Wood Heater Questions x2

[MagraAdam]

Hi guys,
I'm new to the forum, but have been looking around for a while. I'm in Tasmania Australia and my only source of heat is a wood heater. I've got a small house up on a hill with an 80 acre bush block. My heater is an old Saxon freestanding radiant heater. I've got a flat roof with the flue going about 2.2m from the top of the box to the roof, then about 1.7m above the roof with a chinaman hat style cowling on top. I try and only burn dry eluclyptus wood and run it hot. I also keep the flue cleen. The heater is the type with holes above the door that open and close to regulate air flow in, no baffle in the flue, and the plate in the top of the box is pushed to the back, so exhause exits from the front then up the flue which is more towards the back.

I have 2 issues that i can't seem to solve, and i have had it all apart and cleaned the air inlet and flue, and on top of the plate, but can't figure it out.

1: The left hand side of the fire box always burns slower than the right, and the glass always gets dirty on that side with heaps of soot. Soot/creosote even ends up in the left hand side of the air intake and when the fire is out i can put my finger or a stick in there and break off big chips of creosote, like what gets in the flue. I've tried getting the fire nice and hot and then shutting the inlet and using smoke to see if there is a leak in the door seal, but douldn't find one - and i thought more air would mean that side burns more not less.

2: pretty much no matter how well the fire is burning, there just doesn't seem to be a good draw up the flue. The fire can be raging and when i upen the door smoke will exit through the door. it's the same no matter how hot the flue is, how clean the flue is, or how big/small, hot/cold the fire is. opening the door means smoke in the house.. sometimes a little, sometimes a lot. The cowling is basically the same as this https://www.ebay.com.au/i/174049526181 and when i first installed it, it got clogged up fairly easily, so i cut every second leg off it to make the holes bigger. but even when that's completely clean the draw up the flue is terrible.

Any assistance with these issues would be hugely appreciated.

Thanks heaps!

Adam

 

[Halfrsed]

I have similar issues with my Metro (made in NZ) heater.

As to the uneven burning , my suspicion is that either the door seal isn't perfect (my handle is on the side that burns better) or the inlet is slightly more open on one side. These things aren't exactly premium engineering.

And from the day I installed it opening the door would result in a cloud of smoke and superfine ash no matter how slow I go.
I had to remove my smoke alarm as there was no way to stop it screaming several times a day!

 

[MagraAdam]

I have similar issues with my Metro (made in NZ) heater.

As to the uneven burning , my suspicion is that either the door seal isn't perfect (my handle is on the side that burns better) or the inlet is slightly more open on one side. These things aren't exactly premium engineering.

And from the day I installed it opening the door would result in a cloud of smoke and superfine ash no matter how slow I go.
I had to remove my smoke alarm as there was no way to stop it screaming several times a day!

That's exactly the same as mine. Even down to the handle position. Hopefully someone can help us..

 

[Halfrsed]

I've just come to accept it.

I may fiddle with the air control one day but I don't see a complete cure to the smoke.

 

[MagraAdam]

I've just come to accept it.

I may fiddle with the air control one day but I don't see a complete cure to the smoke.

I might try removing the cowling one day and see if it's restricting air flow..

 

[moresnow]

Add more pipe. You have a rather minimal amount now. Even if you remove your cap and insert a 3 or 4 foot section of cheap snap together single wall for testing. Your smoke issue should dissipate with the increased draw. If it works go ahead and remove the cheap single wall test section and add the correct chimney pipe and be done.
Not sure what regulations require in your area but any chimney pipe protruding through the roof over 5 feet needs supports in the US.

 

[Halfrsed]

That could be the answer.
When I installed my heater 11 years ago the instructions stated that the required flue length was 3.6 metres.
Checking the manufacturers website a few years later the requirement was now 4.2 metres minimum.

I haven't added the extra 600 millimetres to mine because I'm getting too old to be climbing on steep corrugated iron roofs.

 

[moresnow]

That could be the answer.
When I installed my heater 11 years ago the instructions stated that the required flue length was 3.6 metres.
Checking the manufacturers website a few years later the requirement was now 4.2 metres minimum.

I haven't added the extra 600 millimetres to mine because I'm getting too old to be climbing on steep corrugated iron roofs.

Find a handy youngster to give you a hand! Possibly enticed with cold beverage when he's done

 

[Halfrsed]

Kids today (I'm actually 64 despite what it says in my profile) are too stoopid and lazy to do any meaningful work.
They can't climb a roof and check their Twitter and Facebook at the same time.

 

[moresnow]

Kids today (I'm actually 64 despite what it says in my profile) are too stoopid and lazy to do any meaningful work.
They can't climb a roof and check their Twitter and Facebook at the same time.

It is a problem I don't miss dealing with. How employers are putting up with this behavior today is beyond me. I say turn off the internet/mothership/cell towers for 10-12 hrs a day! That would be amusing.

 

[MagraAdam]

Thanks all, I think i'll add an extra 1m of flue and see how that goes, and also test the draw without the cowling on.

I completely cleaned out the intake yesterday and also discovered my baffle wasn't in correctly (i'm not sure how i did that, but it must have been at the last flue clean a few months ago, and i've had this problem with the left hand side for much longer)

 

[MagraAdam]

Hi all, a bit of an update.

I measured the surface area of the opening on the cowling, and it was lower than the cross sectional area of the flue (by about 10%). I added some substantial risers to the cap so the opening is now 3.5x more that the area of the flue. So far it seems to have a better draft, but I'll keep an eye on it and reduce the gap a little at a time to limit the chance of rain getting in. Photo attached.

As for the door glass getting dirty and soot getting into the left side (hinge side) of the intake, I have a friend who just installed a second hand heater and the door doesn't seal well all the way around, and it has the same problem with the glass gettin dirty all around the edge. So I'm thinking that the seal needs replacing on mine too. I'll give that a go next.

 

[trains]

Late to the party, but wanted to offer some suggestions too.
yes, I think the flue may be too short, is it double/ triple skin thru the ceiling space, and above the roof line ?
Also sounds like its being affected by pressure differences that the high pitch roof line you mentioned prior, but you also said you had a flat roof, was that the ceiling that was flat and the roof line with pitch ?.
Just want to clarify.
As I dont know its position/ height to the roof top, and pitch angle etc, its difficult to offer suggestions, but if your getting poor draw no matter how hot you burn, I would be looking closely at the position the flue terminates as to the roof line, and how that affects it.
By adding length, and struts to support it, you do two things, you increase draw due to a longer flue, and secondly you may move out of the pressure shadow that is currently affecting the draw.
If you can, get insulated extensions, so the flue stays hotter, and less creosote buildup.

Also, you mention you get quite a bit of creo inside the firebox, and around the air intakes.
That is usually due to burning wet wood, which will also cause build up on the glass door too, notice how it burns away and clears the door glass near the end of its burn, all the moisture has been evaporated, and your left with a short burn time of dry coals which clears the window. yes ? no ?

Either way, it sounds like a combination of poor draw, most likely from wind shadow on the roof ? and wet wood, I normally need 3 seasons to dry dead wood in dry Sth aust, starting moisture of 30% when split, I would expect it could take longer when your relative humidity is higher over in Tas. Yes, close grain, hard gum takes time to move the moisture thru the wood structure.

Also I am not sure if you still have fire bricks inside the firebox, or if it ever had them, I often suggest that lining the base and sides of the firebox with firebricks a good investment in the short time it takes to cut and fit them, as it gives the fire box an easier time, as the fire bricks make the heat transfer to the steel firebox more even, makes the fire hotter, and gives a more even heat to the room over time as well, this can also help with flue gas temp over time, yes you should burn wood on a bed of ash, but putting fire bricks in the base of the fire box both helps the firebox and gives a good base for the ash as well. Its only an inch or so, and worth the time to do so.
some pics of the install, and the roof vs flue position would help.

Argh, just realised I got 2 replies mixed up, and thought it was you mentioning about not being able to get up on the roof due to pitch, but it was MagraAdam's reply.
Thus me asking about if it was roof or ceiling you were talking about. need more coffee.

Still feel its a pressure shadow your both dealing with.
Flat roof on top of hill will cause some interesting patterns and high/ low pressure up there, any chance of getting a smouldering fire up wind of the house and watching how the smoke behaves, could be quite informative for both of you one with flat roof, other with high pitch.

 

[trains]

Hi all, a bit of an update.

I measured the surface area of the opening on the cowling, and it was lower than the cross sectional area of the flue (by about 10%). I added some substantial risers to the cap so the opening is now 3.5x more that the area of the flue. So far it seems to have a better draft, but I'll keep an eye on it and reduce the gap a little at a time to limit the chance of rain getting in. Photo attached.

As for the door glass getting dirty and soot getting into the left side (hinge side) of the intake, I have a friend who just installed a second hand heater and the door doesn't seal well all the way around, and it has the same problem with the glass gettin dirty all around the edge. So I'm thinking that the seal needs replacing on mine too. I'll give that a go next.

Just looked at your chinaman update.
I would suggest you lower the cap to the bent bit in the extensions.
if you raise it up too far, you loose any real help that the curve in the top hat gives for creating a low pressure area under it, and thus help draw the flue gas out, and you increase the chance of rain entry and more down draft as well.
Just raising it up could actually have the reverse of what your trying to achieve.
but yes, removing the bird mesh stuff will help with surface area and thus better flow.

I have heard some have had good results by using the fluecube, but they are pricey, but a cool design.

Or a cheaper alternative.
something like this
https://www.ebay.com.au/itm/6-10-WO...474169?hash=item44398f61f9:g:WhkAAOSwoZle6cT4
not sure whats readily available to you, if your town has a well supplied heater shop with bits and pieces.

 

[MagraAdam]

Just looked at your chinaman update.
I would suggest you lower the cap to the bent bit in the extensions.
if you raise it up too far, you loose any real help that the curve in the top hat gives for creating a low pressure area under it, and thus help draw the flue gas out, and you increase the chance of rain entry and more down draft as well.
Just raising it up could actually have the reverse of what your trying to achieve.
but yes, removing the bird mesh stuff will help with surface area and thus better flow.

I have heard some have had good results by using the fluecube, but they are pricey, but a cool design.

Or a cheaper alternative.
something like this
https://www.ebay.com.au/itm/6-10-WO...474169?hash=item44398f61f9:g:WhkAAOSwoZle6cT4
not sure whats readily available to you, if your town has a well supplied heater shop with bits and pieces.

G'day mate, yeah I intend to lower it, was mainly testing to see if the original design was restricting flow.

 

[MagraAdam]

Late to the party, but wanted to offer some suggestions too.
yes, I think the flue may be too short, is it double/ triple skin thru the ceiling space, and above the roof line ?
Also sounds like its being affected by pressure differences that the high pitch roof line you mentioned prior, but you also said you had a flat roof, was that the ceiling that was flat and the roof line with pitch ?.
Just want to clarify.
As I dont know its position/ height to the roof top, and pitch angle etc, its difficult to offer suggestions, but if your getting poor draw no matter how hot you burn, I would be looking closely at the position the flue terminates as to the roof line, and how that affects it.
By adding length, and struts to support it, you do two things, you increase draw due to a longer flue, and secondly you may move out of the pressure shadow that is currently affecting the draw.
If you can, get insulated extensions, so the flue stays hotter, and less creosote buildup.

Also, you mention you get quite a bit of creo inside the firebox, and around the air intakes.
That is usually due to burning wet wood, which will also cause build up on the glass door too, notice how it burns away and clears the door glass near the end of its burn, all the moisture has been evaporated, and your left with a short burn time of dry coals which clears the window. yes ? no ?

Either way, it sounds like a combination of poor draw, most likely from wind shadow on the roof ? and wet wood, I normally need 3 seasons to dry dead wood in dry Sth aust, starting moisture of 30% when split, I would expect it could take longer when your relative humidity is higher over in Tas. Yes, close grain, hard gum takes time to move the moisture thru the wood structure.

Also I am not sure if you still have fire bricks inside the firebox, or if it ever had them, I often suggest that lining the base and sides of the firebox with firebricks a good investment in the short time it takes to cut and fit them, as it gives the fire box an easier time, as the fire bricks make the heat transfer to the steel firebox more even, makes the fire hotter, and gives a more even heat to the room over time as well, this can also help with flue gas temp over time, yes you should burn wood on a bed of ash, but putting fire bricks in the base of the fire box both helps the firebox and gives a good base for the ash as well. Its only an inch or so, and worth the time to do so.
some pics of the install, and the roof vs flue position would help.

Argh, just realised I got 2 replies mixed up, and thought it was you mentioning about not being able to get up on the roof due to pitch, but it was MagraAdam's reply.
Thus me asking about if it was roof or ceiling you were talking about. need more coffee.

Still feel its a pressure shadow your both dealing with.
Flat roof on top of hill will cause some interesting patterns and high/ low pressure up there, any chance of getting a smouldering fire up wind of the house and watching how the smoke behaves, could be quite informative for both of you one with flat roof, other with high pitch.

Attached are some pics of the roof line and the flue position on the roof. I can get on the roof.

Flue is double skin through the roof and on the outside. Inside has the decorative outer layer.

No fire bricks inside, but they are on my list to get. The manufacturers claim they use extra thick metal so you don't need them, but I still plan to get some.

Also, the glass never clears.. it just builds up thicker and thicker, just in the top (intake side) left (hinge side) corner.

 

[trains]

Attached are some pics of the roof line and the flue position on the roof. I can get on the roof.

Flue is double skin through the roof and on the outside. Inside has the decorative outer layer.

No fire bricks inside, but they are on my list to get. The manufacturers claim they use extra thick metal so you don't need them, but I still plan to get some.

Also, the glass never clears.. it just builds up thicker and thicker, just in the top (intake side) left (hinge side) corner.

Thanks for the pictures, do you have some further away from the house (keeping privacy etc) that shows orientation of house to top of hill, ie where its sitting on the slope, where the flue is in relation to the slope, ie high side or low side etc, and those trees look pretty close to the house as well. maybe a ms paint diagram showing house/ trees etc.

My gut is saying your still dealing with a pressure shadow issue, how well do the windows and doors seal ?
Are you aware of how the wind direction affects the burning of the stove, or does that not matter, not talking about smoke ingress yet, just how the fire responds to wind direction.

What I am thinking is that the shape, orientation of the house to the wind, and tree location results in the inside of the house being lower pressure than outside, and thus when you open the fire box door, high pressure from where the flue exits naturally wants to flow to the low pressure side, ie in the house.
Ok, yes I am where you have been for the last many years with that statement, but picture the prevailing wind traveling across your flat roof, nice high pressure, but where the wind eddies and circles on the lee side of the house creates a low pressure area, that is then drawing air from the house, thus creating a low pressure area inside the house.
thus asking about windows/ doors sealing etc.

Ok, so assuming the inside of the flue is swept clear of the hard class 1 creosote, and is in good condition, the top plate/ baffle of the firebox is clear of fine ash, and the air intakes are clear of house dust and ash etc.

If its a still day, does it still draw back into the house, even with all the windows open ?
On a windy day, if you open the windows to the wind side, thus allowing pressure into your house, does it still draw back into the house. (yeah, I know its winter and cold, but you can test that quickly, maybe even try one room at a time after doing all the rooms on the windward side to see which one has more affect).

You can do smoke tests in each room, light candle, then blow out, watch what the smoke does/ does it flow out the room, towards the windows etc
Same with the stove, open door when cold before lighting, put candle near door, open door, does the smoke get blown away or into the stove ?

Have you extended the flue pipe another section yet as you mentioned you were thinking of doing so.

You have seen what the anti downdraft flue hats look like, can you fab up one and see if that helps.

I have considered making up a fluecube type hat, just to test concept before shelling out the 450 for a proper well made quality one.

re fire bricks, no matter how solid the inside firebox is, adding firebricks helps with the thermal differences with low and high fires, gives a hotter environment for the fire, and helps even out the heat produced to the firebox walls, and thus the room, its well worth adding them to the firebox sides, and floor.

Let me know what you find.

 

[MagraAdam]

Thanks for the pictures, do you have some further away from the house (keeping privacy etc) that shows orientation of house to top of hill, ie where its sitting on the slope, where the flue is in relation to the slope, ie high side or low side etc, and those trees look pretty close to the house as well. maybe a ms paint diagram showing house/ trees etc.

My gut is saying your still dealing with a pressure shadow issue, how well do the windows and doors seal ?
Are you aware of how the wind direction affects the burning of the stove, or does that not matter, not talking about smoke ingress yet, just how the fire responds to wind direction.

What I am thinking is that the shape, orientation of the house to the wind, and tree location results in the inside of the house being lower pressure than outside, and thus when you open the fire box door, high pressure from where the flue exits naturally wants to flow to the low pressure side, ie in the house.
Ok, yes I am where you have been for the last many years with that statement, but picture the prevailing wind traveling across your flat roof, nice high pressure, but where the wind eddies and circles on the lee side of the house creates a low pressure area, that is then drawing air from the house, thus creating a low pressure area inside the house.
thus asking about windows/ doors sealing etc.

Ok, so assuming the inside of the flue is swept clear of the hard class 1 creosote, and is in good condition, the top plate/ baffle of the firebox is clear of fine ash, and the air intakes are clear of house dust and ash etc.

If its a still day, does it still draw back into the house, even with all the windows open ?
On a windy day, if you open the windows to the wind side, thus allowing pressure into your house, does it still draw back into the house. (yeah, I know its winter and cold, but you can test that quickly, maybe even try one room at a time after doing all the rooms on the windward side to see which one has more affect).

You can do smoke tests in each room, light candle, then blow out, watch what the smoke does/ does it flow out the room, towards the windows etc
Same with the stove, open door when cold before lighting, put candle near door, open door, does the smoke get blown away or into the stove ?

Have you extended the flue pipe another section yet as you mentioned you were thinking of doing so.

You have seen what the anti downdraft flue hats look like, can you fab up one and see if that helps.

I have considered making up a fluecube type hat, just to test concept before shelling out the 450 for a proper well made quality one.

re fire bricks, no matter how solid the inside firebox is, adding firebricks helps with the thermal differences with low and high fires, gives a hotter environment for the fire, and helps even out the heat produced to the firebox walls, and thus the room, its well worth adding them to the firebox sides, and floor.

Let me know what you find.

Ok, attached are some pics to show the house and flue, the position on the land, the trees in the distance, and a grab from Google earth and a topology map. Hopefully this helps paint a picture. The flue is on the downhill side of the house which faces west which is where the prevailing wind comes from. On a still day with the house open the smoke still flows out of the firebox. The house is a little draughty. There is a covered veranda on the back of the house (high side of the land) that the air does curl back under, as it's often warmer under there with the smoke curling under.

I haven't extended the flue yet

 

[trains]

Wow, firstly, lovely place you have there, what a view and location.

On the down side, I think you can see the issues you have, flat pitch roofs are the worst for this, the flue location is out in the high pressure area, and the rest of the house is creating a large low pressure area, when you mention the smoke eddying back in under the back verhanda is a classic example.
For pressure differences, you dont need large wind speed, it can happen in still conditions, as the air will move with natural convection and cause pressure differences as well.
Still, descending air from further up the slope will also eddy at the front high point of your place, and cause low pressure all along the front of the house, and under it too.
Do you have an exhaust fan or two for kitchen and bathroom ?

Not sure that extending the flue will make that much of a difference after I saw the profile of the roof, thats one amazing aerofoil, add draughty house, and it only makes it worse.
General rule is 2mt above a flat pitch roof, your at 1.7, so going up to 2.5 is a good start.

If you can get one cheap, or free, try it, as a taller flue is a good thing for your fire, and as you have the worst scenario with a flat pitch roof, 2m+ can only help, but I dont think thats the cause/ solution of your problems from what I can see on my computer.
However happy to be proven wrong, as I am not there, usual disclaimers apply etc etc etc.

A good anti down draft flue, (not H pattern, they are terrible to clean), would be worth while, have a look at whats available, and make one up to prove concept, but I think the real issue lays with the shape and draftiness of your house.
Adding an external air vent for your stove wont help, having windows open on the windward side that did not help show this.

if it was my place, I would set up some smokey fires, and watch the wind pattern over and around the house and look at how the air movement behaved, does it come into the house, that can help you see whats going on.
And look at the candle smoke test inside near the firebox door as well, and chase the path of smoke to see where its going, out a wall vent, ceiling fan, gap between wall and window/ door / ceiling etc, as I think this is your main culprit.

After dealing with the drafts, I would try another flue extension with anti downdraft, if that works, get the outer piece and fit that too, but I dont think its the cure all, it could help, but there are many factors contributing to this from what I can see here.

Until you get the draft sorted, you will continue to have creo from poor combustion, sort that, and you will have a happy warm place.

Sorry I cant offer a clear obvious path forward.
The only reason its drawing back into your house when you open the firebox door is due to pressure difference, yeah its stating the obvious, but you have run hot fires, and even that cant over come the difference that is there.
I dont think your dealing with a "downdraft" from wind direction or shadow off trees etc, or what may happen if you have an over shadowing house/ building nearby, or large tree.

I would not recommend a fan assisted cowl, they are a pain to clean, flog out bearings, and when the wind is up, can make your heater into a forge .

T

 

[MagraAdam]

Wow, firstly, lovely place you have there, what a view and location.

On the down side, I think you can see the issues you have, flat pitch roofs are the worst for this, the flue location is out in the high pressure area, and the rest of the house is creating a large low pressure area, when you mention the smoke eddying back in under the back verhanda is a classic example.
For pressure differences, you dont need large wind speed, it can happen in still conditions, as the air will move with natural convection and cause pressure differences as well.
Still, descending air from further up the slope will also eddy at the front high point of your place, and cause low pressure all along the front of the house, and under it too.
Do you have an exhaust fan or two for kitchen and bathroom ?

Not sure that extending the flue will make that much of a difference after I saw the profile of the roof, thats one amazing aerofoil, add draughty house, and it only makes it worse.
General rule is 2mt above a flat pitch roof, your at 1.7, so going up to 2.5 is a good start.

If you can get one cheap, or free, try it, as a taller flue is a good thing for your fire, and as you have the worst scenario with a flat pitch roof, 2m+ can only help, but I dont think thats the cause/ solution of your problems from what I can see on my computer.
However happy to be proven wrong, as I am not there, usual disclaimers apply etc etc etc.

A good anti down draft flue, (not H pattern, they are terrible to clean), would be worth while, have a look at whats available, and make one up to prove concept, but I think the real issue lays with the shape and draftiness of your house.
Adding an external air vent for your stove wont help, having windows open on the windward side that did not help show this.

if it was my place, I would set up some smokey fires, and watch the wind pattern over and around the house and look at how the air movement behaved, does it come into the house, that can help you see whats going on.
And look at the candle smoke test inside near the firebox door as well, and chase the path of smoke to see where its going, out a wall vent, ceiling fan, gap between wall and window/ door / ceiling etc, as I think this is your main culprit.

After dealing with the drafts, I would try another flue extension with anti downdraft, if that works, get the outer piece and fit that too, but I dont think its the cure all, it could help, but there are many factors contributing to this from what I can see here.

Until you get the draft sorted, you will continue to have creo from poor combustion, sort that, and you will have a happy warm place.

Sorry I cant offer a clear obvious path forward.
The only reason its drawing back into your house when you open the firebox door is due to pressure difference, yeah its stating the obvious, but you have run hot fires, and even that cant over come the difference that is there.
I dont think your dealing with a "downdraft" from wind direction or shadow off trees etc, or what may happen if you have an over shadowing house/ building nearby, or large tree.

I would not recommend a fan assisted cowl, they are a pain to clean, flog out bearings, and when the wind is up, can make your heater into a forge .

T

Thanks for all the assistance!