# Rocket mass calculations

I met a fellow rocket mass heater fan at the cob workshop this weekend. It was great to have someone who knew what I was talking about. James is also interested in hypocaust heating, which was a double bonus.

Our current challenge involves wall penetration. I’ve been thinking and studying and working through what if‘s trying to get the best solution. With James’ council, I think I’m pretty close to a final solution. I’ve got to collect some material and do some testing, but I’m close.

One of the issues I have is dimension. Because I’m doing a wall penetration, and because I’m using a tall radiating container, I’ve got to do some calculations to get the proper dimensional relationship between the rocket mass heater elements. My radiator (pictured at right) is 55″ tall at the shoulder; 20″ taller and 1″ wider than a 55 gallon drum. The rise from the shoulder to the center of the radiating tank is 3″ and the curve is continuous from the shoulder to the center.

The Rocket Mass Heater book provides relational guidelines. A few key relationships are noted here:

• The feed tube should be rectangular or square, not round and the cross sectional area must be smaller than the same measure for the burn tube and the feed tube. The height of the feed tube should be short.
• The burn tube should be wider than tall and no part of the riser or exhaust cross sectional area should be smaller than the burn tube.
• The burn tube should be half the length of the riser.

I’ve got some testing to do ensure I maximize the burn.

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