Working on designing a heavy-duty enclosed wood cook stove. Seeking air flow advice.

[Macchina]

I am looking for some input from others on the design of a stove I am working on. We participated in a hunt on a small island about a decade ago and are planning on going back next year. We weren't experienced hikers back then and we got wet, froze, didn't bring enough food, slept in wet sleeping bags, etc. It actually was an absolute blast! The island has a few strange rules: you can carry your stuff in (and deer out) on a small cart and no open fires. Since the last trip we have taken up winter backpacking and feel much more prepared for a week-long stay on a freezing island. I would love to build a small wood stove this year to boil water by the gallons for hot water bottles before bed (best idea ever whomever did it first). We have made some pretty handy pot holders from laser steel or CNC-cut aluminum in the past but this will be a different project

This stove will be carried into deer camp on a small cart so we're trying to keep the weight under 10 pounds. We would like to boil water in a 3-gallon stock pot. We have used these in the past and they fill about 6 Nalgene/Guyot bottles with water to spare for hot chocolate and tea. It needs to be sturdy to boil about 25 pounds of water. This will only be used on a level dirt surface, so I left any kind of ash tray out of the design. This will not be used in a tent, but may hold a fire for warmth under a tarp while we make dinner around camp.

Any suggestions are welcome! I am concerned about ventilation: should I ventilate the sides or will that release heat. I am attempting to force airflow to travel from under the unit and out through the top, I understand I will need to design or bend something to raise the pot up an inch or two to keep the air gap.

A few notes about the design:
-The sides are interchangeable with each other. The doors are interchangeable and able to be flipped, the supports are interchangeable and will take turns in the middle bearing the brunt of the heat and force.
-The doors hinge open and closed and do not contribute to structure.
-The design creates a stronger structure (until failure ) by transmitting the load through each structural joint from top to bottom. As the supports bend outward, the structure stiffens and locks up. Remove the load to disassemble.
-The top and supports are currently 12ga steel, all else is 16ga steel.
-Weight is just under 8 pounds.










Crude assembly instructions:

 

[Macchina]

We made these pot stands a few years back to boil water in the winter with stoves. It takes way too long, so we use them to support the pot directly in a fire now. They last a few years (aluminum) before the heat degrades them and we have to make more.

 

[JV3]

google kifaru, ed t, seek outside or hill people gear stove...they all sell backpackable wood stoves for ideas.

 

[mewolf1]

IMO boiling that much water at one once will take to much time. I think it would be better/ faster to three or four runs at a gallon or so at a time. When I boil sap in the spring, seems to take an awful long time to get to "rolling boil". Don't get me wrong, I love to build stuff too, and your design, but maybe up-grading your sleeping gear might be a better bet.
Are you tenting it?, if so, a full blown wood stove is my idea of comfort and since you can cart the gear in, it might be worth it.

 

[AngryDaddyBird]

I think unless you leave the doors patially or full open you would benefit by adding air vents on the side about an inch above the burn plate. It would greatly help it burn well especially when burning for long periods of time. An other thing Consider is an updraft tube of 3 or more inches with pot suport on top of the exit. It would help the unit to pull more air in the bottom vents when a bunch of coals are layered over it clogging it. Even just a 2" section helps pull air in.
If you plan on burning in your design for extended periods those are definate options to consider.
I'd take a Silverfire Survivor or checkout Four Dog Stoves for some options on buying a stove.

 

[Macchina]

IMO boiling that much water at one once will take to much time. I think it would be better/ faster to three or four runs at a gallon or so at a time. When I boil sap in the spring, seems to take an awful long time to get to "rolling boil". Don't get me wrong, I love to build stuff too, and your design, but maybe up-grading your sleeping gear might be a better bet.
Are you tenting it?, if so, a full blown wood stove is my idea of comfort and since you can cart the gear in, it might be worth it.

We have our gear pretty much set, we traditionally stay in tents during the winter and hammocks all other seasons (I hammocked during winter once and getting dressed etc. was a bit more refreshing than I'd like to try again).
It gets pretty cold up here (Northern Michigan) and the warmest winter trek we went on (dipped to around 10° F) was spent making and sleeping in 3 Quinzhees. We have all invested in decent sleep gear, however our tents are not something that would accommodated a wood stove. We generally stay in lightweight 3.5 season backpacking tents and would have to invest in canvas if we went with the stove for heat. This picture shows the stock pot boiling morning water through the hut opening:



We are hunting in November, so deep snow shouldn't be a big issue. The island does get very cold though. The stove will ideally be brought on future hikes if we can get the airflow to work out for a nice hot fire. Boiling in an open fire has a lot of issues when you are wearing synthetics and we've doused more than one fire in the past...

The reason we like to boil 2.5 gallons at a time (carried in a 3-gallon pot with a lid) is carrying the water. A bladder or other device doesn't work well to haul the water as it's so close to freezing when it's moving that it freezes up in minutes once it's drawn from the stream. We generally dip the whole pot and carry back as much water as possible in each run to the river. This could be a decent hike through deep snow so limiting trips is important too. If we get a good fire going, we can boil 2.5 gallons in about 10 minutes. The trick is to beat the losses through the sides of the pot by applying enough heat to make the losses negligible. This fire will probably take about 15 minutes to boil, air temperature is probably around 20° F:


The above picture shows how we use the pot stand. We find if you support the pot in the fire and keep the flame fueled from below you get a much faster boil than just balancing the pot on burning logs. 2.5 gallons is very doable and does water for everyone in one go.

The water is cold and difficult to get into pots:



This stove will be built with two main goals:
1. A fun project to complete and use. That is the number one reason. I would love to see it work out well enough to bring it on other trips.
2. ONLY FOR COOKING. The problem with most all backpacking stoves that can accommodate a large pot is that they are designed first for heat and second for cooking. No direct flame makes boiling this much water a no-go:

This is the Hill People stove. It is lighter but cost $400...

 

[mewolf1]

With all these details, I think you are on the right track and have no input on your design. Looks good to me.

We have our gear pretty much set, we traditionally stay in tents during the winter and hammocks all other seasons (I hammocked during winter once and getting dressed etc. was a bit more refreshing than I'd like to try again).
It gets pretty cold up here (Northern Michigan) and the warmest winter trek we went on (dipped to around 10° F) was spent making and sleeping in 3 Quinzhees. We have all invested in decent sleep gear, however our tents are not something that would accommodated a wood stove. We generally stay in lightweight 3.5 season backpacking tents and would have to invest in canvas if we went with the stove for heat. This picture shows the stock pot boiling morning water through the hut opening:



We are hunting in November, so deep snow shouldn't be a big issue. The island does get very cold though. The stove will ideally be brought on future hikes if we can get the airflow to work out for a nice hot fire. Boiling in an open fire has a lot of issues when you are wearing synthetics and we've doused more than one fire in the past...

The reason we like to boil 2.5 gallons at a time (carried in a 3-gallon pot with a lid) is carrying the water. A bladder or other device doesn't work well to haul the water as it's so close to freezing when it's moving that it freezes up in minutes once it's drawn from the stream. We generally dip the whole pot and carry back as much water as possible in each run to the river. This could be a decent hike through deep snow so limiting trips is important too. If we get a good fire going, we can boil 2.5 gallons in about 10 minutes. The trick is to beat the losses through the sides of the pot by applying enough heat to make the losses negligible. This fire will probably take about 15 minutes to boil, air temperature is probably around 20° F:


The above picture shows how we use the pot stand. We find if you support the pot in the fire and keep the flame fueled from below you get a much faster boil than just balancing the pot on burning logs. 2.5 gallons is very doable and does water for everyone in one go.

The water is cold and difficult to get into pots:



This stove will be built with two main goals:
1. A fun project to complete and use. That is the number one reason. I would love to see it work out well enough to bring it on other trips.
2. ONLY FOR COOKING. The problem with most all backpacking stoves that can accommodate a large pot is that they are designed first for heat and second for cooking. No direct flame makes boiling this much water a no-go:

This is the Hill People stove. It is lighter but cost $400...

 

[Macchina]

Boiling 2.5 gallons of water in a fire:
I didn't mean to come across as one of those "2.5 gallons of water boiling snobs", but I happen to have boiled exactly 2.5 gallons of water in a fire quite a few times because we bought quite a few of these pots and built the stands for taking large groups of young hikers on our favorite trails and we now also use the pots and stands for winter hiking.

Stove design:
I don't know anything about. I can make a stand that goes in a fire but my experience ends there. I am an Engineer and know a decent amount about sheet metal so I'm pretty confident in that regard but for all I know this stove could be a complete bust as far as heating water.

Some specific questions:
1. Should I provide more/less ventilation in the design?
2. I think I need to lift the pot off cooking surface to allow airflow, however I don't know how far to lift it.
3. This stove is designed to boil water, not heat a tent. Would it work better to still have a chimney coming off of one end for airflow? Does this create or current or merely provide ventilation?

 

[bucketstove]

Why are you making a SQUARE stove?
Why are you making a folding stove?
Is your stock pot a square pot? A folding pot?
I think you need a round non-folding stove
a round stove for your round pot,
it shouldn't take any extra space that your pot doesn't already take,
its about the size of your pot
you make it using 1mm or 1.5mm sheetmetal weight should be 5lb or under
basically its a metal skirt for your pot , the most important design improvement you can make to get more heat into your pot quicket


The simple version is a VITA stove ... cylinder with a grate and pot supports, the gap between stove and your pot is the most importnat "airflow" consideration (I imagine 14mm for your size pot )

The VITA stove http://www.youtube.com/v/UD2bIQlBgwU
http://www.aprovecho.org/lab/rad/rl/stove-design/category/1
Instructions for Building a VITA Stove

The fancy version would be a sunken-pot collapsible ... http://stoves.bioenergylists.org/henson2buckpopup ... this way you get extra "chimney" height for good draft, and you get full length coverage for the pot skirt (increased heat transfer)

heard of the "caldera cone"? Same idea ... go to hardware store, buy a 3 gallon metal bucket ("pail"), add in some metal skewers for pot supports and you're practically there, just need to turn metal lid into a grate, and punch holes beneath that for primary air ... use the VITA stove instructions as guide

More info on stove design and performance (thermal efficiency , fuel savings, emissions , safety .... ) at http://www.stoves.bioenergylists.org/content/learn-more-about

 

[AngryDaddyBird]

Has anyone seen the New Solo Stove Campfire? I backed it and thinkbit would be perfect for your application.

 

[Macchina]

Why are you making a SQUARE stove?
Why are you making a folding stove?
Is your stock pot a square pot? A folding pot?
I think you need a round non-folding stove
a round stove for your round pot,
it shouldn't take any extra space that your pot doesn't already take,
its about the size of your pot
you make it using 1mm or 1.5mm sheetmetal weight should be 5lb or under
basically its a metal skirt for your pot , the most important design improvement you can make to get more heat into your pot quicket


The simple version is a VITA stove ... cylinder with a grate and pot supports, the gap between stove and your pot is the most importnat "airflow" consideration (I imagine 14mm for your size pot )

The VITA stove http://www.youtube.com/v/UD2bIQlBgwU
http://www.aprovecho.org/lab/rad/rl/stove-design/category/1
Instructions for Building a VITA Stove

The fancy version would be a sunken-pot collapsible ... http://stoves.bioenergylists.org/henson2buckpopup ... this way you get extra "chimney" height for good draft, and you get full length coverage for the pot skirt (increased heat transfer)

heard of the "caldera cone"? Same idea ... go to hardware store, buy a 3 gallon metal bucket ("pail"), add in some metal skewers for pot supports and you're practically there, just need to turn metal lid into a grate, and punch holes beneath that for primary air ... use the VITA stove instructions as guide

More info on stove design and performance (thermal efficiency , fuel savings, emissions , safety .... ) at http://www.stoves.bioenergylists.org/content/learn-more-about

PERFECT! Thank you so much!

 

[gadgetgeek]

a couple of thoughts. The more contact patch you get between the pot and the top of the stove, the better advantage you will get for conductive heating. I would close the top, have a chimney gap, or even better a small chimney section, as that will add draw. As much as you will loose a bit due to the conversion, and the heat having to travel, I think you capture more of the radiant heat and put that into the water, since the heat will conduct into the cooler patch where the pot is pulling the heat in.
Since you are not building a "airtight" stove for use in a cabin or tent, i wouldn't bother with the door, just make the opening a bit smaller and lower down, so the top is below the bottom of the chimney, I'm thinking more fireplace than stove. I think that way you will get a large radiant heating effect from the stove body, nice to sit around, good draw, which helps reduce smoke, and means you get more from the wood you burn. You do want to think about where the air is coming from and where it is going to. The grate seems like a good idea to let air in under the fire, so you may not need more than that. Otherwise go with a solid bottom and rely on the door to ventilate. Most of the time with stoves, the damper/draft is there to regulate the fire, where as for you, you seem to want full burn, so what you want to do is get the smoke out and away, catch as much radiant heat from the fire and conduct that into your water. convection from the flames and air is negligible and ventilation above the fire is just for the smoke, in my experience. In my experience, faster moving air, even if there is less of it, gets a fire going faster than more air, as the convection current is better at sort of force feeding the flames. It takes a lot of open fire to effectively convect.

That my ideas, but I'm not a thermo-engineer, just a guy who grew up with wood stoves.

 

[mtangent]

I have one of the Vargo wood stoves. It has holes in the bottom only. They get blocked way too easily & quickly. I am thinking of drilling side holes.
It sits on integral legs much like yours, & they are too short. If the dirt is soft, the legs dig in, stopping airflow. The ash that falls through the holes quickly fills the space underneath, blocking airflow.
So, maybe make the legs much longer. Use side holes, or just leave the door open.

I would not use a chimney, I would let the hot air vent under the pot. It will flow up & around the sides of the pot, helping to heat it. If you vent the stove through a chimney, the sides of the pot will lose heat.

 

[caseynz]

what about a thermette ? its a real efficient way of boiling water. heres a guys blog about his version of one. http://www.theboilerwerks.com

 

[mykel m]

This looks like the perfect solution to your needs Macchina.
Good first post bucketstove.

My question is why not make it out of Titanium?
If it's too costly I can understand, but it'll weigh much,much less than a steel version, which would be an advantage pushing/pulling a cart full of gear.(especially if you add a deer(s) to be hauled out)