Ash Drawers

How do you guys do your ash drawers, and where in your RMH designs do you put them? I am currently building a RMH, and I plan to have an ash drawer below the feed tube, and then another cleanout at the exhaust exit. I'm not sure how to do the exhaust one, cause you pretty much want things air/smoke tight at that point. Any thoughts?

Abe Connally wrote:How do you guys do your ash drawers, and where in your RMH designs do you put them? I am currently building a RMH, and I plan to have an ash drawer below the feed tube, and then another cleanout at the exhaust exit. I'm not sure how to do the exhaust one, cause you pretty much want things air/smoke tight at that point. Any thoughts?

What are you making the ash drawer from? Pics?

for the one below the feed tube, it will be 16 gauge metal, welded up to form a box. I may put a grill above it to prevent whole sticks from falling down in there.

I don't know if I have seen an ash drawer in an RMH, and I have looked at a lot. Most say they don't produce enough ash to worry about.

R Scott wrote:I don't know if I have seen an ash drawer in an RMH, and I have looked at a lot. Most say they don't produce enough ash to worry about.

really? that seems odd. How do they get the ash out? They definitely produce ash, though it might be taken to a part of the system where they don't see it.

It seems like an ash drawer or something similar would make it easy. On most of the diagrams, I see "ash cleanouts," but I don't now what they are using there.

Abe Connally wrote:for the one below the feed tube, it will be 16 gauge metal, welded up to form a box. I may put a grill above it to prevent whole sticks from falling down in there.

I am new to this, so please take my concerns with a big grain of salt, but it seems to be that grilled compartment below the combustion chamber would be a de-facto increase in the open space surrounding the burn chamber affect air flow and burning.

I think this is a great idea... but I'd be interested to hear if it's been actually done successfully before, and how.

I am new to this, so please take my concerns with a big grain of salt, but it seems to be that grilled compartment below the combustion chamber would be a de-facto increase in the open space surrounding the burn chamber affect air flow and burning.

it wouldn't be below the combustion chamber, it would be below the feed tube. So really, it wouldn't affect the cross sectional area at all.

But, consider that if you have ash buildup in the combustion chamber, you are reducing the cross sectional area.

just doing a google search for "ash in rocket stove" provides a lot of information. Mostly, people say it is a pain to clean out the ash.

Here's one link: http://ilovecob.com/archive/living-with-the-rocket-stove
Under "Maintenance", they say the following:

I’ve been cleaning out the burn chamber on Sundays. It’s best if I let it settle down on Saturday, so I’m not pulling out hot coals. There is around a gallon of ash every week.
...
Reaching down into the burn chamber to remove the ash can be lame. There is room for design improvements here. I’m sure someone has already figured this out?

That seems to be a common complaint.

here's a photo of what I'm talking about with the ash drawer:

and here's from Ianto's book, Rocket Mass Heaters, page 23:

Abe Connally wrote:here's a photo of what I'm talking about with the ash drawer:

If you put a door or easily removable bricks where those bottom two brick are on the left of that picture, it should work. I don't know how long it will last that close to the heat, but at least you could build a cleanout that fits an ash rake.

Abe Connally wrote:and here's from Ianto's book, Rocket Mass Heaters, page 23:

OIC. Thanks for the clarification. I do see the value in this.

A quick google shows various manufactured options, although I acknowledge this may be contrary to the frugal/recycling spirit of the exercise.

http://www.woodlanddirect.com/Chimney/Access-Cleanout-Doors

If you put a door or easily removable bricks where those bottom two brick are on the left of that picture, it should work. I don't know how long it will last that close to the heat, but at least you could build a cleanout that fits an ash rake.

I think if you set the ash drawer down below, like in those diagrams, it won't be exposed to the majority of the heat, because it is sorta shielded by the bricks. I think 16 gauge metal would work, that's thicker than what the metal barrels are made from. Most regular wood burning stoves are made from 16 or even 18 gauge, and they handle the heat just fine.

I'm basically planning to have a metal pan down in that space, that you can pull out when it is full of ash.

I want to make it easy to use and fairly mess-free, that's why I am thinking a drawer instead of just a rake. Pull the drawer out, dump into the ash bucket, and you're done.

Forgive my ignorance, but my understanding is that the ash content is little to none (ideally). Most designs have the cleanout on the chimney end. I suppose the idea is that the velocity of the gas going through the burn chamber is so high that ash is sucked through. Once in the chimney, as the gas cools the velocity drops and ash would fall out, depositing along the bottom.

Here is my planned design. I intend to build the whole system out of circular stove pipe of different dimensions and then insulate with vermiculite/mud. So let's say your feed tube is 6" stove pipe. Can you just drop vertical about 18" into a T fitting? The fire and heat would go one direction through the T. The other side of the T would just be a removable cap. When the fire is burned out, just pull the cap and rake out any ash that may be there. Does that make sense with the T pipe? So the beam of the T would be the bottom when put in the stove, and the post of the T would be the feed chute.

I know there are hundreds of proved designs out there, but I can't help by tinker myself to see what I can do. Referring to my first post, I intend to build a micro RMH. I'm going to model it all with movable insulation (sand) and then once I get the kinks worked out, I'll assemble the permanent setup. If in the model I don't see any ash problems, then I probably won't build in a cleanout in the burn box.

tom Brue wrote:Forgive my ignorance, but my understanding is that the ash content is little to none (ideally).

There's always going to be ash. You may not see it, but there is ash. If you look through a few reports from Google, you'll see people are pulling out a gallon of ash a week.

tom Brue wrote:Most designs have the cleanout on the chimney end. I suppose the idea is that the velocity of the gas going through the burn chamber is so high that ash is sucked through. Once in the chimney, as the gas cools the velocity drops and ash would fall out, depositing along the bottom.

Yeah, some designs also have a cleanout on the exhaust side, and I think that is a good idea, too. I am not sure how to make that cleanout work, though, cause it needs to be fairly airtight. So, no ash drawers, unless they are encased in a closed compartment.

tom Brue wrote:Here is my planned design. I intend to build the whole system out of circular stove pipe of different dimensions and then insulate with vermiculite/mud. So let's say your feed tube is 6" stove pipe. Can you just drop vertical about 18" into a T fitting? The fire and heat would go one direction through the T. The other side of the T would just be a removable cap. When the fire is burned out, just pull the cap and rake out any ash that may be there. Does that make sense with the T pipe? So the beam of the T would be the bottom when put in the stove, and the post of the T would be the feed chute.

I know there are hundreds of proved designs out there, but I can't help by tinker myself to see what I can do. Referring to my first post, I intend to build a micro RMH. I'm going to model it all with movable insulation (sand) and then once I get the kinks worked out, I'll assemble the permanent setup. If in the model I don't see any ash problems, then I probably won't build in a cleanout in the burn box.

Your design might work, let us know if it does. I worry that the stove pipe won't be able to hold up to the high temps, so watch out for that.

I am making mine with sand and stuff, as well, so that I can take it apart, if I need to. I did some outdoor tests with my bricks and heat riser, just to see how it was going to fit together. There was ash in the feed tube, and it got me worried that over time it could start blocking off the combustion chamber. So, I went back to the books (Ianto's) and looked online, and yes, most folks include some sort of ash cleanout below the feed tube. Sometime, they also include one at the exhaust, which I think is a great idea.

ok, we finished our RMH, here is a photo with the ash drawer in the bottom:



here are more photos:
http://www.flickr.com/photos/velacreations/sets/72157632015790209/

And an explanation of it:
http://www.velacreations.com/blog/item/315-rmh.html

This is not a cob model, it is a metal box filled with sand with a RMH in the middle. We wanted to have it so that we could change it if we needed to.

Abe: Technically you have a Rocket Stove of sorts and no kind of a Rocket Stove Mass Heater ! It is an interesting build and I hope you will continue to keep us informed ! Question, Is the primary tank that sits on top of the stove open to the air at any point, or is it a closed system, In other worlds a potential pressurized/steam boiler ! If this is not vented to the atmosphere of the room you need a Boiler grade Steam relief/ pop-off valve - I would pipe the discharge right down the center of the heat riser, that way a failure in the system would rapidly put out the fire ! I hope I can convince you to go to you tube and check out the Video 'Mythbusters - Water Heater'!
I have built 3 Rocket stoves, and helped build 2 Rocket Stove Mass Heaters, and they worked , This does not make me any kind of an Authority, but i have stayed in the house where one of them lives and works past expectations, and a gallon of ash a week sounds high, i'll ask and get back to you, again this may be because other people have modified their system past being a true Rocket Stove ! Again, do some research on the safety of your system, measure your temps, and get back to us, we CAN all learn something from this system ! Pyro - maticly yours Allen L.


# Edit:
Boy is my face red ! I took the sketch you showed us as a "planed build sketch" you can see what caused my deep concerns ! Yes sir! You do Have a Rocket Stove Mass Heater! Yes Sir! You Do have a Rocket Stove Mass Heater! Yes Sir you do have a Rocket Stove Mass Heater ! I had the Idea of the 1st sketch in my head when 1st looked at your pictures, and pre-judged what I was going to see- tho you clearly had a Transition piece to carry exhaust gasses away at the bottom of your Chimney i never saw the third piece of stove work carrying the cooling exhaust gasses down to your chimney ( Except in the Final pictures ) Please accept my sincere apologies , I Think i get it now, again, bringing your build to this forum is a gift from you to us and I'm sure that everyone who will see this will take away some thing that they can use from this, can we please have a little more information on the Temps you are geting and where ! Sincerely Allen L.

I'm obviously missing something here. From what I'm seeing in your pictures (nice shots btw) you have some sort of heat Bell in the combustion chamber before the heat riser. Is this right? Is this where the water/ water-jacket is?

*Edit
Sorry: I've read into your explanation a bit more and I see that you've put thermal mass vertically around the exhaust chimney. Do you get enough dwell time of exhaust on thermal mass to transfer heat well? I'd love to know what the exhaust temps are at the system's outfall. If it's working well (ie: scrubbing enough heat from the off-gasses) then this would be a good fit for those looking at a RMH with a smaller footprint.

allen lumley wrote:# Edit:
Boy is my face red ! I took the sketch you showed us as a "planed build sketch" you can see what caused my deep concerns ! Yes sir! You do Have a Rocket Stove Mass Heater! Yes Sir! You Do have a Rocket Stove Mass Heater! Yes Sir you do have a Rocket Stove Mass Heater ! I had the Idea of the 1st sketch in my head when 1st looked at your pictures, and pre-judged what I was going to see- tho you clearly had a Transition piece to carry exhaust gasses away at the bottom of your Chimney i never saw the third piece of stove work carrying the cooling exhaust gasses down to your chimney ( Except in the Final pictures ) Please accept my sincere apologies , I Think i get it now, again, bringing your build to this forum is a gift from you to us and I'm sure that everyone who will see this will take away some thing that they can use from this, can we please have a little more information on the Temps you are geting and where ! Sincerely Allen L.

yeah, there is some mass, and no, it isn't a water heater, that was just a picture to show the ash space. The real thing here is the ash drawer, as it sits below the feed tube, and catches ash for quick cleanup.

We used sand as the mass on this one, just so it is easy to change/modify later. Look at the Flickr photos to see the detail on the exhaust. We did include a transition bell at the base of the stove pipe.

So far, it works well.

Chris Sturgeon wrote:I'm obviously missing something here. From what I'm seeing in your pictures (nice shots btw) you have some sort of heat Bell in the combustion chamber before the heat riser. Is this right? Is this where the water/ water-jacket is?

*Edit
Sorry: I've read into your explanation a bit more and I see that you've put thermal mass vertically around the exhaust chimney. Do you get enough dwell time of exhaust on thermal mass to transfer heat well? I'd love to know what the exhaust temps are at the system's outfall. If it's working well (ie: scrubbing enough heat from the off-gasses) then this would be a good fit for those looking at a RMH with a smaller footprint.

no water jacket, that was a sketch from another site, basically just looking at the ash cleanout space.

There is thermal mass around the barrel, and the whole thing, actually, plus some around the chimney. There is a heat exchanger on the chimney in another room (upstairs), so we didn't want to take out too much of the exhaust temps, just so that exchanger can heat up a bit.

The thermal mass warms up nicely, I am not sure of the exact temperatures, but after 40 minutes of burning, the sand was hot to the touch (couldn't keep your hand there). The heat exchanger also warmed up like this, and was hot to the touch, so I expect our exhaust temps are up around 150-200F.

Here are some photos of that heat exchanger: http://www.velacreations.com/blog/item/311-heat-exchanger.html

It does fit in a small space, the overall footprint is 4 ft by 19 inches.

It does produce a little ash, not a lot, but some. The ash box works great, by the way, catches everything. It also acts as a secondary air intake. Overall, we are very please with the performance so far. We live in a very mild climate, so we don't run the stove very often. We use maybe 1/2 a cord of wood with the regular stove, so I am hoping we can reduce that somewhat with this design. The thermal mass and heat exchanger was hot for at least 6 hours after our 40 minute burn, so we were very pleased with that.

thanks, you know the ask was one of my concerns with the designs i was looking at...good to see others solved already