smoky, smoky outdoor wood boilers

[phishheadmi]

Hello,

I was just wondering, a lot of people around where I live are installing outdoor wood boilers and I've noticed that unlike traditional wood stoves, these boilers put out the moxt noxious, foul smelling, gross black smoke. My neighbor's is horrible, luckily the prevailing winds take everything away from my direction, but on a still day the whole area just reeks (and I'm a good 600' through the woods from him). I've noticed this on many of the outdoor boilers I've seen, why is this? Are people not operating them right? I had one guy tell me he only burns unsplit 4' lengths of green poplar because it smolders and lasts all day...I thought 'wow, this goes against everything I know about heating with wood, but maybe I'm just not familiar with a boiler's operation'. What gives?

 

[Eric Johnson]

It's almost impossible to burn wood cleanly when you have a firebox surrounded by water, which will never get over 200 degrees. So virtually all conventional wood boilers are going to smoke and produce creosote during much of the burn cycle. An added problem with most outdoor wood boilers is they have very large fireboxes, which encourages people to load them to the gills, resulting in more wood smoldering when the heat load is satisfied and they go into idle mode. It doesn't help that the people selling them encourage people to burn green wood. And some people see them as handy incinerators for household garbage.

Modern gasifiers, including some outdoor models, get around this problem with a refractory-lined combustion chamber located underneath the firebox. Smoke produced in the firebox is drawn down into the secondary combustion chamber through ceramic nozzles, where it is burned at high temps (2,000+ degrees) and converted into heat. These boilers are much more efficient and much less polluting, as most of the nasty stuff has been incinerated before it gets to the chimney.

 

[MrEd]

Hello,

I was just wondering, a lot of people around where I live are installing outdoor wood boilers and I've noticed that unlike traditional wood stoves, these boilers put out the moxt noxious, foul smelling, gross black smoke. My neighbor's is horrible, luckily the prevailing winds take everything away from my direction, but on a still day the whole area just reeks (and I'm a good 600' through the woods from him). I've noticed this on many of the outdoor boilers I've seen, why is this? Are people not operating them right? I had one guy tell me he only burns unsplit 4' lengths of green poplar because it smolders and lasts all day...I thought 'wow, this goes against everything I know about heating with wood, but maybe I'm just not familiar with a boiler's operation'. What gives?

Garbage in, garbage out. I am sure that even the poorest designed OWB would smoke less if the owners had a clue about how to make a fire. Unfortunately, at least in the past, the OWB manufacturers actually included in the sales pitch the benefits of being able to "burn anything". Now they are going to pay the price with additional regulations and out-right bans in many places. I've seen these smoke factories in action, and I can tell you if one was sitting next to my property line I'd be after them to remove it thru any means possible (i.e. lawsuits, pushing for a bans, board of health etc).

I'll support the right to burn whatever you want on your property, as long as you can prove the pollution doesn't end up on my property.

 

[atlarge54]

No doubt they're pretty smokey but they don't have to be terrible. I try to load mine when it is calling for heat (solenoid opens air supply NO BLOWER). Last night 8PM I loaded with a couple nice hunks of DRY hard maple. Today at 2PM I removed a couple shovels of ash raked coals and added 3 medium sized pieces of wood which immediately started burning with nearly no visible smoke. Now the boiler is off (air supply) and there is a small amount of smoke. This evening when the boiler is calling for heat (air supply open) I'll add wood. Once the wood has turned to coals there is NO visible smoke. My boiler was warming my home most of the day with ZERO visible smoke. The heaviest smoke occurs at the start of the burn cycle with a large amount of wood, I try to minimize that. Does anyone know what the separate BTU values of burning wood are? It seems like the first part of the load, flame w/o a nice bed of coals doesn't generate as much heat as the coals burning. I certainly understand how bad they can be when operated with careless abandon.

 

[Eric Johnson]

I've wondered about that, too. I think it's a combination of things. First off, all wood contains moisture, so a fresh load is going to lose some of its heat to steam. Secondly, if the fire in your boiler has burned out, the water in the system (and probably the house) has cooled off to the point where much of the energy produced by the initial burn goes into getting the system/zones back up to temp. As anyone who has fired up a boiler from a dead cold start knows, it takes a lot of burning before you see any heat in your house. And finally, boilers are most efficient when they're up to temp, so moisture or no moisture, you're not getting your most efficient burn until the system is up to temp anyway.

OWBs can smoke a lot, it's true, but so can wood stoves, furnaces and indoor boilers. It's just that OWBs stick out like a sore thumb and thus get blamed for everyone else's smoke. I do a fair amount of driving around the rural Northeast, and the vast majority of smoke I see is coming out of chimneys, not OWB stacks.

 

[sfriedri]

In terms of the inefficiency of the OWB, I guess there are different ways to quantify how much energy is wasted in unburned wood gas. If someone has switched from an OWB to a gassifier, then comparing the amount of wood burned is obviously one method. For people that have gassifiers, I guess one could also do an experiment to see how much additional heat you get from the secondary combustion. A crude way to do this on an EKO would be to burn a load with the bypass open, starting from a cold start and cold storage tank and see how much temperature gain there is compared to running it with the bypass closed. The only problem is you would end up with a good coating of creosote on your flue pipes.

 

[MrEd]

Or and old tire.....

 

[flyingcow]

I've wondered about that, too. I think it's a combination of things. First off, all wood contains moisture, so a fresh load is going to lose some of its heat to steam. Secondly, if the fire in your boiler has burned out, the water in the system (and probably the house) has cooled off to the point where much of the energy produced by the initial burn goes into getting the system/zones back up to temp. As anyone who has fired up a boiler from a dead cold start knows, it takes a lot of burning before you see any heat in your house. And finally, boilers are most efficient when they're up to temp, so moisture or no moisture, you're not getting your most efficient burn until the system is up to temp anyway.

OWBs can smoke a lot, it's true, but so can wood stoves, furnaces and indoor boilers. It's just that OWBs stick out like a sore thumb and thus get blamed for everyone else's smoke. I do a fair amount of driving around the rural Northeast, and the vast majority of smoke I see is coming out of chimneys, not OWB stacks.

Last line.... coming out chimneys, not OWB stacks. Pointing out he obvious...the chimneys are alot higher. That is the major problem

 

[sinnian]

Another problem is that most OWB stacks are too short, or much shorter then what one would find on a chimney on a house. Typically, the higher the stack, the quicker the rise, the less nuisance to your neighbor. Additionally, most house chimneys are free of tree over hangs, unlike OWB where leaves and/or bows will keep the smoke from rising and thus ends up being a nuisance to their neighbor.

 

[eco-one]

has any one of you looked into the 275 eco-one from aqua-therm they are very close to .60 in the epa standards the are very clean after about 8 minutes i know ive seen it done and that does not have all the refractory that every body has in a epa aproved owb.if you read all the warranty on all these refractory stoves and maitaence on cleanig and inspecting every month i just dont like refratory against steel you get 2000 + temp against steel it is bound too warp,rust,break down,and crack.throwing big chuncks of wood on the refractory i dont think this will last long

 

[Eric Johnson]

Do you work for Aquatherm, eco-one?

 

[rowerwet]

My sister and brother-in-law have an owb, they get smoke mostly from the idle part of the cycle, they get a chimney fire every week or so from the creosote. this is no big deal for an owb as it just burns the pipes clean. They are in Lake Placid, NY and everyone burns wood up there so no complaints about smoke unless you are burning trash etc.

 

[eco-one]

Do you work for Aquatherm, eco-one?

I build them for aqua-therm we are the only one make the aqua-therm from the start, started back in 1982

 

[warm in VT]

Just to chime in as an OWB owner now....... Everyone that has seen mine since it has been running in Oct. has been amazed by little or no smoke. I watch it carefully and keep tabs on it and have found that it emits much less smoke than any chimney with a woodstove running in a house. I am also running the new gassifier OWB as well which keeps the smoke down as well. As it has been stated here many times, it is more often operator error or cause than it is the boiler causing the smoke.

 

[ISeeDeadBTUs]

I can make the GW100 emit black smoke by over fueling (too much surface area) . I can also make it run VSF. But the temp/dew point of the outdoor air affects things too.

No way you can compare an 8-hour cycle from the GW to what my oil-fired would produce over an 8-hour time frame. Yep, a fresh load will emit water and some particulate. But for the bulk of the cycle, you wouldn't think the GW was running. Can't say the same for the oil-fired boiler stack.