Wood Stoves - 10/2 Rule for Chimney Height

 

In order to determine proper chimney height above the roof, measure from the side of the chimney horizontally. As you move up the chimney, the length of the measurement increases.  Once this measurement reaches 10 ft. this height on the chimney is your base height.  The chimney must be 2 ft. taller than the base height.  If the chimney is closer than 10 ft. from the peak of the roof, the chimney must be 2 ft. higher than the peak of the roof. The 2 ft. above the base height does not include the cap.

Most problems with woodstoves are caused by improper hookup or operation.  The biggest problems come from not getting enough air through the stove or simply not getting catalytic stoves up to proper operating temperatures.

A properly installed chimney is key to having proper draw.  This is especially important with use of a kit chimney, as most masonry chimneys are built by contractors who are familiar with the rules of chimney installation; however, most kit chimneys are installed by the customer, or a general contractor who may not know how to set a proper chimney height in relation to the structure (refer to illustration 1).  Kit chimneys can also be affected by outside temperature more so than a masonry chimney, so installation of a "chase" (a structure built around a kit chimney that is insulated) may be needed.

A newer house, or a house that has been reinsulated, or has had siding and/or insulated windows installed could cause difficulties, as well.  A chimney must pull a certain amount of air out of a structure in order to provide sufficient combustion air into the stove.  In order for the chimney to remove air from the structure, ample "make up air" must be allowed into the structure to compensate for a "tight house".  A structure that is well-insulated and sealed may not allow this airflow to happen. 

A basement installation can have similar effect, as the basement will always have a slightly lower air pressure than the upper floors of the house due to "stack effect" - this is caused by warmer air rising inside the structure much as it does in a chimney. As the air is bottled up in the top of the house, it is leaving the lower areas of the structure; air usually does not leak into a basement freely enough to compensate. 

Installation of an outside air source should correct this.  The outside air intake should be run in as short and direct a route as possible, and should be installed with pipe no smaller than the opening on the stove. Refer to your stove model's owner's manual for specifics.

Most masonry chimneys and kit chimneys have a port or door which makes cleaning of the flue easier.  These clean-out doors should be sealed as air tight as possible when using the stove; the reason for this is that in order to pull air through the stove, a chimney should not have any other openings where air could be pulled into the flue other than through the stove.

If air is being pulled into the flue from anywhere other than through the stove, the amount of available air for the fire is being reduced, causing a bad burn - and more importantly, the air being pulled in through the leak is much colder than the air moving through the stove, which will cause a cooling effect in the chimney and will allow creosote to build up more rapidly in the flue.

Most importantly, the flue size must be at least the same diameter as the exhaust opening on the stove - it can be bigger, but it cannot be smaller.

Please refer to the wood stove owner's manual, the vent pipe owner's manual, and all local codes. Consult a licensed contractor if you are unsure in any way of your ability to properly install the stove and pipe.