Your Burning Questions (a.k.a. FAQ's)
QUESTIONS ABOUT WOOD STOVES
What is the difference between catalytic and non-catalytic wood burning stoves?
In catalytic combustion the smoky exhaust is passed through a coated ceramic honeycomb inside the stove where the gases and particles ignite and burn at a temperature that is less than half the temperature required for the combustion of the gases without the catalytic action. Catalytic stoves are capable of producing a long, even heat output. The catalyst can last up to six seasons or more if the stove is used properly. Over-firing, burning garbage or treated woods, locking the catalyst down at extremely high temperatures will causes thermal shock and neglecting regular cleaning and maintenance can cause the catalyst to break down prematurely.
Catalytic stoves are slightly more complicated to operate.
Non-catalytic stoves utilize firebox insulation and a secondary burn chamber that injects pre-heated combustion air and turbulence through small holes in a baffle system above the fuel in the firebox. Non-cats have less even heat output and a bit shorter burn times than do catalytic stoves but create a more pleasing flame presentation and are much less expensive to maintain.
What's the difference between an EPA stove and a non EPA stove?
The EPA certified wood burning stoves burn wood more efficiently and cleaner than traditional types of wood stoves. These wood stoves can provide a nearly smokeless burn, producing maximum heat while using less firewood.
Each EPA certified wood stove or wood heating appliance is tested by an accredited laboratory to meet a particulate emissions limit of 7.5 grams per hour for non-catalytic wood stoves and 4.1 grams per hour for catalytic wood stoves, except in the State of Washington, where these values are 4.5 grams per hour for non-cat wood stoves and 2.5 grams per hour for catalytic wood stoves.
Many older stoves from the 1970's and 1980's that still may be in use commonly put out well over 90 grams of particulate emissions.
Additionally, a pre-EPA stove from the 1970's and 1980's averaged around 20 - 25% efficiency, while current EPA approved stoves range from 75% to as high as 90% efficient. This equates to burning less wood to get the same amount of heat.
An EPA certified wood stove can be identified by a permanent metal label affixed to the back or side of the wood stove. Switch and upgrade to a certified stove that is now over 10 times cleaner burning!
How is zone heating different than central heating?
Zone heating is putting the heat where you need it most versus central heating systems which can distribute heat to the whole house. Zone heating with a space heater such as a wood ( or gas or pellet) stove, fireplace or fireplace insert can save the homeowner significantly on their overall heating bills.
Zone heating creates a cozy warm area for the family to gather allowing the central heating system to be set lower. The zone that one can heat with a space heater is determined by the design of the home. The more open the house plan, the larger area (zone) one can heat with a new heating appliance. Why heat every nook and cranny when you are not using that part of the house?
Zone heating is direct heat. The duct systems of most central heating systems have significant heat loss before getting the heat to the livaing areas. Thye longer the run of the heating ducts, the greater the loss.
Where should I locate my new stove?
First, the area selected to install a new stove may be limited to the location of the existing venting system or by factors like obstructions above the installation that precludes installing a new chimney system.
Second to consider is the area that one wishes to heat. Stoves are space heaters, sometimes referred to as zone heaters. For maximum enjoyment and heating effectiveness, install your new wood stove in a major living area where the family spends leisure hours and which provides heat flow to other areas is usually a strongly preferred location for the stove.
A third consideration is the space requirements. Wood stove installations must meet minimum clearances between the stove and nearby combustible surfaces plus the hearth or floor protection must extend beyond the front and all sides of the stove. These requirements are clearly stated in the owner's instruction manuals. Local codes must also be followed.
Why does the glass on my wood stove soot up?
Soot will appear on the glass if the firebox temperature is low or if the lighting off period is too short. When first firing the stove a lot of combustion air must be supplied to establish a good fire and warm up the chimney. Open the air controls. Once the kindling fire is well established dry wood can be added. The combustion is then controlled by the primary air control. Wet or green (unseasoned) wood or poor draft conditions might also cause sooty glass. Also never let logs touch the glass or it interferes with the air wash and sooting of the glass will result.
Does my wood stove need floor protection?
Yes, wood stoves require a hearth or stove pad unless installed on a concrete slab. Some wood burning only require ember protection while others need thermal protection. Many stoves supply (sometimes as an option) a bottom heat shield that reflects the heat away from the hearth. The bottom heat shield is then usually required unless the product is installed on the foundation level. . Always check the manufacturer's installation requirements for R values and minimum size before installing your wood stove and always install according to the stove manufacturer's instructions and local building codes.
Why does my wood stove draft poorly?
The main function of a chimney is to create draft for combustion and to transport the flue gases out of the building. A good draft is vital for a good combustion. We consider a normally good draft to be at least .05 water column inches as measured by a draft gage. The chimney creates the draft, not the appliance.
Essential for the draft is the construction of the chimney. A tall chimney gives more draft than a short one. If the draft is insufficient one solution is to build a taller chimney. The chimney diameter should never be less than the diameter on the appliance flue outlet. A circular chimney liner normally gives a better draft than a square one. Use of flue pipe elbows reduces the draft.
If elbows are used it is always better to install with 2 X 45 degree elbows, instead of one 90 degree one.
Combustion air is essential for the draft
An open fireplace requires approx 300m3 air each hr, while a “closed” fireplace requires approx 30m3 per hr. A kitchen duct / ventilator can suck much more air than a chimney. This will create a negative draft. and a negative chimney draft causes smoke to come into the room.
Influence of the wind
Draft disturbance can be caused by tall trees, cliffs or tall buildings. The problem can normally be solved by making the chimney taller.
Draft is simply hot air rising. High temperature creates strong chimney draft. A good result is achieved when the height and diameter of the chimney fits the appliance. Too strong a draft can cause the heat to be sucked too fast into the chimney. Too strong a draft can be regulated with a damper or a draft regulator.
• Wood quality: Wood with a lot of moisture can cause more smoke than the chimney can dispose of.
• Air systems like air condition, bathroom or kitchen fans might take their need of air from the chimney (negative draft)
• Operating errors: Always open the damper and primary air control before you reload the stove - open the door slowly.
• Flue pipes: Remember that elbows (90 degree) and long horizontal flue pipes make restrictions on the draft.
• A chimney that is too short could give insufficient draft for the fireplace.
• A chimney that is too cold can cause low - or negative draft. The flue liner must be correctly connected to the fireplace and the chimney - and have the right dimensions.
• A blocked chimney could be caused by a birds nest, soot, or tar.
The best solution for a poorly drafting chimney may be a new product called a "Draw Collar" which is a device installed on top of the stove or fireplace insert that warms up the chimney with an electric coil to get the chimney to draw when the stack temperature is low.
QUESTIONS ABOUT WOOD BURNING FIREPLACE INSERTS
Can I install a wood burning insert into my factory built fireplace?
There are very few manufacturers of wood burning inserts that are listed and approved to be installed into the manufactured or "zero clearance" type fireplace.
Those that are listed have very exacting installation requirements that may be difficult if not impossible to achieve.
We highly recommend not installing an insert into one of these types of fireplaces.
Is a wood burning fireplace insert right for me?
Casual use of an open fireplace is not efficient and does require frequent fire tending using a lot of firewood.. Oversize fireplace flues sweep the firebox heat up the flue and even worse, the draft of the fireplace gathers up the heated room air as well. A few hours of casual fireplace use can force your central heating system to work harder and cost you money! Also when you are not using your fireplace you are losing a lot of your heat up the chimney because most dampers and glass doors do not fit air tight they allow heated room air to be sucked up the chimney, costing you lots of money. A properly installed fireplace insert solves this problem and puts the heat in the room where you want it.
Here are a few guidelines and suggestions when shopping for that new insert. First be sure to bring in the measurements of your existing fireplace, width, height and depth are the most important. Many customers take a digital photo of their fireplace and bring it in, which helps us immensely.
CHIMNEY The first thing we do when installing a fireplace insert is to toughly clean your chimney. We want to install the insert into a clean environment so no odors can come back into the house.
CHIMNEY LINERS Fireplace chimney flues are oversized, so installing an insert will require a stainless steel chimney liner to be installed from the insert to the top of the chimney. All gas inserts require aluminum liners to be installed to the top of the chimney. The reason for this is that the new insert is so efficient that it can't keep the big old masonry chimney hot enough to establish a good draft.
ELECTRIC Many inserts use electric blowers to extract and distribute the heat from the inserts firebox. A nearby electric outlet is required or to eliminate the exposed cord from the surround you may wish to have us install a UL approved hidden wire kit.
SIZING Inserts are sold as two or more components: the insert plus a surround panel and sometimes an optional front. The insert must physically fit into the firebox. The surround panel is designed to cover the gap between the insert and the actual fireplace opening size. Surround panels are offered in differing sizes and styles giving each insert several options.
CLEARANCES Each product is tested and listed to minimum clearances from combustible top and side fireplace trim as well as from combustible mantles. The dimensional depth of the facing trim and of the depth of mantle is important factor when measuring.
HEARTH EXTENSION All wood inserts require the hearth to extend in front of the insert opening. This is a stated distance that varies with each product and is stated in the product manual.
How do I measure my fireplace for an insert?
First, open the glass doors if you have them and measure from side to side at the front of the fireplace opening to establish the Width of the opening.
Second, measure the Height at the front from the bottom of the fireplace to the top of the opening.
Then measure the Depth of the fireplace from the back to the front of the opening in the middle of the fireplace. We realize that most fireplaces have tapered sides and that is ok.
If you have a digital camera or one on your phone, simply take a couple of photos of your fireplace and bring them in with your dimensions. This is like us being there, and is very helpful to us.
We are also happy to come out to your home, at no charge, to help you if you should need it.
QUESTIONS ABOUT GAS FIRED FIREPLACE INSERTS
How do fireplace gas log sets and gas fireplace inserts differ?
Gas Fireplace Inserts are designed be installed (inserted) into approved wood burning fireplaces. Designer fronts and surrounds are offered in several styles. An approved gas liner must be installed into masonry chimney to vent a gas-fired insert. Gas Fireplace Inserts are available as heater-rated high efficiency appliances that are capable of heating even large areas. Direct Vent Fireplace Gas Inserts are enclosed behind a fixed glass front as the outside combustion system is part of the venting making them ideal for tightly insulated homes or poorly drafting wood burning fireplaces.
Gas Log Sets are sold complete with a grate system to hold the set of artificial logs, (several styles and sizes are available) a gas burner (propane or natural gas) and even a glowing ember bed to give the set a realistic appeal. Vented gas sets are approximately 20% efficient and are designed to allow casual fire burning rather than as a serious heat source. Most homeowners opt to install a glass door enclosure on their fireplace when using a vented gas log set as the damper is pinned in an open position. Vented Gas log sets are not a remedy for poorly drafting fireplaces and should not be installed into them. We really don't recommend the use of gas logs as they are so very inefficient and the fact the you must leave the damper locked open all the time, waste an enormous amount of your homes energy and cost you a lot of money. Highly efficient gas inserts are definitely the way to go..
QUESTIONS ABOUT VENTING SYSTEMS
Can I vent my woodstove and oil furnace on the same flue?
Most state codes do not allow more than one appliance to be installed into a single flue. So NO you can't and it would be very dangerous to do. A flue is a separate passage way within a chimney structure. Many chimneys have multiple flues so several different appliances can be housed into a single chimney.
How do "air cooled" and "solid pack" chimney systems differ?
Air cooled chimneys were designed as a component for manufactured open wood burning fireplaces. These fireplaces are casual use appliances and produce very little heat. Air cooled chimneys have no insulation; they stay cool by circulating cold air past the inner flue. As a result, the air cooled flue stays colder than an insulated chimney resulting in reduced draft and a greater chance of creosote formation. They are also not required to undergo severe chimney fire testing.
Solid pack chimneys are manufactured insulated chimney systems designed for wood and coal stoves as well as for many oil fired appliances. These appliances can produce high flue gas temperatures and can generate large amounts of creosote (which can cause a chimney fire) when tended improperly. These chimneys known in the industry as Class A Chimney Systems are certified to higher safety standard which requires that the chimney system withstand repeated 2100°F chimney fires. They utilize high temperature insulation and warm up quickly making them less likely to accumulate creosote therefore increasing your safety.
QUESTIONS ABOUT GAS HEATING STOVES AND FIREPLACES
Do any gas stoves or gas fireplaces work without electrical power?
Yes, most gas stoves and gas fireplaces work with a standing pilot light so no electrical power is needed to ignite or run the appliance. In the northeast region of the USA, many homeowners seek an alternate heating source to use during the frequent power outages due to wind, ice and snow storms. The standing pilot heater-rated appliances are a great option. The optional blowers, if installed, will not work during the outage but most units rely on the radiant heat transfer and convection heat so they will work just fine with no electric power. Many of the new electronic ignition fireplaces, inserts and stoves are "Green Smart" and have a built-in battery back-up that allows the unit to be started on simple AAA cell batteries in the event of a power failure. This feature saves you money on the operating cost of keeping a pilot running when it is not in use.
GETTING STARTED WITH WOOD BURNING
Why do I need to install a stainless steel liner for my wood stove or insert?
Some people think the only justification for lining a perfectly good chimney is that it will help line your hearth retailer’s pockets with more of your hard earned cash. After all you just plunked down somewhere between $800 and $3000 (or more) for the stove and now they are trying to get more! Please let me explain how this extra step is going to help not just you, but also your chimney sweep and maybe even the fire department. And here’s the kicker, it will even save you money in the long run.
There are five very good reasons for lining a chimney.
1. Creating the proper flue size.
2. A chimney that is lined from the stove to the top is easy to keep clean.
3. A lined chimney is a safer chimney.
4. Some chimneys that are lined and insulated work better.
5. It may also be a code requirement.
Creating the proper flue size.
Some chimneys are built with one purpose and then used for another at a later time. A perfect example of this is the fireplace chimney. These chimneys have large flues that are designed to evacuate the copious amounts of smoke and gases that are created by burning wood in a fireplace with a large opening. The conclusion that many people arrive at after living with this situation is they are throwing a lot of wood into a fireplace that is nice to look at but doesn’t give off much heat! The logical next step is to put a wood burning fireplace insert into the existing masonry fireplace. Here is where the liner will help. Although the chimney usually already has a terracotta liner, the size of the liner is a minimum of 8”x12” and usually 12”x12” or larger. Some would say, “If my chimney is already lined why do I need another liner inside of it?” So here is the answer. The flue exit on most of the new E.P.A. rated wood burning inserts is 6” in diameter. When the engineers that designed these stoves were testing them they performed most of their tests on a 6” flue. And therefore it stands to reason that these puppies are going to work a whole lot better on, you guessed it a 6” flue. I have used the fireplace as an example but there are many chimneys in older homes that were built with over-sized flues that will work better if lined.
A chimney that is lined from the stove to the top is easy to keep clean.
In some cases when an insert is installed into a masonry fireplace an installer will use a “direct connect” to connect the stove to the chimney flue. In this case a short length of stainless steel flexible liner is connected to the top of the insert and run through the damper and up above the bottom of the first flue tile. The remaining damper opening is then sealed with a steel plate or ceramic fiber blanket. This installation may work fine but it creates more expense when it is time to clean the chimney. To properly clean the entire chimney in this type of installation the stove and the venting should be removed and then reinstalled after the chimney is cleaned. Chimney sweeps don’t enjoy all of this extra work and therefore charge accordingly. If an insert had been installed in this same fireplace with a full liner the chimney sweep can run his brush and rods right down to the stove. In this case the only extra step is removing the top baffle, which is very easy to do.
I recently saw a report about a house that burned because of a chimney fire. Now chimney fires can start because of more than one reason. One is creosote build-up and that should not be an issue if you are burning an E.P.A. certified stove properly with “Good Wood” and “Good Draft”. Another reason is the chimney may be too close to combustible materials. A liner and in some cases an insulated liner can make a chimney much safer. Of course if you are unsure about the condition of your chimney you should always consult a professional like a certified hearth retailer. Now if the house in the news report had an E.P.A. certified stove connected to a properly installed liner there is a good chance that the local firemen would have been back at the station perfecting a new recipe instead of out risking their lives putting out a fire!
Most chimneys that are lined and insulated work better. One of the best things about using a chimney liner when it’s needed, is that the stove will work better. When the stove works better you will be happy, and when you are happy so will your hearth retailer. Reminds me about a saying I use often pertaining to my wife, I’m sure you’ve heard it. When Mother is happy, everybody’s happy! Some chimneys are built outside the house, which is not conducive to “Good Draft”. A large flue as I have mentioned earlier will only magnify the problem. The solution here may require adding an insulated liner, which will allow the flue to stay warmer and as a result will contribute to better draft. Another important point and an opportunity to bolster my claim that a liner may save you money can be made about improving performance and efficiency when installing a liner. If the stove is running well you will be getting more heat from the stove and get your money’s worth from your wood.
How do I start a good fire in my new wood stove?
To start a fire you should have at least six things:
4. Dry wood
5. Matches or a lighter
6. Stove top thermometer
Draft is a force in your chimney that is the result of a temperature difference between the air inside the chimney and the air outside that causes a pressure difference. This pressure difference causes the air inside the chimney to rise up and exit from the top of the chimney. To learn more about draft see my article called “Good Draft”.
Fire starters are usually made of a wax impregnated material like sawdust and when one or two is placed under the kindling wood makes fire starting easy and without the smoke that you can get from using newspaper.
Kindling is wood that is very dry and split into pieces that are no bigger than 1 inch by 1 inch.
Dry wood is wood that has been stacked, split and allowed to dry under cover until it reaches 20% moisture content. To learn more about dry wood see my article called “Good Wood”.
Matches or a lighter…need I say more.
A thermometer is like a speedometer, it will tell you if you are burning hot enough or too hot.
Now we are ready to start a fire! Like anything else in life starting a fire will be much easier and be more successful if we build a good foundation. Start by placing a couple of fire starters (We like the Rutland brand) on the bottom. Then I use plenty of kindling. I lay down three or four layers of kindling in opposing directions so air can circulate through the layers. At this point I add a few small logs, because by this time there isn’t much room to put in much more. I am assuming for this example that draft is present. With my match or lighter I light the two fire starters. Now I can set the air control wide open and close the load door. An important point is that you should NEVER open your ash pan door to get the fire going. This can damage the stove and greatly reduce the useful life of the stove. I leave the air control wide open until my thermometer reaches 400 degrees. The fire will burn robustly and do a great job of warming up the chimney and establishing a strong draft. At this point the kindling has probably burned down enough so I can add more wood. When this additional load has caught and I am still seeing a surface temperature of at least 400 degrees I can now turn the air control down for an extended burn.
Why does my chimney have poor draft?
The single most important ingredient for successful wood burning in a modern, clean burning heating appliance (wood stove) is DRAFT! What is draft? Well hold on to your hat, because I’m going to tell you.
The dictionary has many different definitions, one of which is “a drawing or a pulling”. Incidentally one of my favorite definitions of draft in the dictionary is the one that refers to “a portion of beer”, but I will leave that for another, perhaps later discussion.
Draft in purely technical terms is draft is a difference in temperature between the flue gases in the chimney and the atmosphere outside the chimney that create a pressure difference”. In nature areas of high pressure flow to areas of low pressure all things being relative. We are not talking about a very strong force either. The force of good draft is so weak that it must be measured with very sensitive equipment. In scientific terms it is measured in inches of water column, or somewhere between .05 and .1 inches.
Before moving on let’s look back in time because as we all know, history is one of the best teachers. If we only used this historical knowledge more, life would be so much easier. In the beginning when fires were in caves everyone smelled like smoke, which was probably a blessing compared to how they might have smelled otherwise. As time passed our ancestors discovered the chimney and the best location for the chimney. Of course they knew that the best place was in the middle of the dwelling and running up through the highest point of the structure. Of course I have oversimplified this journey there was no doubt plenty of unsuccessful trial and error before arriving at this happy place.
Flash forward to the present and look at the current state of chimney location. For a few different reasons, mainly aesthetics and space concerns many of our poor chimneys have been relegated to the cold desolate outdoors. I am fond of saying, "outside chimneys may look nice and act as an anchor to hold the house down during a hurricane, but the truth is that they usually don’t work very well”.
So what exactly is a good chimney?
A good chimney is one that removes exhaust and also draws combustion air into our clean burning heating appliance. As I have said it does this because of the force in it called draft. The funny thing is that this force should exist in the chimney even if a stove is not connected to the flue! I have witnessed the “miracle” of draft in some chimneys that was so strong, that a piece of paper placed over an open thimble, would be held in place by the flow of air up through the chimney! There are always examples of chimneys that defy logic and work when they should not. I have talked to people who own chimneys that are, 10 feet tall, originate in a basement, have 5 feet of horizontal run, 4 elbows and are outside. They swear to me that they work just fine! Don’t be fooled by these anomalies they just got lucky!
There are some constants in chimney construction and location that support good draft.
- Locate the chimney inside the insulated envelope and try to have it terminate above the highest point of the dwelling. (A warm chimney is a happy chimney!)
- Make the flue the same size as the as the outlet on the stove. (Just as water flow will slow as a river widens, draft will be weaker if the flue size is too big or be restricted if the flue is too small.)
- Use a round flue if possible. (Exhaust flow doesn’t like corners)
- Try not to introduce bends or elbows in the chimney. If you have to use elbows try not to use more than two, and if you can use 45 degree elbows instead of 90’s.
- Avoid horizontal runs if possible and if you must use them keep them short. 3 feet is an absolute maximum! (It is not natural for smoke to go sideways!)
- Make sure there are no other openings into the chimney that are diluting the draft, such as leaky clean-out doors or alternate thimbles. (This has the same effect as trying to suck soda with a cracked straw.)
- Check around the proposed termination for obstructions like overhanging branches.
- A good rule of thumb for minimum chimney height is 14 feet.
- Don’t locate a chimney in a one story addition attached two a multiple story dwelling.
- Beware of cathedral ceilings. Even if they are in the next room they might affect the performance of the chimney.
- H.V.A.C. ducts, floor vents, and cold air returns can negatively affect draft.
- Be aware of anything that might remove air from the house like bathroom fans, kitchen range hoods, ( particularly down-draft), open second floor windows, exhaust fans and open fireplace dampers to name a few.
- Make sure the chimney is cleaned regularly and don’t forget about the cap and connecter pipe.
- Start and burn your fire hot enough to help sustain good draft. (A stovetop thermometer is a must.)
Inside Chimney vs. Out Side Chimney. Does it matter?
I would say it matters, “tons” which is incidentally what a masonry chimney can weigh, but I will tell you more about that later. To understand more about this subject let’s identify and define the major players in our game.
The Chimney is a vertical structure extending above the roof of a building for carrying off smoke. (Merriam-Webster)
The Stove is any manner of contraption with a load door that you can put wood in, some means of controlling combustion air, an outlet to allow smoke to escape and if you bought a good EPA stove it looks good even when it’s not burning.
Draft, which is a temperature difference between the inside of the chimney and the air outside which causes a pressure difference that allows the air inside the chimney to rise up and exit from the top of the chimney.
The Inside is a place that is warm and dry and tastefully decorated and a good place to have a glass of wine with your significant other when it’s cold and raw outside.
The Outside is that cold and raw place that I was just talking about!
Since the Renaissance period when the world suddenly became a much happier and artsy place people have been building chimneys inside the domicile. The British may not have contributed greatly to the artistic community but they knew that the chimney belonged inside the house. The Pilgrims may have endured a great deal learning how to adapt to the new world but they brought the knowledge with them that the chimney should be built in the middle of the house. Somehow this state of enlightenment has eroded and many chimneys (even as you read these words) are being built outside of the house.
So why exactly does the inside chimney function better than the outside chimney? It has a lot to do with the mysterious and wonderful force of draft. Remember in my definition I mentioned that draft was a temperature difference that causes a pressure difference. So getting back to the beautiful (looking) masonry outside chimney, we are going to have quite a challenge heating up tons of mass to create and maintain our desired temperature difference. That poor chimney is outside, where remember it is cold and raw and now we not only want it to look good but to work as well! If we are starting with a cold stove and it is 20 degrees below outside, the air inside the chimney may be 20 below too. Depending on other factors going on inside the house such as negative pressure, air may actually be coming down the chimney which is far less desirable than say Santa Claus. We might just get a house full of smoke before we get the chimney warm enough to support draft.
As a side note let’s talk a little about why an old “air tight” stove that cost $600 worked on that outside chimney and this new $2000 EPA certified stove won’t. The older stove was not very efficient and that meant that lots of the heat being produced went up the chimney. This worked very well to warm up the chimney but was also a great waste of heat. The newer EPA certified stoves are far more efficient and don’t lose nearly as much heat up the chimney. In a chimney that supports good draft and when burning good DRY hard wood you can expect to burn less wood and get more heat than you would have from the old “air tight” stove!
Now let’s move the chimney inside the house and see what happens. It all sounds so easy on paper! One thing I haven’t mentioned is that the chimney should also exit the top of the house at or as near as possible to the top of the insulated envelope. Our inside chimney is a happy chimney. The house acts like a big blanket wrapped around it to keep it warm. Now we can go back to that 20 below zero day but this time most of the air in the chimney is 70 degrees. (Or very close to the same temperature that the air in the house is.) When we start a fire in a stove that is connected to this chimney the smoke is going to go in the right direction because we already have that all important temperature difference that will support good draft! The fact is that this chimney will probably be drafting even in a static state or when there is no fire in the stove. That as they say is “a good thing”! So the moral to the story is, “If you have a choice build your chimney inside the house where it will be happy and more importantly so will you!”
What does house pressure have to do with my wood stove?
Did you even know that you house was under pressure? Do you care? Read on and you will see that Indeed it does have a profound effect on the successful operation of your stove.
So what is house pressure? Well to explain what it is we have to understand a little about relativity. Don’t worry you don’t have to be Einstein to understand relativity. First to make sure we are all on the same page we are talking about air pressure! The pressure inside the house is relative to the pressure outside the house. It may be either higher or lower than the pressure outside. If the pressure inside the house is positive or higher than the pressure outside and a window or door is opened air will leave or flow out of the house. If the pressure inside the house is negative or lower than the pressure outside the house air will flow into the house when that door or window is opened. If for some reason all of the doors and windows in the house were open equilibrium would be reached and the pressure would be the same inside and out. Nature loves balance! That seems easy enough to understand. Nature has its own very predictable but perhaps not very well known rules. One of them is that areas of high pressure flow to areas of low pressure. Of course when it comes to burning a wood stove in the house we will be looking at what effect house pressure has on chimneys.
Wouldn’t it be great if that was all there was to it! We could all high five and walk away. Of course as with most things in life there is a little more to it than that. In fact in most houses there is an area of negative pressure, an area of positive pressure and a magical place in between called the Neutral Pressure Plane (NPP). The NPP is the place where the pressure inside the house is equal to the pressure outside the house. They are all in a state of flux, changing quite literally with the wind and many other factors. The negative pressure area is typically located in the lower portion of the house and positive area is normally in the upper portion. The NPP as I have mentioned is between them. The NPP is often depicted as a straight line but it can actually be slanted or wavy and can jump around from level to level.
So let's apply some of what we are talking about to wood stoves and chimneys. There are two openings in our system, the door or the air control on the inside of the house and the chimney termination on the outside. If we put our system in an area of negative pressure the chimney, which is a conduit that air or flue gasses can flow through, might like an open door or window, allow air to flow into the house, especially if it is an outside chimney. If we locate the system in an area of positive pressure the air should flow out of the house.
Now let's add some variables that can sabotage our system. Anything that will take air out of the house mechanically like, but not limited to down draft ranges, bathroom exhaust fans, dryers, whole house fans, shop exhaust fans and range hoods can create negative pressure. Recessed lighting is another culprit. If not sealed properly they are like holes in the ceiling that air will flow through and raise the NPP creating a greater area of negative pressure. A masonry fireplace with an open damper may be taking air out of the house and creating negative pressure. Some people sleep with a window open on the second floor and that can raise the NPP. There are other culprits but I think you get the picture.
So what is the solution to stopping all of these forces that are trying to get between us, and a nice warm fire in the woodstove? The best possible solution is to locate the chimney inside the house and have it run up through the highest point in the insulated envelope. The opposite of this is a chimney that is located outside, which is almost certainly doomed to fail. If the chimney is inside the house and terminates through the highest point of the roof we achieve many desirable results. First and foremost we keep the chimney warm. A warm chimney is a happy chimney! This is because a good chimney produces draft and draft is a temperature difference that produces a pressure difference that pulls air or flue gasses up the chimney. It is much easier to keep a chimney warm when it is located inside the house. Just think of what the temperature difference would be when it is 70 degrees inside and below freezing outside. Because the warm happy chimney is producing strong draft it will be able to compete with all of the other forces that are trying to keep it from doing its job. Remember that pesky little NPP I was talking about? Well the chimney if located inside the house will have one that is higher than the NPP in the house and the result will be a chimney that has draft even when the stove is not running! Let's not forget the best part, with all the cards in our favor the wood stove will be responsive to control and provide sought-after heat.
What makes good firewood?
There are many different factors that affect the outcome of successful wood burning. Many will argue as to which one is most important but instead of arguing let’s just start with wood!
If a tree falls in the woods, and there is no one there to hear it, does it still make a sound? Well if nobody told you yet, yes it does make a sound. The real news is that when a tree falls it begins to decay and releases Carbon Dioxide. Coincidently the very same release of CO2 occurs when we burn wood! In the greater scheme of things the effect on the atmosphere is virtually the same. Why does this matter to us? Because unlike when fossil fuels are burned releasing otherwise trapped CO2 into the atmosphere, when we burn wood we are NOT adding to the Green House affect! Now I don’t know about you, but knowing that, is making me feel all warm and fuzzy.
We see trees as a renewable source of energy that when cut, split and dried under cover will provide heat. In a word wood is “FUEL”! The question we have to ask our-selves is what type of wood makes the best fuel to burn in our modern EPA rated wood burning appliances? And the answer is “It depends”.
In the Northeast almost everyone (not quite everyone, believe me I’ve talked to a few) knows that good dry hard wood like oak, beech, maple, ash and birch are best. However in some areas like the Rocky Mountains soft wood is plentiful and hard wood is almost nonexistent. Can you burn dry soft wood? You bet! You just can’t achieve the long burn times printed on those darn brochures with dry soft wood. The main difference between dry hard wood like beech and dry soft wood like quaking aspen is density. Beech is more dense (no that doesn’t mean the aspen is smarter) so there is more weight in the same amount of volume. So on a larger scale there is more heat value or BTU’s in a cord (4’x4’x8’ or 128 cubic feet) of beech than there are in a cord of quaking aspen. In plain English a cord of beech will burn longer and give off more heat (In the same appliance, chimney, house, etc.) than the cord of aspen.
Has any one picked up on the fact that I keep using the word DRY in front of wood? We have all heard it and said it but what does it mean? Is finding dry wood like finding the Holy Grail? During certain times of the year it can be. Dry wood does not come from a place advertised in a newspaper in October. Dry wood does not happen at the speed of e-mail or cell phones. Dry wood is the result of a long and deliberate process that involves planning and dare I say thought. They say that good things are worth waiting for and if you have ever tried to coax heat from wet wood you will agree.
Let’s attack this subject from a different angle and talk about “wet wood” or as some call it “green wood”. As an old Vermonter once told me the same thing that makes wood wet makes maple trees so popular in the springtime. The stuff coming out of those taps and dripping in to those buckets, you know, sap. They pour all that sap into great cauldrons and build blazing fires under them (with good dry hard wood). The sap bubbles and boils and gives off great clouds of steam but at no time has the sap ever burst into flames…because IT’S WATER! And as we all know water does not burn, as a matter of fact ask any fireman it’s what they use to put out fires! In scientific terms moisture content in wet or green wood can be 50% or more! That would mean that a log weighing 4 pounds would have 2 pounds of water in it. Even so called, dry wood has about 20% moisture content but for our purposes that is just fine.
So how do we obtain this elusive prize? It’s quite easy actually if we plan ahead and use our heads. Depending on the species, wood should be cut, split and allowed to dry under cover from 6 months to 2 years. The woodpile should be elevated off the ground, with pallets or some other method and be covered on top but left open on the sides. It is important that the wood is protected from rainfall, but is allowed to be gently caressed by the warm summer wind. Another good idea is to get the woodpile out in to the open as much as possible. There is nothing quite as powerful as the sun when it comes to properly seasoning wood. Sounds crazy I know but your wood will thank you the following winter by providing you with plenty of nice heat.
One other important tip is log length. If you have a stove that will accept a 22” log and you have your wood cut to 16” length you are leaving part of your “tank” empty. Have your wood cut 2” shorter than your firebox dimension and then if there is a little variation in actual length the logs will still fit.
My final point is about timing. The right time to buy wood is well before it is going to be burned. A nice bonus as well is that the cost can be considerably less for green wood. Remember depending on the species the seasoning time can be as long as 2 years.
HEARTH INDUSTRY NEWS
What stoves qualify for the 2011 federal tax credit?
A federal tax credit for installing a new corn, pellet, or wood (biomass*) burning stove can save you up to $300.00 on the price of your next stove!
Most of today's quality wood burning and pellet burning stoves are pre qualified. Ask your local hearth shoppe for details.
The general guideline are as follows:
•10% of the cost of the stove, up to $300. (The cost of the fuel is not included).
•Tax credit in effect in 2011. The stove must be installed in your primary residence between January 1, 2011 and December 31, 2011.
•The stoves must be used for heat or water heating and have a thermal efficiency rating of at least 75% as measured using a lower heating value.
•The law defines "biomass fuel" as any plant-derived fuel available on a renewable or recurring basis, including agricultural crops and trees, wood and wood waste and residues (including wood pellets), plant (including aquatic plants), grasses, residues, and fibers.
•The stoves must be used for heat or water heating and have a thermal efficiency rating of at least 75%. Ask us about the stoves that qualify!
•To verify tax credit eligibility, make sure you get a Manufacturer’s Certification Statement.
•To qualify, file tax form 5695 with your tax return statement.
*The law defines "biomass fuel" as any plant-derived fuel available on a renewable or recurring basis, including agricultural crops and trees, wood and wood waste and residues (including wood pellets), plant (including aquatic plants), grasses, residues, and fibers.
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