Hunting Trailer Mini Stove

[Blitzkrieg]

Hey everybody.

I've been lurking here a while and learned lots but now I need some direct guidance.

I built my own hunting/camping trailer and just recently built a wood stove and installed it in the trailer for quiet heat while hunting moose up north.

I've done a few test burns keeping track of temperatures at critical points and I've come to the conclusion that the stove works too well. I'd like to be able to burn it less hot while maintaining safe flue temps to not build creosote. With a minimum charge of wood or even compressed logs and the air intakes closed down to minimum allowing proper flue temps, the temp inside the trailer quickly skyrockets above 40C. If I wait for the temp to drop down to comfortable levels in the trailer (several hours), there are no coals left to start the next log and I have to make a new fire.

The stove is fairly high tech for being home made, it has primary and secondary air dampers, a downdraft baffle plate and fire brick insulated firebox. The current flue diameter is 4" and the chimney is right around 6' tall. The firebox is roughly 9"W x 13"D x 10"T.

Everything works as it should and smoke never enters the trailer even with the door wide open. It reacts well to being dampened down and obviously throws insane heat. The 4" flue runs through a 6" stovepipe insulated with stone wool to protect areas where it passes through the trailer and keep flue temps high.

Now for my question, if I modify the stove and run a 3" double wall SS stove pipe through the existing 4" flue (effectively making a triple wall flue to quadruple wall insulated chimney) can I expect hotter flue temps with a cooler stove temp and increased burn time with reduced heat output?

The firebox is sized similar to a cubic mini grizzly and they use a 3" flue system. I would simply do my own tests but the 3" flue is going to cost around $200 CDN and I would like to be reasonably sure this is going to work before ordering.

I will post some pics so you can get an idea of what I'm talking about.

 

[Blitzkrieg]

Some pics of the stove during construction if they help.

 

[barnaclebob]

How much wood do you run through it? I'm not sure creosote is much of a concern if burning relatively small amounts of good wood at lower temps. It shouldnt be that hard to sweep anyway.

 

[Blitzkrieg]

I just installed it this weekend so I've only had it burning 3 or 4 times for testing. It won't be used that often except for a few weeks straight in the fall. It's not so much the creosote buildup that I'm worried about since I can sweep that out before and during my hunting trip. It's more about getting a good clean burn without producing too much smoke. My thought was that with a smaller diameter flue it would stay hotter and burn up any residual smoke from the dampened down fire before exiting the cap.

Right now if I dampen it too low it starts smoking and the flue temp drops down below 200F.

I might just get some 3" duct and rig it up for a test burn to see if it helps. Then I can order the 3" SS flue if it works out.

The other reason for wanting to go down to a 3" flue would be to lower the exterior temp of my homemade insulated chimney even more. Currently with the stove roaring and flue temps just over 400F I'm getting around 170F on the outside of the insulated portion. Its within safe temps for the surrounding materials but doesn't leave a lot of margin if the stove starts over firing.

 

[Blitzkrieg]

Or maybe I should just install a flue damper and not worry so much about flue temps?

 

[barnaclebob]

I think the stove is just too big for your application. Smoke is created by incomplete burning so you need smaller fires burning hotter. You might need to use smaller splits to keep a small hot fire going or just crack a window.

 

[electrathon]

I would start by getting rid of the grate. It is a woodstove, not a fireplace. Then build smaller fires.

 

[Blitzkrieg]

I'll try it out without the grate and see if it burns cooler. Thanks for the tip.

 

[bholler]

You stove clearances look pretty tight as well. Do you have clearance around the insulated section of the chimney

 

[Blitzkrieg]

Its a very small trailer so I had to go with tight clearances. The aluminum checker plate is spaced off the wall to leave a 1" air gap behind it and so far even with the stove top at 800F the checker plate remains cool to the touch.

The insulated chimney is in contact with wood at the moment but I'm planning on cutting the pass through holes bigger to leave an air gap there as well. At 170F there shouldn't be any chance of it causing problems in contact with wood but better safe than dead I guess.

This is why I've been doing so much testing and I obviously won't be sleeping in there until I'm 100% sure it's safe.

 

[begreen]

Looks pretty cool for a home brew, but I am little concerned about the hearth and the heat it will be dealing with. The legs look short,, but that may be the camera angle. What was used to construct the hearth?

At 170F there shouldn't be any chance of it causing problems in contact with wood but better safe than dead I guess.

That's a risky assumption. I have seen 180º hw pipe ignite wood over time due to pyrolysis. Definitely fix this.

 

[bholler]

Its a very small trailer so I had to go with tight clearances. The aluminum checker plate is spaced off the wall to leave a 1" air gap behind it and so far even with the stove top at 800F the checker plate remains cool to the touch.

The insulated chimney is in contact with wood at the moment but I'm planning on cutting the pass through holes bigger to leave an air gap there as well. At 170F there shouldn't be any chance of it causing problems in contact with wood but better safe than dead I guess.

This is why I've been doing so much testing and I obviously won't be sleeping in there until I'm 100% sure it's safe.

With a proper ventilated heat sheild you should be able to get that stove to 12" clearance to combustibles. It doesn't look like 12" to me. I also don't see a gap at the bottom and the shield isn't big enough. It needs to cover any combustible within 3'

 

[Blitzkrieg]

The hearth is only temporary since I didn't have anything else to put under there. It's currently just ceramic tile. My plan is to build a platform out of hardiebacker cement board. The legs are 6".

As for the 12" clearance to combustibles, keep in mind that this is not a residential installation and since the stove isn't listed, no clearance would meet any code anyway.

I used the cubic mini wood stove as my inspiration for this project and with a heat shield they specify a 3" clearance to combustibles. If residential codes were to apply to recreational installations like this, it would be impossible to install a wood burner in a trailer. I take full responsibility for this installation and am aware of the risks.

Thanks for your concern though, the insulated chimney will definitely be spaced off the wood first priority, a proper hearth is second.

 

[bholler]

The hearth is only temporary since I didn't have anything else to put under there. It's currently just ceramic tile. My plan is to build a platform out of hardiebacker cement board. The legs are 6".

As for the 12" clearance to combustibles, keep in mind that this is not a residential installation and since the stove isn't listed, no clearance would meet any code anyway.

I used the cubic mini wood stove as my inspiration for this project and with a heat shield they specify a 3" clearance to combustibles. If residential codes were to apply to recreational installations like this, it would be impossible to install a wood burner in a trailer. I take full responsibility for this installation and am aware of the risks.

Thanks for your concern though, the insulated chimney will definitely be spaced off the wood first priority, a proper hearth is second.

12" with a proper ventilated heat sheild does meet code for unlisted stoves. The cubic mini is also a shielded stove very different from yours. I am only telling you this because my years of experience make me concerned for your safety with that install. I am not nearly as concerned about code compliance as I am with your safety.

And for the record the codes covering mobile homes would apply here.

 

[bholler]

Sorry I just noticed you are in Canada so I don't know the codes that apply there.

 

[Blitzkrieg]

Thanks again for your concern, I have until the fall before I will need to use this stove so I have lots of time to make adjustments and I really do consider all your suggestions. The design of my stove is such that there is either fire brick or a double wall (cavity for intake air) around the entire firebox. The hottest parts of the stove are the top and front.

Since I am the manufacturer of this stove I am currently in the process of deciding on my own clearances based on measured temperatures and I will definitely adjust as necessary.

I also plan to add a heat shield of the same checker plate above the stove angled upward to direct the convected heat outward, this will also be thoroughly tested for safety.

I will try a test burn without the grate to see if it runs cooler and longer and holds embers for more time.

 

[bholler]

Thanks again for your concern, I have until the fall before I will need to use this stove so I have lots of time to make adjustments and I really do consider all your suggestions. The design of my stove is such that there is either fire brick or a double wall (cavity for intake air) around the entire firebox. The hottest parts of the stove are the top and front.

Since I am the manufacturer of this stove I am currently in the process of deciding on my own clearances based on measured temperatures and I will definitely adjust as necessary.

I also plan to add a heat shield of the same checker plate above the stove angled upward to direct the convected heat outward, this will also be thoroughly tested for safety.

I will try a test burn without the grate to see if it runs cooler and longer and holds embers for more time.

What temperature thresholds are you using for your testing? Are you checking those temps under overfire conditions?

 

[Blitzkrieg]

I read on this site that 117F over ambient is safe so I am shooting for no more than 100F over ambient to be even safer. Every time I run the stove I am checking temperatures with an infrared thermometer literally everywhere. I'll probably need new batteries in the thermometer soon since I use it so much. I have a full size fire extinguisher within arms reach at all times.

Over fire testing will be done once I am 100% confident in safety at normal operating temps. I'll probably have to open all the doors and windows its gonna throw so much heat.

If you have better suggestions on temp thresholds I'm all ears.

 

[bholler]

I read on this site that 117F over ambient is safe so I am shooting for no more than 100F over ambient to be even safer. Every time I run the stove I am checking temperatures with an infrared thermometer literally everywhere. I'll probably need new batteries in the thermometer soon since I use it so much. I have a full size fire extinguisher within arms reach at all times.

Over fire testing will be done once I am 100% confident in safety at normal operating temps. I'll probably have to open all the doors and windows its gonna throw so much heat.

If you have better suggestions on temp thresholds I'm all ears.

That is a fairly good threshold. But 170 would be my upper limit. Also how are you testing the wall behind the shield

 

[Blitzkrieg]

For now all I am able to do for testing the wall is checking at the edges of the shield but I have a set of thermocouples that I plan on rigging up with a digital display this weekend using a raspberry pi. For real time info.
I kinda wanted to get the stove running the way I want it to before I go changing around its placement. Hence the thoughts on reducing flue size.

I'll keep that overall 170F threshold in mind thanks.

 

[begreen]

I read on this site that 117F over ambient is safe

Link please. That needs to be corrected. Here is a shot of where hw heating pipes went through wood.

 

[Blitzkrieg]

Safe drywall temps

This is my first post at hearth.com I fired-up my new Hearthstone Shelbourne woodstove this afternoon after the break-in burns. I have the minimum clearances for a corner installation with the rear heat shield and double wall chimney pipe-- 6 inches from the back corners to the wall. My...

www.hearth.com

 

[bholler]

Link please. That need to be corrected.

Isn't it 80 degrees for ul testing?

 

[Blitzkrieg]

You also have to keep in mind what UL testing is for. It's for a worst case scenario where some unknowing homeowner installs the stove with absolute minimum heat shield up against a cedar shake wall with fur balls and old newspaper accumulating behind it.

My installation is unique and I know that my heat shield will far outperform a chunk of tin somebody finds at the scrapyard (I've seen installs like that). This is 1/16" thick polished aluminum spaced exactly 1" out with non combustible minimum contact spacers.

UL gives a heavy margin of safety for the minimum install. This stove and trailer will never be sold or used by anyone other than me.

 

[begreen]

Here is a shot of where hw heating pipes went through wood. What you do in your trailer is up to you, but taking things to the limit does not make it safe. If you can create a 1" gap with a larger pipe collar (8") that would help.

Isn't it 80 degrees for ul testing?

I don't have time for looking this up right now, doing taxes. I thought it was 90º but could stand corrected.