The transition to greener homes is more imminent than ever
By MAUREEN MCGEARY MAHLE
Over one quarter of all homes in the U.S. are all-electric. But for those of us accustomed to fuels like natural gas or propane, electrification is a hot topic. Multiple factors are driving this trend: (1) concern over greenhouse gas emissions; (2) climate change policies promoting electrification; (3) growing evidence of the safety and health risks from combustion within the home; and (4) more effective and lower cost technologies for electric heating, cooking, and renewables.
Both consumers and contractors can be resistant to change despite great success stories with electrification. And once fuel-based systems are installed, replacement is seldom cost-effective until the equipment’s end of life. Furthermore, not every existing home is a good candidate for full electrification. Unlike fuel-based systems capable of blasting out high-temperature air for short periods of time, heat pumps work best delivering moderate temperature air for longer periods of time. A leaky or poorly insulated home in a cold climate might require very large electric heat pumps or inefficient electric resistance back-up heat.
To electrify successfully, first lower those loads with a solid thermal envelope. This helps to increase occupant comfort and minimize operating costs. Thanks to more stringent energy codes, new construction homes should be on track for easy heat pump integration. Adding insulation, air sealing, and better windows/doors to existing homes helps set them up for success with heat pumps. Where envelope upgrades are not possible, a hybrid approach that utilizes fuel-based back-up heat may be appropriate.
Second, consider going all-in to manage costs and capture benefits. Even a small use of natural gas for cooking or supplemental heat triggers the utility’s monthly supply service charge, and that adds up annually. A true cost-benefit picture of home energy should include human health and carbon along with utility bills. With great solar options available nationwide, becoming net-zero (or near-zero) is within reach for many homes.
Third, seek out a knowledgeable HVAC designer who can help to:
Evaluate heating, cooling, and hot water needs collectively, not separately. A ground source heat pump may be able to provide hot water along with space heating and cooling. Packaged air source heat pump water heaters essentially ‘steal’ heat from indoors, making them a benefit in summertime (free cooling!) but potentially increasing wintertime heating needs. Split heat pump water heaters with outdoor condensers or even well-insulated electric resistance tanks may be a better choice for certain designs.
Navigate the pros and cons of various system types. Ground source systems may be most efficient but carry higher installation costs. Air source heat pump efficiency is typically best when 1-2 indoor units are matched to one outdoor unit, but there may be practical reasons (space, equipment selection) to connect multiple indoor units to one outdoor unit in a multi-zone configuration.
Keep occupants comfortable by placing registers or indoor heads away from areas where people sit or sleep, since blowing warm or cool air for long periods might be uncomfortable for some individuals.
Design good filters for ducted systems. Pleated media, MERV 13+ to capture small particles, an air-tight housing, and easy access make for good filtration – and a healthier home.
Fourth, get a quality installation. Seek out climate-specific guides on placement, protection, condensate lines, refrigerant lines, and proper charge. Resource centers like the Northeast Energy Efficiency Partnership have useful guides. Ask for start-up documentation you can pass on to the homeowner so that the system can be easily serviced in the future.
Last but not least, educate occupants about their systems and how to use the controls, change filters, and keep outdoor units clear from ice, snow, or other debris.
Maureen McGeary Mahle leads the Residential Building Services team at Steven Winter Associates, Inc., a leading research and consulting firm specializing in energy efficient and sustainable buildings. In July 2020, she moved into her first all-electric home.