Do You Need a Permit for an Outdoor Wood Boiler in MA?

Yes. In Massachusetts an outdoor wood boiler needs a building permit under the state building code, and the unit itself has to be one MassDEP has certified, placed at fixed distances from your property line and your neighbors' homes (State Fire Marshal advisory; MassDEP certified units).

That makes it one of the few heating jobs with three separate gatekeepers: the state air regulators, your town's building department and, in some towns, the board of health. The state calls these units "outdoor hydronic heaters." Most sellers call them outdoor wood boilers or outdoor wood furnaces. Same thing.

Who has to approve an outdoor wood boiler?

More offices than for an indoor boiler. The State Fire Marshal's advisory to fire chiefs explains that these units are not regulated under the state fire code, "however, a building permit for the installation is required" under 780 CMR. The same advisory says MassDEP can enforce its whole regulation and that municipal boards of health may enforce its operating, visibility and setback rules (State Fire Marshal advisory).

Some towns route the whole job to the board of health. Warren's solid fuel appliance application states at the top that exterior wood furnaces and boilers "are permitted through the Board of Health," not the inspector of buildings (Warren solid fuel permit application). The Warren building department page has the office's contact details.

What	Who decides	What they look at
The unit you buy	MassDEP	It must be on the certified list (Step 2 models since May 15, 2020)
Where it sits	MassDEP, enforced locally	Setbacks from property lines and neighbors' homes
The chimney	MassDEP, enforced locally	Stack height when a neighbor is within 150 feet
The installation	Building department	Building permit under 780 CMR
The wiring	Licensed electrician	Electrical permit, issued only to the electrician
Local rules	Board of health	Town permit or regulation, where the town has one

Which outdoor wood boilers are legal to install?

Only certified ones, and fewer than the list suggests. MassDEP publishes the list of certified models and says "only listed units may legally be sold and installed" in Massachusetts. Since May 15, 2020, only the models marked with an asterisk, which are U.S. EPA Step 2-certified, are legal to sell and install (MassDEP certified units).

Check the exact model number against that page before you sign anything. A model name without the asterisk, or a unit bought used out of state, cannot be installed here even if it once appeared on the list. Units without an asterisk that were legally installed before May 15, 2020 may keep running.

How far from the property line does it have to be?

It depends on the size of the unit. Under 310 CMR 7.26(52), a residential-size heater (rated at 350,000 Btu/hr or less) must sit at least 50 feet from any property line and 75 feet from any occupied dwelling it is not serving (310 CMR 7.26(50)-(54)).

A commercial-size unit, above 350,000 Btu/hr, needs 275 feet from any property line and 300 feet from a neighbor's home. An owner can apply to MassDEP for a variance on the property-line distance, but never below 200 feet, and MassDEP will not vary the 300 feet to the nearest occupied dwelling.

Then there is the chimney. If the unit is less than 150 feet from the nearest occupied dwelling it does not serve, its permanent stack must reach two feet higher than the peak of any roof within 150 feet. On a typical house lot, that means a tall stack.

What can you burn, and when?

Clean wood, wood pellets made from clean wood, and a short list of others. The regulation allows clean wood (no paint, stain or preservative), clean-wood pellets, heating oil or natural gas as a starter or backup fuel in dual-fuel units, and other biomass MassDEP approves. It bans 20 items by name, including trash, yard waste, plywood, particleboard, coal and painted wood (310 CMR 7.26(52)).

Season matters for older units only. An uncertified unit installed before December 26, 2008 may not run from May 16 to September 30 unless it is at least 500 feet from the nearest neighbor's home. A newly installed unit is certified by definition, so this limit does not apply to it. The opacity limits do, all year: smoke may not average more than 20 percent opacity for two minutes in any hour.

How often do these permits show up?

Rarely, in the records we hold. Across our Massachusetts permit files, which lean toward larger towns that publish permits online, one 2025 permit description names an outdoor wood boiler, and it is the electrical permit for its wiring. Wood heat is more common in rural towns, and in a town like Warren the approval sits with the board of health, so these jobs often leave no building permit trail we can count.

That is why the paperwork question matters more than usual here. If your installer says "no permit needed," ask which office told them so. For the indoor side of a heating change, the furnace, boiler and AC replacement permit guide covers the gas and electrical permits, and our wood stove permit explainer covers stoves and inserts inside the house. For town-by-town permit totals, see the Massachusetts building permits report for August 2026 and the Worcester County page.

What should you ask the installer?

Five questions before any money changes hands:

• What is the exact model, and is it marked with an asterisk on MassDEP's list?
• How far will it sit from my property lines and the nearest neighbor's house? Get it on a site sketch.
• How tall will the stack be, and is any roof within 150 feet?
• Who pulls the building permit, and does our town also want a board of health permit?
• Who is the licensed electrician pulling the electrical permit for the pumps and controls? Electrical permits go only to licensed electricians (electricians consumer fact sheet).

If you are still weighing wood against other heat, masshomecomfort's heating and cooling contractors in Massachusetts page lists installers by town.