Barrel stove improvements?

Hey all.  I've really been enjoying the site, but this is my first time posting here.   I've got a small problem that I'm hoping someone here can help me with.

So, I recently built a standard double barrel wood burner using 2 55gal steel drums (horizontally oriented, one atop the other - bottom is the burn barrel).  I was hoping to use it to take the edge off the cold in a large uninsulated pole barn this winter, but I'm a bit disappointed in the results.   It only seems to get above 300 degrees F if I toss in 5+ logs and keep all the vents wide open and its not actually radiating out that heat more than abt 5 feet in any given direction.   I tried pointing a fan at it, with marginal success.  I'm also burning mystery wood, at the moment.   I got 2 cords of dried, half-split logs for pretty cheap, but it seems to be a random assortment of type and size.

My question is, does anyone have any ideas for upgrading one of these?  Or troubleshooting, if that ought to be my first step?  

Hi Bill. Welcome to Permies!

My immediate reaction is that you're burning wet wood, and most of the heat you generate is blowing up the flue as steam rather than radiating out as heat.

How big is your pole barn?

Hi Bill;
Welcome to Permies!
I had a double barrel stove in my uninsulated shop building for years.
It only radiated heat about 5' just like yours.
I could have it partially orange and jumping off the floor and 20' away tools would be sticking to my hand!

I cured it by building a double barrel 7" batch box with brick bell!
My shop has never been warmer!

A batch box with barrels and brick bell would be the gold standard for your situation, but you could improve things a lot just by turning your barrels vertical and putting them over an 8" brick J-tube. This would be an easy, quick build that would introduce you to the concept and working of rocket combustion technology. I have experienced that an 8" J-tube can work fine coupled to a 6" metal chimney as long as it has fundamentally decent draft.

You would have to feed the fire every half hour or so, but if you are working in the shop that should not be difficult. You would use much less wood for the same or better heat. I think vertical stacked drums would radiate farther and more evenly than horizontal barrels (assuming you have more than an 8' ceiling to work with.) Adding a brick bell to hold and moderate some of the heat would be an upgrade after you have the basic setup, and as you gain confidence you can progress to a batch box.

As you mention uninsulated, a quick and easy if not dirt cheap step would be to put reflective mylar bubble wrap insulation on the walls, as shown in Thomas' picture. That would both reduce infiltration within the wall surface if you do not currently have tight walls, and bounce heat back at you instead of letting cold walls suck it out. Do the same on the ceiling too.

The 5 minute fix is to run the chimney pipe down to a couple inches off the bottom of the top barrel, turning it into a bell/stratification chamber. That will get you a little more heat while you gather materials for a rocket.

I have wondered if the barrel stove doors will work for a batch box…

Cast iron doors will take the heat, but the air intakes are generally too small to feed a batch.

Not easy to run a pipe down in the upper barrel with the flange size they use.
Starting might be slow and smoky until a good draft is started.

The experts have given great advice as per usual!
I will suggest you add mass around the stove, and way to dry out your wood that won't risk setting it alight.

Here is a Permies thread that illustrates adding mass to conventional wood stoves :Thermal Mass

Hey!   Its taken longer than I'd hoped to get back to this post, but I'm here again!

I attached a pic of the burner below just for reference.   6" flue - probably 18' long up to the top of the chimney outside

My shop area is about 2800 sqft with 16ft ceilings.    The farmer that lived here before me parked his equipment in here, and apparently never saw the need to insulate it.  Its a little drafty tbh, but nothing that cant be shored up, for the most part.   That's on the to-do list this weekend.  I'd love to throw up some reflective barriers but I expect it'll be prohibitively expensive, this year, unfortunately.  

I've seen "brick bell" mentioned several times, and just to confirm, I understand a bell is like a primary exhaust chamber in place that soaks up heat before the exhaust exits via the flue?   Would this increase creosote buildup if my flue is staying colder?     I do have a place in town where I can get free bricks, luckily.    I've never tried mortaring bricks together, but I s'pose I'm up for the challenge.

I've also seen j-tube mentioned a few times.   I looked it up and got kind of an idea how what it is and how it works.     Would it actually put off more heat?    It does seem like it'd save on wood.    

If I were to come up with some brick, what exactly would I want to do with it?

A rocket combustion core, either J-tube or batch box, burns all combustible material including the smoke, so there is zero creosote to go up the chimney. That is what makes masonry heaters in general and rocket stoves/mass heaters in particular viable. All the heat can be harvested as long as there is still enough draft for the chimney to work. A 16' tall interior chimney will work great except in startups where the shop is colder than outside, when it will need priming to start the draft.

2800 square feet is huge, especially with 16' ceilings, and I don't see a single heat source ever warming that satisfactorily unless it is well insulated. Can you subdivide a section to keep warmer?

Yea, I can to an extent.   Its partitioned into thirds, with drop down tarps from the trusses lol.   Thick ones, though.    I'm thinking about adding some barrier to the bottom of the trusses as well, as only the middle third has that now, and my chimney is in the north section.  That should cut a few cu ft out and provide something of an air barrier.  

That's good to know about full combustion - I didn't realize that was the goal with the rocket design.   I think I'd feel much better about that in general.   I'll pop over to that forum section and see what I can learn.

Thanks!

Hi Bill;
Here are the threads about my initial shop build and the most recent rebuild.
You might find them helpful.
https://permies.com/t/94980/Brick-Bell-Shop-Heater
https://permies.com/t/181421/Batch-box-rebuild
https://permies.com/t/190599/Finishing-touches-Shop-Dragon-rebuild

Glenn Herbert wrote:2800 square feet is huge, especially with 16' ceilings, and I don't see a single heat source ever warming that satisfactorily unless it is well insulated. Can you subdivide a section to keep warmer?

Good call. I was thinking that too. It's not hard to knock together a warm space inside a building.

The other option is to get a high volume fan (like a hotwired furnace fan) and point it at the ceiling. That's where all your hot air is. Move it around.

If you use a big fan to move warm air from the ceiling, I would suggest locating the fan in the coldest corner of your "heated" space, so you get the maximum exchange of air temperatures.

If the heating comes and goes on demand, it's important to watch for condensation issues in a work space with fine quality tools.

The variable heat means that the humidity is also variable, and as the air cools the moisture condenses. Keep your finest tools and bits in closed containers. My 2c.

I'm wondering if it would make any sense to just build a batch box style RMH with another barrel and some brick right next to my current double barrel stove and just pipe my exhaust gasses into that since its already connected to the chimney?    I attached a very crude drawing below to help picture it.  The purple shows the exhaust path.     But I figure that will add a little extra surface area to radiate heat from at least.    I'd like more masonry, I think,, but I've got limited space to work with and I really don't want to move the double barrel situation as the flue is a royal pain to deal with when not supported from the bottom.  

Does the inclusion of the existing double barrel setup in the design really add anything or, more importantly, will it cause any problems?

Hi Bill,
Seems like your idea is very doable to me.
If you have the exhaust from the batch box entering the bottom barrel about half way up and extend the (insulated) outlet pipes close to the bottom on both barrels, they will act as effective heat stratification chambers.
You could also line them with bricks to retain some heat as well.

Gerry Parent wrote:Hi Bill,
Seems like your idea is very doable to me.
If you have the exhaust from the batch box entering the bottom barrel about half way up and extend the (insulated) outlet pipes close to the bottom on both barrels, they will act as effective heat stratification chambers.
You could also line them with bricks to retain some heat as well.

I'm happy to hear that!    Its late in the year for major reworks, but we have a few days coming up that I can use to mortar some bricks effectively.   And I just happen to have a spare barrel and some stove pipe on hand!     I'm really not sure how best to line 2 lifted cylinders with brick, tbh.     I would if I knew how to get a good heat transfer out of it...   but I dont have high hopes for that one

For clarification Bill, I was thinking you could dry stack the bricks inside of your two barrels.
Being sideways,  the barrels will be difficult to do all the way around, but the bottom half would be easy.
Of course if the barrels were vertical then you could dry stack the bricks all the way around the perimeter from top to bottom without a hitch.