Clean Burning Fires - for efficiency
I think all fires should be clean burning fires, whether you're using the fire to heat your home, incinerate trash, clear weeds or whatever. There isn't anything pleasant about smoke.
Focus on making fire because that's what does the work. When we minimize smoke, we maximize work accomplished.
Smoky fires are unpleasant to be around, they are especially offensive to those with sensitivities to airborne particulate, and they are inefficient.
When it comes to wood burning appliances, unnecessary smoke deposits flammable material in the flue that can come back later in the form of a chimney fire. I've never had one, but my neighbor assures me that it sounds like a freight train, turns the stove red hot, and showers the roof with sparks.
With many reasons to have clean burning fires, let's look at the basics of how to create and maintain them.
If we burn dry material, it tends to combust quickly and much more cleanly than material that is wet or otherwise has a high moisture content.
Burning from the top down will allow smoke to rise up through the fire and be consumed. Smoke is a flammable gas, so keeping its origin lower than the flame will cause it to rise up through the hot flames where it will be burned instead of escaping out flue.
Provide sufficient combustion air to create clean burning fires. This is perhaps the leading cause of excessive wood smoke from older and cheaper wood stoves on the market. They typically don't have sufficient air intake for complete combustion, so smoke is created as a sign of their inefficiency.
Build and maintain a hot fire. It takes a certain amount of heat to make things burn. More heat means that things more readily burn - that includes smoke. New fires often let smoke escape up the flue because stove temperatures aren't hot enough to encourage complete combustion. Clean burning fires must be hot burning fires.
Even if you place new wood on a the fire inside a hot stove, if it gets sufficient air for combustion, the resulting smoke should be very limited because conditions in the firebox (heat, air and circulation) should promote burning of smoke that off-gasses from the wood.
Avoid long burning fires that smolder. It may seem like a good idea to have a fire that burns all night long, but any "slow bake" fires like that won't be clean burning fires. Instead, they'll promote smoke and deposit creosote in your chimney.
Use modern well-made wood heat appliances that are engineered for complete combustion. It's part art and part science to maintain a clean burning fire inside a stove, but there are manufacturers that have accomplished just that. Their technology focuses on causing smoke to linger where it's hot and oxygen rich, and this promotes complete and clean combustion.
For older stoves, carefully and thoughtfully consider a modification that promotes more air, a hotter firebox, and a longer duration for the combustion process. My personal philosophy has been "burn the gas, not the wood." That has led to clean burning fires in two stoves that I have modified.
Modifying any wood burning appliance is tricky and laden with potential for problems, so consult with someone who has experience before you even think about making any change to a wood burning appliance. And, if you do make a change, conduct extensive outdoor testing before you put the appliance back into service.
And to be on the safe side, never use a wood burning appliance (modified or not) unless you're there to monitor it while it's in operation. Remember, it's a fire inside your house, so give it the respect it deserves.
The best general advice I can give you is to monitor your stove and flue output to determine whether you're contributing to the problem of wood smoke, or you're getting the most energy out of your wood heating appliances by promoting efficient combustion.
Ceramic glass doors are a great way to study and monitor what's going on inside the firebox. I monitor flue output by going outside and taking a look during various stages of burning. That way, I know what works and what doesn't.
It's a quaint idea that the moonlit cabin in the country on a snow covered night has a meandering trail of smoke coming up from the chimney, but the truth is this shows:
- inefficient combustion
- lost fuel
- reduced heat output
- accumulation of flammable material in the flue
- unnecessary smoke for those nearby
We don't have to be perfect when it comes to heating with wood, but it's worth some effort to get this right simply because it's in our own best interest to do so.
Although I live quite a distance away from my nearest neighbor, they shouldn't have to put up with stench or excessive particulate output from my fires. That's simply another reason that I focus my efforts on maintaining clean burning fires.
Done with Clean Burning Fires, back to Heating with Wood