I want to start this issue with something a couple shared with me, not something I found myself.

Because sometimes the most helpful story isn’t the one from my files.

It’s the one a homeowner hands you, almost in passing, while you’re both standing in a house they are looking at buying.

I was walking a buyer through an inspection a while back, and partway through, the conversation drifted to the house they’d just sold.

They’d put in a high-efficiency furnace the fall before.

A real upgrade.

The kind of thing you list as a selling feature. And it was one.

It just came with a catch nobody had mentioned to them.

That winter, when it got really cold, they started getting headaches. Nothing dramatic. The kind of thing you blame on dry air, a cold going around, or just being tired. It came and went, and they lived with it for weeks before anything changed.

Eventually, they called their furnace technician back out.

He found the problem.

The exhaust vent — one of those white plastic pipes that runs low on the outside wall — had partially iced over. Not fully blocked. Just restricted enough that some of what should have been venting outside was finding its way back in.

The furnace wasn’t broken.

It was doing what it was built to do.

The problem was the vent, the ice, and a house that didn’t have the right warning system in place.

Here’s the part that should worry you a little.

This isn’t a story about a bad furnace.

It’s not even necessarily a story about an installer who cut corners.

This is what a correctly working high-efficiency furnace can do in the wrong conditions.

Older furnaces often vented through a metal flue up through the roof. Many high-efficiency furnaces vent through plastic pipes that exit low on an exterior wall.

That means the exhaust vent can end up right where snow, drifting, ice, landscaping, leaves, or stored items can block or restrict it.

And most homeowners don’t think to check it.

It’s not a filter.

It’s not something that smells bad.

It’s not a flashing warning light.

It’s just a pipe on the side of the house.

And that’s exactly what makes it easy to miss.

Carbon monoxide doesn’t announce itself. You can’t see it. You can’t smell it. You can’t taste it.

The symptoms can also feel ordinary at first — headache, nausea, fatigue, dizziness, or just feeling “off.” Almost like you’re catching the flu.

So the furnace can be heating the home normally while the house is quietly developing a serious safety concern.

That family had no idea that upgrading their furnace created something new to watch for.

Most homeowners don’t.

This isn’t new information for me.

I carry a CO tester on every inspection I do.

And FYI: Most older homes don’t have one

So where should they be?

If your furnace, water heater, fireplace, boiler, or any fuel-burning appliance is in the basement, that level needs its own CO detector.

A detector upstairs is not the same thing as having protection near the source.

That doesn’t mean putting it directly above the furnace or right beside the appliance. A little distance is important so the detector can read the room properly and avoid nuisance alarms from normal startup conditions.

The simple version:

Every level needs coverage.

Especially the level with the furnace.

This one matters at night.

Bedroom doors are often closed. People are asleep. Nobody is walking around noticing symptoms.

A CO detector needs to be close enough to wake people up through a closed bedroom door. Or better yet, install one in each bedroom.

If the home has bedrooms in different areas — for example, a primary bedroom on one side of the house and kids’ rooms on the other — each sleeping area needs nearby coverage.

One detector in a random hallway may not be enough.

This is the one almost nobody checks.

Carbon monoxide detectors don’t last forever.

The sensor inside the unit wears out over time. Many CO detectors are only rated for about 5 to 10 years, depending on the manufacturer.

And this is important:

A green power light does not mean the sensor still works.

It usually means the unit has power.

That’s not the same thing.

Check the manufacture date or expiry date. If it’s past its service life, replace it.

Take a few minutes and check your home:

✅ Do you have CO detection in each bedroom, if required in your area?

✅ Do you have CO detection on every level of the home, including the basement?

✅ Do you have CO detection near fuel-burning appliances, but not directly beside the furnace?

✅ Are detectors installed according to the manufacturer’s instructions?

✅ Are the detectors still within their service life?

✅ Have you checked the manufacture date or expiry date on the back of each unit?

✅ Do the batteries need to be replaced?

✅ If you have a high-efficiency furnace, are the outside intake and exhaust pipes clear of snow, ice, leaves, stored items, or shrubs?

A green light usually means the unit has power. It doesn’t always mean the sensor is still good.

Check the date.

Check the placement.

Check the vent pipes.

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Want to learn more about Carbon Monoxide and CO Detectors?

NFPA — Carbon Monoxide Safety
A clear homeowner-friendly overview of CO safety, alarm placement, and why carbon monoxide is so dangerous.
https://www.nfpa.org/education-and-research/home-fire-safety/carbon-monoxide
CPSC — Carbon Monoxide Alarms
Helpful guidance on CO alarm placement, testing, batteries, and replacement.
https://www.cpsc.gov/Safety-Education/Safety-Education-Centers/Carbon-Monoxide-Information-Center/CO-Alarms
CDC — Carbon Monoxide Poisoning Basics
A plain-English explanation of CO poisoning symptoms and why CO can be so hard to recognize.
https://www.cdc.gov/carbon-monoxide/about/index.html

There’s one simple maintenance task that can help your water heater last longer.

Most homeowners know they should do it.

But 99% of people never do it. Do you?🏠💧