Running DIY WoodStove over night in a small cabin & safety issues

[TLM]

The farce is the regulations here require you to have an external air vent into the room for a stove over 4.5Kw (IIRC).

Ouch! Maybe somebody should have told them the idea is to warm the cabin. A very small closable vent makes sense if there are other air sources. I have seen designs where the flue pipe is used to warm the incoming air, a good idea as long as it does not cause water condensation in the pipe.

not suitable for wood burning stove such as alders

I have burned dry alder for some while without ever having any problems. In fact it is the preferred wood for heating smoke saunas and many use it for smoking fish.

 

[Stew]

The stoves with 60mm pipe tend to have smaller firebox. They are mostly for camping portable wood stoves.

The 127mm flue pipe is for the larger woodstove. The stove is about twice to thrice the size of firebox space.

When the 127mm flue was reduced to 60mm, the stove smoked a lot with strong wood burning smell. I was wondering if it is caused by the reduced flue. But then there are other factors which might cause excessive smokes in the burning such as type of wood (incompletely seasoned, trees which are not suitable for wood burning stove such as alders and some other unsuitable woods), or over filling the stove before starting.

From the start, the stove was not enthusiastic in burning, and fire was keep dying with lots of smoke. I kept on lit the woods in the stove with a gas torch. The fuel woods in the stove were surely dry enough then, but it just burnt with ambers rather than flames with loads of smoke whole session. It was first time I have seen poor burning like that. Will give another try with the 127mm pipe alone.

On the night I was not sure what might have been the real cause for excessive smoke from the pipe.

If you have reduced the flue from 127mm to 60mm then I think you've reduced the flue to ~25% of the original size.

 

[Pattree]

Will give another try with the 127mm pipe alone.

Excellent idea. Let us know how you get on.

 

[British Red]

If you have reduced the flue from 127mm to 60mm then I think you've reduced the flue to ~25% of the original size.

Just so. If you reduce the flue and hence airflow out to 22% of it's design then 78% of the oxygen in is also stopped. This will make all fuel burn far less efficiently & could potentially risk carbon monoxide production. Best case the fire will burn smokily and too cool.

 

[Broch]

Whereas I agree in principle with everything said about the restricted flue, it is also true that some fires will not draw properly with a wide flue especially until the flue is hot enough to create good gas flow - there is an element of gas velocity required as well. The flue has to be balanced with the size of the stove and the inlet gas volume.

 

[spader]

If you have reduced the flue from 127mm to 60mm then I think you've reduced the flue to ~25% of the original size.

Wouldn't it be about 50% reduction? I was kinda pessimistic the reduced pipe diameter to that portion would work well. But just gave a try to test. The result was excessive smoky burns with strong smell.

I was still unsure the result was due to the pipe diameter reduction or the other factors such as the type of fuel (wood) or seasoning condition, or the stove design itself.

 

[spader]

Ouch! Maybe somebody should have told them the idea is to warm the cabin. A very small closable vent makes sense if there are other air sources. I have seen designs where the flue pipe is used to warm the incoming air, a good idea as long as it does not cause water condensation in the pipe.


I have burned dry alder for some while without ever having any problems. In fact it is the preferred wood for heating smoke saunas and many use it for smoking fish.

I read somewhere on the internet, there are type of woods unsuitable for woodstove burning. It listed a few tree names, and one of them was alder.

In my wood stove burn, they were holly tree twigs, blackthorn twigs, birch barks and birch trees, and some type of conifers. They smoked a lot from the flue while burning.

 

[spader]

Excellent idea. Let us know how you get on.

Sure, will update with the result here.

 

[spader]

Just so. If you reduce the flue and hence airflow out to 22% of it's design then 78% of the oxygen in is also stopped. This will make all fuel burn far less efficiently & could potentially risk carbon monoxide production. Best case the fire will burn smokily and too cool.

This is a strong possibility. Will give another test burn. This time with the full 127mm flues only, and the same type of fuel.

The wood stove is installed outdoors in the patio.

 

[Pattree]

Nope. Half diameter x half diameter x pi

127 very approx 120 sq cm
60 very approx 30 sq cm

 

[Stew]

Wouldn't it be about 50% reduction?

No, sorry.

Click me: 60mm diameter = 28.2743cm2

Click me: 127mm diameter = 12667.7cm2

So it's 0.22319994947780578%

 

[TLM]

In my wood stove burn, they were holly tree twigs, blackthorn twigs, birch barks and birch trees, and some type of conifers. They smoked a lot from the flue while burning.

Can't comment on those here non-natives but birch bark contains a lot of wax and the resulting soot is very sticky. Conifers that contain a lot of resin tend to behave a bit like that. My experience on alders (2 sp.) is though that they burn quite well and relatively clean. Being very low density by volume you have to burn a lot more than some hard woods, by weight about equal.

 

[spader]

Can't comment on those here non-natives but birch bark contains a lot of wax and the resulting soot is very sticky. Conifers that contain a lot of resin tend to behave a bit like that. My experience on alders (2 sp.) is though that they burn quite well and relatively clean. Being very low density by volume you have to burn a lot more than some hard woods, by weight about equal.

In this blog, it lists alder as unsuitable for wood stove for the reason,

"
Alder
Alder burns quickly while producing very little heat, which is not what you want for a woodburner."

Here is the full list of unsuitable woods for wood burner.

 

[spader]

Nope. Half diameter x half diameter x pi

127 very approx 120 sq cm
60 very approx 30 sq cm

No, sorry.

Click me: 60mm diameter = 28.2743cm2

Click me: 127mm diameter = 12667.7cm2

So it's 0.22319994947780578%

Ok.

 

[spader]

From the posts in the thread, I have learned following points so far.

1. Wood stoves don't need to be fully sealed for safe operation.
2. Wood stoves need the front door for feeding the fuel kept open for a while for enough air intake for complete combustion when more woods are inserted into the stove or initial lit.
3. If wood stove leaks smoke into the room or space from the stove, then it is something wrong with the flue pipe installation or air pressure (i.e. strong winds directly hitting the pipe exit hole)

 

[Pattree]

Don’t worry so much about what is wrong. Have fun playing with it until it runs right.

Just looking over your posts: you seem to be burning small diameter twigs and branches. I’m not sure how that translates.

I’m pretty sure that your stove is designed to burn something like quartered logs 100mm - 120mm wide. It won’t burn through the night on small branches.

 

[TLM]

Alder burns quickly while producing very little heat, which is not what you want for a woodburner."

That is what I said - low density - but it burns well. If one wants to regulate the temp of an oven alders are much better at that than the denser species. For maximum heating the more dense woods are better. Really depends what one wants.

By weight the calorific value of hard woods is practically same.

 

[Falstaff]

Ok, Better chuck my 2p's worth, as it's what I do for a job:
There is a see-saw balance between air in vs air out plus burning temp/volume and height of flue. Get any of them wrong and it affects the rest, and the efficiency of the burn.

Then there is the fuel itself, a cheap moisture meter is worth gold - ideal moisture is 15-16%, despite the industry fix at minimum 20%. Too dry or too small, and it will burn too fast and most of the heat goes up the chimney. Conversely, too large or too damp and it will not burn well, temperature will probably be too low for good combustion. 20% moisture means 200 ml water (2/3rds coffee mug) for every kilo of wood that has to be burnt off as steam, = no heat into room. Start fires with spray-paint can sized logs and lots of kindling - an open kindling Jenga pile on the spilt logs with a firelighter on top works very well. Then add the bigger stuff.
Hard wood is harder to get going as needs more heat, but lasts better than softwood. Roughly the same heat from a kilo of each, just a quicker or slower heat release over time. Alder and Silver Birch burn quite fast, although both are apparently listed as hard woods.
Do not burn Willow!!! It produces road quality tar and clogs up stoves and flues at an amazing rate - frequent cause of chimney fires. Not sure about Leylandi, Think I'd give it a miss.

Smoke is unburnt fuel and means something in the balance is not right, and if you have a smokey smell then the fumes are getting out and not going up the chimney = bad health news. CO alarms are pretty good but a lot depends upon their positioning even in a tent. Stick 'em in dead air corners/non-circulation areas or by the fresh air inlet and they are useless, then you become the Canary.

Closing down a flue size at the stove outlet can be done professionally, but has an impact on the draw, and slows it down, sometimes fatally. 60 to a 125 is not good, shuts it down too much.
It's a big technical subject, beset in domestic buildings by a myriad of Regs, all valid & due to historic fatal experience. The barn issue is a familiar outlier one, over 5Kw needs an air supply but is generally overkill, but can be needed. We had an incident once where someone put sand draught excluders at the doors, and a 3-month old baby got hurt.

 

[spader]

Ok, Better chuck my 2p's worth, as it's what I do for a job:
There is a see-saw balance between air in vs air out plus burning temp/volume and height of flue. Get any of them wrong and it affects the rest, and the efficiency of the burn.

Sure great info and advice, thank you.

 

[spader]

This youtube video on running wood stoves in hot tents were also interesting. He seems to prefer larger wood stoves. The video has many interesting points to think about in all manner of running wood stoves be it portable hot tent wood stoves or home base larger wood stoves.