Rocket heater not very hot-

I have a question. I may need to make a small video or maybe someone can tell me something without it. I built a rocket heater but it does not get real hot like I see from so many who built them. I will try to describe what I have. I have an outer shell of heater made from an old hot water heater. I believe its about 15" across. The stove resembles in many ways the commercially sold Liberator rocket stove. The burn tube or chamber is made from 5" square metal tubing welded together. That burn assemble has a 45 degree bend again like the Liberator design. The top and bottom of the old hot water heater have 1/4 inch plate as I cut the top and bottom portions -the rounded portions off the hot heater so it was flat or square. Surrounding the 5" square tube inside of the hot water heater shell I used a 18gallon metal barrel to surround the 5" square tube. The air space that is inbetween the barrel side and the outside of the square tubing is filled with sand. The floor of the home I like in would not be able to stand a mass build so I wanted some residual heat and thought the inner barrel with sand may just hold on to the heat. When I watched videos I heard and also read that if you used metal tubing for a burn chamber it would spald from the high heat and the heater would basically be worn out. I had already gotten these materials together and so I built it. Now here becomes the issue. This heater does burn although as many comment about these you have to use very small diameter pieces of wood. This heater does sound like a rocket when it burns. I even have a duct booster on the stove pipe at chimney which has a rotary switch which I have in stove pipe just as it enters chimney. I use this to make sure as heater starts to have a super draft to get the thing running well. So what's the problem- well I read and see how so many on here use a digital thermometer and have heat of 2,000 degrees- that is how hot the stove gets. This makes the space heated get very warm. My heater runs ok but with or without the extra draft the hottest it ever gets is 600 degrees. To me it sure looks an awful lot like the Liberator stove and I expected it to burn out however I have other heat in the house which I am glad of because the heater I built just doesn't seem to warm everything up like it should. The stove is built so I would have to build another to make it work different so what could I do to make the thing burn hotter. It looks right but just doesn't get that super temperature. Thank you

Sounds interesting but I cant quite picture your design, sand is more of an insulator than a dense mass, but I am not sure where you have placed the sand?
The only way to get high temperature is by using correct dimensions and adding efficient insulation in the right places.
If you could supply a drawing or some phots I am sure we can help……

Hi Howard;
I agree with Fox that we need visual aid.  Photo's are best.

You are correct in that ultimately the metal will fail in your build.
BUT until then it will work just fine.

You've built a 5" J tube... that is small.
600F is not bad for a 5"
My 8" J reached 1100F a few times but more commonly was running 800F
You may be able to tweek things a bit and hit higher temps but no promises.

Consider this.   A brick bell does not weigh nearly as much as a solid rock and cob mass does.
An 8" J tube can be built using a bell rather than a solid mass...
Food for thought...

Agreed, pictures are worth thousands of words...

My little 6 inch stove routinely reached 2,000 degrees inside the stove, so although a 5 inch may not have as much draft, i am thinking it should get hotter than what it is now.  Until the small 5 inch burn chamber plugs with ash of course...

Some points - is the stove the same size all the way through ? 5 inch start to finish ?

Chimney - my rocket burned beautifully - until i tried to shorten the chimney ( blocking my solar panels) - then it literally ran like crap.  Would not heat up, backdrafted - you name it.  A poor chimney ( or no chimney) can really effect performance some stoves.  How tall is the outside chimney ?

I also try to make the insulated riser as efficient as possible.  The more of a temperature difference between the inside of the riser, and the outside of the riser - the more powerful your draft inside the stove will be.

Just my thoughts...