First attempt at a rocket heater

Finally got it out of my system and made a rocket heater. Thanks for all the inspiration guys. Feedback, positive and negative welcome.

I like the idea of the side glass wall. Do you have secondary air supply?

Could you please give us details on the construction? do you have pictures of the work in progress"


Thanks

This really came out nice, I love the steam punk look with the large screws and bolts! It is so darn cool, the glass is nice, great fabrication work.
I like your air controls as well, nice tear drops.

Looks like you used stainless steel exhaust tubing.

caotropheus, it doesn't have a secondary air supply, in fact regretfully I didn't get around to including any features in the riser to get the vortex working well.  I intend to play around with what I can over the coming days. I can easily access the the burn chamber by removing the fuel box section so hopefully I can get something in there to improve the vortex.
trying2hard, thanks for the compliments. The steam punk look wasn't intentional, I was just working with what I had and the limited selection of hardware available in the one horse town I live in. I'm happy with the way it looks although my wife was a bit shocked when she saw it first. "You're not bringing THAT into the house!!" She's come around to it after I promised her she wouldn't be cold again. :) 
I'll post some pics of the work in progress shortly.

Nice fabrication and as already said the glass door looks great  Well done mate looks like a nice clean burn with plenty of draught. you must be happy with that.

After some trial and error I managed to get the stove running on pellets but I'm not really happy with the heat output. It doesn't really get up to full throttle. Max 284F 140C on the top of the stove which is poor.  Also, it tends to go out after a while. I'm wondering if I need a separate fresh air feed from the outside? I can take a feed form the attic which is open at the eves so it's windy up there.  I'd be grateful if someone could advise me on this one.  Thanks for reading.

Oh! and another thing. I have a feeling the riser isn't insulated enough, it just has about an 1" of perlite. Could this cause problems.

You may be right Brian it could be negative pressure backing up.

Try opening a window or a door and then open the air inlet and see what happens. It looks like you have plenty of volume for intake.

The other thing I noticed was how much chimney pipe was running horizontally, you may need to increase your angle up to increase the draft if negative pressure is not the issue.
Also did you implement the vortex action with secondary air feed like me and ppotty1 did?

This really increases the btu output and reduces fuel consumption.

Trying2Hard wrote:

The other thing I noticed was how much chimney pipe was running horizontally, you may need to increase your angle up to increase the draft if negative pressure is not the issue.
Also did you implement the vortex action with secondary air feed like me and ppotty1 did?

This really increases the btu output and reduces fuel consumption.

Thanks Dale, I appreciate your advice. I've been getting high temps and a good draw with dry wood, up to 280c 536f which leaves me thinking the horizontal flue is fine. The pellets just cant get up above 280f which is useless. Unfortunately I didn't take your advice and install a secondary air feed. Duh!! Do you think, from looking at my set up, that it's possible to get one in at this stage?I'm able to remove the firebox/burn tube section if that's any help.

By the way, what temps should I be getting off the top of the stove? Thanks for reading.

I think you can still run a secondary air tube, you could fashion it to slide in and rest in one corner of the bottom of your burn chamber and run it just up under the updraft tube right where the updraft tube and the firebox chamber meet. Check out Jeff Crutchfield's channel on youtube he took some temp readings. I never did, I figured if it was good enough to bake us out of the rv then it was good enough for me, besides being a po boy I could not afford a laser thermometer.

The issue with the pellets not performing is the draft, it is not strong enough to cause an intense flame.

What you can try is build yourself a constrictor that can slide into the burn chamber, put it right before the area the pellets would be burning at, by narrowing the air intake entrance this will induce a greater velocity of the air intake and should get the pellets roaring.

Great advice, I'll fit a secondary air and see how she performs. I've been looking at Jeff's wood pellet set up which is a much more sophisticated arrangement than mine and have decided to go with his design. He's getting serious temps from his stove, over twice what I'm getting and more.
Back to the drawing board.
Regarding the flue, is it really necessary that the flue outlet is higher than the roof line? and should the flue be the same diameter or more than the riser/vortex? These might also be causing problems with my set up as the top of the flue outside is about 4' below the apex and the flue diameter is 4" while the riser is 5"

Fitted a secondary air tube today and added a small step in the burn chamber to create a vortex. Definitely makes a difference. Thanks again for the advice

Probably a bit too late, but can you make a video and show us a comparison between wood burning and pellet burning? Can you make this comparison outdoors with a simple vertical chimney? What is your chimney pipe diameter? What is the rocket stove core dimensions (burn chamber and riser tube)?

Thanks

caotropheus wrote:

Probably a bit too late, but can you make a video and show us a comparison between wood burning and pellet burning? Can you make this comparison outdoors with a simple vertical chimney? What is your chimney pipe diameter? What is the rocket stove core dimensions (burn chamber and riser tube)?

Thanks

Hi caotropheus, thanks for responding. Unfortunately the stove is installed and it would be a major head ace to take it outside. However, I can give you the details you asked for and any other info you might need. The chimney pipe diameter is 4". The riser is Inside diameter 4 5/8" with only 3/4" of perlite insulation. The burn chamber is  a 7' length of 5" box section with a  3 3/4" inside diameter pipe welded to the end  that slides into the 4 5/8 inside diameter  L of the riser. The length of this pipe is 4". ( I hope this all makes sense :roll: )

Yesterday I increased the height of the outside chimney by 8' to bring it 2' above the roofline ( it was way below before this). This seems to have increased the draw but the stove isn't reaching temps above 190C / 375F on the top of the stove. The sides of the firebox have reached 700 F.  I have the feeling this stove isn't preforming properly because something critical is wrong with the design which I guessed :pale: 

Thanks again.

Glad the secondary air and vortex action helped out.
Sounds like you got your system going well.

Would be good to hear an update from you after a week or so of using it.

What I think it is happening is that most of the combustion and heat dissipation is occurring at the burn chamber, where the glass is located. When hot gases reach the bend to the riser tube they are just hot and no longer in combustion. If you look at other people's heaters, like Kevin Bacon or Jeff Crutchfield they have their combustion close to the riser tube, so there is still conduction occurring inside the riser tube and this transfers a lot of heat to the top of the heat exchanger. Your stove to accommodate the glass has a fairly big combustion chamber and the exit of this combustion chamber is reduced to a much smaller diameter pipe. If you take a look at physics of fluids, there is a big loss of energy in the gases in this reduction from a big chamber to a smaller pipe. That is why you have nice heat near the glass and not so hot at the heat exchanger. Further more, The stoves of other people have a pretty linear combustion chamber, same diameter along its length. Flow of fluids in this circumstances is faster and easier and that is why they get more heat at the exit of the riser tube.

This does not mean that your stove is not efficient and that you're not burning most of your potential fuel. It means that you are not getting your heat where you want it to.

Now, go ahead and do like us, not satisfied with the current stove, start planning the second stove! :twisted:

caotropheus,  you de man!! I inserted a stainless tube into the firebox same diameter as the exit burn chamber and hey presto! different stove. What you said made perfect sense. The main combustion was in the firebox so I've transferred it to the riser upping the temp in the bell. I'll post a video tomorrow. Thanks for the tip.:-)
Edit: The max temp on the top of the bell so far is 240c /460f well below what Jeff is getting, 700f plus. I'm wondering if I need to insulate the riser more, 20mm of perlite probably isn't enough. Also, flue exiting the stove is getting VERY hot. Jeff said this might mean poor combustion in the riser.

The insulation of the riser tube plays some rule on keeping rising combustion products hot but I do not believe it can make a difference of tens of degrees hotter like you expect. You have a rocket stove core inserted into the heat exchanger ("bell" like you call it) that by it self keeps hot gases at more or less 200ºC. This hot environment makes a good insulation to the riser tube as well.

You have a nice stove that produces a lot of heat in the primary combustion chamber portion and some heat as well at the heat exchanger ("bell") as well. So, I have a question, why is it important for you to have the top of the heat exchanger as the hottest portion of your stove?

As far as I understand stoves and heat sources in private homes, it is important this heat source to be located as close as possible to the floor because hot air rises and it warms up more homogeneous your room like this way. At home, every time I fire the stove I switch on the ceiling fan to push down hot air that accumulates close to the ceiling.

One other aspect is that I made a cooking rocket stove with a vertical fuel feeder with one horizontal combustion chamber and I was having trouble reaching high temperatures at the top of the riser tube. It would boil water, but not in a hurry. If combustion occurs closer to the riser tube, temperatures will be higher a the riser tube exit, that is for sure. Secondary air will help as well and the vortex will allow better combustion of smoke an gases.

caotropheus wrote:

You have a nice stove that produces a lot of heat in the primary combustion chamber portion and some heat as well at the heat exchanger ("bell") as well. So, I have a question, why is it important for you to have the top of the heat exchanger as the hottest portion of your stove?

The only reason was I thought, from my limited knowledge, it was where the hottest point should be as it's at the top of the vortex. I'm learning a lot from this first stove and will build the next one differently but I'm determined to get this one working as best as I can with whatever changes are necessary. In hindsight, I probably should have experimented a bit before building this one to get a better understanding of how they work. I'm learning the hard way but at least I'm learning:) 

The hottest part of the exchanger will always be the top as its directly over the riser. I will do a vid on the temps on my stove at various points including the flue. temps decrease toward the bottom of the exchanger but after say 15 mins you cant touch it.
The flue will get hot where it exits the exchanger it has to, but exit temps from the flue are much lower than a normal stove and much cleaner. 
Well done so far mate great looking stove, was going to say you can only extract so much energy from a given amount of any fuel and if your combustion is sound in the riser then more fuel might be the answer to higher temps.

Llke the look of it Brian with the side glass. The wife may come around if you black lead it. You can buy lead polish from most diy stores. It gives a uniform colour to the steel trouble is you have to polish it once a week. I think it is a better look than black paint.

Great build will keep watching

brianchulo wrote:

Finally got it out of my system and made a rocket heater. Thanks for all the inspiration guys. Feedback, positive and negative welcome.

Hello brianchulo, I just seen your video and I wanted to say Congrats on your first RS build, very nice workmanship.  

I am gearing up for my first RS build and I also wanted to have a side inspection glass on my burn chamber. After seeing how nice yours looked, I am already planing a trip back to the glass shop to replace the small piece I just bought!  :P 

I see that you have an adjustable sliding cover over your air intake holes.I have noticed in the past, that by incorporating a spring over the hold down bolt, this will help with trouble free movement.

Metal likes to gall when bolted together and heated without any lubrication, whether its liquid or a brass/copper washer.Unlike metals like SS and mild steel are even worse for galling when used together.

I like to use a intake or exhaust spring from a little junk gas engine, these springs are designed to be used in a high temp application already. 

Looks like a winner, to me!