Heat II

Last January I did a post about small DIY wood stoves with the promise of some methods for venting. Right after that I built several more stoves out of steel, messed around with some vent pipes and pretty much forgot about it. At that time I had no tent to use a small wood stove in and I didn't feel like throwing down the cash for the really nice lightweight vent that I wanted buy and show you.

new black iron model with removable heat exchanger

The whole kit, minus the cook top, after first test with light weight vent

  Well I finally got my shit together and built a canvas pyramid tent and got the stove pipe. I'll explain the venting and new stove ideas now and will go over the tent details in some later post. First: I chose to use steel (black iron) instead of stainless. Steel is way cheaper and lighter, it's also a lot easier to work with. ie easier to cut and bend. The cost of an entire 4X8 foot sheet of 26 gauge is about 35 bucks, stainless is about triple. Also it seemed the perceived radiating heat from the stainless one was less. I could hold my hand close to a red hot stove without really feeling hot. Maybe it was just me, but I asked a guy I've done contracted work with, that builds and refurbishes refractory and really high temp burners, and he seemed to believe there was some truth to it.

This is a three piece tapered vent, well used and holding up great. You can make it whatever length or #of pieces to fit inside your stove. three happens to be just right for my larger stove.

detail of a groove seam

 Second; I built a heat exchanger that "plugged in" to the existing stove design. The drum is the same size as the stove and has the same spot welded pockets, in the same places, for ease of construction. Both ends are capped and a baffle was added to the inside to trap the heat. I also added a cook top that will fit on either the top or bottom sections and  fits neatly inside with the vent and the legs. The idea behind the heat exchanger is simple, more heat for less wood. My thought was that if you had two people on the same trip the stove could be divided equally by weight. It would also be no problem to bring both pieces in a sea kayak. A canoe would be fine too, as long as your not portaging. Weight is not much of an issue and it might be nice to have a heated space on a cold, fall or spring trip. Kayaks are roomy but not roomy enough for my full blown canvas tent and stove.Third; the vent, stove pipe, whatever you want to call it. I could think of three methods to use  all of which work the same...get the smoke and flames out of the tent in a safe manner.

this is a four piece vent that fits inside the stove made from light 30 gauge snappy pipe 

detail of cut-out section for breaking down pipe to roll inside one another

  #1 is a stove pipe I built many years ago for my large wall tent and stove. I consists of tapered pipes that slide into one another. The seam is made with a brake and finished with a groove seamer tool. This is my least favorite method, getting the taper just right is a pain in the ass to layout. If you don't have a brake, groove seamer, or a stake, to hammer the seam together your not going to be able to make this. It is however, very strong and safe, but heavy, and looks like you might actually have some skills with metal.

a bit of wire will hold pipe together in the worst conditions

  #2  Is the cheapest and most readily available, but also heavy. The size of the opening on my stove is three inches to match three inch galvanized "snappy" pipe you can buy at any home improvement store. It snaps together with a snap lock that is formed into the pipe. If you cut the pipe into lengths that will fit into the stove they can be nested inside one another but only if they are un-snapped.  If you've ever tried to get a full length of snappy pipe apart it's not really possible without destroying it. Here's the trick, after the pipe is cut to length,  cut out lengthwise, a center portion of the female side of the lock. Leave a couple inches on either end so the pipe will still hold itself together. Since it's only locked in on the ends, it's not hard to squeeze it back apart.You will also have to crimp the raw ends so they fit into one another. If you don't want to buy a hand crimper for 20-30 bucks just buy short 2 foot pieces and use the portion with the factory crimpped end and discard the rest. I also drill holes through opposite sides after it's together so I can pass a little wire through the joint for safety. You can choose to use these or not, based on conditions, but if they're there you always have the option.

bam

this can be rolled either way... vent or storage

  #3 The nice, light, expensive, trick, vent is a piece of stainless shim stock. This one is much more expensive than the others (65 + dollars after shipping at Mc Master Carr) but looks really cool and is as fancy as you can get with a portable wood stove. The shim stock comes in 12 x 50 inch or 12 x100 inch lengths, is 304 or 308 stainless and is four thousandths thick. Don't bother with the 316, it's more expensive, The 316 is for corrosive resistance and will never have any benefit in this application.  My system only needs a 50" length  but I bought to 100" so I would have two, one for me and one for a friend. This system is cool because you roll it the long way to use as a pipe and the short way to store inside the stove. I cut the piece in half and then cut one inch off the long side to use as my rings to hold it together when rolled up either for storage or vent. Finished size was 11x50". The spot welded rings are just a hair under three inches so  I can slide it down over the stove connection and make it tight when the pipe is installed. You could use cable or some other means to keep the pipe from springing apart but that should be done before you ever get into the field so your not fumbling around when it really counts.

  I saw some guy on you tube with a piece of pvc to roll it up the long way, I found it completely unnecessary. The shim stock doesn't really have a lot of memory to it and can be rolled up free hand on a table. I found this out when I rolled it up in a real roller at 45 deg angles while alternating which side I rolled it on...flipping it over repaetedly. This is a technique used for forming tight cones out of sheet metal, it did't make any difference when I rolled up the shim stock into a long pipe and back to a tight roll for storage. Don't bother with the PVC, but definitely practice rolling it in the comfort of your warm home.

Stove and canvas tent on front of bike. Stove is strapped to a rack and the tent is in a handle bar bag. This combo is about 9 pounds, not ultra light but safe and super comfortable when set up. On the other hand I've never known winter camping to be light weight  

first test of heat exchanger and tent....in my front yard

  Back to the 11x50" size. If you make a stove in which the vent is going to fit inside, make sure it's large enough for the collapsed pipe. My stove finishes at about 11.250 inside, so I have a nice fit for the 11'' by 3"dia. collapsed pipe. This is important to keep in mind, the stretch out for a 3 inch dia pipe is 9  7/16 (3 x  Pi...3.141) and will leave approximately an inch and a half for overlap if your blank is 11x50. The stretch out for a 4inch would be 12  9/16 so if you make a bigger stove with a bigger vent, the shim will not work. Obviously you can make your opening whatever size you want based on what you can get at a hardware store but going to a four inch or greater vent will eliminate being able to use the shim stock.

is that hot enough for ya ?

removable cook top fit on the stove or heat exchanger

 Testing; I had my kids out in the newly finished tent and stove system a couple weeks ago when the temps were around the minus 10 F range. We were so warm we were wearing t shirts. I got the stove as hot and as red as I could get it with no ill affects to it's integrity. The tent didn't start on fire either.

cook top during first live action field test

light weight, heated , winter camping

            Hopefully you found this interesting or helpful.  Although I'm a professional sheet metal worker with a full shop at my disposal, anyone can can build a stove with readily available pieces and parts found in various stores, thrift shops and dumpsters. You can do a lot with a tin snip, pliers, drill and pop rivets.... have fun and good luck.    D Rider out