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The Hazards of Heat: Is Your Furnace Safe to Use?

We can experience some brutally cold winters here in Michigan, and as such adequate heating is crucial to our everyday comfort come that time of year. However, furnaces are complex systems and failing to keep up with proper maintenance can negatively impact your safety as much as your wallet. Having your furnace inspected by Technical Hot & Cold before you have to use it doesn’t only help you to save money on repair costs and energy bills, but it can also save your life. Isn’t that worth the $69 we charge for it?

Let’s take a look at the most dangerous safety hazards that furnaces can pose.

Carbon Monoxide

Carbon monoxide (CO) is a byproduct of any equipment that creates heat by burning fossil fuel, including furnaces that run on natural gas. When inhaled, it leeches oxygen from the body which can cause serious damage to the brain, heart and other organs. The scariest part of carbon monoxide is that it’s both colorless and odorless, often going undetected until it’s too late, and resulting in about 500 deaths and 15,000 emergency room visits per year according to the Center for Disease Control (CDC).

Cracks in your furnace’s heat exchanger are most commonly to blame for carbon monoxide leaks, as this component is responsible for separating fume exhaust from the “clean” heated air that gets distributed throughout your home. Even though carbon monoxide can’t be seen or smelled, there are a few ways to detect a leak:

  • Yellow burner flame (it’s supposed to be blue)
  • Streaks of soot around your furnace
  • Excessive moisture on nearby walls, windows and other cold surfaces
  • Excessive rusting on flue pipes and other pipe connections
  • No upward draft in your chimney
  • Water leaking from the base of your chimney, vent or flue pipe
  • Rust on the outside portion of the vent pipe

Carbon monoxide is measured in parts per million (PPM), and it doesn’t take much of it to be harmful. To put it in perspective, oxygen normally comprises about 200,000 PPM of the air we breathe. A CO concentration of just 70 PPM is enough to cause negative symptoms in healthy adults like headaches, nausea, confusion and more within minutes, while a CO concentration of 400 PPM is enough to cause unconsciousness and death within a couple of hours.

THC takes great care to ensure that your family is kept safe from carbon monoxide poisoning by checking CO PPM levels in five key areas: ambient air, mechanical room, burner area, supply air stream and undiluted flue gas.

  • Ambient air: This is the general air throughout your home. If you or someone in the house frequently smokes cigarettes or burns scented candles indoors, it’s common for us to measure CO concentrations between 2-6 PPM. Anything above 6 PPM is considered unusual and will be addressed immediately.
  • Mechanical room: This is the area around your furnace. If CO PPM levels read higher here than in the ambient air of your home, this is considered unusual and will be addressed immediately.
  • Burner area: This is the area of the furnace that produces carbon monoxide as a result of burning fuel to create heat, which is normal. A higher level of CO PPM here than in the ambient air may indicate that combustion products are not moving towards the burner and heat exchanger like they should be, and we might have to make an adjustment.
  • Supply airstream: This is the “clean” warm air that gets distributed by the blower through the ductwork and into your home. An increase in CO PPM levels here may indicate a flaw in the heat exchanger, and we might have to perform a repair or replacement.
  • Undiluted flue gas: This is the raw gas fuel running through the flue pipe on its way to the burner. It’s normal for most modern furnaces to have a CO level of less than 50 PPM in the flue, and older natural draft units can safely skate by with levels as high as 200 PPM. However, a furnace with CO levels higher than 200 PPM in the flue should never be in operation without being adjusted or repaired first.


Furnaces produce heat by burning a mixture of air and fuel and use an actual flame to do it. When dirt, grime, grease and other contaminants are allowed to gunk up the burner, they can inadvertently cause a house fire. Other common fire safety hazards with furnaces are frayed wires and corroded electrical components. Addressing these things should always be handled by professionals like THC who have the proper equipment, training and experience to perform the inspection and any needed repairs safely.


The natural gas that powers your furnace is highly flammable. If allowed to leak throughout your home via a ruptured gas line, even a small amount has the potential to cause an inadvertent explosion should it come into uncontrolled contact with another active ignition source.

The good news is that natural gas is a little easier to detect than carbon monoxide, although just as dangerous. That being said, any gas line leaks and repairs should always be handled by one of the professionals at THC. Here are a couple of warning signs:

  • Smell of “rotten eggs” or “garbage”
  • Hissing or whistling noises near the furnace area
  • Unexplained discoloration or death of houseplants

If you suspect that there might be a natural gas leak in your home, do not do any of the following:

  • Turn on any electronics or appliances (like a stove burner)
  • Turn on the lights in any room
  • Light a match or candle
  • Turn on your furnace
  • Start your vehicle if it’s in the garage

Professional HVAC technicians like Technical Hot & Cold know what furnace safety hazards look like on the technical level and can correct them before anyone gets hurt. Ready to schedule a furnace inspection or have questions? Give us a call at (734) 326-3900 or click the button below!

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