Mickelson Plumbing & Heating, in Missoula, Montana was recently hired to add back-up heat to a wood-fired hydronic system serving three buildings; a home, a shop and a lodge. The system, which draws heat from an Econoburn gasification boiler and 800-gallon buffer tank, served the family well last winter. But in the spring of 2014, their lives changed.
The family’s oldest daughter, who’s 10 years old, came down with a mysterious illness that rendered her incapacitated from the neck down. After spending time at several hospitals, she ended up in critical care in Spokane, WA. Here, doctors discovered that she was plagued by a rare disorder called Guillain-Barre syndrome.
The life-threatening disease causes the body’s immune system to attack the central nervous system, and recovery times – when patients are fortunate – last a year or more. Needless to say, the girl’s parents are spending as much time as possible by her side. This means that more often than not, nobody is home 200 miles away in Montana.
They realized that their daughter’s condition wouldn’t stabilize before the onset of heating season, so Mickelson was called to install a supplemental heat source for when nobody is available to put wood in the existing boiler.
In September, owner Andy Mickelson and Service Technician Chris Paul arrived with a 399 MBH Burnham Alpine condensing boiler and a Fan-In-A-Can combustion air system for the wood boiler.
“The first thing we did was plumb the new boiler into the two-inch supply for the big buffer tank,” said Mickelson. The tank supplies water to Watts manifolds and PEX for in-slab radiant, domestic hot water tanks, Modine Hot Dawg H20 unit heaters, and Magic Aire coils in the home’s ductwork. Connecting all the buildings is pre-insulated, 1-1/2-inch Watts R-Flex supply-and-return tubing underground. A variety of Taco pumps and zone controls are used throughout. The tank and system are designed for 160°F water on average.
They were surprised by how quickly the big buffer tank heated up after firing the boiler. “It went from about 70°F to 125°F in about 40 minutes. Of course that’s on hi-fire. They’ll see much lower fuel consumption once the boiler is just maintaining setpoint and firing at a lower input.”
With efficiencies up to 95% and sizes from 80 to 399 MBH, the Alpine comes standard with a five-year parts and labor warranty. Mickelson and Paul used a Honeywell T775 staging control to fire the Alpine if the wood boiler does not begin to raise the buffer tank temperature within the programmed interstage delay period.
“The T775 control gave us the benefit of a multi stage, outdoor reset control which is completely stand alone,” explained Mickelson. “The buffer tank was programmed to maintain a 160°F at design conditions with a low reset to 110°F. Most of the terminal units are fan coils, requiring a slightly higher supply temperature. With the wood boiler’s built-in bypass control and the Alpine’s heat exchanger design, low return temperatures are not a factor.”
When the wood boiler was first installed, the property owner hadn’t been concerned about leaving the boiler room open to supply combustion air to the wood boiler. But the reality that the two youngest daughters could make their way to the boiler room on their own sunk in. Young hands and hot pipes being incompatible, they decided they wanted a way to shut the door without choking the boiler.
Typically, a wood boiler isn’t any more sensitive to fluctuations in combustion air than a traditional boiler is, but given the mechanical room’s tiny size and its tight new construction, Mickelson wasn’t willing to leave it to chance. If the boiler didn’t receive adequate air, it might not reach temperatures high enough to re-burn flue gasses (gasification), which results in much higher efficiency and nearly smoke-free operation.
The Econoburn wood boiler delivers an 87 percent thermal efficiency rating, and is available in sizes from 100,000 to one million BTUs. What makes the boiler unique is that as wood is burned in the firebox, fresh air is blown downward through the logs and coals. This creates a mixture of hot air and wood gases that are forced through a refractory – or second combustion chamber, creating a torch-like combustion of the retained gases. The smoke and creosote vapor that would normally go up the chimney as visible smoke is instead burned at nearly 2000°F.
Mickelson’s solution to provide ample combustion air with the mechanical room door closed was to use a Fan-In-A-Can, made by Field Controls. The unique product is what the name implies; a fan inside a “can”, attached to a pipe that draws air from outdoors. Fan-In-A-Can is an engineered system, and when properly sized to the application, supplies the precise amount of air needed in close proximity to the combustion appliance.
With several configurations and single-fan sizes that range from 50,000 to 1.8M BTUS, the Fan-In-A-Can can be used to supply combustion air for just about any atmospheric combustion appliance.
Wired to the power supply from the wood boiler’s combustion blower, the Can actually starts before the blower comes on. Half a second later the Can proves, and the blower starts. When the temp control on the boiler is satisfied, the Can shuts off with the blower. The system will allow the boiler room to be sealed without concern of having adequate combustion air.
With the boilers, buffer tank, and hundreds of feet of underground PEX, the hydronic system contains more than 1,000 gallons spread out among three buildings. Given Montana’s wicked winters, Mickelson wanted to be sure that if makeup water was being added to the system, antifreeze wasn’t being diluted. An Axiom MF200 glycol feeder was added to round out the new system upgrades.
With any luck, the family’s little girl will return to Montana before spring. Whether LP or wood is the source, she’ll have a warm homecoming.
Date started: 9/2014
Date Finished: 9/2014
Size of Project: Approx. 7,700 sq. ft. total in three buildings
Workers onsite: 2
Boiler — Burnham Alpine condensing LP boiler, 399k BTU input
Buffer Tank – Niles Steel Tank, 800-gallon ASME
Pumps — Taco Bumble Bee, Taco 0015, Taco 2400, Taco 007, Taco 0013
Underground Pipe – 870 lineal feet of 1-1/2-inch Watts Radiant R-Flex insulated pipe
Relays — Taco SR and ZVC relay boxes, Honeywell T775 staging control
Manifolds – stainless steel Watts Flowmeter
Piping — Watts RaniantPEX+, Watts Onix EPDM
Tools Used — Rothenberger ROPOWER portable compact threading machine, Milwaukee M18 cordless power tools
Valves — Taco Zone Sentry zone valves, Watts ball valves
Separators — Taco 4900 Series
Combustion Air Supply – Field Controls Fan-In-A-Can model CAS-3 with 120 VAC control circuit.
Other — Axiom MF200 Glycol mini-system feeder, Axiom acid neutralizer