Ventilation Still Matters

Some of the time-proven basics still prevail in construction, no matter how "high tech" we become.

As we make our homes tighter to minimize energy consumption, we continue to discover new side effects. The most recent wave of "discoveries" includes the facts that certain appliances may not function well and certain contaminants might be kept in a tight house that would otherwise be vented to the outside.

Gas and oil (combustion) appliances need air for proper performance. In tight homes, they may not get enough combustion air. Further, other typical equipment, such as bathroom and kitchen exhaust fans, will deprive combustion appliances of adequate oxygen for normal performance. This is especially true in tight homes.

It is becoming more and more apparent that make-up air should be provided in certain areas of the home where there are combustion appliances. This can be in the form of louvered vents through the wall or ductwork to reach more inaccessible areas.

That appliances should need make-up air is certainly not a new discovery. Any combustion process requires air to sustain itself. However, the evolution of residential construction has been rather haphazard, seldom taking the whole system into account. As we focus on one area (energy efficiency for example), seldom do we consider all of the consequences of our focus. This was particularly evident during the energy crisis in the late 70s and early 80s. Many homes were overinsulated, and the lack of ventilation for the structure itself led to many moisture-related problems, including premature paint failure and rot.

Now we are discovering that efficient combustion appliances require air that might not naturally be available in our newer, tighter homes. If your appliances are not performing well, it could easily be the result of inadequate make-up air.

There is another consequence to this situation. If negative pressure (depressurization) is developed in the house, combustion by-products can actually be captured and retained in the house, contributing to a decline in indoor air quality. Various devices, such as exhaust fans and combustion appliances that require more air than is available, will create negative pressure (lower than atmospheric pressure outside). As a result, odors and contaminants are "captured" inside the house. In the worst case, negative pressure could capture carbon monoxide inside the house, creating a potentially dangerous situation.

We recommend that you review your home to determine if there is adequate air being brought into the house to support various exhaust fans and combustion appliances. The easiest way to do this is with a burning candle. While your heating equipment is running, hold the candle near the edge of a closed exterior door. If the flame "leans" toward the interior, your house is probably depressurized and make-up air is needed. You should check several locations before drawing any conclusions.