Wood Stove buying Primer

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  • l article written by Don Jordan, National Certified BOCA Local Building Inspector and Mechanical Inspector.)

    (Note: This is a primer - some of the points relate to existing chimneys and fireplaces and others to new construction of same)

    Please read and ask questions before you purchase a stove. many buyers start out asking which stove is best. The main concern is already missed. You are buying a stove without factoring the installation process. The first question one should ask concerns what is required for a safe and successful installation.

    1. Existing Chimney?
    What are the dimensions of the existing chimney liner? Is the chimney tall enough to draft correctly? One-story ranch homes have short chimneys. Many manufactures specs call for a certain minimum vertical length to draft correctly (usually around 16 feet)

    2. Shared Flue?
    If it is being shared with another appliance (furnace, fireplace) it can not be used. One flue or chimney per unit is the proper guideline - with a possible exception for certain gas units.

    3. What is the condition of the chimney and liner?
    When was the last time it was cleaned and inspected? Are the clay flues relatively straight and aligned? Does the chimney have any missing, damaged flue tiles, or mortar missing between flue tiles? Also look for missing or deteriorating bricks and for excessive creosote build up. All creosote should be cleaned and removed to prevent a fire hazard

    4. Have you factored in its location?
    Chimneys located on outside walls with 3 sides exposed to the weather draft poorer than central located ones. Will I need a full liner? Do I have room for it? Should it be insulated?

    5. Liners - Which are best?
    Corrugated are cheaper but not as good as smooth round ones. Governing codes require HT 2100 and UL approval 103. Some liners are tested with insulation meaning insulation must be used to meet code requirements. Flue size constraints may rule out insulated liners, so one must use the better grade liner without insulation. You might be lucky and have a separate good condition 8 by 8 clay flue, where a connector pipe is all that is needed. Read the article on Hearth.com about Passing Though a Wall to assure safety in the connection to an existing chimney.

    6. Using your existing fireplace to vent the stove?
    NFPA 211, 2003 requires ALL 6 inch flue collar stoves to have a full liner if the fireplace flue is in an exposed outside wall chimney. A shorter "direct connection" is allowable in certain instances when it is being connected to an interior fireplace chimney. But a typical 12x12 flue is too large to draft from a 6" collar. A full liner is required and there is plenty of room for insulation. An 8/12 clay flue, having inside measurements of 6.75" by 11", can be a tight fit for a liner. Quite a chore insulating it in that confined space, especially if, the flues are not aligned or you encounter an offset.

    Code also requires the Damper area to be blocked off - read the article on Hearth.com about fabrication of block off plates.

    7. What to do with the damper obstacle?
    The damper plate should be removed. The remaining opening is usually less than 6". There are a couple of options here - The damper frame can be broken out so that the 6" will fit through. Another option is to ovalize the flue. Even though it remains the same interior area, ovalizing creates friction (A great place for creosote build up). Add the fiction associated with corrugate liners and the friction is compounded worse. The code calls for closing off the damper area with a metal plate. A couple of final points about venting. Do not assume because your fireplace drafted ok the new wood stove will also. Your fireplace ut large amounts of heat and air up the chimney, which help it draft. If the fireplace is marginal, you should definitely line the chimney and insulate if possible. Consider extending the chimney a few feet using masonry or other safe method.

    8. Connecting or Stove pipes -connecting the stove to the flue.
    They have to be no less than 24 gage steel and pitch upward to the chimney inlet. A better product to use is welded seam 22 gage connector pipe. Again horizontal runs should be as short as possible with fewest directional changes. Some Stove Manufacturers list the maximum length of run and maximum turns or elbows Each connector pipe must fully pushed in so that no corrugation is seen and have 1.5" overlap, and be fastened by sheet metal screws or rivets - 3 equally spaced per joint. Clearance to combustibles of single wall pipe is 18" in all directions Double wall pipe or triple wall pipes reduce the clearance distances, but once used the rest of the run must be Double wall - you can not go back to single wall.

    9. Stove final placement.
    Can your stove satisfy clearance to combustibles? Its time for research. Most new stove manufacturers have web sites where you and download and read the installation manual. Stove A, with a heat shield may fit your location, where stove B, does not have that option and will not comply. Most manuals have diagrams indicating the minimum requires distances to sides top ect. and required hearth pads or extensions. Be careful with the clearances to the loading doors. In USA 16" min. is usually required, but if the stove is listed and testes for 18 then it is 18 In Canada it is at least 18".

    10. While you have your manual, check for venting requirements. There is often a way to build a reduced clearance enclosure (called an alcove installation). Do not assume the surface is non-combustible so therefore it is ok. Heat can transfer through tile or bricks. Such protection must factor thermal conductivity, or the ability to reduce heat transfer to the combustible underneath. Same goes for the Hearth extensions, they have to be non-combustible and thermal resistant. UL approved rugs do not satisfy thermal resistance for use as hearth extensions.

    11. At this point you may know what model stove should work or not. A word about heating area and BTU output claims. They are often overstated and tested in laboratory conditions. Quite different from many "real world" conditions. Check with your dealer, installer or other owners of the stove for their experiences.

    12. Can you install a stove?
    Warranty issues aside, are you equipped to handle 450 lbs? I takes two People to handle the liner installation plus dealing with heights over 30 feet. For many people, such an installation is beyond their capability and it is best to have the professionals deal with it. Do your research and find a retailer or installer you are comfortable with - one that stands behind the products. You might pay more but if problem arises you want to know the solution will be handled in a timely professional manner.

    13. Permits
    Yes permits are required. If things do not go well with your installer, the inspector can be your best route to resolve. You spent all this money, it make sense to get a professional opinion that all is safe and that it meets code. My advice to the consumer is to use a payment plan. Pay for the stove and installation materials, so much on completion, and final payment after a satisfactory inspection. Most dealers should find this agreeable. Some states also have contract guideline laws, check with your consumer or attorney generals office. Other states keep records of complaint against manufactures and retailers. While poking around it might be a good idea to check them out before you get involved.

    14. Ownership
    There is a learning curve with any new stove or fireplace. Learn how to get the desired results of your new appliance. The best learning tool is a stove thermometer. Your chimney and stove should be cleaned and assessed before every heating season. You also should monitor chimney condition during the heating season.

    15. A word about common sense and safety.
    Make sure your smoke detectors are working. Carbon monoxide sensors are cheap enough; there is no excuse for not having them. Keep small children away from the stove. Have a working fire extinguisher available. Do Not Burn Trash or pressure treated/glued wood products.

    Link added BeGreen 10/24/2006:
    For an excellent publication on the many things to consider before buying and installing a new stove follow this link:
    Woodstove Installation Guide
    And here is a thread in the forum on the topic: