Wood stove struggles on still, warm days....?!?!?

Heyo team,

I've done a bit of a search and haven't come up with anything - lord knows I could have missed it.

I need help/ideas/opinions about a draught problem.

In about June we pulled the LPG range out of our bus and replaced it with an Esse Bakeheart.  Love it.  Use it every day.  Got it in just in time for winter and we were so much more comfortable with a wood stove than the diesel heater we used the winter prior.  Now that it's summer we still use it boil the kettle for coffee in the morning and cook our dinner in the oven on the residual heat from the morning fire.

This is the first wood stove I've owned/used and I'm still getting the hang of it.  Went well all winter.  As summer sets in we seem to be riding the struggle bus - generally the fire is taking longer to catch and there's much more smoke until it gets started.  I installed it myself, so am super clear that there are dynamics I just can't understand and don't mind being told I did something wrong.  

I probably would have just struggled through summer with it, except this morning the smoke decided not to go out the chimney at all and cascaded into the bus from around the stove door, around the hot plate, and even down through the fresh air inlet on the bottom of the stove.  I pulled the flue apart, checked for blockages, put it back together in about 5 minutes, burned a small fire in it and it seemed to work fine....

Random facts I think might be applicable:

The NZ govt suggests the top of the flue be at least 4.2m above the floor the stove is installed on - we'll be just pretty close to that height, though have run it with one less section of flue pipe and it ran fine (didn't burn as hot, used less wood, some smoke when we added wood).  

There's one section of flue pipe indoors with a heat reflector on it, then it moves to triple wall all the way to the cowl in a straight run - no bends.

I've recently cleaned the stove and the flue pipe (and looked in it again today) so I know there isn't a blockage.  

I have removed the hose we connect to the fresh air vent for the summer so it keeps the bus cooler, but our bus is already leaky so, while it could be, I struggle to really see it being an air tightness issue.

The wood we're burning is dry.  

The stove has a catalytic converter.

Things I suspect might be problematic though I'm really just making it up:

- The bus was relatively shut up last night - though the kitchen window directly across from the stove was cracked enough that the washing machine outlet hose was still hanging out of it but maybe it was too little air flow?  Even if that is the case, though, usually the skylights are open and the kitchen window is cracked so it doesn't seem like lack of airflow is why we would be struggling more lately...and again, we're not terribly air tight.

- We have a pretty high diurnal temperature difference so it was warmer inside the bus than it was outside this (and most mornings).  Perhaps the triple wall flue pipe worked in conjunction with the lower outside air temperature and gave us cold air plug...and taking it apart this morning let the flue heat up enough to draught smoothly when I burned my test fire?  

- We back onto about 5 acres of bush with trees that will be several metres higher than the flue pipe and the nearest parts of the canopy will only be 4 - 5 metres away from the top of the flue?  I thought I read that we should still be fine even with a closer obstruction than that but again I have no idea.  Perhaps winter winds created the draw that we needed to help us hide from the fact that the flue is actually too close to nearby obstructions and our summer still air just isn't going to let the stove cope as well?

Other thoughts/ideas?

I'm on the verge of buying a $500+ Flue Cube, but defo want to explore other options first and, given the choice, would prefer to spend that $500 on plants for the perennial garden.

Thoughts?  Ideas?  Questions?

As an aside, we've recently talked about replacing our LPG barbeque with an outdoor rocket barbeque so hopefully no matter the situation we'll soon have a viable alternative.  Still though, I'd like to be able to use our stove the way it was designed, ya know?

Hi Tom;
I had to look up the Esse Bakeheart stove.
It looks very nice.
I did not read anything about it having a bypass on it.  Does it have one?

I am not familiar with wood burners using a catalytic burner.
From what I have been told, some stoves have a starting position for the flue and then a catalytic position once it is running.

Temperature inversions can make any stove hard to start, however, making one run completely backward is not common.
Preheating the indoor portion of the stovepipe might help start a draft.

My thinking is close to Thomas’s.  How high is the chimney above the anywhere in the roof within 10 ft.  How high is the chimney above the room peak?

For start up, open the stove door for a few minutes before trying to fire it up.  Assuming that it is warmer inside than outside, the airflow should begin to move up the chimney.

Thanks fellas...

Thomas - it's pretty fancy, probably worth more than the actual bus, but after agonising over the decision when we came across this stove it was clear that it is the right tool for the job.  The only control on the stove is the stove damper itself.  Nothing else.

John - the top of the chimney cowl will be about 2 metres above the top of the roof, so just slightly more than that for the ceiling inside the bus and just slightly less than that for the flat mount solar panels on top of the bus.  It would be more than 10' to the nearest tree, but not much more than that.

Tomorrow I will try opening the stove door all the way for a couple of minutes before lighting the fire.  I'll also try shutting it completely tonight - I forgot (thus forgot to mention) that I've gotten in the habit of cracking the door after the morning fire has burnt out to use the draught to pull out some heat (a little from the fire, mostly from solar gain) from inside the bus and replace it with fresh air.  Works almost imperceptibly but it does work.  Hadn't thought about it pulling cold air down over night as some of our heat works its way out.

Thanks again fellas.

A couple points:

Are you preheating the chimney at all before attempting to light the fire? I twist up a paper match and hold it at the outlet of the stove until I notice the draft pick up before lighting the fire. This ensures proper draft before any smoke is being created. You said you have a window cracked usually - maybe crack the door instead, as having the fresh air coming in at floor level can help since it is below the intake of the stove.

The draft will have the most trouble starting on the warmest days. The temperature differential between the bottom of the stack and the top is a large part of what creates the draft in the first place, so if it is nice and warm outside your interior air doesn't have as much force lifting it past the outside air to create the suction at the bottom. This is also a reason to preheat the chimney before attempting to light the fire, but just to say that the draft will be weaker the warmer it is outside.

Cheers for that, Ezra.  

I haven't been preheating the chimney. Whether for a quick fire for boiling the kettle, or starting the fire for the day I always do the same thing - stack small wood in a grid shaped pattern and put paper or cardboard through the centre of each level of wood, then light each piece of paper/cardboard on one end and close the door enough to leave a big enough air gap for the fire to get started but a small enough gap that smoke doesn't escape into the living space.

Tomorrow I'll also try lighting something above the baffle plate but below the outlet and cracking the door, too.  If I have an easier go of it, I'll work on narrowing down which thing or things helped the most.

Seriously appreciate the input folks.

We have a Waterford Stanley cookstove in our little yurt. Our chimney height is a little short of the recommendation, so we occasionally struggle to establish a draft. Over the years, what I have found is that if I light it with the damper open (exhaust going straight up flue) and the air feed open slightly, I can preheat the stovepipe until it is too hot to hold my hand to it (double wall pipe). Then, I close the air intake (ash cleanout) door and turn the damper to circulate the exhaust gases around the oven chamber. The fire immediately slows down for a few seconds, then (ideally) revives.
If this technique still doesn't lead to a good draft, it is usually because it is time to clean the stove. A little ash can collect in just the right spot to choke the draft. When I've got a squeaky clean chimney, a squeaky clean stove (all the passages around the oven chamber), and dry firewood, there is no reason for the stove to give me grief. But then, I don't live in an island paradise. I do have weird issues when I decide to light the stove in summer.  

To add - 15 years ago when I was just starting to heat with wood I found this forum incredibly helpful - hearth.com - it is very active and contains as much science as you would ever need. It covers all aspects of heating with wood from growing and harvesting to storage to burning to specific discussions about different stoves. Full of very experienced people, great resource.

Hearth.com

I agree with comments above suggesting it has the hallmarks of a downdraft issue. As you suggested, you may have had some helpful winter breezes.

Looking at the .pdf user manual, it seems your chimney is shorter than the recommended minimum. Before spending a ton of money  on gadgets, I think adding more chimney is probably the next move.

The following chimney guidelines must be followed:
o Be a minimum 4.6m high from top of the cooker to the chimney pot.

Right-o.  Fire is currently burning away and not smoking us out.  

It's funny to learn more intimate details about things that then seem obvious only after you know them.  It's always clear when the fire is going to take because of the sound - the sound of fire in a wood stove.  Having lit a piece of paper above the baffle plate and let it burn for a minute or two I realise that sound is the draught.  

Seems I've got a new fire starting routine.

Ezra - thanks for the hearth.com recommendation.  I'm so disenfranchised with the internet lately that I'm pretty much either here or Google Scholar.  Good to know about other good resources.

Douglas - I can't remember where I picked this up from, but I have the distinct feeling that the 4.6m flue height recommendation is about UK standards and not specifically about what the stove needs to function properly.  Probably I picked it up from the Australian distributor who has put out more information on the stove than Esse themselves and since - he would have mentioned AU/NZ standards I'm sure.  That said, if it functions well at 4.6m I guess there's no reason not to add more flue pipe - at least no reason that isn't about aesthetics.

I'm glad your stove is working now. You're absolutely right, every stove has a personality and various moods. Did you notice a shift of wind, air pressure, humidity, anything like that?

We also had a discussion of this recently, with some potentially useful chimney caps that assist with a good draft in challenging conditions. https://permies.com/t/28492/wood-stove-smoking-badly

Personally, FWIW, I take a stove manufacturer's minimum numbers as their recommendation for proper stove operation, not regulatory compliance. If that is true, and my math holds up, your chimney looks to be about 1.2 m / 4 ft short. That's a substantial amount of draft. But perhaps that is for single wall pipe. I know from experience that insulated pipe changes operating conditions for the better, and that adding to an insulated chimney can be a royal PITA.

Hope everything works out for you!