Wood Gun

Wood Gun™ Multi-Fuel
Gasification Wood Boiler

Wood boiler - front view with doors openThe Wood Gun™ wood gasification boiler by Alternate Heating Systems, Inc. utilizes the most advanced technology available in wood burning today.  We believe, and *independent testing laboratory results indicate, that this is the most efficient wood-burning device built today.  This uncompromising multi-fuel system is ideal for residential, commercial, and industrial applications where wood and wood by-products are available as a primary fuel source.  The Wood Gun™ wood boiler comes in sizes ranging from 100,000 to 1,000,000 BTU's.  

The Wood Gun™ wood boiler employs a down-draft wood gasification design which burns wood of all types and moisture content.  These wood boilers work by drawing the wood gases off using an induction fan and then burning them underneath the wood so that much more complete combustion occurs. The wood is continually heated by the burning gases beneath it so that the gases continue to rise from the wood - the wood itself doesn't burn, only the gases.  Since only the gases are combusted, the AHS wood boiler can burn wood with a wider range of moisture content than can a non-gasification wood boiler.  An additional feature is automatic switchover to oil heat, gas heat or electric heat backup.  An optional lockout feature maintains the secondary fuel mode in the event the wood charge is expended.

Particle Fuel Delivery

When burning chunk wood in an AHS wood boiler, if the system is properly sized, the fire box typically only needs to be loaded two or three times a day (unless extreme cold conditions prevail).  Our automatic particle fuel delivery option is ideal for customers with access to uniformly sized wood pieces, chips, pellets, etc.  If you want to burn both chunk wood and wood particles in your AHS wood boiler, it only takes about fifteen minutes (after shutting the system down and allowing it to cool) to change the system from one wood type to the other, but chunk wood can still be loaded even when using the particle fuel delivery mechanism.

A close inspection will quickly reveal why the Wood Gun™ wood gasification boiler is the standard by which all other wood burning appliances are judged. Many of these unique features are found only on the Wood Gun™.

How Superior is the Efficiency of the Wood Gun™ wood boiler?

The Wood Gun™ wood boiler is a combustion system capable of burning wood and wood-based waste at a very high combustion efficiency, resulting in very low stack emissions.  Stack sampling on operating units has yielded particulate levels 50% less than the best results obtained by conventional up-draft boilers.  This level of performance is due to a number of unique design features not found on other wood waste combustion equipment.  In fact, the Wood Gun™ is so different that conventional wood boilers cannot be modified to incorporate these features without a complete redesign.

Stack Temperature

The stack temperature is an indicator of how completely the fuel is being combusted.  The Alternate Heating Systems Inc. Wood Gun™ Boiler operates with one of the coolest stack temperatures of any wood boiler on the market (if not the coolest).  The stack temperature of a Wood Gun™ runs at less than 300 degrees fahrenheit (typically 260 - 280 degrees).  The low stack temperatures of our boilers are almost unheard of on the market.

Carbon vs. Stainless Steel in our Wood Boilers

The internal surfaces of a Wood Gun™ Wood Boiler include any surface touched by the flame, smoke, wood or exhaust.  The internal surfaces may be manufactured with carbon steel or stainless steel - it's your choice.  We recommend stainless steel because carbon steel will show deterioration within 10 years though the unit may continue to function for as much as 20 years.  We have had stainless steel boilers in service for 19 years, and they show no sign of deterioration.  We use 1/4" thick 304 stainless steel (as opposed to 409) for unsurpassed quality.


  • Automatic cycling on and off in response to heating or hot water demand.

  • Domestic hot water coil provides abundant quantities of hot water.

  • Exceptionally safe and clean burning. The use of dense refractory material cast into specific shapes causes complete combustion to occur at temperatures of up to 2000° F.

  • When operated properly in the gasification mode, visible smoke is eliminated and creosote formation inside the chimney is prevented.

  • The large cyclone separator removes most of the fly ash resulting in very low emission.

  • Spontaneous re-ignition of the wood will occur after an off period of 2-8 hours. Factors such as the quality and quantity of the fuel charge as well as the size of the unit also determine how long a system can go without burning and then have spontaneous re-ignition occur.

  • Automatic fuel delivery systems are available for wood waste products such as sawdust, shavings, woodchips and densified biomass.

  • Wood Gun™ readily adapts to new or existing hot air systems through the use of a heat convection coil.

  • The design maintains all heated walls at the same temperature using a "water wall".  This constant temperature eliminates stress fractures caused by differences in temperature between components of the stove thus increasing the life of the stove.  In addition, this design produces greater efficiency because heat that is normally lost through a drywall is captured in the water wall.

Diagram of Wood Gasification Boiler

The Swirl Chamber


The SWIRL CHAMBER is where 90% of the heat exchange takes place in the Wood Gun. The Wood Gun refractory emits 2000 degree fahrenheit exhaust air temperature which is directed into the SWIRL CHAMBER and has an exiting exhaust air temp of only 275 degrees at high fire. This unheard of heat transfer efficiency is due to our unique design. The exhaust air spins through a large diameter drum assisted by a 3400 rpm draft inducer making a swirling action. Both the exhaust air and the ash from the wood, scrub the walls of the heat exchanger at a high rate of speed, in turn keeping it clean and efficient. This self-cleaning action prevents the troublesome routine cleaning of the heat exchanger that has plagued the Wood Boiler industry for years.

*The temperature varies from Boiler size, wood quality, moisture content and flue height. 

The CYCLONE ASH SEPERATOR is where the majority of the ash is collected. Since the design of the Swirl chamber is to use the ash as a cleaning agent, we can allow the ash to exit the boiler with the exhaust air.  The speed of the ash is increased using a high velocity orifice, discharging it into a cyclonic action device (the CYLCONE), spinning the heavy particles out of the exhaust stream and finally funneling them into the stainless steel ash pan allowing the exhaust to exit the cyclone top into the chimney pipe. 

Illustrated Features

Routine cleaning of combustion chamber
is necessary to maintain optimum performance. Easy-open Inspection Doors Front and rear make cleaning a snap.
Improved Air Valve design permits easy replacement of gasket disc.

The Air Valve closed.
Removable Clean-out Plug provides
direct access to combustion chamber
Draft inducing fan produces high velocity and intense flame in combustion chamber. Unlike conventional heating equipment, the flame production in the Wood Gun ™ follows a downward path with temperatures of up to 2000° Fahrenheit.
Inside the wood chamber looking through the wood loading door.


Alternate Heating Systems, Inc. standard sized Wood Gun™ Boilers are smaller than the intermediate sized boilers but pack in the same features and performance.

Wood Gun™ Wood Boiler Specifications*
Model: E100 E140 E180 E200 E250
BTU/H (Max.) Wood 100,000 140,000 150,000 185,000 230,000
Oil (optional) ** 80,000 130,000 160,000 160,000 230,000
Heating Surface 30 ft2 39 ft2 46 ft2 55 ft2 70 ft2
Water Capacity 60 Gal 80 Gal 80 Gal 95 Gal 140 Gal
Fire Box Capacity 6.5 ft3 10 ft3. 14 ft3 18 ft3 22 ft3
Max. Log Length 26" 30" 30" 38" 46"
Door Opening 14" x14" 14" x14" 14" x14" 14" x14" 14" x14"
Height 58" 64" 66" 66" 74"
Width 26" 26" 31" 31" 31"
Depth 44" 48" 48" 56" 66"
Flue Size 6" 6" 6" 8" 8"
Weight (lbs) 1,400 1,650 2,100 2,400 3,000
Domestic Coil Gal/min (Optional) 5 5 5 5 5
Rec. Sizing (BTU/hr) 70,000 100,000 140,000 175,000 220,000


Model: E500 E1000
BTU/H (Max.) Wood 500,000 1,000,000
Net Steam Rating (BTU/H) 376,000 752,000
Heating Surface 116 ft2 192 ft2
Water Capacity 210 Gal 435 Gal
Gas/Oil Chamber (water capacity) 16 Gal 50 Gal
Height 90" 102"
Width 34" 48"
Depth 72" 78"
Flue Size 8" 12"
Weight (w/o gas/oil - lbs) 4,500 9000
ID Fan .75 HP 2.0 HP
Minimum Boiler Room (w/o Gas/Oil) 12'x15' 16'x16'
Minimum Boiler Room (with Gas/Oil) 14'x15' 16'x18'
Load Door 18"x18" 18"x18"

* Specifications and design subject to change without notice.
All specifications shown are approximate.

** Models E180 and above have a built-in oil firing chamber that is present whether
or not the oil burner option is ordered (see Wood Gasification Boiler diagram
above).  On models E100 and E140 the oil burning chamber is external
to the unit and is only included when the oil burner option is ordered.

Producing More BTU's

If more BTU's are needed than the maximum produced by one of our boilers, then two or more boilers may be used together to produce the amount of BTU's needed.

* Results of Fire Tests at
Arnold Greene Testing Labs
 Model:  E180 - E200     Construction:  Stainless Steel 1/4" Plate 304
 Volts:  110-115          Amp:  4          Stack Size:  6" (positive pressure)



 Net stack temp:  126 degrees  Net stack temp:  227 degrees
 Smoke non-visible, hardwood  Smoke non-visible, #2 fuel oil
 Total Efficiency:  84.6%  Total Efficiency:  85.75%


Optional Wood Gun™ Wood Boiler Accessories Include:

  • Domestic hot water coil
  • Additional coil fittings
  • Four hour cycle timer with on/off switch and pilot light
  • Burner firing tube (Model E100, E140)
  • Manual Backup:
    - Oil backup package with Riello F5 burner (E100, E140)
    - Gas backup package complete including firing tube (E100, E140)
    - Oil backup package available separately - includes firing chamber, oil burner nozzle, L6006A Honeywell Aquastat, selector switch, indicator light and Wayne burner
    - Gas backup package available separately - includes firing chamber, oil burner nozzle, L6006A Honeywell Aquastat, selector switch, indicator light, and Riello burner
  • Automatic switchover and lockout fan delay package - for oil or gas burner backup - hydronic unit only
  • Automatic switchover and lockout fan delay package - steam units
  • Oil backup package (Riello) purchased separately (Models E180, E200, E250).  Includes oil burner, nozzle, selector switch, and indicator light.
  • Gas backup package purchased separately (Models E180, E200, E250).  Includes gas burner, nozzle, selector switch, and indicator light.
  • Fuel feed tube and dual draft (Models E100, E140, E180, E200, & E250)
  • Electric backup package (Models E100, E140, E180, and E200 only)
  • Fittings only for electric backup
  • Steam control and fittings package (Model E180, E200, E250)
  • Smoke exhaust hood with 265 CFM blower (standard) or 362 CFM blower

The Alternate Heating Systems Water Wall

Each Alternate Heating Systems boiler, heater and furnace is designed so that every piece of steel is in contact with the water in the system that is used to transfer heat to your radiant floor heat system, radiator, baseboard hot water, or heat exchanger.  This design ensures the most rapid and efficient heat transfer from the firebox into the water.  Efficiency is increased compared to other boilers that do not have this feature by allowing less heat to escape from the boiler surfaces before it is captured in the water.

ASME Certification

The American Society of Mechanical Engineers certification is available on any of our boiler lines for an additional charge.  This certification assures that the pressure vessel has been designed and constructed in accordance with the ASME Code.  This certification is required for all commercial installations.  The certification is also required for some residential installations depending upon local codes - it is up to the homeowner to determine the need for an ASME certification on any boiler purchased.