By Johnathan Mason, Ace Chimney Service.
Of everything we check on a chimney, the one that matters most is whether combustion gases are leaving the building. Carbon monoxide has no smell, no color, and no taste, and the early symptoms look like a winter cold. A chimney is the system that carries it out, which makes chimney condition a carbon monoxide question as much as a fire safety one. Here is what every household in Crystal Lake should have covered before heating season.
Where does carbon monoxide come from?
Any appliance that burns fuel produces it: a wood fireplace, a gas fireplace or insert, a furnace, a water heater, a gas range. In normal operation the venting carries it outside and nobody is exposed. Problems start when the venting is blocked, cracked, disconnected, or when the house pulls the exhaust back down the flue instead of letting it rise.
The chimney faults that cause it
- A blocked flue — an animal nest, leaves, or a collapsed liner section.
- Cracked flue tiles letting gas pass into the chimney chase and from there into the house.
- A damper left closed or stuck partly shut.
- A disconnected or corroded appliance connector at the furnace or water heater.
- Negative pressure in a tight house reversing the draft.
- An oversized or cold flue that never establishes an upward draw.
Know the symptoms
Headache, dizziness, nausea, fatigue, and confusion are the common early signs, and the detail that gives it away is that they improve when you leave the house and return when you come back. If more than one person or a pet is affected at the same time, treat it as carbon monoxide until proven otherwise. Get everyone outside into fresh air first, then call 911. Do not go back in to open windows or investigate.
Alarms are not optional
Illinois requires carbon monoxide alarms within a set distance of sleeping areas in homes with fuel-burning appliances or an attached garage. Beyond the legal minimum, put one on every level of the house, test them monthly, and replace the unit itself at the end of its service life — sensors expire, typically after several years, and a dead sensor in a working-looking alarm gives false reassurance. Check the date printed on the back of yours this week.
What an annual inspection actually protects
This is the honest reason we push annual service. A sweep removes creosote and reduces fire risk, but the inspection alongside it is what confirms the flue is open, the liner is intact, the damper works, and the appliance connections are sound. Those four things are what stand between combustion gases and your living room. Book a chimney inspection before the furnace comes on, and see the chimney services hub for the full list of what we cover. Prices are published on the pricing page.
Booking in Crystal Lake
Ace Chimney Service has served Crystal Lake and McHenry County for 29 years. Insured and bonded, price up front, seven days a week from 7 AM to 7 PM. Call (815) 320-0883.
Frequently asked questions
Can a wood fireplace produce carbon monoxide?
Yes. Any combustion produces it. A wood fire with a blocked or faulty flue is a genuine exposure risk.
Where should carbon monoxide alarms be placed?
Near sleeping areas as Illinois requires, and ideally on every level of the home. Follow the manufacturer instructions for height and distance from appliances.
Do carbon monoxide alarms expire?
Yes. The sensing element has a limited life and the unit should be replaced at the manufacturer end-of-life date, which is printed on the housing.
My alarm went off but I feel fine. What do I do?
Get everyone outside and call 911. Do not assume it is a false alarm, and do not re-enter until responders say it is safe.
Is a gas fireplace safer than a wood one?
Neither is inherently safe or unsafe. Both burn fuel and both depend on sound venting. A gas appliance with a blocked vent is just as dangerous.
Can I detect carbon monoxide by smell?
No. It has no odor at all. Any smell you notice near a fireplace is smoke or fuel, not carbon monoxide, and an alarm is the only reliable detection.
Does an inspection test for carbon monoxide?
An inspection verifies the venting path and appliance connections that prevent it, and we flag anything we find. Continuous monitoring is the job of your alarms.
Do you serve Crystal Lake and the surrounding towns?
Yes. We are based in Crystal Lake and serve the whole of McHenry County, including Algonquin, Cary, Woodstock, McHenry, and Huntley, seven days a week.
Published August 22, 2026