Tiny Wood-burning Stoves

The link below has a collection of smaller wood stoves for tiny houses. Some are reasonably priced but say they are not rated for residential use - I don't know what this means. In two weeks or so I will move into and will need to heat an UNinsulated 160sf shipping container in Western Oklahoma where the wind comes blasing down the plains. The average daily minimum temp in F according to NOAA is in the low 20s December - February. Will the smaller stoves work to keep this container in the 50s or 60s?

I am concerned about the everpresent windiness and extended gustiness (it's not uncommon to blow 20+ and gust in the 30mph range for a full day) as it concerns the flue - will the wind cause problems with the fire and if so is there a safe way to manage this? Also, I'm not thrilled about putting a hole in the roof, can I put the flue through the wall near the ceiling? It's an 8-1/2' tall container.
Tiny Life Supply Wood Stoves

Hi Denise;  
Straight up is best with a chimney ... but if you must. A double 90 thru the wall will work.
It is a spot for creosote leakage though.
As far as the steady high winds.  
You will need a high dollar spinner cap on top of your pipe, to control downdraft.
You will need to guy wire that chimney if you want it to stay standing in that high wind.
You may need to get up over night to feed that tiny stove when it is excessively cold and windy.
All these things are doable.  By next winter you will be better prepared.

A few thoughts to answer your concerns.  Not rated for residential use means they have not gone through the certification process to be EPA compliant.  That may mean the stoves are not well built (meaning air tight) or it may mean they did not want to invest capital in the government red tape to certify.  As with any wood stove a carbon monoxide detector is a good idea.  A leak will fill up that container pretty quickly.  Don't "wake up dead".  Get an alarm.  Test it.  Keep it in working order.  

Any stove will heat that small a space.  A metal container will conduct that heat outwards, so may require more fuel.  A "rhino lined" or rubberized finish on the outside will keep your container from rusting and give a insulative coat to keep you warmer.  If you do the roof after installing your flue, it will also waterproof the opening.  If you decide to berm up the container with soil in the future, the lining will protect the metal from rusting.  Small stoves also means a lot more work cutting logs to fit the firebox.   Something to consider.  How much work do you want to save in cutting logs and does it justify a larger stove (or more $) to save the labor?

The flue out the ceiling (straight pipe) as opposed to out the side (90 degree turn) is a safety issue.  Creosote build up in a chimney can lead to excess heat that can burn down a house.  Less of a problem in a non combustable metal box however.  Just keep the wood cured (dry) and don't let smoke build up in the flue.  The roof is flat so does not need excessive height to clear the Ridgeline (shorter pipes are hotter and less build up.)  Use whatever chimney design you want and you should be fine.  Thomas makes good points about the chimney cap and guy wire.

Please be careful: too small a stove is a royal PITA. You will quickly learn to hate a "tiny tin tent heater" with every ounce of your being.

The minimum size useful stove has lots of mass, and is at least partially lined with firebrick. It should hold heat for a while, not only for warmth but to hold coals so refiring is quick and painless. It should have a large enough firebox to accept real firewood, so you don't have to feed it every hour or two.

You can probably get a good deal on a used mid-sized stove.

How big is your woodpile? You may wish to double it; I suspect you will go through a lot of wood.

The taller the chimney the better. Especially if you're not putting in a double-wall insulated chimney. If it's single wall, consider having a longish section inside to capture more heat. Agree about the spinner cap -- I've used one and it makes a big difference in making the stove draw well.

FWIW, I have the Drolet Hunter as a portable heater. Paid $100 new because the paint was scuffed. Boy do I have a list of real-world improvements for that tin can. Avoid.

I think I'd buy and build  a barrel stove kit, pile mass all around it and run it all out most of the time.
I think I might want two tees with caps instead of 90 degree elbows, planning ahead for cleaning.

Not directly related, consider having  an earth berm on the windward side.  It will go a long way toward shelter from the wind.  Of course , you are the only one who can determine the tradeoffs (money, damage to land, possible damage to container, etc).  I would be careful to not having the earth touching the container unless you were certain all precautions were taken.

William Bronson wrote:I think I might want two tees with caps instead of 90 degree elbows, planning ahead for cleaning.

Good thinking. Another option is adjustable elbows. The stove will draw a bit better than a 90 degree elbow, and a flexible cleaning rod can get around the corners.

John F Dean wrote:Not directly related, consider having  an earth berm on the windward side.  It will go a long way toward shelter from the wind.

Agree. Even strategically placed tarps will make a huge difference.

Even though there are fewer risks from creosote going straight up,  I can understand you wanting to protect the integrity of your roof.  With any arrangement, there are tradeoffs.  Even though you have high winds, you are in a fairly warm part of the country as winter weather goes. I would run the pipe straight out from the stove and through the wall. Where you would normally place a 90 degree to go upward ...instead place a T. This will allow for an easy clean out ..be sure to have a removable cap at the bottom of the T. The trade off is that you will lose more heat and have a somewhat greater creosote risk.  The benefits are you will protect your roof and any chimney fire will be outside your metal structure.  Even so, invest in a few fire extinguishers.

And on top of the comments about the stove itself make insulating it a high priority. Any insulation is better than none. Old carpets layered thickly for the floor, for a start. Can you contact a carpet company and make a deal for them to give you some old rolls of carpet removed from job sites? Any kind of fabric hangings for the walls - curtains, sheets etc...

The double problem with keeping a metal box warm is the lack of internal thermal mass, and the highly conductive skin. It will cool down fast when the stove is out.

Can you do a rocket mass heater build? Combine seating with heating?

I ought to have mentioned that this is a temporary set-up to get me out of the hated apartment. In spring I will move the container to its forever location but don't want to do this now as it requires concrete piers, engineer, final insulation decision, details, blah blah blah. Here is the topic for my temp container set-up. Temporary Container Living Set-up Suggestions?

A berm may be a good idea once it's in its permanent place. I am thinking of setting a storage container on the windward side of the house container. Tarps I'm sure would be a nightmare because of the noise they will cause in the wind. Unless you've lived on the plains or are a sailor you might not know how obnoxious a constant 15-22mph wind is.

I looked up barrel stove kits and parts on amazon and it looks like it would cost $190 for barrel, shipping, kit, not including a grate or stovepipe. Then there is the whole cutting a barrel in an upstairs apartment...

If anyone has time to look at the stoves in the original post here and comment on or suggest one I'd be grateful. I will keep the stove even after I have electricity (because we just had an ice storm and some in Oklahoma had no electricity for two weeks!!) but it will be taking up valuable real estate inside the 160sf container.

William Bronson, can you direct me to a picture of two tees with caps in case this will work with a regular wood stove? I'm not understanding what you mean.

Douglas Alpenstock, thanks for the advice about tiny stoves and short wood. I don't have a woodpile at all so it's probably easier to buy regular size wood.

I'm grateful to you all for your suggestions.

IMO the only two worth considering are the Drolet Spark and the Drolet Pyropak.

Both are EPA certified, meaning they are efficient and burn more of the wood products inside the stove itself (less firewood used, less creosote buildup).

Both have brick linings (at least partial) which is critical.

The Spark leaves room underneath for fire tools, which matters in a tight space.

The glass window in the door is really nice, both for warmth and aesthetics, and for monitoring the state of the fire.

Note the minimum chimney is 12' -- I would suggest going taller if at all possible. Efficient stoves don't operate well with a short chimney.

My 2c.

In the picture below one could use a tee with a cap in place of the 90degree elbow.
I've not found a picture of this arrangement and there might be good reason for that.

An insulated chimney is far, far better for many practical reasons. But it is a significant expense also. They're heavy, so I'm not sure how to stabilize it on a shipping container.  

Ace, Home Depot, Lowes, Tractor Supply and Menards all seem to have barrel stove kits, and I think they all will ship to the store for free.
There are exceptions, I cant get that service from Home Depot for  fire clay or perlite here in Ohio.
Many of these places will also have the kind of shop stove described above , stoves not rated for habitations.
Barrels are probably best sourced from craigslist,  which at a different time of year might also be a place to buy a stove.

It occurs to me that a Mr. Heater Buddy propane heater might be better for your first winter.
You would be paying for propane, but you might be paying for firewood anyway.
If you decided to get rid of it latter it might have resale value.
Having it could create a worry free warm time/space to work in, giving you a place to assemble a barrel stove, for instance.
Even installing a pre-built wood stove will take some time, and being warm while you do it could make for a much better experience and outcome.

I’ll say it again - the lack of thermal mass is a big issue for your situation. Your internal temperature will swing wildly with the stove. You also suggest cost is an issue.

Is building a RMH out of the question? Paul eg al build a pebble bed thermal mass which looked like it would be suitable for a temporary installation and quite cheap.

William Bronson, I had the same thought about a propane heater today. I went to Tractor Supply, Ace, etc today and I only found 1 smaller stove in town. Wood stoves seem in short supply because of the pandemic. I don't have any wood cut either. There are none that are decent on craigslist.

There are Mr. Buddy heaters in town though. The fact that they are ventless concerns me a bit in part because of the moisture I hear they put out, and the container is probably really airtight though I will have a French door in one side. Is the Mr. Buddy something I need to turn off at night? I have a 20# and 70# propane tank also. Does the tank need to be outside of the container? I really like the idea of something simpler than a woodstove especially since I will need to move the container in a few months.

Michael Cox, I looked for smaller, lighter RMH plans today, do you have a link? I would consider an RMH if/when I add another 20' container to the first one. My 'living room' in this container will be about 8' x 6' at best.

Ventless propane is NOT your friend. Especially in a seacan. Bad idea.


A direct vent propane heater would have a number of things going for it...but gosh would you use a lot of propane. Ick.

But if you need to buy wood.. is good dry wood available? Whats the cost per cord? Convert to $/btu and compare to propane...

My heater is a Martin MDV12VP, heating a fairly well insulated 28ft tinyhome. Build quality did not impress me, especially relative to cost, but it has worked well for 3 winters thus far... I would probly try a different brand next time.

I think a direct vent propane unit is a great companion to a woodstove; I can leave for a week or two in midwinter and nothing will freeze.. and redundancy is nice.

I second the concerns about a ventless propane heater in an uninsulated seacan. The walls will be dripping. It is a valuable tool for temporary use (I have a Buddy heater handy) but I would not use it as a primary heat source while I'm sleeping in a space without ventilation (unless I have TWO carbon monoxide detectors maybe).

It's worth keeping in mind that this is a get-through-the-winter project. So yes, there will be inefficiencies galore -- but trending toward something better.

I've only read about Mr Heater Buddies  on RV, teardrop camper and van living forums.
From what I gather,  they do need some ventilation and they do produce some condensation.
Not all Mr Heaters are meant for use indoors.
I've considered them for my greenhouse, as backup.
A carbon monoxide detector is considered a must.

Chances are that someone online has lived in an unfinished container with one of these things for heat, we just need to find them.

Related idea.
There are tankless propane water heaters out there that have pretty good reviews.
If you used one to heat water in  55 gallon drums,  or IBC tote or what not,  you'd have a nice bit of heated thermal mass.

You need to look at a stove rated for 1600+ sq ft, being an uninsulated tin box. Most of those are sized for well insulated tiny houses.

The Kimberly or Katydid are probably the best fit from on that site, but you pay for it.

Michael Cox wrote:I’ll say it again - the lack of thermal mass is a big issue for your situation. Your internal temperature will swing wildly with the stove.

The architect who designed my brother's house, made the this mistake in designing his own super insulated house in the 1980s. Instead of stone, his walls were metal. So he insulated it well on the inside. But when he did not close the door fast when entering or leaving the house, the temperature would drop significantly because of lack of thermal mass.

Note that this was in Belgium with a moderate sea climate with mild winters ;-)

The 60 seconds I spend trying to find the pebble RMH thread failed, and I don't have time right now to look properly. It was a wooden box with the ducting for the bed directed through it, then filled with small pebbles to act as thermal mass. It struck me a suitable for your situation because it is essentially temporary.

That said, you have also now added that you don't have dry firewood available. That is an essential first step for any stove system, but especially so for a small stove. A big stove, once it is going, you can get away with chucking on wood that isn't properly dry so long as the stove is sufficiently hot. The stove dries out the damp wood, then it burns. In a smaller stove tis works much less well. You have a smaller firebox, smaller reserve of dry hot wood compared to the wet being added, and less time to get the fuel dry before the stove cools too much and burns inefficiently.   You need to take a look at firewood prices in your area and figure out how much properly seasoned (2 years cut at least) wood costs. With the added issues of the labour of using a wood stove and regulating temperature in your container you might find it comparable cost to go for propane or similar.

If you don't have dry firewood, I would look at an off grid pellet stove.  No power needed and they can hold enough pellets for a 12 hour burn.

Hi Denise,

Of course, this is your decision. I am hearing about someone who is planning on spending the winter in an uninsulated shipping container, without a supply of dry firewood, and with no heat hooked up.  From where I sit, I see a train wreck.  Give this careful thought. Putting this off by 3 or 4 months could buy you a considerable safety net weather wise and the luxury of time.  A pellet stove might work,. But do consider the cost of 2 bags of pellets per day for the winter.  And, you need a dry place to store those bags.  My feeling is that you need to grab your beverage of choice and have a long talk with yourself.  If you are still determined to go ahead, you will have a good deal of support here.

My wife has a woodstove in her house (now occupied by my stepdaughter) with almost exactly the setup as posted by William Bronson. The pipe from stove to horizontal insulated chimney is a 2' vertical and an elbow, no actual horizontal bare pipe. She pulls/tips the elbow out of the insulated pipe and lifts the assembly off the stove for cleaning. Simple and easy, and a smooth elbow for flow rather than a tee to make eddies and an extra joint to seal at the tee cap. The outside tee (capped) makes running the cleaning rod from the ground simple and safe.

A pebble bed RMH for temporary setup may work well, though it does still involve building effort and wood purchase and splitting (likely not really fully seasoned and dry). A small propane heater for this first winter might be less total expense and certainly effort now. This depends on how difficult it is to get refilled propane tanks home from the source in winter. I found when I heated a tiny travel trailer with propane that a dual-source regulator was invaluable, so I could just switch tanks with a flip of a valve and refill the empty at my leisure instead of having to go out in the snow at night to unhook and replace a tank.

Do you have access to electricity? I'm assuming not. A nice south window to let in winter sunshine during the day would be nice but may not yet be feasible. I lived off grid in a 196 sq ft tiny house at 6000 ft elevation without a wood stove the first winter and night time temps in Dec and Jan were single digits but upper 20s to mid 30s and plenty of sunshine during the day. I bought a good size tent to set up in the middle of the one and only room (think insulated shed). I bought a smaller tent to sleep in and placed inside with a Dollar General $8 6x8' carpet/rug and placed my twin mattress on top. All my summer clothes were bagged up and placed between North wall of the 2 tents. I should have thought to get a free standing shelf so my "insulation" would go up higher. I had lots of quilt blankets and 2 cats to keep me warm at night. I did have a small propane Buddy heater to warm up my inner tent for 30 minutes before bed time and then turned it off and closed my inner tent but with towels and close pins so my cats could go in and out to litter box. I had to use my Buddy heater sparingly as I only had two 20# tanks.

I used a rocket stove outside for cooking with cinder block walls to block the prevailing wind. This saved on using propane. I used lots of tin foil to warm up food on an old aluminum pie pan that I bored 5 holes in to place my warm overs to warm quickly. I usually cooked only twice per week and ate left overs or pb sandwiches.

Since you are in a metal container, you might go as far around your inside walls with free standing shelves with your clothes, socks, coats, extra linens and such. You could also stack plastic bags from stores between tent walls if you can collect enough. Maybe heat some water and place in a couple of water bottles for under blankets. It will be very cold in the morning so you'll want to cook some coffee, tea, or broth to warm you up and while waiting do some light exercise, sweeping, any movement to warm you up. Also start a Buddy Heater for a bit. Your body can get used to cooler temperatures but you don't want to get too cold. Also, I froze bottles of water overnight outside and kept a cooler for food.

Of course a wood stove would be nice but I wasn't able to do it by myself and I was stuck. Also wear a stocking hat and gloves to bed and double up on socks. I had lost weight before winter and I was able to wear sweat pants under my big jeans.

Good luck. I'll be thinking of you.

M.A Carey

M.A. Carey - Now that is practical experience I can use. I was thinking about stacking my stuff around the edges inside the container. Also using a tent. I figured it is doable as a biography I once read told of living in a log cabin in Canada and waking up to 50 below temps on the worst days. But they had a wood stove to warm it up. I can also stack large hay bales around the outside which will help with the wind and perhaps on top. Thanks for the encouragement!

If you can get hay bales there for not too much money, they would obviously help a lot with insulation, and you can use them for mulch or soil building next year. Some places may have low-grade "mulch hay" not suitable for animal feed and cheaper than prime hay.

Tarping over the top of the stack with well-secured tarps will keep the hay much drier and more insulative as well as keeping wind out of the hay layer. The hay ought to reduce flapping noise too. Billboard Vinyls has their 14' x 48' tarps on sale right now, very heavy duty and ideal for your purposes. Shipping may bring the cost to around $140, or $215 for two.

Holy smokes! I personally know people involved with four unvented gas heater episodes here in my region. In all four cases, one of the people in the space went unconscious or almost unconscious, but luckily in each case there was another person or people who was still alert enough to turn off the device and open the space up before anyone died. One episode was actually in a shipping container last winter, workers who were living on site of a project. Another episode early last winter, my friends say they'd turned off the heater and opened the door a couple of times before sleeping but it still happened. Unvented gas heaters are popular here but they are only okay in old very leaky houses, and just for a short time while people are awake and up and about. The problems come when people are trying to make their house airtight to conserve heat, but they still use the unvented gas heater. Also sleeping with it on is a good way to wake up dead. (The gas here is "liquid petroleum gas" and I don't know if that's propane but I think it has the same effect. Combustion uses oxygen and produces CO2 until there is insufficient oxygen left in the room and it starts producing CO, carbon monoxide).

No. Just no unvented propane in a shipping container.

Even with some other source of heat such as a good wood stove, please keep in mind two issues.

1) Combustion requires air. If you are running a wood stove (with a chimney, of course) make sure there is some inlet for fresh air. Shipping containers can be quite airtight, and that can be a problem.

2) Whatever your heat source, whether it is a wood stove or electric heaters, moisture might condense on the walls. In an occupied space, even if you are not cooking or bathing in it, the warm air will hold much more moisture than cold air can. The cold walls of the shipping container will drip condensation and soak anything that is touching the lower walls. If you are cooking or bathing in the same space, it will be worse. It happens when the warm air, holding lots of moisture, moves to the wall and cools down, at which time it can no longer hold all that moisture anymore, which has to condense on something. If your climate is not very cold, this condensation might not be a huge issue.

Here where the winters are very cold, it turned out to be a problem when some prefab company donated lots of minimally insulated airtight container-like rooms as emergency housing after a natural disaster. People pushed their beds up against the wall, woke up to ice on the walls, and then by evening the ice had melted down and soaked their bedding.

My travel trailer propane heater was built in and used outside air supply and exhaust. I would agree with Rebecca that this kind of appliance would be necessary; it would obviously be much more expensive than a "Mr. Buddy" type portable heater.

Ventless wall heaters seem to run around $200-300 (US), while direct vent heaters mostly start around $500 and go up. I did find one at Home Depot, good size for your space, but it is currently out of stock. https://www.homedepot.com/p/Ashley-Hearth-Products-11-000-BTU-Direct-Vent-Propane-Heater-DVAG11L/309809921

Rebecca Norman, All very important points. What did you heat with in Ladakh?
Glenn, Wood stoves and vented heaters are in short supply this winter, both new and used.

It would not be a good idea to have the propane tank inside

I think all of my thoughts have been mentioned already, but I'll go ahead and list them out.

1.  Insulate your container with whatever you can find.  Hay would be great -- pile some over the top of the container and put a big tarp over it (and strap the tarp down really well).  My mother and step-father have two big containers they use for storing stuff and a work area, and they were able to get old billboard tarps, which are really heavy (you would need help to get one up there).  I have no idea how you go about finding those.  My step-father had a scrapyard for a while, and I think that's how he got his.

2.  Add mass however you can.  Could you get bricks or tiles and lay down for a floor?  You could use them for a patio later, maybe.  And whatever stove you put in, surround it on three sides -- both sides and the back -- and underneath with bricks or stone or sand inside a box or something!  

3.  Make sure you have a working CO2 monitor!  And don't use an unvented propane heater of any kind.  I use one, but my house is an old, very leaky, farmhouse, and we have no air quality issues, just lots of drafts.  A shipping container will be much tighter and you WILL have air quality issues, whether you are using a wood stove or a propane heater.

4.  See if you can get dry firewood before you make a decision on what kind of heater to get.  If you can't get firewood, it's better to find out now before you spend money on the stove.

5.  If you do end up with a wood stove, don't get one of those tiny little boat stoves that are so cute.  Get one big enough to hold a fire through most of the night -- it's not too bad if you need to add wood once during the night; personally I have to get up at least once every night anyway to go to the bathroom.  But you don't want to have to add wood every hour on the hour, or risk freezing to death.  It's true that a big stove may cook you out, but the mass will help with that, and if you get too hot, just open the door!  We heated a 20' X 30' cabin with a 55 gallon barrel stove in the Interior of Alaska, and it often heated us out, even at -70 F (the cabin was insulated, thankfully).  We just opened the door when that happened, and got some fresh air in the house.  Was fun watching the fog roll in down low and out up high, LOL!  You aren't 'wasting money' by doing that, not really, and the fresh air is good for you.  The barrel stoves are cheap, easy to make (you'll need a drill and a metal-cutting blade), NOT airtight, and take large chunks of wood.  Put some sand or bricks in the bottom of the stove and it will last for a long time.  Either pound the top flat, or get someone to cut a chunk out and weld a steel plate onto the top, so you have a cooking surface.  With a folding camp oven, you can even bake on top of it.  A large kettle of water on top of the stove is another source of mass to hold heat, too.  When you don't need the barrel stove anymore, you can probably sell it for what you have into it, or close to that.

6.  You can burn green wood if necessary, but you will still need some dry -- half and half works, if you have the fire going well before you add the green stuff.  But you'll get more creosote in your chimney that way and may end up with chimney fires.  If you go that route, try to deliberately have a chimney fire frequently to burn the creosote out before it gets too thick.  (Chimney fires scare me half to death.  When we lived in that cabin I mentioned, my ex would do the deliberate burn when I wasn't home -- he didn't even tell me he was doing that until much later!)  

7.  Another advantage of a bigger stove is you will be able to bank the fire for the night if it's not going to be really cold at night.  The tiny stoves don't have enough room for the ash and coals to do that very well.

Kathleen, I agree with your post except ... the chimney fire comment gives me pause. From my perspective, it's really hard to do this in a controlled way, and there is a danger of warping or damaging the piping in a way you can't easily see (esp. double wall insulated). I would worry about increased options for failure, leading to a house fire.

I have to admit that the chimney fire thing worried me considerably, too!  It was single-wall pipe almost to the underside of the roof (13' above the floor), and we didn't see any sign of warping.  You can buy chemicals to throw into the stove which causes the creosote to burn out; I think what it does is make a controlled chimney fire.  It is definitely better to have a regular small chimney fire, than to wait and end up with a big one, though.  

Burning dry wood will help make this unnecessary, though.

Kathleen

denise ra wrote:Rebecca Norman, All very important points. What did you heat with in Ladakh?

My house is passive solar heated. Rammed earth, so it's got lots of thermal mass, quite the opposite of a shipping container. I attach a plastic sheet as a greenhouse on the south side of the house from October to April or May, which provides heat on sunny days, as well as growing space all winter.

For backup, I've got 1 square meter of electric heated floor in the living room, which is really sweet to sit on; and an electric mattress pad which replaces the essential hot water bottle I used to use for my feet in bed; and a little portable electric heater that I bring out sometimes.

Actually though, I'm planning to get a wood stove installed this year. And unfortunately I probably can't buy dry wood, and don't have any of my own yet. Oops!

A slight tangent... For keeping warm inside your bed, consider a couple moving blankets. My body runs cold. Hunny needs cold to sleep at all. He's the main support here, so I'm surviving 40* F just fine under a bedspread and one moving blanket.

The whole idea of intentionally setting a chimney fire sets my nerves on edge. On the other hand, so do the agricultural controlled burns, in fields - yet they do have their benefits for crops. I think the chimney fire version bothers me because of the risk of losing the house. But, if I ask sweetly enough, maybe Thomas Rubino, our resident pyro-pro will come in, and give us all a few pointers. Oooooh, Thomas? Help us out, please? I've got some of this chimney stuff on my mind, too.

There really is no good excuse for causing your own chimney fire.
But people have been doing it since your great grandfather's time. Is the excuse you'll hear...
That doesn't make it smart or right.

Have enough chimney fires in a masonry (block) chimney and the clay liner will fail. This will let the fire crumble the concrete block part of the chimney and now your looking at wood being exposed to high heat and  your chimney's structural integrity is badly compromised.
Switch to insulated pipe. You can not see the condition of the inner pipe without taking them apart. If the inner pipe fails the "insulation" will also fail and now you have nothing but a single wall pipe next to your wooden rafters.
Last but not least is just plain old single wall pipe. This is by far the scariest to experience but also has no hidden surprises.  If a pipe is glowing orange /white  a few inches from your wooden portions of your house. At least you know where to get some water too, unlike the "safer" insulated pipe or the "really safe" masonry  block chimneys.

I've been alone in a house having a 2 AM surprise chimney fire.
You wake up thinking that a locomotive is running inside your little house...
And then you realize that you can see in this very dark room??? Why ? Because the stove pipe coming thru the floor and up thru the roof is glowing orange / white and its suddenly  getting really warm...
This will awaken you faster than anything. Vaulting down the ladder to the ground floor you will be using your good winter gloves to grab the damper and try to shut down the stove. Then you'll be throwing water in your antique box stove and then grabbing chunks of still burning wood to pitch out the open front door.... Did I mention it was below zero out that night as well as very windy???

Its now maybe twenty minutes later. The house is getting cold , it smells like smoke everywhere. You realize you have not much in the way of clothes on... your good gloves are ruined... But your not burnt...
You get dressed thanking your lucky stars your alive and the house is still standing.  You assess the situation as being reasonably ok now...
AND then you realize that you now have to relight that very same stove,   as its the only source of heat... And its getting cold quickly.

The above story is completely true.  I did relight the fire & the house did not burn down.
I was 21 or so and dumb as a post.  The house was a rental and the owner didn't care... the next day he told me that he always caused chimney fires at his house! That way it happened when he wanted it too...
A real hold my beer kind of guy...
Later that day, I bought my very own chimney brush and learned how to use it.
I preferred to not burn up in a house fire...

Fires can kill you, they can destroy your home!  
Clean your chimney !!! Its not that hard and it just might save your life.

Better yet why not build a Rocket Mass Heater???  
Never have to worry about creosote again!!!