young boy pinching his nose because of furnace smells

Phew, What’s That Smell? 4 Furnace Smells To Watch For

Furnaces heat and distribute air through your home. Sometimes, problems can occur with a furnace that result in unpleasant or weird odors, either radiating from the furnace itself or blowing out of the ducts and vents. Here are four different furnace smells and what you might want to do about them!

Common Furnace Smells

Gas Smell

This one is pretty straightforward: if you smell a sulfur or rotten egg odour coming from your furnace or vents, you may have a natural gas issue. Regardless of whether the smell comes from your vents or from the furnace itself, shut the unit off immediately. Leave your home as quickly as you can, making sure to turn the gas off on the way out if possible. Call your gas company — they will be able to safely shut the gas off to your home so that a technician can diagnose the issue.

Natural gas leaks can be the result of a cracked or otherwise damaged heat exchanger, or due to issues with the gas line itself. In either case, don’t try to diagnose the leak yourself. Trained technicians have the equipment and knowledge to fix whatever’s wrong safely, once the gas has been turned off.

Dusty Burning Smell

This is by far the most common of the furnace smells we encounter  — for many people, this smell is an annual occurrence. During the summer months, furnaces typically sit unused. In many homes, particularly homes with pets and families, dust will begin to build up in the furnace. Once autumn rolls around and the furnace kicks in, all that dust gets burned away. Unless the furnace has been cleaned prior to getting turned on, you can expect to smell a funky, burnt dust smell for a few minutes the first time you run your unit. There is little to no risk of fire or health concerns stemming from burnt dust. If the smell bothers you, you may want to book a furnace cleanup or tuning prior to turning your unit on for the first time. This ought to eliminate or minimize dust smells, while also ensuring your furnace is operating safely and efficiently.

Moldy, Damp, or Funky Smell

While furnaces typically don’t have issues with moisture buildup, it’s not unheard of, particularly in high humidity areas. If you smell a sour, earthy, or otherwise funky odor from your vents or furnace unit, you may have a moisture issue in your system.

Moisture is one of a few ingredients that contribute to mold and bacteria growth, the others being darkness, oxygen, and warmth. Your ventilation system has the last three items covered, so if moisture gets trapped in the system somehow, you can very quickly have a mold problem on your hands!

Before panicking, make sure that the source of the smell isn’t something more mundane. Are there any air intakes positioned near potentially smelly objects like garbage cans or compost bins? Is the smell localized to one room or area, or present throughout the home? Once you’re fairly confident that there aren’t any obvious sources for the odor, call a technician to inspect your vents and furnace. Fixing a mold problem involves removing the mold itself, as well as diagnosing and fixing whatever moisture problem is present. If the source of excess moisture is a leaky pipe or damaged roof, the repair is simple enough. If the air in your home is simply too damp, a dehumidifier attachment will reduce moisture content in the air, preventing mold as well as improving your home comfort.

Another possible cause of funky, sour smells in your ventilation system is pest infestation. Rodents and other small pests can cause all sorts of damage to the ventilation system. Their urine and feces can collect in air ducts, spreading foul odors and potentially dangerous microbes through your home. Pests can die and decay inside ducts as well. An inspection will quickly identify any pest issue you may have.

Chemical/Burning Plastic Furnace Smells

If you smell a strange, acrid, burning plastic smell from your furnace, you may have an electrical issue. Electrical components, particularly the blower fan, cycle on and off frequently. Over time, these components can wear out and become inefficient or perform poorly. As components wear out, they can begin to generate more heat than usual. This can sometimes cause burning smells as the materials in the fan motor overheat.

Another possible cause of a burning plastic smell involves frayed or poorly connected wires in your furnace. Either of these issues can cause short fuses, damage other furnace components, or even cause electrical fires. If you smell burning plastic, turn your furnace off immediately and call a furnace repair technician!

Read more about common furnace problems including unusual noises or how to choose a filter.

Dog covered by blanket when heat won't come on

My Heat Won’t Come On! What Do I Do?

Furnaces are the sort of thing you probably don’t think about until something goes wrong. When the weather’s nice and the sun is shining, we rarely stop to think about whether or not our furnace needs a tune-up or a filter change. Then, the cold weather hits, we flick the thermostat on, and… nothing. The heat won’t come on. Maybe you wait a few minutes to see if it just needs to warm up, but nothing happens. Now you’re in trouble – it’s cold outside and you have no heat!

Your top priority is to diagnose and fix the problem. You can’t go through a winter without heat, after all. But sometimes that’s easier said than done. Unfortunately, when the first big cold snap hits in autumn or winter, many Denverites find out their furnace either doesn’t work or doesn’t work well — all at the same time. Getting an appointment within 24 hours with a heating professional during peak season can get tricky — it’s one of the reasons Swan recommends getting your furnace tuned each Fall before the weather turns. That way, you have peace of mind that when the first snow falls, your furnace will come on without a hitch.

Find out how our monthly maintenance program can save you money and keep your heating and cooling systems running better, longer!

But we’re past that now. The furnace isn’t working and you’re getting chilly. What do you do? First, call for help. Even if you can’t get an appointment today, you will want to get booked in before someone else snags your appointment slot! In the meantime, your priority is to keep warm and comfortable until help arrives.

Use Alternative Sources When The Heat Won’t Come On

Provided your furnace is out but your electricity is still on, you have some options for keeping the house warm without a working furnace. In fact, most of us have a big heater right in the middle of our kitchens.

The Oven

Now, it isn’t safe or energy efficient to turn the oven on broil and leave the door open to heat your home. If you use a gas oven, you need to be extra-cautious. Without adequate ventilation, running a gas oven for hours can be very dangerous. However, the ambient heat from cooking a roast, for instance, will gently warm the kitchen and any adjacent rooms over the course of a few hours.

Space Heaters

Another option when your heat won’t come on is to use space heaters. Many of us have space heaters to supplement our furnaces in particularly cold areas of the home, or just as an emergency backup. If you don’t have one, you can find affordable and efficient infrared heaters for as little as $30 or so. These won’t put out enough heat to warm your entire home, but will provide enough heat to warm a single, smaller room, or part of a larger room. There are many varieties of space heaters. Be sure you know how to operate your particular heater safely, and don’t leave it unattended.

In case of a longer-term furnace outage, you may want to consider renting a more powerful heater. Be sure you understand how to safely operate any large heater. Many of them run on kerosene, propane, or other fossil fuels that will require adequate ventilation to operate safely.

Wood Stoves and Fireplaces

Finally, many homes still have fireplaces and wood stoves. If yours is in operating condition (don’t assume your chimney is clean and ready for a fire if you never use it — chimney fires are extremely dangerous!) and you have some dried firewood available, wood stoves and fireplaces generate plenty of heat and some cozy ambience to boot!

Dress for the Conditions

When your heat won’t come on, the cheapest way to stay warm is to bundle up. Pull out the heavy down blankets and Christmas sweaters! Layering clothing helps your body retain heat and dramatically lowers the need for heaters. You might not be totally comfortable in a cold house — bathing isn’t ideal, and fingers and toes still get chilly — but you can endure it by dressing for the conditions.

Use and Heat Fewer Rooms in Your Home

Heating an entire house is a big challenge. Furnaces make it easier and more efficient than ever — when they work. Heating an entire detached home with electric space heaters can get expensive quickly, and often means you’re heating rooms with no people in them. When your heat’s out, close off any rooms you don’t really need to use right away and focus on heating rooms where you and your family can camp out for a while. People generate a lot of heat, so a group of people in one room will lessen the load on any portable heaters you’re using. If you plan on using other rooms soon (like you’re headed to bed), just move heaters into the new room an hour before you plan on leaving the already-warmed area. As one room cools off, the next will warm up.

Take an Impromptu Staycation!

If all else fails and you won’t be able to get your furnace fixed and heat restored promptly, consider spending a night or two with friends or family, or at a hotel. This isn’t always feasible, but in some situations, like during a long-term winter power outage, it may be the safest and simplest way to stay warm.

Woman being kept awake by furnace noises at night

4 Furnace Noises (And What They Might Mean)

Background noise is a reality of modern living. From the buzz of your refrigerator’s compressor to the low hiss of your water heater, we hear a lot of sounds around the home. We become so familiar with these household noises that for many of us, a new or different noise from an appliance is our first sign that something’s going wrong. This is especially true when it comes to your heating and air conditioning systems! In this article, we’ll look at four common furnace noises and what they might mean for the health of your heating system. Remember that the only way to be sure of what issue your furnace has is to book an expert inspection. These tips should help point you in the right direction and assist you when describing the issue to your HVAC professional and deciding if furnace repair is needed.

Furnace Makes a Whistling Sound

One of the most common unpleasant furnace noises is a whistling sound. Whistling furnaces can be shrill and may be quite loud or fairly subtle depending on the type of furnace and the nature of the issue itself.

First, try to identify roughly where the sound is coming from. If you hear whistling in one room but not in any others, it may actually be a blockage or air leak in your air ducts or a partially closed air vent rather than an issue with the furnace itself. Sometimes, if a new furnace fan or furnace has been installed recently, the volume and velocity of air being blown through your home’s air ducts will increase. Normally this isn’t an issue, but in some cases the increased air pressure can expose gaps in your home’s ducts and create a whistling sound.

The blower itself could have a mechanical issue causing squeaking or whistling sounds, as well.

If the whistling sound comes from the furnace and not from a vent or duct, the problem is usually an airflow issue, though it could also be a mechanical problem with the blower itself. As a furnace blows warm air throughout your home, the air passes through a filter, then into your ducts and out of your vents. A clogged or dirty filter may reduce airflow through your system and cause whistling noises as the air forces its way through the filter. Loose bolts or other fittings on the furnace itself may also cause rattling or whistling noises.

One final possibility is that your furnace has a gas flow issue. A damaged or defective gas valve could be the culprit. Always leave gasfitting and valve repairs to a trained professional! Issues related to gas flow can be dangerous and should be inspected and fixed as quickly as possible.

Furnace Makes a Loud Buzzing or Humming Noise

While all furnaces generate some ambient noise, most of the time furnaces run quiet enough that it is not disruptive. Especially loud buzzing or humming, either when the furnace starts up or throughout its operation, can indicate a variety of mechanical or electrical problems. The main culprit would be an issue with your blower fan motor. If the sound is loudest during startup, this is very likely the reason. The fan motor itself may be dying, or the electrical components powering the fan may be worn out or faulty.

If the issue worn out or faulty electrical components are causing the issue, the buzzing or humming noise will be loudest at startup and typically diminish or stop once the fan is up to speed. This is because the fan draws the most power and is under the most strain when it starts. Once it’s running, the power draw drops significantly, so the noise will typically decrease as well. If it’s a blower fan issue, the noisiness may or may not improve after startup.

Replacing electrical components like a capacitor or transformer is fairly affordable. A service technician can quickly diagnose and replace the faulty component, often on the first visit. Replacing a blower fan is a more involved job that requires removing the existing fan and rewiring the replacement.

Furnace Makes a Banging or Booming Noise

Sometimes it’s hard to tell if a furnace is running louder than it ought to. If your furnace is making banging or booming noises, you’ll probably figure out pretty quickly that something’s wrong!

One cause for banging and booming furnace noises concerns your home’s air ducts. Just like whistling ducts, air pressure problems may be the cause of banging noises in your home. If your air ducts are undersized for the furnace or you have a clogged filter, the air pressure may be too extreme and cause the metal ducts to expand and contract, causing occasional loud bangs as the metal pops in and out of place. This is an annoying problem and may reduce the longevity of your system, but it’s not particularly dangerous to you or your family.

The second cause for banging or booming noises is more dangerous. If the source of the noise is the furnace itself and the noise occurs when the system starts (or shortly after), it may be what’s called a delayed gas ignition. Delayed gas ignitions occur when the gas to air ratio is poor (either too much gas or too much air in the mix) or the ignition is otherwise delayed by a faulty, worn out, or dirty component. Delayed gas ignitions can be dangerous for you and your furnace. Essentially, each banging noise from your furnace is the result of an explosion. This is because the gas cannot ignite until the gas to air ratio is within a certain range. A delayed ignition means that gas has had time to build up. Once it finally ignites, the excess gas burns very quickly, causing a small explosion. It’s like when you light a grill after the propane has been running for a few seconds.

Delayed gas ignitions risk damaging your heat exchanger, which can be very costly to repair or replace. Anything to do with gas flow issues is a safety risk and must be dealt with immediately! Fortunately, you can avoid encountering these issues (and save yourself a big repair bill) by scheduling annual furnace maintenance appointments. Our annual maintenance plan is an affordable way to extend the lifespan of your HVAC systems and prevent potentially dangerous issues like delayed gas ignitions from occurring.

Furnace Makes a Gurgling, Dripping, or Splashing Noise

This one might seem counter-intuitive. How can a fiery gas furnace be making watery noises? In most cases, these sorts of noises come from newer, high efficiency furnaces. Because of the way high efficiency furnaces vent exhaust fumes, they may produce condensation from moisture in the air that must be drained. When there’s an issue in draining this condensation, it may cause gurgling, dripping, or other watery sounds. Usually, these noises are easy enough to sort out. A full or clogged drain pan or a blockage in the drain pipe itself may be the culprit.

If you hear water sounds coming from vents or air ducts instead of the furnace itself, this could indicate a more serious moisture problem in your home. Be sure to get the issue inspected immediately, as moisture can cause very serious issues like widespread mold growth or even structural damage to your home.


Noises can tell you a lot about what’s going on with your furnace. (Furnace smells can give you a clue too!) Use the tips above to get a sense of what the issue might be. If you’re worried there is a serious issue or just want peace of mind that everything’s OK, schedule a furnace inspection or maintenance appointment with Swan!