Carbon Monoxide and Your Chimney: The Venting Hazard Lakewood Homeowners Miss
Most people think of a chimney as a fireplace concern, but the flue that vents your furnace and water heater is a carbon monoxide safety system. Here is how it fails on older Lakewood homes, and the warning signs to take seriously.
Your chimney is a safety system, not just a fireplace accessory
When people picture a chimney, they picture the fireplace, but on most Lakewood homes the chimney is doing a far more critical job year round: venting the combustion gases from the furnace and the water heater up and out of the house. Those gases include carbon monoxide, an odorless, colorless gas that is dangerous at low concentrations and deadly at higher ones, and the entire reason the appliances vent into a chimney is to carry that gas safely outside. When the chimney does its job, you never think about it. When the chimney fails to draft properly, those same gases can spill back into the living space, and because carbon monoxide has no smell, the first warning is often a headache, nausea, or worse rather than anything you can detect on your own.
This is the part of chimney safety that gets the least attention precisely because there is no fire to look at and no smoke spilling visibly into the room. A homeowner who never uses the fireplace still depends on the chimney every time the furnace cycles on a cold Lakewood night. That is why we treat the venting flue as seriously as the fireplace flue on every inspection, and why a chimney problem on a home with no fireplace at all is still a problem worth catching.
The orphaned flue, and why it haunts older Lakewood houses
One of the most common venting hazards on the west side is what the trade calls an orphaned flue, and it usually traces back to a furnace upgrade. For decades, a typical Lakewood home vented both its furnace and its water heater into the same masonry chimney flue, sized for the combined output of the two appliances. When the old furnace gets replaced with a modern high-efficiency unit, that new furnace usually vents out the side wall through a plastic pipe instead of up the chimney. That sounds like progress, and for the furnace it is, but it leaves the water heater venting alone into a flue that is now far too large for it, with none of the heat the furnace used to provide to drive the draft.
An oversized, cold flue does not pull the way it should. The water heater's exhaust, including carbon monoxide, rises slowly if at all, lingers, and can spill back into the basement instead of going up and out. The moisture in that exhaust condenses on the cold masonry too, corroding the flue and the liner from the inside over time. This is not a rare edge case in Lakewood, it is the predictable result of a very common furnace upgrade on a very common type of house, and most homeowners have no idea it happened. When we inspect a chimney on a home that has had a furnace replaced, checking whether the remaining appliance is now orphaned in an oversized flue is one of the first things we look at.
Warning signs, and the fix
There are signs a venting flue is not doing its job, and they are worth knowing because the gas itself gives no warning. Streaking or staining around the appliance connections, rust on the furnace or water heater vent or on the damper, a white crusty residue on the masonry where flue gases have condensed, moisture or a musty smell in the basement around the chimney, and of course any carbon monoxide alarm going off are all reasons to have the chimney looked at promptly. So is the simple history of a furnace replacement, since that is what creates the orphaned-flue situation in the first place. None of these should be ignored, because the consequences of a venting failure are not a nuisance, they are a health and safety risk.
The fix, when it is needed, is usually to reline the flue with a stainless liner sized correctly to the appliance that is actually using it, so the water heater or furnace vents into a properly sized passage that drafts the way it should. That is exactly the kind of work where the sizing has to be right, because a liner too large or too small is its own hazard, and it is why we install relines to NFPA 211 and verify the draft before we leave. The most important step, though, is catching the problem, which is why we check the venting on every chimney inspection and why a working carbon monoxide detector on every level of the house is non-negotiable regardless of what your chimney looks like.
Why detectors and inspections are partners, not substitutes
It is tempting to think a carbon monoxide detector makes a chimney inspection unnecessary, or the reverse, but the two do different jobs and you genuinely need both. A detector is your last line of defense, an alarm that warns you once carbon monoxide is already in the living space. An inspection is the line of defense before that, the one that keeps the gas from getting in at all by confirming the chimney is venting properly. Relying on the detector alone means waiting for a hazard to reach you before you know about it, while relying on the inspection alone leaves you without a backstop if something changes between visits. Together they cover both ends: the inspection prevents the failure, and the detector catches it if prevention is ever undone.
There are practical rules for both. Put a carbon monoxide detector on every level of the house and near the sleeping areas, test them on a schedule, and replace them at the interval the manufacturer specifies, because the sensors wear out. On the chimney side, have the venting flue inspected yearly, and especially after any change to the appliances, since a furnace or water heater swap is exactly what creates the orphaned-flue hazard in the first place. In a Lakewood home full of older masonry chimneys and decades of appliance upgrades, that combination of a working detector and an honest yearly look at the flue is the most reliable protection there is against a gas you cannot see or smell.
If your Lakewood home has had its furnace replaced, or you see rust, staining, or condensation around where the furnace or water heater vents, the chimney is worth an honest look, because a venting failure carries a carbon monoxide risk you cannot smell. Call 740-430-5989 for an inspection, and keep a working CO detector on every level either way.
When you are ready, call 740-430-5989 for a chimney inspection.