Homes need to breathe. Fresh air is needed for combustion in furnaces, fireplaces, wood stoves, gas water heaters and clothes dryers. As people make their homes more energy efficient by sealing cracks, adding insulation and doing other things to prevent heat loss, homes can become starved for air. This is especially true when you're using exhaust fans and vented appliances which draw more and more air from inside the house; air from the outside can be pulled into the home, possibly down the furnace vent or fireplace chimney. This is called "backdrafting" and can cause carbon monoxide (CO) to form.

CO is a colorless, odorless gas produced when fuel is not burned completely. Automobiles, charcoal or wood fires and improperly vented or air-starved coal, oil and gas furnaces can produce CO.

Be aware of these CO signals:

• Headaches, nausea, dizziness
• Excessive humidity, heavily frosted windows
• Fireplace smokes, won't draw
• Furnace vent backdrafts (See Fresh Air Check below.)

To prevent homes from becoming starved for air, the Minnesota Uniform Mechanical Code requires that all new homes be built with a special duct that brings outside air directly to the heating system. All furnace and boiler installations in existing homes are also required to have a combustion air duct.

To determine if your home is receiving sufficient fresh air:

1. Close all doors and windows.
2. If you have a fireplace(s), build a fire. Wait until the flames are burning vigorously.
3. Turn on all exhausting devices, such as:
   • Kitchen and bathroom exhaust fans
   • Dryers (gas and electric)
   • Attic fans
4. Turn on all exhausting devices, such as:
   • Heating equipment
   • Water heater
5. Turn on all vented gas appliances, such as:
6. Wait 10 minutes for drafts to stabilize.
7. Hold a lit match below the heating system draft hood air intake (see illustration at right).
   • If the match remains lit and the match flame pulls toward the draft hood, this indicates sufficient fresh air. Check draft hoods on all other equipment also (gas space heaters, water heaters and additional heating systems). Return appliances and exhausting devices to their original condition.
   • If the match goes out, it means the vent may be plugged and/or the air supply in your home may be inadequate.
   • Check for plugged vent connectors and chimneys. Repair stoppage and test again.
   • If the match goes out even when vent is clear, additional air must be brought into the structure from outside. Refer to the Minnesota Uniform Mechanical Code or contact a qualified heating contractor or your local gas utility service department.

If your house is starving for air, a vent or fresh air intake needs to be installed directly to the furnace area; until it is installed, limit use of clothes dryers, fireplaces, furnaces, and mechanical exhaust fans. Operating more than one of these devices at a time can contribute to backdrafting if your home doesn't have an adequate fresh air supply.

Materials used for ducting must meet standards described in the Minnesota Uniform Mechanical Code. Flexible ducting is not recommended because ridges create turbulence which reduces air flow. Before installing a duct, check with your local Building Codes office for size and materials. Here are examples of installations of fresh air ducts.

1. Be sure duct is sized in accordance with the Minnesota Uniform Mechanical Code.
   
2. Place the outside air intake duct (A) at least one foot above grade level.
   
   
3. Cover the air intake with 1/4-inch mesh screen and hood.
   
4. The duct must discharge the fresh air at a level no more than one foot off the floor (B).
   

To help keep incoming cold air in one place instead of allowing it to spread across your basement floor, build a closed-bottom containment box out of sheet metal or use a 5-gallon bucket that allows air to flow freely in and out. Drop the combustion air supply duct into the containment box and attach the duct permanently to it. To avoid restricting airflow, the box or bucket cannot be more than one foot high.

This method is permitted by code. However, experience indicates potential problems such as shorter equipment life, poorer performance in unusually cold temperatures and possibly voided warranties.

1. Be sure the duct is sized in accordance with the Minnesota Uniform Mechanical Code.
   
2. Place the air intake duct (A) at least one foot above grade level.
   
3. Cover the air intake duct with 1/4-inch mesh screen and weather hood.
   
4. Install duct in the return side of the heating system (B).
   
5. A register without a damper (C) must be installed in the plenum of the furnace. Its free area size must be at least one half the free area of the common vent.
   

1. Be sure the fresh air duct (A) is sized in accordance with the Minnesota Uniform Mechanical Code.
   
2. The duct must discharge the fresh air at a level no more than one foot off the floor (B).
   
3. Ventilation air must be supplied to the furnace area through two openings to the main house area located as follows:
   
   • A ventilation air outlet grille located in a wall or door, at a level higher (C) than the draft hood opening. The area of the grille must provide 1 square inch of free area for every 2,000 Btus per hour of natural gas input to the gas equipment in the area.
     
   • A ventilation air inlet grille located in the wall or door, level with or below (D) the combustion air inlet to the lowest burner. The area of the grille must provide 1 square inch for every 2,000 Btus per hour of natural gas input to gas equipment in the area. See following example.
     

Example:

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With a furnace of 80,000 Btu input, there are 40 units of 2,000 Btus. 40 X 1 inch = 40 square inches. A grille 10 inches X 4 inches = 40 square inches. But since only the free area of the grille, and not the slats, is counted, two grilles (an inlet and an outlet) that measure 10 inches X 6 inches each, are used for this furnace. Their locations are shown.

To ensure safety, give your home heating system periodic care. Proper maintenance will also extend operating life, save energy and increase efficiency. Follow manufacturerÕs recommendations in caring for your system. If your heating system is not working properly, contact a qualified heating contractor or local utility service department.

Make sure fresh air intake remains clear of snow, leaves, or other debris. Never block it.

Call your local natural gas utility company or the Minnesota Blue Flame Gas Association at (763) 424-1841.

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