Thermo-siphon

Did it, done it, got the t-shirt. Use a Biasi 3-wood running on coal. The Samson thermostatic draft control is the missing link for safety. Also a fusible plug. Caleffi Solar DC circ battery-direct. Radiators all got TRV's except the bathrooms for min. flow. Heat 3500 sq.ft. in a cold climate (coldest temp reached was -38, it was still t-shirt weather inside, baby crawling around naked) on 15W continuous draw. No storage, the cast rads provide quite a bit of storage. Wouldn't want to run that boiler on wood, but a Varmey like you say with thermosyphon storage would be fine. B-pressure welder should be able to weld in a port for a Samson draft reg. and you'd be all set. I'd try it but I could never go back to wood with coal at $40/tonne.