Friday, April 28, 2023

Are wood stoves the back-up heating solution in our electrified future?

With longer and more frequent power outages, back-up heat options are limited

By Darian Dyer and John Ackerly

Heat pumps are now the second most common heating appliance in the United States after natural gas furnaces, and the Biden Administration is heavily promoting them to decarbonize home heating. But power outages are also more frequent. According to the U.S. Energy Information Agency, the average American spent twice as long in the dark in 2021 as they did ten years ago. 

The electrification of heat has become a global solution to avoid the direct use of fossil fuel heat. 

For Americans in colder parts of the country, back-up heat is essential and wood stoves are already the second most common source of secondary heat in the U.S. - after electricity. “Wood stoves may become more popular as more homes switch to heat pumps,” speculates Tom Butcher, a Research Engineer at Brookhaven National Lab in New York, who is a leading expert on oil and wood heat. 

The availability of back-up heat is one of many barriers to households shifting to heat pumps and few heat sources don’t need electricity other than wood stoves. While wood stoves are common and practical in rural areas, they are by no means an obvious, or desirable, choice for many in suburban areas, much less urban ones. 

Severe weather events are more common


Ice storms inevitably lead to a surge of sales in wood stoves, and nowhere was this more evident than northern New York and the Montreal area when an ice storm was so bad it brought down long-distance transmission lines in 1998. In the recent past, a 2022 December winter storm racked up 1.6 million outages across the United States. In September of 2022, Hurricane Ian caused 2.78 million outages. In early 2021, Texas saw 4.4 million outages from a winter storm that revealed just how fraught our energy infrastructure is as rolling blackouts were instated and fossil fuel infrastructure froze over.

The North American Electric Reliability Corporation (NERC) concluded that a “large portion of the North American BPS (bulk power system) [was] at risk of insufficient electricity supplies during peak winter conditions” in their 2022-2023 Winter Reliability Assessment. Currently, almost all of the colder parts of the US are at an elevated or high risk of insufficient electric supply during the winter months. NERC also projected the growth rates of electricity peak demand and energy in North America will increase for the first time in recent years.

The U.S. electricity customer was without electricity for 7 hours on average in 2021. But the average number of power outages, and the average length of power outages per state does not make distinctions between rural and urban outages. Rural and suburban areas are more vulnerable to outages, especially in remote areas, and these outages are usually far longer than urban ones. Some areas measure power outages not in hours, but in days.


Seasonal weather events are annual occurrences that many expect to affect them at some point, particularly in their access to electricity, no matter what state or territory they live in. However, this threat is only heightened by the likelihood that climate change is increasing the frequency and intensity of extreme weather events. In addition to extreme weather events, two concerns loom over the U.S energy grid when it comes to supporting our electrical energy needs: aging infrastructure and limited transmission capacity

Back-up heat options


There are few good back-up heating options, especially low-carbon ones. Gas or propane fireplaces, or stoves, can work without electricity, as do indoor kerosene heaters. Even more common than wood stoves, but far less effective, is the traditional open fireplace which radiates heat to people right in front of it, but does little to warm the rest of the house. 

Wood stoves are an obvious choice for many (or their far more expensive cousin, the masonry heater, which is an effective whole-house solution if you can afford it). The other obvious choice for tens of millions of Americans is a back-up gas generator, which can cost as little as $500. Again, most gas generators aren’t powerful enough to run heat pumps but can run a pellet stove, or even a gas furnace.

Home batteries, like Tesla Powerwalls, and electric vehicle batteries that can be run in reverse to provide power to a home, open up more back-up heat options. But home batteries or EV car batteries can run out quickly and many only provide 2-8 hours of juice if connected to a heat pump. However, they can easily run a pellet stove for several days, or indefinitely if they are being recharged during the day with solar panels. (There are a few gravity fed pellet stoves on the market but they can be more finicky.)

The average pellet stove uses about 100 kWh per month- as much electricity as a refrigerator or a heat pump water heater. Geothermal heat pumps can use 3 or 4 times that much in a month.

Wood stove retailers see the writing on the wall and many are adding heat pumps to their businesses. One major stove manufacturer, Napoleon, is the first to market their own line of heat pumps. Pellet stove manufacturers could do a better job marketing and selling back-up batteries which are available for $100 - $200 and will automatically take over if the power goes out when you are not at home. 


The other major consideration is stress on the grid during winter peak load events, which are occurring more frequently. As more homes electrify their heat and their cars, some grids will be under tremendous stress during cold snaps. Back-up heaters could be used during cold snaps and utilities could also incentivize their use by raising electric rates when electricity supply is limited. In the coming decades, many homes will still have legacy gas, propane, and oil heaters for their back-up heat. Wood and pellet stoves would be an excellent heating technology to help avoid collapsing the grid and reduce fossil fuel usage. In places like Vermont and Maine, where a quarter or more homes have wood or pellet stoves, the grid is already benefiting from their use during cold snaps. 

A French study found that among single-family homes in 2020, with an estimated 7 million wood log and pellet appliances in France, domestic wood heating covered 24% of the heating needs. Moreover, it found that more than 70% of wood and pellet appliances were in use before the 7 p.m. peak electricity demand. Similarly in Vermont, if 70% of wood and pellet heaters were in use during peak electric demand, it would take a significant load off the grid, as more homes switch to heat pumps, according to a presentation made by Adam Sherman,  Advanced Wood Heat’s Role in Renewable Energy and Clean Heating Policy, at Brookhaven National Lab.

Longer power outages will be a part of the future for many if not most Americans in both colder and more moderate U.S. climactic zones. Planning for back-up heat is not just a task for homeowners but also policy-makers promoting greater electrification.