RMH draft lowers as the barrel gets hotter

As the title says i have this issue when using oak wood and in the morning when its low atmospheric pressure here( the lower the atmospheric pressure the less rockety my stove is ,but thats anotther issue).
I am aware that my barrel is too small and gets hot fast but the stove its also small ,just 6 cm ( 3 inches)burn chamber .
The barrel its from stainless steel ,food grade 316 ss wich is the more temp resistant stainless steel and its a beer keg with 50 litters volume (12 gallons).

Right now im trying to chill the barrel with a fan and il inform you if the draft gets better.
Otther improvements ideas are also welcome .

Mihai;  System of a size smaller than 6" often have draft issues. This is why they are not recommended.
Yes, outside air pressure certainly has an effect on draw.
A 12 gallon barrel of any material is very small.    
Equalization of temperatures will certainly lessen draw.  The cooling gasses dropping thru your barrel keep your draft active. A too hot barrel will cause a stall and in extreme cases could cause a reversal of flow and your feed tube would become the riser.

thomas rubino wrote:Mihai;  System of a size smaller than 6" often have draft issues. This is why they are not recommended.
Yes, outside air pressure certainly has an effect on draw.
A 12 gallon barrel of any material is very small.    
Equalization of temperatures will certainly lessen draw.  The cooling gasses dropping thru your barrel keep your draft active. A too hot barrel will cause a stall and in extreme cases could cause a reversal of flow and your feed tube would become the riser.

Ive started the fan chilling of the barrel and in 10 minutes the stove is roaring and works great now with longer flames.
I made this tove to such a small size because i want to build a feeding mechanism that will feed wood non stop for at least 3 days without having to babysit the stove.
And it will be an outdoor stove with the barrel chilled by a fan wich recirculates the air from the greenhouse out to the stove barrel then sends it back heated.
Ive mountes the stove indoor and ive used it without the fan because i couldnt finish this project in time for this winter.

An update after 45 minutes:thr stove started roaring like never before and the exhaust has probably 40 degrees C.
The temperature in the grrenhouse rised with 4°C and the red coals dont accumulate as it happened before because of the low draft.They are burned fast altough im using oak and outside its low atmospheric pressure.

The fan consumes only 25 watts and has a really high flow .Its an expensive 500-700 brushless fan ( ebm papst last year generation) but i paid only 50 dollars on it.
I want to build a generator that will use heat from the stove to make electricity to run the fan wich its just 25 watts of power and also works on 12V.

Next thing needed its a metal jacket like forced air cooled motors have,to chill the barrel better.

The equalization of temperature that I think Thomas is referring to is the temperature inside vs outside the riser. The closer they are = less draft, the further apart = more draft.
Of course this is just one influence on draft but have you room for more or better insulation on your riser? For example, a "5 minute riser" made from ceramic fiber blanket is probably the most compact riser your ever going to get to fit into your tight space.
Relying on a fan to do something the stove should already do naturally though is a bandaid solution and can become a much bigger issue if it decided to stop working.  

Gerry Parent wrote:The equalization of temperature that I think Thomas is referring to is the temperature inside vs outside the riser. The closer they are = less draft, the further apart = more draft.
Of course this is just one influence on draft but have you room for more or better insulation on your riser? For example, a "5 minute riser" made from ceramic fiber blanket is probably the most compact riser your ever going to get to fit into your tight space.
Relying on a fan to do something the stove should already do naturally though is a bandaid solution and can become a much bigger issue if it decided to stop working.  

That fan its brushless and build to run non stop for about 30 years or so.Much longer than the stove can last and its only 25 Watts at 12 volts.It made for high end gas heating furnaces and wood gasification heating centrals.
It wont fail and because the stove will be mounred outdoor,it wont be a big issue that the fan stopped working.

As for the 5 min riser,ive ordered a ceramic blanket as Thomas recommended allready.

I choosed thin aluminum single use  plates to make  the metal jacket wich will cover the barrel and inbetween them the fan will blow air.
Couldnt find otther source for such thin aluminum .
Il have to straighten them and bind them together.
For when the stove will be installed outdoor,the aluminum jacket will be covered in rockwool for insulation and then another layer of metal sheet to keep the rock wool dry if it rains or snows.

Mihai do you not have a source for aluminum roof flashing? Its pretty thin and easily formed into many shapes. Comes in a roll of various widths and lengths. Available at most hardware stores.