Wood Gasification & Rocket Mass Heaters — FarmPal

Ultra-efficient wood burning systems that use gasification to extract maximum energy from wood. Rocket mass heaters capture 80-90% of heat energy (vs. 30-50% for conventional wood stoves), heating homes with a fraction of the wood.

How It Works

A rocket mass heater burns wood in a super-insulated combustion chamber (J-tube) at very high temperatures, gasifying wood and burning exhaust gases. Hot gases pass through a thermal mass (cob bench, stone, etc.) which stores and slowly radiates heat for 12-24 hours after the fire goes out.

Site Requirements

  • •Indoor space with adequate floor support for thermal mass (very heavy)
  • •Chimney/flue path through exterior wall or roof
  • •Access to sustainably harvested firewood
  • •Space for thermal mass bench or bed (6-20 feet long)
  • •Floor that can support 2000-5000+ lbs of mass

Components

Feed Tube
Vertical tube where wood is loaded
$50-200
Burn Tunnel
Horizontal combustion chamber
$50-200
Heat Riser
Insulated vertical chimney creating powerful draft
$100-300
Barrel/Bell
Captures rising heat, forces it down through mass
$20-50
Thermal Mass
Stores heat in cob, stone, or concrete
$50-200 for ducting
Exhaust Ducting
Route hot gases through thermal mass
$100-300

Sizing Guide

System size depends on space to heat and climate

Formula
6-inch core: ~500-800 sq ft | 8-inch core: ~800-1500 sq ft (well-insulated homes)
DIY Minimum
$150 (salvaged materials, free cob)
DIY Typical
$300-800 (new firebrick, pipe, barrel)
Professional
$3,000-8,000 installed (rare most are DIY)
Annual Maint.
$0-50 (chimney cleaning, firewood)

DIY Steps

1
Design & Planning

Size the system for your space. Calculate thermal mass needed. Plan exhaust routing through mass. Ensure adequate foundation support.

⏱ 1-2 weeks research and design
2
Core Construction

Build the J-tube combustion core from firebrick or refractory material. This is the heart of the system precise dimensions matter.

⏱ 2-3 days
3
Thermal Mass Construction

Route exhaust ducting through a cob bench, stone bed, or concrete mass. Cover with cob (clay + sand + straw) sculpted into furniture.

⏱ 3-7 days

✓ Pros

  • •80-90% combustion efficiency (vs. 30-50% conventional)
  • •Uses 1/4 to 1/10 the firewood of a conventional wood stove
  • •Burns so clean the exhaust is nearly invisible
  • •Thermal mass radiates heat for 12-24 hours after fire goes out
  • •Can burn small-diameter wood (branches, prunings) no splitting needed

⚠️ Safety

  • •Carbon monoxide is a risk with any combustion install CO detector
  • •Floor must support the weight of thermal mass (consult structural if in doubt)
  • •Clearances to combustibles must be maintained
  • •Chimney must extend above roof peak