Top 10 Questions About Furnaces

Customers ask a lot of questions when they call the office. Many times they want to know if they really need to schedule a service visit or if something they hear, smell or see is nothing to worry about. Here are the top questions and answers to whether you need service.


10. Can My Furnace Cause a Fire or Explode?

Heating equipment may be the 2nd leading cause of house fires, but that is mostly from space heaters. Furnaces are pretty safe, but they can catch on fire. One way a furnace can catch on fire is if there is a problem with the blower motor. It doesn’t happen a lot, but blower motors can stop working for some reason and cause the furnace to overheat. Furnaces also run on combustable gas, whether that is natural gas or propane. (Oil furnaces or burners are pretty rare in the Charlotte area where we are located, but a lot more common in the Northeastern United States). If something goes wrong with the supply line or a leak is created somewhere near the furnace, there is the possibility of explosion or fire. Chances are your furnace won’t catch on fire or explode. It is much more likely to just stop working properly. In fact, carbon monoxide is probably a bigger danger than fire or explosion.

Carbon Monoxide Alarm

9. Can a Furnace Leak Carbon Monoxide?

The short answer is yes. Carbon Monoxide is a danger with gas-fired furnaces. Incomplete combustion can create carbon monoxide in the furnace, but the furnace is designed to vent these gases safely out of the house. If there is a problem with the vent system, carbon monoxide can lead into the rest of the home. The most common venting failure is when the heat exchanger has become old and worn out. The heat exchanger is the metal part of the furnace that is heated by the burners. Air from the cool air return duct flows across the heat exchanger and is warmed before being distributed to the vents in your home. The exhaust gasses normally don’t ever mix with the air flowing to your heating ducts, but this can happen if there is a crack or hole in your heat exchanger. Instead of being sucked out through the venting system, carbon monoxide can leak into the air that is being circulated through your home. Because carbon monoxide is both deadly and impossible to detect by sight or smell, it is very dangerous. A damaged heat exchanger needs replacement to be safe.

You should always have at least one carbon monoxide detector in your home to help alert you in case a problem like this occurs. This is a good reason to have regular maintenance visits every year before the heating season as well, so that a technician can test for carbon monoxide leaks and problems that can cause them.

8. Why Won’t My Pilot Light Stay Lit?

Less of a concern than it used to be because there are no standing pilot lights on newer furnaces. So if you are wondering where your pilot light is on a newer furnace, you most likely have an electronic ignition system instead of a standing pilot light. However, some furnaces last a really long time, especially when they are only lightly used here during our mild Carolina winters. If you still have a furnace with a standing pilot light, then the most likely cause of the problem is a problem with the thermocouple, which is the part that checks to make sure the pilot light is lit before allowing gas to flow into the furnace. Thermocouples are exposed to the pilot light constantly and therefore will eventually wear out. The bigger question you may want to ask yourself if you have a pilot light furnace is if it is time to replace it with a much more efficient model that doesn’t needlessly burn gas to keep a pilot light lit all summer long.

7. Furnace Humidifiers – Lots of Questions

There’s not really one specific question here, but we do get asked a lot about furnace humidifiers. Are they safe? Should we use them? Will we create mold in our house if we use one? In the coldest part of the winter (usually January around Charlotte), the heat can run quite a bit in your home. This will dry it out more than your air conditioner running in the summer and can cause some discomfort. A humidifier can improve your comfort.

Inside view of a Trane Furnace

6. Why Won’t my Furnace Turn On?

There are many reasons that your furnace won’t turn on. Maybe the thermostat has a problem. Maybe the furnace isn’t getting a supply of natural gas. Or the problem could be with something mechanical in the furnace. It does seem strange that something just sitting there during the summer months won’t turn on when you need it when it first gets cold in the fall or winter. Scientist are constantly studying why things break, but it really comes down to entropy. As defined here, it basically means that the natural state of things is for them to decline into disorder or break. It takes effort to keep things from breaking, like maintenance on a furnace. So most likely your furnace won’t turn on because something has broken. Here are 6 Common Furnace Problems that could be the answer to this or the next question.

5. Why Won’t my Furnace Stay On?

This probably is a bigger head scratcher for most people because the furnace starts up, will generally blow a little warm air and then before heating the house to the desired temperature, shuts off. A few likely problems:

  • Overheating. Like a lot of appliances, your furnace has some safety built in. In this case, a heat sensor will shut the furnace down if things are not working right to prevent it from burning your house down. Oddly, one of the most common causes of this problem is failure to replace your air filters regularly which chokes off the cool air supply to the furnace.
  • A bad switch, sensor or thermostat. All are fairly simple repairs for a trained service technician, who will replace the bad part with a new one.

Water Dripping

4. Why is my Furnace Leaking Water?

If you have a high-efficiency gas furnace (90% or higher AFUE on the Energy tag) then the most likely cause is condensation. Normally, the condensation should be channeled to a drain. However, just like with air conditioning systems, condensation drains can become blocked and cause water to puddle. You should have a drip pan installed with a water sensor that shuts the furnace off to alert you to the problem..if your system was installed properly. Worse news would be that the heat exchanger has failed.

For conventional furnaces, this shouldn’t be a problem. If it is, then you probably have an improper installation of a flue pipe. Or, if you have a furnace humidifier, there could be some type of leak causing the problem.

Air Filters

3. Furnace Filter Questions

We get a lot of questions about furnace filters. How often should you change them? What is the best type to use? See our article about air filters.

2. Why is my Furnace Making Noise?

Some noises are normal. Others are a sign of trouble. Every heating system makes some noise. Depending on the location of the system, you may hear more or less of the normal operating noises. However, if you furnace starts making new or unusual noises, that is a sign something is probably wrong.

Furnace is making a loud noise when it starts

  • Your just hearing some expansion and contraction in the ducts or the air filter shifting as the air pressure changes. You can probably figure this out by standing near an air return when the furnace turns on.
  • There is a problem with your ignition system. Most likely dirty burners allowing gas to flow too long before ignition. Yes, what you are hearing is essentially a small explosion in your furnace burner chamber. Get this looked at right away. The force from this type of ignition can destroy your heat exchanger and require furnace replacement.

Furnace is making a buzzing noise

This is probably a problem with the blower motor. It may just need a little lubrication or it may need to be replaced. This could also be a transformer problem which would require a part replacement.

1. Furnace Smells

Noise is a pretty big worry, but a smell that seems to be coming from a furnace can also be a mystery. Some smells are less worrying and more perplexing. Here are a few of the common “my furnace smells” questions.

Furnace smells like something burning

Burning plastic, burning rubber, burning dust, cigarette smoke, or burning hair are all smells that can describe what your furnace smells like.

Burning dust is by far the best scenario and this is especially true if it only happens the first time you turn your furnace on after a long summer of dormancy. The simple explanation is that dust has accumulated on the inside of the furnace over months of non-use and when the furnace turns on, it actually does burn the dust. Some people describe this smell as burning hair which can cause some confusion.

A smell of burning oil, burning plastic or burning rubber is bad. Your furnace is probably overheating. The best thing to do is to shut it off immediately and call for a service visit.

Furnace smells like sulphur or rotten eggs or maybe skunk

Call your natural gas supplier to investigate immediately and follow their safety instructions. Sulphur or rotten egg smells are additives to natural gas so that leaks can be detected. A skunk smell could also be a natural gas leak, as skunk is very similar to the odor additives put in natural gas. A natural gas leak can be very dangerous, especially in an enclosed indoor space like where your furnace is located.

A skunk smell could also be from a skunk under the house or in your crawl space.

Furnace smells like fish

This might not be your furnace at all. A fish smell is often caused by electrical problems. The plastic used in electrical boxes, etc or in ceiling lighting covers can give off this fish-like smell when it becomes hot. Sometimes the furnace kicking in will spread the smell around throughout the house so you think it is a furnace or ductwork problem.

Another fish-smell source can be spray foam insulation. This doesn’t just pop up though, unless you’ve just had some renovations done and the foam recently installed.

In either case, it isn’t your furnace.

Need some Help?

If you are in the Charlotte metro area, we can help you with your furnace problem. Learn more about our furnace repair services or request an appointment today.

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