Over the years, many fireplace users have complained that smoke was coming back into the home when they use their fireplace. They would often tell me that this used to not occur when using the fireplace, and that it’s a new problem. Sometimes there would be an interesting twist… like smoke was only coming in…
Over the years, many fireplace users have complained that smoke was coming back into the home when they use their fireplace. They would often tell me that this used to not occur when using the fireplace, and that it’s a new problem. Sometimes there would be an interesting twist… like smoke was only coming in from another portion of the chimney such as a basement fireplace installation when using a main floor fireplace, or that smoke was entering from the central heating appliances into their vicinity in the basement. This occurrence is many times caused by negative air pressure in the dwelling space. Such a pressure difference when compared with outdoor (ambient) pressure is onset be the installation of new energy efficient windows or doors, or by the installation of better insulation in the ceiling or walls, but it can even be by other less obvious changes… penetrations through upper level ceilings for electrical fixtures, or additional power venting inside of the house. With negative air pressure unwanted smells, VOCs (volatile organic compounds) mold spores, or smoke can linger in or worse yet, enter the house. Indeed building code took recognition of this problem in the early 1990s with the introduction of codes to redress this as exhibited in the photo from code G2407. At that time the problem was labeled “sick air syndrome”. For many unsuspecting home owners, the newly contracted sick air syndrome was unintentionally caused in an attempt to make their home more energy efficient.
Correction of negative air pressure is often by installation of an outdoor sourced air duct back into the house. When houses have a central air duct system in place, the most common place to install such a vent is into the return air duct-work. This means that every time the duct-work in the house is circulating air, the central air duct circulating fan is automatically sucking air into the return air ducting system from outdoors, thereby increasing indoor air pressure relative to ambient pressure. Correction of negative air pressure in a scenario without a central duct air circulation system will involve such a duct piped in from the outside, but dumping outdoor air into the mechanical room close where the air is directly available to be consumed by central heating appliance(s) such as a boiler, or a water heater tank.
