# Flue cleaner



## Downunder Bob (May 13, 2017)

Hi guys, 
Wondering if someone within the collective knowledge base can help me. especially among those who heat their homes with enclosed wood fires.

I have such a wood burning heater, it is fully enclosed with combustion air control and flue damper, I burn mostly hard wood, mostly Australian red river gum, A very hard and dense wood great for high heat output and long slow burn,  also use a small amount of pine just to get a good fire burning then load up with the red gum. 

My question is about flue cleaning. Here in Downunder there is a product called "Smart Burn", which is supposed to clean and keep clean the flue on such a heater. It consists of a steel pipe about 1.5"dia. and 6"long the ends are folded closed but not air tight, and it contains some unidentified metal plus some other unidentified special ingredients. 

In operation the device is placed in a front corner of the firebox prior to starting a fire, the fire is set and started in the normal way, with extra fuel (wood) added as required. The heat of the fire melts the metal and slowly releases the unidentified special ingredients as a vapor, which cleans the flue. I know it sound like a con, but it does appear to work. I have been using this product since the heater was first installed, and I say it appears to work as a recent inspection of the flue showed it to be reasonably clean, 

My heater is 11 years old and was built into the house when the house was built. The heater is typically used for about six months of the year, I tend to run it 24 hours a day in the 3 months of winter, with 6 to 12 hours during the late Autumn (fall) and early Spring as required. 

The flue gasses are not very hot as the heater has a water jacket on both sides and the back walls of the firebox which heats some 500 ltrs. of water which supplies all of the hot water needs for the house, kitchen laundry bathrooms etc. some 400 ltrs of that water is held in a storage tank and the remaining 100 ltrs or so are circulating in pipes within the concrete slab to heat the whole house.

My question for the knowledgeable members is what could the mysterious metal be and what might the magic ingredients dissolved within that metal be. The metal appears to be a bright silvery metal maybe zinc or aluminium or alloys of them. I guess I could to some tests on the metal and identify it, but more importantly what are the magic ingredients.

The manufacturers blurb states that the device should last for about three months of normal use, which means two per year with my usage, and that is what I do, replacing the device about midway through winter. The real problem is that they want $60.00 per unit, I figure there has got to be a cheaper way. If only I can find out the ingredients.

Thanks,
Bob.


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## f350ca (May 13, 2017)

I've seen manufactured logs here that are supposed to clean the flue. Think you through one in once in a while. I've never used them or seen the one you describe. Unless your damping the stove down most of the time cresote build up shouldn't be a problem anyway. I use a wood fired boiler that either is full bore with a 1/2 hp draft blower when it requires heat or fully smothered when at temperature. In 11 years I've brushed the flue twice, just to say I did it, there was only a bit of ash in the pipe. This has been a miserable year, I had it going for 6 months.
Have you tried running without it?

Greg


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## RJSakowski (May 13, 2017)

I have burned hardwood for heat for the past forty years.  The heating system is thermostatically controlled and during idle periods, oxygen is limited to create a smoldering fire which is conducive to creosote buildup.  Creosote buildup used to be a problem for me for several reasons.  One cause was a more efficient heat transfer so the flue gases were relatively  cool, allowing water to condense on the flue pipe during idling periods.  Another cause was having a fairly rough surface for creosote to form and bond to.  A third reason was burning wood which was not dried sufficiently.

About 25 years ago, I lined my brick chimney with a fully welded stainless steel pipe.  The pipe was in four foot sections with welded seams and I welded the sections with my MIG welder on the rooftop as I lowered the pipe.   About ten years ago, I replaced  my home-built furnace with a fairly efficient heat exchanger with a commercial unit which was less efficient.  Finally, about five years ago, I started processing firewood several years in advance, storing it under cover.  I currently have a supply carrying me into 2020.

My flue system is closed so that under conditions which might initiate a chimney fire, there is no oxygen available for a thermal runaway.  Burning well dried wood has helped as well by reducing moisture going up the flue and increasing flue gas temperatures.  Creosote does form but flakes off the smooth surface of the liner and falls to the cleanout at the bottom of the chimney.  I collect typically several gallons during the course of a heating season.  I have never had a flue blockage or chimney fire.  

As to your question, I'm not sure what metal would be used. Almost certainly, it will be a low melting point metal.  If it is zinc, zinc oxide is toxic, which should be a consideration.
One source I  had seen suggested throwing a few aluminum cans into a hot fire, claiming manganese from the aluminum cans would react with the creosote formations.  A popular commercial product which comes as a powder contains trisodium phosphate as an active ingredient.  I also recall throwing salt on the fire would remover creosote from the flue.   As a former chemist, I don't see how any of these would be particularly useful but I have not personally tried them.


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## woodchucker (May 13, 2017)

I have a spray that is supposed to keep the creosote down. I haven't been burning fires in about 4 years. maybe later I'll see if I can find it. Maybe it will say what it contains.

edit: found it, no ingredients listed.


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## hermetic (May 13, 2017)

Maybe you should look into secondary air feeds which feed heated air from outside the burn chamber and inject it above the fire in order to burn the creosote and any remaining hydrocarbons in the smoke. I am experimenting with a rocket stove type heater for my workshop, and have found it burns so smoke free and cool that I can use it with a balanced horizontal flue, which is smoke free 30 minutes after lighting.


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## CluelessNewB (May 13, 2017)

Many of the chimney cleaners contain trisodium phoshate (TSP).  (Rutland brand products)

Here is a link to the MSDS for  "Creosote Sweeping Logs" http://www.homedepot.com/catalog/pdfImages/94/94a7aac4-0220-46ad-ac9e-7f16da5ba7f9.pdf


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## Rustrp (May 13, 2017)

Most of the creosote cleaning devices are designed to mix with the smoke and flue gases. When used as directed they don't cause harm to the chimney or flue. A zinc and sodium mixture may be the ingredients for your device. The biggest fault or harm done using the chimney cleaning remedies is; If a little works this good, a lot works better. The salt, copper sulphate remedies create acid and can be harmful in larger quantities but when used wisely they do a good job.  The best and fail safe method is to clean your chimney or flue pipe manually each year. I use copper filings and fine copper strips to do the job and give the chimney a yearly visual inspection. The copper filings do create lots of flame color. 

The down side of your heating system is the low temp flue gases. The positive side is the heated water for multiple uses. You could experiment with some ingredients listed as home remedies and use them in a similar manner as the device you purchase. Based on what you stated the color of the mysterious metal/mixture happens to be, I would lean towards a zinc and sodium mixture, especially with the zinc having the lower melting temperature.


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## Downunder Bob (May 14, 2017)

RJSakowski said:


> I have burned hardwood for heat for the past forty years.  The heating system is thermostatically controlled and during idle periods, oxygen is limited to create a smoldering fire which is conducive to creosote buildup.  Creosote buildup used to be a problem for me for several reasons.  One cause was a more efficient heat transfer so the flue gases were relatively  cool, allowing water to condense on the flue pipe during idling periods.  Another cause was having a fairly rough surface for creosote to form and bond to.  A third reason was burning wood which was not dried sufficiently.
> 
> About 25 years ago, I lined my brick chimney with a fully welded stainless steel pipe.  The pipe was in four foot sections with welded seams and I welded the sections with my MIG welder on the rooftop as I lowered the pipe.   About ten years ago, I replaced  my home-built furnace with a fairly efficient heat exchanger with a commercial unit which was less efficient.  Finally, about five years ago, I started processing firewood several years in advance, storing it under cover.  I currently have a supply carrying me into 2020.
> 
> ...



Thanks RJ. 
My system is only manual with just a lever to control the flue and another one for combustion air. The flue has from new been SS pipe and is therefor quite smooth, that maybe why I don't have a problem. I didn't use anything for the first couple of years, but then saw this stuff for sale at the local hardware shop, bought some and have been using it ever since. 

My only concern is that it's costing about $120 a year, and if I can find out what is in it then maybe I can save some money. I've got a couple of new ones on order, so when they arrive I'll cut one open to see if I can identify what is in it. I've also got an old one so I'll cut that open as well, I expect all the magic additives may well have been used up but that might make it easier to identify the metal. I do get some black glassy tar like substance that I clean out of the base of my heater so that's most likely what is happening to it.


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## RJSakowski (May 14, 2017)

Creosote forms from condensation of wood tars from smoke.  Smoke is caused by incomplete combustion.  Running hot oxygen rich fires to  create more complete combustion and reduce condensation will substantially reduce buildup.  It is an unfortunate fact that wood fires tend to be oxygen starved as limiting combustion air is the usual means of controlling the fire.  

In my case in particular, the fire is controlled by a thermostat so the furnace cycles through active burns and smoldering idle periods. The smoldering periods are  the worst case for creosote buildup.  My problem stems from the fact that there is necessarily an air leak to keep the fire burning.  A much better solution would be to completely cut the air so the fire goes out and use a gas fired ignitor system to restart the combustion when heat was needed.  Someday, I may actually get around to making that modification.

Wood creosote is a complex mixture of low volatility organic compounds which I see as mostly unreactive with the exception of oxidation through burning (I am stretching my organic chemistry knowledge here; my last class was 44 years ago).  As such, I don't see much use in the "magic" ingredients found in creosote removers.  Any metals would most likely be oxidized in the fire and the amount of those oxides entering the chimney would be minimal.  IMO, the major benefit comes from running a hot, oxygen rich fire in the application of those treatments.  The the hot flu gases will dry out the formations distilling out the higher melting point compounds, leaving product which are more like coal than tar.  The excess oxygen will burn some of the deposits; basically a controlled chimney fire.  Some of the products recommend cleaning the chimney before using the product to prevent an uncontrolled chimney fire.

One major improvement in my case was decommissioning the external chimney and recommissioning the original chimney running through the center of our house.  With our cold Wisconsin winters, condensation would be a problem to the extent that water vapor would condense out and form an ice pool at the bottom.  When I went back to the original brick chimney, I added the stainless liner and filled the void with vermiculite insulation.  The result was much lower heat loss and less condensation.

Another improvement came from not building a fire in mild weather.  I have the luxury of having a dual heating system, a propane fired furnace and a wood burning furnace.  In mild weather, a wood fire mostly smolders, creating creosote.  While it is not a fire hazard in my case, I find the odor obnoxious.  We burn mostly wood but use around 100 gallons of liquid propane for heating in fall and spring when we just want to take the chill out.


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## Downunder Bob (May 14, 2017)

RJSakowski said:


> Creosote forms from condensation of wood tars from smoke.  Smoke is caused by incomplete combustion.  Running hot oxygen rich fires to  create more complete combustion and reduce condensation will substantially reduce buildup.  It is an unfortunate fact that wood fires tend to be oxygen starved as limiting combustion air is the usual means of controlling the fire.
> 
> In my case in particular, the fire is controlled by a thermostat so the furnace cycles through active burns and smoldering idle periods. The smoldering periods are  the worst case for creosote buildup.  My problem stems from the fact that there is necessarily an air leak to keep the fire burning.  A much better solution would be to completely cut the air so the fire goes out and use a gas fired ignitor system to restart the combustion when heat was needed.  Someday, I may actually get around to making that modification.
> 
> ...



 Thanks RJ,

 I understand teh concept of the hot oxygen rich fire. Because our winters here are not as long or as cold as yours. We never go below 0c usually mid winter overnight low is about 4c. with much milder shoulder seasons. with mid day temps up around 15c and overnight low about 7c. I suspect our homes are not as heavily insulated as is typical in US. Very few parts of the country ever get snow, just on the mountain tops for a few months. Some years even our ski fields have very little snow, and they to use snow making machines..

My heater will usually run for up to about 6 or even 8 hours on a load of wood, if I cut the air back once it's really going with a good bed of hot coals. I don't really regulate it by shutting the air on and off more by how much wood I use and how often I re stoke it. When it's not too cold, like right now, I'll set a good hot fire with enough wood to burn for about 4 -6 hours, and let it burn out. this will put enough heat energy into the water storage tank and the concrete slab, which will keep the house a fairly constant 22 - 23c. I usually just run the heater in the evening. Then in full winter it will run day and night, just regulating by how much wood I put in and how often.

So I guess I don't need this clean burn stuff, but I'm still curious as to whats in it and does it really work.

I can also heat with gas, we have natural gas supplied here and I can heat the water tank with gas, but generally prefer not to. The hot water will circulate through the pipes in the concrete slab, keeping the house nice and  warm. I do use it occasionally when there is just a slight chill and it's not worth lighting a fire, or maybe a sudden unexpected cool change and I don't have any wood ready. The only problem with that is the slab has quite a lot of thermal inertia and does take a while to warm up, and then also to cool down 

Our wood heater is situated in the lounge room as a feature, so it's nice to look at the fire through the glass door, also convenient to toss another log in.


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