Woodstove Installation and Exhaust Air Testing

Published on January 17, 2020

For those of us who love the smell and comfort of a woodfire, there are many things to consider in your home before installing a woodstove, including an exhaust air test. Wood fires require significant air for the burning process. They also need air to exhaust the products of combustion. When a woodstove is installed in a home, the certified installer must determine if fresh make-up air is required to be supplied to the unit based on the manufacturer’s specifications. This will help to ensure that the woodstove functions properly during use.

What many homeowners do not realize is the potential for trouble with the exhausting of the unit itself. In older homes, there was usually enough air coming into the home via the air leaks that a strong enough updraft was created in the chim­neys. This meant that all of the smoke would go up and out of the home. Today, many homes have been upgraded through retrofits and are made to be much tighter than they ever were originally.

Exhaust Device Spillage

In most homes today, we tend to install exhaust-only fans, such as bathroom fans, a kitchen range hood, or clothes dryer. Other sources of depressurization in a home can be draft-induced furnaces or water heaters. The combination of these exhausting fans with tighter homes can lead to a serious problem known as exhaust device spillage.

Exhaust device spillage occurs when you have some or all of these fans working simultaneously, which create a negative pressure on your home. In some cases, this negative pressure works against your woodstove’s ability to exhaust its products of combustion properly. This can result in smoke entering and mixing with the house air and creating a potentially toxic situation by mixing in deadly carbon monoxide (CO) gas.

BSG Can Help

Air pressure is not something that can be seen with the naked eye. It is very important to have your home tested, using the proper tools. With the use of a blower door, licensed, registered energy professionals can test your home by performing an exhaust device depressurization test on your home. This test measures the amount of negative air pressure that becomes induced on your home, should all of the exhaust fans within it are left running.

By testing and measuring your home, energy advisors can let the homeowners know that their indoor air-quality is not being compromised by CO gas while the woodstove is operational. Building officials are becoming increasingly aware of this and are requesting this type of testing for all new installations of woodstoves, regardless of the age of the home.

The standard acceptable rate of depressurization allowed is -5 Pascals of induced pressure. Simply put, if your exhaust fans create more than a -5 Pascal pressure difference on your home, changes will need to be made before a woodstove can function safely within it.

If you’re wondering if your woodstove is functioning properly, or are looking to install a woodstove in the future, contact Barrier Sciences Group. We’d be happy to discuss your concerns and schedule an exhaust device depressurization test on your home. You can call our office at 1-866-333-3920, or fill out a contact form on the BSG website. Someone will be sure to get back to you as quickly as possible!