Build an L-Bench RMH: Annex 6-inch Plans Revealed

Permies.com's six-page Rocket Mass Heater Plans for Annex 6-inch L-shaped Bench include scale drawings (floor plan, elevations, sections, cutaway), photos, and builder's notes for constructing an efficient, clean-burning RMH with L-shaped heated bench, perfect for regenerative permaculture homes integrating thermal mass and passive solar. The design leverages super-efficient wood tech for minimal fuel (twigs/branches), storing heat in 20+ feet of cob mass for multi-day warmth. Detailed specs: 6-inch system—12-inch feed, 18x6-inch burn tunnel, 54-inch riser, manifold to L-bench (10x8 feet footprint). Materials: Firebrick core, clay-perlite insulation, cob finish. Construction notes cover foundation, drum integration, channel forming (cardboard collar method), and venting. Performance: Holds 40-50°C bench temp 48 hours post-burn, suits earthship retrofits or greenhouse adjacency. Insights for practitioners: Airtight seams with clay slip, mass thickness (12-18 inches), integration with trombe walls. Visual aids enable precise replication, addressing common pitfalls like insufficient riser height. This resource provides genuine depth for self-builders in off-grid contexts, with scalability for larger masses.