Water heaters and carbon monoxide: the risk, the signs and the alarms

If the alarm goes off

The CPSC's steps are short:

1. Move outside to fresh air right away.
2. Call 911 or the fire department.
3. Count heads to make sure everyone is out.
4. Don't go back in until responders say it's safe.

The same applies if you have symptoms and no alarm, or the alarm isn't sounding: leave and call the fire department from a neighbor's home, the CPSC says, and see a doctor and tell them you suspect CO.

Symptoms

The CDC lists headache, dizziness, weakness, upset stomach, vomiting, chest pain and confusion as the most common symptoms, often described as flu-like. The CPSC adds that low-level CO feels like the flu without the fever, and that slow household leaks are easy to mistake for it. People who are asleep can die before they notice anything.

The CDC says more than 400 Americans die every year from unintentional CO poisoning not linked to fires, more than 100,000 visit an emergency department and more than 14,000 are hospitalized.

How CO gets out of a water heater

The CDC says CO is in the fumes any time fuel is burned, including in furnaces and gas appliances. A working vent carries a water heater's exhaust outside. Problems start when it doesn't:

• Backdrafting. Exhaust spills out of the draft hood into the room instead of rising up the vent. Our backdrafting guide shows the signs and the match test.
• Loose or badly sloped vent pipe. The CDC says horizontal vent pipes on appliances like water heaters should rise slightly toward the outdoors, which keeps CO from leaking out of joints that aren't fitted tightly.
• A blocked chimney. The CDC recommends checking or cleaning the chimney every year, because debris can make CO build up indoors.
• A blocked outdoor vent. Power-vent and direct-vent heaters often exhaust out the side of the house, where snow can cover the opening, as it covered the furnace vents in the Plymouth case below. Keep it clear.
• Poor combustion. A. O. Smith's gas heaters have a thermal switch that shuts the burner off when a blocked vent or too little combustion air causes poor combustion. If yours keeps tripping, have the venting and air supply checked before it's reset.

The CDC's advice is to have the water heater, furnace and any other gas, oil or coal appliance serviced by a qualified technician every year.

Where to put CO alarms

The CPSC recommends battery or battery-backup CO alarms on every level of the home and outside sleeping areas, and says interconnected alarms are best because when one sounds, they all do. It advises against attics and basements unless someone sleeps there, and against spots near heating vents or behind furniture or curtains. Test them monthly.

Alarms wear out. The CDC says to replace one as the manufacturer directs or every 5 years. Massachusetts fire officials say 5 to 7 years depending on the model, and that newer alarms have a sealed 10-year battery and are replaced whole at 10 years. Plug-in alarms can run their backup battery down during a long power outage.

The Massachusetts rules

Massachusetts requires CO alarms by law. Nicole's Law is named for 7-year-old Nicole Garofalo, who died in January 2005 when her Plymouth home filled with carbon monoxide after snow blocked the furnace vents during a power outage, according to the Town of Hull's fire prevention page (see our Plymouth page).

• Who: homes with fossil-fuel equipment, such as boilers, furnaces and water heaters, or an enclosed garage.
• Where: every level, including habitable parts of basements and attics. On levels with bedrooms, the state Department of Fire Services says within 10 feet of bedroom doors.
• When you sell: the local fire department inspects the CO alarms before the sale or transfer, Hull's page explains (see our Hull page).
• When you replace a gas water heater: the state gas code, 248 CMR 5.00, says no vented gas appliance may be installed or replaced unless a CO detector is on the same floor, and on each habitable level of a home.

Landlords must also install and maintain CO alarms in every unit with a source of CO, the Department of Fire Services says.

Local pages mentioned

• Plymouth, MA
• Hull, MA