Should local governments regulate outdoor wood boilers? – Part 1

Although popular and cost-effective, many outdoor wood boilers produce a lot of smoke, creating potential health risks and nuisance complaints. Local governments can reduce that risk though zoning standards.

The pleasant sight and smell of wood smoke wafting from a rural house chimney is a sure sign of winter in Michigan. Increasingly, that smoke is not coming from a home chimney, but from an outdoor wood boiler. For some, the smoke volume emitted from these units is hardly pleasant.

Outdoor wood boilers (officially called hydronic boilers) are relatively large wood-burning units that are installed outside homes, providing heat by circulating hot water from the outdoor boiler through underground pipes to exchange units in the house. They are becoming more popular in Michigan as a cost-effective and potentially safer way to use wood as a home heating fuel. The challenge with these units is that many designs burn wood inefficiently and at lower temperatures than indoor units, emitting a large quantity of smoke that can be a nuisance and a potential health risk.

As outdoor wood boilers become more popular, community leaders may, if they haven’t already, receive complaints from neighbors about smoke from these units. Can or should a community address issues associated with outdoor wood boilers through zoning regulation?

In some very rural communities, homes and these wood-burning units are so far apart that the potential for conflict is small. More densely populated rural and urban communities are another matter. A study by the Michigan Department of Environmental Quality (MDEQ) estimated the concentrations of emissions from conventional, low-efficiency residential outdoor wood boilers. This computer simulation predicts smoke densities that could affect health hundreds of feet from the boiler smoke stack. Those effects could easily extend beyond common accessory structure setback requirements and impact neighboring home owners. Short smoke stacks often installed with these units, some as short as five or six feet, allow smoke to more easily drift to places where it can be inhaled. This potential health risk builds a strong case for regulation.

There are alternatives, however. Newer outdoor wood burner designs are much more efficient and greater efficiency means less smoke. A voluntary Environmental Protection Agency (EPA) program certifies high-efficiency outdoor wood boilers. Phase 2 Qualified boilers are approximately 90 percent cleaner than conventional units and are widely available. The (MDEQ) study predicts that high efficiency units produce smoke emissions below health impact levels. Although their initial cost is higher than conventional models, high-efficiency boilers can pay for themselves through the need to buy and burn less wood.

A MDEQ fact sheet summarizes the relationship between outdoor wood boilers and air quality. The EPA’s Burn Wise web site includes excellent information about wood burner efficiency and a list of Phase 2 Qualified outdoor wood boilers.

For additional information about energy issues in planning and zoning, see the Michigan State University Extension land use website.

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