New government programs encourage people to make their home more energy efficient and green. But before you cure your home of its addiction to energy, make sure you follow the first rule of medicine: do no harm. Some cures can kill you, or at least make you sick, from colorless and odorless carbon monoxide gas (CO).
In order to understand why improvements made in the name of energy efficiency can do harm, you first need to know two simple rules about how combustion appliances, like gas furnaces, work. First, all combustion (burning) requires air. Second, burning without sufficient combustion air can produce harmful byproducts, such as CO, and can create conditions where the harmful byproducts remain in your home.
The next thing you need to know is where combustion appliances get combustion air. The preferred source is from outside the home, including ventilated attics and crawl spaces. Combustion air drawn from outside air is usually provided by two openings, one within 12 inches from the ceiling and one within 12 inches from the floor in the room where the appliance is located. There are specific rules for the size of these openings. Never block, cover, or change these openings in any way.
The other source of combustion air is from inside the home. Combustion air drawn from inside works (although not well from an energy efficiency perspective) when the home has enough air leaks to replace the combustion air with outside air and when there is sufficient open space near the appliance from which it can draw air. There are specific rules for how much space is required to provide air for combustion appliances. Never make changes to the home, such as adding doors or closing rooms, that change the amount of open space available to combustion appliances.
The final piece to the puzzle is to realize that appliances in the home compete with each other for air. Clothes dryers use a tremendous amount air when they operate. A clothes dryer in the same room as a gas water heater, for example, is a recipe for problems. Exhaust fans, such as those in kitchens and bathrooms, can draw air from the home. Wood-burning fireplaces can use significant amounts of air as can gas fireplaces (unless they are completely sealed). Finally, appliances will compete among them for available air.
You change the air flow dynamics in a home when you make seal openings between the home's interior and places like attics, crawl spaces, and exterior walls, and when you seal leaky forced-air heating and air conditioning ducts. You also change the dynamics when you add new appliances, such as a wood-burning stove, or a decorative gas fireplace, or a high capacity kitchen exhaust hood. Air sealing and adding insulation can deprive appliances of the air they once used for safe combustion. Adding new appliances can cause increased competition for air. Both changes can cause once safely operating appliances to become unsafe.
High levels of CO can kill within minutes or at most a few hours. A CO alarm should detect lethal levels of CO and you should have at least one alarm in a home with combustion appliances or with an attached garage. Lower levels of CO can produce flu-like reactions such as head aches, drowsiness, and nose and throat irritation. Carbon monoxide alarms may not detect low level exposure, but exposure over time can make you sick. Smoke alerts are usually not CO alerts, although some models combine both into one unit.
Before you make any changes described in this article, an energy audit consultant should conduct a thorough evaluation of your home. This consultant should be trained to detect air pressure differences that can cause combustion appliance malfunction. This consultant should also test your combustion appliances for excess CO production and should determine the most cost effective and safest ways to cure your home of its addiction to excess energy. This testing will cost several hundred dollars, but it is well worth it both for peace of mind and for the expert advice. A good energy audit will help you save money by saving energy and by making the most cost effective energy efficiency improvements. It will also help keep you and your family safe.