The Danger You Cannot See, Smell, or Taste
Carbon monoxide is one of those hazards that sounds distant until it is not. It has no color, no smell, and no taste. You cannot tell it is in the air by looking around or by sniffing the basement. The only thing that warns you is a working alarm, or your own body starting to feel off.
On Long Island, where a large share of homes heat with gas or oil boilers and make hot water with gas or oil water heaters, the risk is worth taking seriously every heating season. Most of the time these systems run safely for years. But when something goes wrong with combustion or venting, carbon monoxide, often shortened to CO, can build up inside a home without anyone noticing.
This article explains where CO comes from, how boilers and water heaters can produce it, what the warning signs look like, how to place and care for alarms, and what to do if one goes off. It is not meant to scare you. It is meant to give you the plain facts so you can make a few simple choices now, before the cold weather settles in.
What Carbon Monoxide Is and Why It Is Dangerous
Carbon monoxide is a gas produced when fuel does not burn completely. Natural gas, propane, oil, wood, and gasoline all produce it when combustion is incomplete. In a healthy, well-adjusted appliance, the amount produced is small and the exhaust leaves the house through a vent or flue. The problem starts when the appliance is burning poorly, or the exhaust has nowhere to go.
When you breathe CO, it enters your bloodstream and attaches to the molecules that normally carry oxygen. Your body then gets less oxygen than it needs. The early symptoms are easy to mistake for something else: headache, dizziness, nausea, tiredness, confusion, and a sense of being unwell. Because they look like the flu, people often do not connect them to the home.
Higher levels, or longer exposure, can cause fainting and much more serious harm. Infants, older adults, people with heart or breathing conditions, and pets can be affected sooner. One useful clue is the pattern. If everyone in the house feels sick at the same time, feels better when away from home, and feels worse again on return, that is a reason to take it seriously and get checked.
How Boilers and Gas Water Heaters Can Produce CO
Both boilers and water heaters burn fuel to make heat, so both can produce CO if something is off. The most common causes fall into a few groups. The first is poor combustion. Burners that are dirty, out of adjustment, or worn out do not burn fuel cleanly. A heat exchanger with cracks or heavy buildup can also disrupt the flow of exhaust.
The second is a blocked or damaged vent. The exhaust from a boiler or water heater has to travel up a flue or out through a vent pipe. Bird nests, debris, rust, collapsed sections, loose joints, and corrosion can all restrict that path. When the flue is blocked, exhaust gases can spill back into the room instead of leaving the house.
The third is not enough air for combustion. Appliances need a steady supply of fresh air. In a tight, newly sealed basement or closet, an appliance can run short of air, which leads to incomplete burning. Adding insulation, weatherstripping, or a new enclosure around a utility area can change the airflow without anyone realizing it.
The fourth is a combination of competing equipment. A powerful kitchen exhaust fan, a clothes dryer, or a fireplace can pull air in a way that interferes with a nearby appliance’s venting. This is called backdrafting, and it is more common in tightly built homes.
Age plays a role too. An older boiler or water heater is more likely to have corrosion, worn parts, and cracked components. That does not mean every older unit is dangerous. It means they deserve regular attention.
Other Common Sources Around the Home
Boilers and water heaters are not the only possible sources. Gas ranges and ovens, fireplaces, wood stoves, gas dryers, attached garages with running vehicles, and charcoal grills used too close to the house can all contribute. Space heaters that burn fuel indoors are another risk.
Portable generators deserve a special mention, especially after a storm. When the power goes out, it is tempting to run a generator in the garage, in the basement, or just outside a window. This is dangerous. Generators must be run outdoors, well away from doors, windows, and vents, because the exhaust can drift back inside quickly. People are harmed every year by generators run in the wrong place during outages.
Knowing the full list helps when you are trying to figure out why an alarm is going off. The source is not always the boiler, but the boiler and water heater are two of the first places a professional will check.
Warning Signs Your Equipment May Be Producing CO
Your appliances sometimes give hints before an alarm does. Watch for a yellow or orange flame on a gas burner, where a healthy flame is mostly blue. Look for soot, black streaking, or brown staining around the boiler, the water heater, or the vent pipe. Rust or water streaks near the flue, and a flue pipe that looks loose or disconnected, are other red flags.
Pay attention to the pilot light. A pilot that keeps going out, or burns weak and flickery, can point to a draft or venting problem. A stale, stuffy smell in the utility area, or excessive moisture and condensation on windows near the equipment, can also be signs of poor combustion.
Then there is how you feel. Recurring headaches, tiredness, or nausea during the heating season, especially if they ease when you leave the house, deserve a closer look. Pets acting sluggish or unwell is another clue. None of these signs prove there is a problem on their own, but any of them is a good reason to have the system inspected.
A reminder: a lack of warning signs does not mean everything is fine. CO can be present with no visible clue at all, which is exactly why alarms and regular maintenance matter so much.
Snow, Ice, and Blocked Vents in Winter
Many modern high-efficiency boilers and water heaters vent through plastic pipes that exit through a side wall of the house, rather than through a chimney. These vent terminations sit close to the ground, which makes them vulnerable in winter. A heavy snowfall, drifting snow, or a plow pile can bury the opening and block the exhaust. Ice can also build up around the termination.
When a sidewall vent is blocked, many modern units will shut down for safety, and you may notice a loss of heat or hot water. That is the equipment protecting you. But not every system behaves perfectly, and not every installation is ideal, so it is smart to keep the area clear rather than relying on the safety shutoff.
After each snowstorm, take a moment to walk around the house and look at the vent and intake pipes on the exterior wall. Gently clear snow and ice away from them by hand or with a soft broom, taking care not to damage the pipe. Keep the area clear of shoveled piles, planters, and stored items. If you are unsure which pipes belong to your heating equipment, a technician can show you during a tune-up.
Dryer vents, furnace intakes, and other terminations on the same wall can be affected by snow as well, so it is worth checking all of them.
Carbon Monoxide Alarms: Placement, Testing, and Replacement
A working CO alarm is your most reliable early warning. The general guidance is to have one on every level of the home, including the basement, and one outside each sleeping area, so it can be heard from the bedrooms. Local codes and manufacturer instructions vary, so check the details for your alarm and your area. Many people choose combination smoke and CO units, which can be convenient, but make sure each one is rated for both hazards.
Placement matters. Follow the manufacturer’s instructions on height and distance from appliances. Do not put an alarm directly next to a fuel-burning appliance, in a very humid area, or right beside a vent, where it can give false alarms. Keep alarms clear of furniture, curtains, and dust.
Test your alarms regularly, usually once a month, using the test button. Replace the batteries when needed, and do not ignore a chirping alarm. A chirp can mean the battery is low, or it can mean the alarm has reached the end of its life. CO alarms wear out. Most have a limited lifespan, often between five and ten years depending on the model, and many show an end-of-life warning. The manufacture date is printed on the back, so check yours.
If you are not sure how old your alarms are, replace them. They are inexpensive compared with what they protect.
What to Do If the Alarm Sounds
Treat a CO alarm as real until proven otherwise. Do not open a window and go back to what you were doing. Get everyone, including pets, out of the house and into fresh air right away. Once outside, call 911 or your local emergency number. Do not go back inside until emergency responders say it is safe.
If anyone is feeling dizzy, nauseated, confused, or has a headache, tell the dispatcher. Those symptoms need to be checked by medical professionals even after you are outside.
After the emergency is handled, do not simply reset the alarm and move on. The cause needs to be found. Fire department or utility personnel may measure CO levels and may shut off equipment. Do not restart a boiler, water heater, or any suspect appliance until a qualified technician has inspected it and confirmed that it is safe to run. In some cases, a repair or replacement will be needed first.
A single brief alarm does not always mean a leak. Alarms can be triggered by low batteries, end-of-life, or real but temporary conditions. But because you cannot tell the difference on your own, the right response is always to treat it seriously, get out, and get it checked.
Annual Tune-Ups and What a Technician Looks At
The single most useful thing you can do for CO safety, beyond alarms, is annual service on your boiler and water heater. A good tune-up is not just a quick glance. A technician typically inspects the burner and flame, checks combustion, cleans parts as needed, examines the heat exchanger where it is accessible, looks over the flue and vent pipes for blockages, corrosion, and loose joints, and checks the safety controls.
They may also test the exhaust gases with an analyzer and look at the air supply to the equipment. For water heaters, they can check the draft hood or vent, the condition of the tank and connections, and the relief valve.
Fall is the best time to schedule this, before you start relying on the system every day. It is also a good moment to ask questions. If your home has been renovated, if you have added a new exhaust fan or sealed up the basement, or if your boiler is getting up there in years, mention it. Those details change what a technician should look at.
Regular service also tends to help with efficiency and reliability, so the visit is not just about safety. A system that is clean and adjusted properly usually runs better and breaks down less in the middle of a cold snap.
When Repair or Replacement Is the Safer Choice
Sometimes an inspection finds a problem that cannot be solved with a cleaning. A cracked heat exchanger, serious corrosion, a failing flue, or repeated combustion problems may mean the appliance should be repaired by a qualified technician or replaced. It can be tempting to put off that decision, especially when the weather is cold and budgets are tight. But a system that cannot be operated safely is not a place to cut corners.
Ask the technician to explain what they found in plain terms, show you the problem if possible, and walk through the options. Good technicians are happy to do that. If you want a second opinion, that is reasonable too.
Minutemen Sewer and Drain serves homeowners across Nassau County, Suffolk County, and Queens, and our team handles heating system work as well as plumbing. If your boiler is making odd noises, running poorly, or you just want it checked before winter, our boiler repair services are a good place to start.
If you have questions or want to schedule a visit, reach out through our contact page. And if an alarm ever sounds, the order is always the same: get out first, call 911, and deal with the equipment afterward.