How Do I Know I Have a Cracked Heat Exchanger?

In most cases you will not know for certain. A crack in a heat exchanger is hidden inside the furnace, and only a licensed technician with the right tools can confirm one. What you can do is recognize the warning signs and act on them promptly.

If a carbon monoxide alarm sounds or you suspect a crack, shut the furnace off at the thermostat and the furnace switch, get everyone out of the house if anyone feels unwell, and call a licensed technician before running the furnace again.

What the heat exchanger does

In a gas furnace, the burners fire inside sealed metal chambers called the heat exchanger. The blower pushes your household air across the outside of those chambers, where it picks up heat, while the exhaust from combustion stays inside and is vented outdoors. The whole design depends on those two air streams never mixing.

A crack or hole breaks that separation. Combustion gases, which include carbon monoxide, can then end up where they should never be. Carbon monoxide has no color, smell or taste, so you cannot count on your nose.

Warning signs worth noticing

None of these proves a cracked heat exchanger, since other furnace problems can cause them too, but each one is a reason to have the system inspected.

• Soot on or around the furnace, which suggests combustion is not happening cleanly.
• Heavy rust, flaking metal or corrosion on the furnace or its vent.
• An unusual chemical or sharp odor while the furnace runs.
• Moisture or water pooling around the furnace. This can also come from condensate drains or a humidifier, so it needs a technician to sort out.
• Anyone in the home feeling unwell whenever the heat is on, especially if they feel better after leaving the house.

Why the signs are not a diagnosis

A crack can be small and hidden. A furnace can show none of the signs above and still have a problem, and a sooty furnace can turn out to have something simpler. That is why guessing, or going by how the flame looks, is a poor plan. Professional inspection is the reliable answer.

Technicians use inspection cameras and combustion analyzers to look inside the exchanger and to measure what is leaving the flue. That is a different level of information from anything visible outside the cabinet, and it is why an inspection is worth the appointment even when everything looks normal.

What to do if you suspect a problem

Turn the furnace off. Open a few windows if it is safe to do so. If anyone feels unwell, go outside, and call emergency services if someone is seriously ill. Then call a licensed HVAC technician and leave the furnace off until it has been inspected. Do not try to repair or seal anything yourself.

If the technician does find a crack, the usual options are replacing the heat exchanger or replacing the furnace, and the right one depends on the furnace's age and condition. Ask for the findings in plain terms, and ask to be shown what they found.

Lowering the risk

Heat exchangers wear out. Most furnaces last around 15 to 20 years, and metal that has been heated and cooled thousands of times can eventually fatigue. Restricted airflow makes it worse, because a furnace that overheats stresses its metal, so change the filter regularly and keep vents open.

Keep working carbon monoxide alarms on every level of the house and near bedrooms, and test them and replace them following the maker's instructions. An alarm is your last line of defense and it costs very little.

Air-Tech's technicians can inspect your furnace and tell you what they find. If you have a warning sign, or just have not had the furnace looked at in a while, call (509) 392-2021. The office is open weekdays 8 to 5, and emergency service is available around the clock.