Monday, December 12, 2016
How to stop back puffing and other chimney drafting problems
Although Back-puffing can and will happen with any fuel burning appliance [gas / propane / oil / wood / pellet fuel] this article will deal with wood as it is the most noticeable. Gas and propane do not have an after smell after being burnt and the back-puffed emissions will NOT be noticed in the home unless you have a Carbon Monoxide detector. Oil back-puffing may leave stringy black bits around the home but, again, no smell as acrid as wood.
Every house which has a chimney [vertical or side vented] or uses heating elements of any kind should have a working carbon monoxide detector. Check it twice each year, at the same time as you check your smoke detectors and change any batteries. With wood heat, the clearest sign that your chimney is not drafting properly is that your house fills up with smoke. This is not an occasional puff of smoke back into the house when the outside wind briefly creates a downdraft. That's normal. Another common cause for downdrafts is lower pressure inside the house caused by operating an exhaust fan in a well-insulated house. Usually the basement heating unit is the most problematic. That can be diagnosed by turning off all exhaust fans and appliances that exhaust to the outside of the home [central vac, bath and kit hood fans, dryers, etc] until the fire has been started and the updraft is established. Learn what your homes ‘load’ is. A clogged chimney is the most common cause of ongoing drafting problems. Even seasoned wood leaves normal ash buildup in the chimney, so chimneys should always be swept at least once a year -- in the Spring --to remove dangerous soot build-up from any fossil fuel. Chimney sweeping in the late spring or early fall will also ensure that no bird or animal nests, leaves, or other obstacles are obstructing the chimney or flue caps before the appliance is used again in the winter. Even an unused chimney can be riddled with spider webs that Can cause a blockage. Any of these can also cause a chimney fire
Heavy snow outside can plug a chimney. Gas codes do not stipulate the height of a vent above the roof where as wood codes state the chimney MUST be a specific height. Many gas chimneys are too short for our snow build-up in the north and can become buried by snow fall. Properly installed flue caps (chimney caps) should keep this from happening under normal snow conditions. However, weather doesn't always follow normal snow conditions. If there is more than a foot of snow on the roof or if there is wind, drifting snow can block even properly installed flue caps.
Take a look at your chimney to see if the flues are still above the snowline. If they are not, do not light a fire or turn on the appliance until the snow around the chimney has been cleared. This condition can cause carbon monoxide buildup inside the house in the same way as a plugged exhaust pipe causes carbon monoxide buildup inside a car.
Chimney drafting problems can also be caused by the design of the chimney. With wood use, all chimneys should extend at least 2 feet above the highest roofline within 10 feet of the chimney top and be a minimum of 36” above the roof surface. It doesn't have to be higher than the peak of your roof, only higher than anything within 10 feet. Anything less than this will cut back on air circulation.
So the rule of thumb is….Ensure your chimney/vent is not clogged by dirt, debris, soot or animal/bird nesting’s, have your carbon monoxide detector in proper working order and check your chimney cap for clogs and the height of the snow around the chimney. A reputable chimney sweep will check your flue channel to ensure it is clear and free running when sweeping the chimney and you should mention to them if your experience any back-puffing problems with any of your heating appliances. An article by Yvette Aube
