# How much wood "hissing" is tolerable? How bad is it for the chimney???



## Swedishchef

Hi guys

I have been burning some maple lately. The odd piece hisses for about 10 minutes max. Normally on the lowest part of the wood, a white foam appears. I keep the fire roaring while it is doing this and once it stops, I turn down the primary and let the secondaries take over.

I am hoping that the hot flue temps are preventing condensation in the chimney. How bad could it be?

I have not burned wood like this the entire winter. it has only been of late.

Thanks
Andrew


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## shredd_guy

Burn it baby.  just throw a 2 by 4 in there to help heat it up faster.


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## sebring

Your wood is hissing and foaming at the mouth? Welcome to the unseasoned wood club. Keep an eye on the pipe leading to the chimney. Thats where I see most of the creosote buildup.


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## dougand3

Tolerable to me is a minute or less hiss when a split lands on a hot bed. Foaming is definitely NOT tolerable. You need drier wood or you're going to goo up your pipe and chimney in short order.


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## Swedishchef

I figured there would be 2 schools of thought: add some wood to help drive out the moisture and the other to get rid of it. The funny thing is that it is maple that has been c/s/s/ for over 3 years now.

I think the foaming is simply t he nature of the moisture: it's from maple..aka maple sugar? Like I said, after 5-10 minutes (from a COLD start) it is gone.

Andrew


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## begreen

My goal is totally dry wood. It's been successful for several years now and shows in a clean chimney so I'm not changing it.


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## Swedishchef

Another interesting point: within the wood that hisses (like I said it's only a few pieces), all the other wood is fine. I have a mixture of yellow birch and maple. Same size splits: NONE of the yellow birch hiss and SOME of the maple does. I am thinking it's the off gassing/boiling of the sugar inside the wood (???).

Andrew


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## dougand3

A good thing to test: Take a split and re-split. Test Moisture Content on the inside side. I've burned ~1 cord of Silver Maple this season. It has been CSS for only 1 year. (We do have many 90+* summer days and bright sun here, tho). My MC is 15-17%. If you have Sugar Maple - may behave differently.


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## Woody Stover

If this wood has been drying for three years I wouldn't expect to see this kind of moisture present...type of wood shouldn't make a difference. Could some splits be slightly punky...from dead branches maybe? If so, they might absorb a bit of water if rain hits the end of the splits. The fact that only a few of the splits are wet, not all of them, points to something like this happening. So does the fact that the splits stop hissing fairly quickly.
You could try letting this Maple dry out by the stove for a week or two and see if the problem goes away. It doesn't sound like you'll get a lot of gunk in the flue from the occasional hisser, but I would keep an eye on it nonetheless.


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## Hass

Some of my pine does this... It's bone dry. Usually I see sap start oozing out if I watch carefully enough. It tends to be on splits where a limb was cut off.


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## begreen

Maybe this discussion is best kept exclusive of softwood. Pine resin may still have some moisture content, but it's so oil laden that it will easily burn.


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## nate379

I get it with birch as well.  



			
				Hass said:
			
		

> Some of my pine does this... It's bone dry. Usually I see sap start oozing out if I watch carefully enough. It tends to be on splits where a limb was cut off.


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## par0thead151

start work on on next winters wood and you will not have hissing wood.
i have yet to have one piece hiss this year, as i have wood that is stacked and dry for 1.5 seasons after learning how much of a PITA it is to burn wet wood...


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## shawng111

Swedishchef said:
			
		

> I figured there would be 2 schools of thought: add some wood to help drive out the moisture and the other to get rid of it. The funny thing is that it is maple that has been c/s/s/ for over 3 years now.
> 
> I think the foaming is simply t he nature of the moisture: it's from maple..aka maple sugar? Like I said, after 5-10 minutes (from a COLD start) it is gone.
> 
> Andrew



I have maple that does the same thing and that wood seems dead bone dry but still hisses, my thought was the sugar or sap in the wood boiling out, only lasted a few minutes and burned like a gas soaked rag.  Shawn


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## CTYank

Swedishchef said:
			
		

> Another interesting point: within the wood that hisses (like I said it's only a few pieces), all the other wood is fine. I have a mixture of yellow birch and maple. Same size splits: NONE of the yellow birch hiss and SOME of the maple does. I am thinking it's the *off gassing/boiling of the sugar* inside the wood (???).
> 
> Andrew



Most unlikely, for many reasons.

One of the first things that happens within fresh splits is the fermentation of plant nutrients. Don't believe me? Sometime when fresh sugar maple splits are stacked inside a shed, close the door for a bit, then step inside. Ever been to a winery?

Try over-cooking some sugar on the stove sometime, for grins. No hissing, plenty of really yucky black poo, etc. (Make sure wife is out-of-area.)


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## fraxinus

Fifty pounds of wood dried to 15 or 20% moisture content - in other words, very dry wood - still contains 7 to 10 pounds of water. This still has to boil off, so some sizzle is inevitable. I'm not sure that wood with 0% moisture content would be anything more than powder.


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## rijim

If your getting good/normal stove top temps that's a good sign, if not, more cause for concern.  I would check/clean any connecting pipe and chimney maybe a month into burning and see how it looks; that will give you the real answer.  

Jim


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## Swedishchef

Thanks for the replies guys.

I am glad that I am not the only one who gets this problem. Like I said, the wood is 3 years old. That's why I have a hard time believing it's still wet.

I already have wood that is 2 years old for next winter. Buy then it will be 3 years old. In fact, I have wood already c/s/s for the next 3 winters.

CTYank: I understand what you're saying about burning sugar on a stove. But something tells me that what is boiling out is sugar with moisture (small amounts). The bubbles that come out are like foam, not water. I have tried burning green wood in the past in firepits, etc. I know what wet/hissing wood is like.

I agree with SHawnG: it burns like a gas soaked rag after the hissing is done.

For example, I just lit a cold stove start. I put a piece of maple inside. I will try and see if it happens and if it goes, take a picture. I still think it has to do with the sap: rock maple is one of the only hardwoods that you actually TAP INTO to get a liquid to come out... drop by drop into a line or intoa  bucket.

Another thing I just noticed: the moisture is coming out ONLY on the bottom of the piece of wood, nowhere's else. Yet flames are burning all around it. Hrm....

Andrew


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## Woody Stover

Swedishchef said:
			
		

> something tells me that what is boiling out is sugar with moisture (small amounts). The bubbles that come out are like foam, not water.
> Another thing I just noticed: the moisture is coming out ONLY on the bottom of the piece of wood, nowhere's else. Yet flames are burning all around it.


I've seen the foaming on non-Maple species as well...
The bottom of the wood is where the most coals are, and the most heat. That's where any moisture will first be seen, and where you'll see the most moisture. I think moisture in the wood is pulled toward the driest (hottest) area...


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## Hardrockmaple

Swedishchef said:
			
		

> Thanks for the replies guys.
> 
> I am glad that I am not the only one who gets this problem. Like I said, the wood is 3 years old. That's why I have a hard time believing it's still wet.
> 
> I already have wood that is 2 years old for next winter. Buy then it will be 3 years old. In fact, I have wood already c/s/s for the next 3 winters.
> 
> CTYank: I understand what you're saying about burning sugar on a stove. But something tells me that what is boiling out is sugar with moisture (small amounts). The bubbles that come out are like foam, not water. I have tried burning green wood in the past in firepits, etc. I know what wet/hissing wood is like.
> 
> I agree with SHawnG: it burns like a gas soaked rag after the hissing is done.
> 
> For example, I just lit a cold stove start. I put a piece of maple inside. I will try and see if it happens and if it goes, take a picture. I still think it has to do with the sap: rock maple is one of the only hardwoods that you actually TAP INTO to get a liquid to come out... drop by drop into a line or intoa  bucket.
> 
> Another thing I just noticed: the moisture is coming out ONLY on the bottom of the piece of wood, nowhere's else. Yet flames are burning all around it. Hrm....
> 
> Andrew



All I have burned for many years is maple, yellow birch and some apple, beech. It is my experience that when you have hissing and foaming on any wood, that wood is wet. "Sugar" or hardrock maple is my predominant wood burned and is c/s/s for 12-14 months prior to burning, very rarely do I get "hissing and foaming" from it. It goes into the stove at indicated 10-20% mc on my moisture meter. 

High "sap" content indicates high water content. I'm surrounded by maple sugar camps and get the majority of my wood from these camps. Maple which has been been harvested from the higher dryer hillsides is much better than that cut from low country and which, when cut, often I find the heartwood has deteriorated to basically a hollow tree. Nothing scientific here, just general information gathered by myself and my sugar camp owning friends.


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## gzecc

Swedishchef said:
			
		

> Thanks for the replies guys.
> 
> I am glad that I am not the only one who gets this problem. Like I said, the wood is 3 years old. That's why I have a hard time believing it's still wet.
> 
> I already have wood that is 2 years old for next winter. Buy then it will be 3 years old. In fact, I have wood already c/s/s for the next 3 winters.
> 
> CTYank: I understand what you're saying about burning sugar on a stove. But something tells me that what is boiling out is sugar with moisture (small amounts). The bubbles that come out are like foam, not water. I have tried burning green wood in the past in firepits, etc. I know what wet/hissing wood is like.
> 
> I agree with SHawnG: it burns like a gas soaked rag after the hissing is done.
> 
> For example, I just lit a cold stove start. I put a piece of maple inside. I will try and see if it happens and if it goes, take a picture. I still think it has to do with the sap: rock maple is one of the only hardwoods that you actually TAP INTO to get a liquid to come out... drop by drop into a line or intoa  bucket.
> 
> Another thing I just noticed: the moisture is coming out ONLY on the bottom of the piece of wood, nowhere's else. Yet flames are burning all around it. Hrm....
> 
> Andrew


I've had problems with norway maple taking forever to dry. If its a large piece, they really hold on to the moisture.


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## SmokeyCity

hissing mean the boiling water is coming out as steam
wood is not dry

thats what ECO BRICKS are for!


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## MetMan

I didn't see anyone ask if the wood is covered or uncovered. Could it be a few top pieces got a little rain/snow on them and it's just surface moisture?


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## firefighterjake

I wouldn't worry about it too bad . . . but I am thinking this wood is not as prime as it could or should be.


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## Swedishchef

I totally understand why everyone is saying that the wood is simply NOT dry. But how the ^#%$ can it not be? Open sun and wind for 3 summers, it was c/s/s during that time AND it is in my greenhouse which acts as a KILN. The wood has that hollow/dry sound when knocking, has turned colors to a greyish tint and seems darn dry to me. I guess the center it still damp then.

Hardrockmaple: you only dry yours for 14 months?!?!?! Mine has been sitting in sun/wind for almost 3 years...that is why I am having a hard time with it "being wet".

It is not surface moisture, I can see it coming out of the edge of the wood. My stove top temps still reach 700 and my flu temps 400-500.

I think I will blame it on aliens or wood gremlins. Because I am not willing to accept that I need to dry my damn wood for 4 years before burning it! lol.

And unfortunately, I don't think it's simply surface moisture. I will get a picture of a piece todya or tomorrow and post it for viewing.

I still think it's something of a water/unknown mixture. In a stove the temps should hit 800+ degrees F easily within the beginning of the burn. This "stuff" is like a foam or bubbles and can actually DRIP down the edge of the wood for 5 minutes or so. At 800F, all moisture would evaporate instantaneously and would not have time to froth and drip....or would it?

Andrew


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## dougand3

Another possibility....Stacking too tightly. I used to stack 3 x 16" splits in a 48" crib. No room for air to circulate. 10-15% of the center line would get punked because it stayed damp in there. Now, I stack more loosely and just get more cribs.


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## Ken45

Swedishchef said:
			
		

> I totally understand why everyone is saying that the wood is simply NOT dry. But how the ^#%$ can it not be? Open sun and wind for 3 summers, it was c/s/s during that time AND it is in my greenhouse which acts as a KILN.



"open sun and wind" sounds like it's also exposed to rain.

Greenhouses are often humid.   

When it's stacked outside, is it in single row stacks, or multiple rows stacked together?

Ken


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## Swedishchef

It is exposed to rain. You can't have it all I guess: sun, wind and no rain. Either no sun and no rain with wind, but if you have sun, ya gotta have rain 

My greenhouse is not humid. I opened the bottom walls of the greenhouse to allow a crosswind. The roof acts like a magnifying glass, temps can reach 30C on a 20C day and the front door open, bottoms rolled up, the wind blows through it.

When it is outside, single row, 4 feet away from the next rown. Face of wood is towards the wind to allow wind to blow through...

From now on, bop bricks only   Too bad I have 3 years of wood left.


Andrew


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## shawng111

Swedishchef said:
			
		

> It is exposed to rain. You can't have it all I guess: sun, wind and no rain. Either no sun and no rain with wind, but if you have sun, ya gotta have rain
> 
> My greenhouse is not humid. I opened the bottom walls of the greenhouse to allow a crosswind. The roof acts like a magnifying glass, temps can reach 30C on a 20C day and the front door open, bottoms rolled up, the wind blows through it.
> 
> When it is outside, single row, 4 feet away from the next rown. Face of wood is towards the wind to allow wind to blow through...
> 
> From now on, bop bricks only   Too bad I have 3 years of wood left.
> 
> 
> Andrew



I'm with you swedischef, I have oak cut same time as this maple and if i thought anything was going to hiss because of any moisture it would have been the oak, but as it turns out its the maple, still think personally this is more to it than mere moisture, just a crazy guess


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## babzog

My maPle hisses and foams too, whereas the locust, dried in the same woodshed for the same year is just fine. Maybe maple needs 2+ years?


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## barkeatr

I HAVE some two year maple that hisses, its been under cover for most of that time.   I think its due to our climate. After reading that post i did not have to look to see where that person lived.  I think this upstate NY lower Canada area is particularly high summer relative humidity and the sun really only comes out (30% clouds or less)  one day out of 8 or ten.  Ten percent or less cloudy days are maybe one every twenty days or twenty five or worse.   This is purely my perception, having lived here.  Further, your micro climate could be even worse.  I live in the foothills of the adironacks and in the summer the clounds form daily around ten am...its almost like its the moisture from the forest rising up.  I did size some solar equipment once and looked at charts that showed actual solar radiation hitting the ground and my area faired worse than Seattlle WA, and i dont think that chart took in my special little micro climate.  we live in a tropical rain forest that has winter.   anyway, long story short..the relative humidty in our area drastically slows dry time and hitting the highest dry percentages is not possible.  the foam your seeing at the end of a burning log is probably the same foam that maple syrup operators scoop off thier boiling sap. i believe teh foam is full of impurities and minerals..but Im not sure.


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## Ken45

Swedishchef said:
			
		

> It is exposed to rain. You can't have it all I guess: sun, wind and no rain. Either no sun and no rain with wind, but if you have sun, ya gotta have rain



The sun only affects the top layer, the top layer blocks the sunlight from the rest of the pile but the rain drips down.   

Sun is at an angle.  If you cover the top, the sun will still get to the ends of most of the stack.

I think a cover of some sort is best, preferably one that leaves as much air get to the stack as possible.  We store our wood in a carport, open on all four sides.   When that gets full, I'll start putting the racks outside but I'm going to put scraps of metal roofing over them.

Bottom line, IMO, your wood is hissing because it is not properly seasoned.

Ken


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## gzecc

How about a moisture reading? A moisture meter is very cheap, and it takes some of the guess work out of the equation.


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## Lumber-Jack

gzecc said:
			
		

> How about a moisture reading? A moisture meter is very cheap, and it takes some of the guess work out of the equation.


That's exactly what I was thinking as I was reading some of these posts in this thread. 
Speculating such things as how many months the wood has been sitting, whether it's top covered or not, how humid the region is, how much sun or wind the area gets, and things like these, just to (guess) at how dry some-body's wood "might" be??? For goodness sake people, get yourself a moisture meter and be done with it. Gota be one of the cheapest wood burners tools out there next to matches, and probably the most asked and pertinent question in this forum is, "How dry is your wood?"

On the topic of wood hissing, my dry lodgepole pine makes a light hissing noise when I stick it in a hot stove, I think most wood does if you listen carefully enough. Anyway, my wood is very dry, <15% MC. I know, I have a moisture meter. ;-)


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## Swedishchef

Hi guys

Well, after trying to figure out what was going on I decided 2 things:

1- I purchased a moisture meter. one piece I tested indicated 22% and another one indicated 18%. So I think that eliminates the "wet wood" concept.

2- I spoke with a friend who is a forestry engineer. He explained the following: when rock maple (sugar maple) dries, so does the sugar inside of it. Like we all know, "dry" wood still has 10-20% or so of moisture. He explained that as the wood heats up, the moisture is driven out (outgassing of moisture and VOCs). The moisture then re-dissolves the crystaline dried sugar as it passes through the wood  until it's exit point (along with impurities as barkeatr suggested). The foam is a mixture of moisture with dissoved sugar. As he said, that's why all the other wood of the same age doesn't foam: the moisture simply comes out as water vapour and is evaporated immediately whereas the sugar maple's water is mixed with sugar.

Andrew


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## mywaynow

Interesting to note that the foaming comes from the last 1/4 inch or so of the wood's outer layers.  I see it more with rounds than splits, so I am going to say the bark has something to do with what I see.  Some very small (2 inch) rounds with over 2 years in the stacks will hiss/foam.  Never for long, but they do it.  May be surface rain that gets absorbed into the outer layers.  My stuff is covered though, so it should not be that.


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