A hopefully easy question regarding J shaped rocket mass heaters

I have only just begun to look into these rocket mass heaters, and its a fascinating idea. I do have one question at the moment though - the area that you put the wood in to be burned, why is it always so short? Couldn't it be made taller for a  sort of gravity feed effect? I dont really have any dimensions in mind yet, nor do I know what I would build it out of even. My uncle has been talking about salvaging a regular wood burning heater from our old house so that he can do away with his propane heat. I remember when we used this heater and its efficiency is just absolutely awful so this whole situation has me thinking about a better way to accomplish this task. His house is quite small so I think a thermal mass heater would work quite well. If I get the chance I will probably build a few smaller heaters for our various shops and other less flammable work areas before I do one for a home.

Hi devin and welcome to permies! The simple reason for the lower height of the feed tube relative to the riser is so that it doesn't start producing its own stack effect and work against the system, causing poor draft, smokeback, and even complete reversal of the flow.

Thank you, that makes a lot of sense. I suspected it would be something about air flow. If I think of something interesting while I am tinkering with these ideas I will certainly share

Hi Devin,

Welcome to Permies.

Thanks hope everyone had an enjoyable holiday