for example.
While electrification with renewable energy is a worthy initiative in our efforts to reduce carbon emissions and combat climate change, full electrification does have some shortfalls. For one, it puts more stress on the power grid, which is already at a breaking point. Power outages are growing in frequency and, when the power grid does go down, an all-electric home will not be able to supply the heating, cooling, lighting, and hot water needed. But homes equipped with a propane standby generator will be protected from the significant damage a power outage can cause. A reliable propane generator helps homeowners avoid damage to appliances and electronics, spoiled food, and loss of heat or air conditioning.
In addition, electric heat pump systems such as water heaters and space heaters aren’t as efficient when temperatures drop. When electric systems are combined with high-efficiency propane systems, one or the other takes over when the conditions are right, helping to combat stress on the power grid and high-demand surcharges. These hybrid systems are highly efficient and the fastest approach to move toward a zero emissions structure. What’s more, a propane-fueled furnace is expected to last up to 50 percent longer than an electric heat pump.
The Ins and Outs of Dual-Fuel Systems
In a dual-fuel home, electricity, and sometimes on-site solar, are providing primary power for lighting, ventilation, and electric heat pumps. But the efficiency of heat pump systems falls off when temperatures drop, or when additional energy-dense solutions are needed, such as for water heating. Smart thermostats detect when an electric heat pump is no longer heating the home efficiently, especially when the outside temperatures drop. It automatically moves over to utilize the high-efficiency condensing propane furnace, which provides a lower-cost and higher-comfort heating option under those colder conditions. The percentage split between electricity and propane depends on the home’s location and climate.
Aptly-named systems such as the Heat Pump Helper or Heat Pump Companion provide a cost-effective alternative to electric resistance strip heating for auxiliary heat in an air-source heat pump. A heat pump solution installed in the air handler moves hot water from the propane tankless water heater across hydronic coils to create hot air that is then blown through the existing ductwork to heat the home. The supplemental heat provides support to the electric heat pump so that it does not need to engage its backup system, reducing wear and tear on the system and providing greater efficiency and resilience at a lower cost.
Project Highlight
Bill Owens, president of design/build firm Owens Construction and a green building advocate, supports building dual-fuel homes with both electricity and natural gas or propane. In fact, he renovated his own 1970’s mountain chalet outside of Flagstaff, AZ to be zero energy ready. Rather than trying to run his home solely on solar and battery backup, he incorporated a high-efficiency mini-split heat pump system, which can handle the heating load in moderately cold conditions, and a backup propane furnace to heat the first floor and crawl space, which helps when temperatures drop to as low as -30oF.
He then was able to install a smaller propane generator to handle the electrical needs of the furnaces, water pumps, refrigerator, and smart home features that will kick in in case of a power outage. “In a fairly severe environment or environments that are far enough away from the grid, there is no perfect panacea with just one energy source,” Owens says. “We’re literally at the end of the grid. 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.”
