Water Heater Tank

Hi everyone , I have started on my rocket heater . I picked up a gas water heater for free , the guy said it even works fine , i told him i was doing a project but didn't get into details . I got it home and tore into it straight away , removed the outer skin and the polyurethane foam , then i cut the top off with my grinder and a thin cutting wheel ; This makes a nice clean cut . I have a 4 " OD pipe in the middle welded to the bottom . I bought a pipe along with other pieces from the scrap yard . This second pipe slides over the one already there . I plan on the recommended 1-1/2" from the top of the stove to the to of the pipe inside . The lid as I'll call it will have a 1" steel band welded to the top portion of the lid all the way around to keep the lid in place and it will give me access to the inside when needed . Today i purchased a 4 " square tubing 28 " long for the fuel feed . I have just one question ; is the 4 " pipe large enough to work properly ?

Perry MacDonald : At this point you are committed to the course that you are on, because you have seen someone else announce that they have created an all metal Rocket Mass
HeaterRMH, and because you have some welding experience this seemed like a natural to you!

For the purposes of getting the most out of your creation before trying a more conventional build for a first attempt at an RMH,I would recommend placing as much insulation
around the outside of the combustion chamber and heat riser as you can and still leave the 1.5 -2.0'' gap around the outside of the heat riser, then immediately connect an
exterior vertical chimney that is at least 5' taller than any outdoor objects, and then try a series of burns to teach your self how to feed your RMH.

Please Be Aware that you want a thin wall stovepipe to help transfer heat into your Thermal Mass, you do not need any more 4'' square pipe ! I would recommend 5'' round though
that may be hard to find ! Sincerely wishing you good luck, hope this is timely, and helps a little ! Big AL!

Thanks Al ! For your encouragement . I do hope this works out , I hate failure . I'm going to think a little longer about how to go about this so i don't overlook anything .