Problem:

Homeowner Question: Why is smoke coming into my home from my fireplace/woodstove now, after my insulation was upgraded?

Problem Diagnosis: Backdrafting

Cause: Why is this happening?

Now that the house is more air tight, it gets depressurized when you use your fireplace/woodstove or other exhausting appliances. Before, air was able to enter your house through leaks within the building envelope to replace the air being exhausted by the appliance. Now, the outside air cannot enter the home through leaks in the building envelope as easily so the home experiences a negative pressure while the appliance is operating. When the appliance shuts off the negative pressure in the house draws exhaust gases back down the chimney and into the house. This is referred to as back-drafting. When combustion gases leak from a combustion appliance into a house it is called combustion spillage. Combustion spillage is often caused by back-drafting. It can also be caused by the operation of a larger exhaust appliance such as a dryer running while a wood stove is operating.

Solution: Back Drafting

You should contact a ventilation specialist and have them perform a depressurization test to determine if a make-up air system, direct-vent retrofit, or ventilation system is required, or if the current system needs to be rebalanced. Many manufacturers include a combustion air line with their appliances to help reduce the possibilty of back-drafting and combustion spillage.