Cracked Heat Exchangers

Scam alert! This heating season, numerous Dayton heating contractors are lying about cracked heat exchangers in an attempt to sell more furnaces. We give free second opinions on cracked heat exchangers. In a typical season, our NATE certified furnace technicians confirm less than 10% of these as real cracks. The other half turn out to be unethical tactics to sell new furnaces. This fall, the poor economy has pushed unethical contractors even further. So far this season, we have run at least fifteen second opinions on cracked heat exchangers and we have yet to confirm a single crack!

In this post, I’ll share a few tips that can help homeowners recognize heat exchanger fraud. First let’s have a quick primer on the terminology and function of furnace heat exchangers.

The heat exchanger plays a central role in any furnace. It separates the warming flame from the air in the home. The burning fuel warms the heat exchanger which in turn warms the air in your home.

What are the dangers of a cracked heat exchanger?

Many people in the Dayton and Cincinnati areas heat their homes with fossil fuels (natural gas, propane, or fuel oil). When fossil fuels burn they produce fumes containing carbon monoxide, carbon dioxide, water vapor, and soot. A furnace depends on the heat exchanger to contain these dangerous fumes and safely conduct them to the chimney while transferring the valuable heat into the home. If the heat exchanger is compromised by a crack or rust, flue gases and carbon monoxide will leak into the home resulting in illness and possibly death of the occupants.

What is the cause of heat exchanger cracks?

Overheating causes nearly all premature heat exchanger cracks. When a furnace cannot get enough airflow, the heat exchanger overheats and suffers excess stress from expansion and contraction. Over time, the heat stress causes cracks near weak areas such as bends or welds. The most common cause of an overheated heat exchanger is as simple as a dirty air filter. A clogged air filter restricts airflow through the furnace, overheating the heat exchanger, and eventually resulting in stress cracks.

An over-sized furnace can also cause overheating and heat exchanger cracks. We frequently see too much furnace with too little ductwork or too little house. A furnace with under-sized ductwork will lack proper airflow and suffer a similar fate as that of a clogged filter. Rusted Trane Heat Exchanger

The situation of a large furnace on a small home will take a bit more explanation. Natural gas combustion produces  water as one of its byproducts. When a furnace first lights, the flame impinges on the cold heat exchanger and water vapor from the flame actually condenses on the inside of the heat exchanger. After just about ten minutes of run time, the heat exchanger reaches operating temperature and the condensation evaporates. An over-sized furnace heats the home so quickly that the furnace shuts off after only a few minutes, so the heat exchanger stays wet and rusts from the inside out. The frequent cycling of an over-sized furnace also increases the expansion – contraction heat stress on the heat exchanger.

Proper diagnosis of a failed or cracked heat exchanger.

Diagnosis of a heat exchanger crack typically starts with a no-heat service call. A cracked heat exchanger allows air from the furnace blower to interfere with the flame causing it to flutter or even roll out. This trips a safety switch and shuts down the furnace. Beware of an unethical technician who finds a crack with a camera on a furnace that seems to be running just fine. While big cracks start as small ones, some technicians will search for anything that looks like a crack in order to sell a new furnace and earn a commission. We’ve even seen some technicians draw a line on the heat exchanger with a pencil, show the homeowner the line on a fiber optic camera, and convince them they are looking at a dangerous crack. In 2009, the AHRI published a guideline for inspecting heat exchangers which states: “Any crack or hole that is big enough to affect combustion will be easily visible to the naked eye. Do not use water, cameras or smoking agents to check for leaks. Furnace heat exchangers joints are not hermetically sealed, so a small amount of leakage is normal.”Cracked Heat Exchanger

In most cases, a true crack will disrupt the flame or set off a carbon monoxide detector in the home. If you suspect a false diagnosis, call us for a free second opinion.

If a technician has condemned your furnace due to a cracked heat exchanger, I would suggest explaining to the technician that you will want to see the crack with your own eyes when they remove the furnace. An honest company should have no problem standing behind their diagnosis. With the heat exchanger removed, the crack should be obvious even to the untrained eye as in this picture. If the problem is not evident, make the company reinstall your old furnace and report them to the Better Business Bureau .

Typical cure and cost

Unfortunately, heat exchangers cannot be repaired. When a heat exchanger cracks or rusts through it must be replaced. Because the heat exchanger is at the center of the furnace, nearly the whole furnace must be disassembled. Even if the parts are covered under warranty, the labor and freight will start around $500. Without a warranty, a heat exchanger replacement could run as much as $2,000 (more than the cost of a new entry-level furnace).

The problem with replacing a heat exchanger is that the central cause of the problem is not addressed. In my opinion, heat exchanger failure is usually due to the furnace being oversized for the house or the duct work. The best solution is to replace the whole furnace with a right-sized furnace (typically 1-2 sizes smaller). When you add up utility rebates, tax credits, factory rebates, and the energy savings of a properly sized furnace, a furnace replacement can actually be cheaper than repairing the old furnace.

If you would like more info on cracked heat exchangers or if you need to schedule a free second opinion, feel free to call our office at 937-748-0220 or contact us through this website.

David Watkins