We are building a 6 inch rmh using Erica and Ernie's plans. We are using 1/2 firebricks for the heat riser, and are proposing using a 15 inch barrel packed with perlite to insulate the heat riser. That would give us 3 1/2 inch clearance inside the 55 gallon drum. Is that sufficient for good air flow? What would be the ideal diameter for the heat riser plus insulation inside a 22 inch 55 gal. drum? Thanks.
