As a furnace cleaning company, we sometimes get calls for issues that would be more appropriately referred to a furnace repair company. Sometimes customers with furnace troubles attempt the process of elimination to reach a diagnosis, eliminating the least-expensive potential fix first (cleaning). Though there is some minor overlap between cleaning and repair, if your furnace is not working, your first call should be to a repair company.
With that said, furnace cleaning can help minimize the need for furnace repair, and on occasion, the recommended repair is simply to clean a specific malfunctioning (read: dirty) part. Additionally, furnace cleaning technicians are typically equipped to replace minor parts, such as flame sensors and hot surface igniters
Your Furnace's Sequence of Operation
To understand the relationship between furnace cleaning and the unit's smooth functioning, it helps to understand a furnace's "firing order," formally known as its sequence of operation. This is the series of steps a gas furnace runs through before generating heat. In a nutshell, once heat is summoned by the thermostat, the draft inducer motor begins whirring. The air pressure switch then monitors the air flow being generated by the inducer to make sure it is sufficient, and if it approves, a connection is made between the inducer and the hot surface igniter. The igniter then glows and the gas valve opens, creating a flame. The flame sensor, for its part, then asks, is there a flame? If the answer is yes, the process remains uninterrupted and heat is generated. If the answer is no, the system will shut down, in order to prevent the release of raw gas into the atmosphere with no flame to consume it. This process continues until the thermostat reaches the desired temperature.
Any interruption to this sequence of operation will effectively halt the furnace, and there are plenty of factors that can contribute to an interruption. If the draft inducer is compromised, for example, the pressure switch will not communicate to the igniter that everything is A-okay, and the igniter will not spark. Dirt and debris can play a major role in these interruptions. A furnace flue clogged with debris would prevent the inducer from creating enough draft to close the pressure switch, stopping the process before it even gets started. A worn or dirty flame sensor incapable of detecting a flame would result in the gas valve shutting off. You get the idea.
The Primary Goal of Furnace Cleaning
Despite furnace cleaning sometimes resolving what would seem to be repair issues, its chief aim is maintenance—helping to keep the system in working order by improving air flow through the removal of system-clogging debris. As explained above, a single dirty component can stop the heating process in its tracks. Maintaining system cleanliness will minimize disruptions to your home's heating.
An additional aim of furnace cleaning, and HVAC system cleaning in general, is the improvement of indoor air quality: by removing debris and contaminants from your furnace and other system components, you reduce the number of pollutants circulating throughout the system only to be expelled into your living space. That same debris that clogs up HVAC system parts and hinders air flow doesn't do your lungs any favors either.
Overlap Between Cleaning and Repair
If we refer back to our sequence of operation and the issues that can disrupt it, we have to consider that sometimes the problem is as simple as a single faulty part. Though the lifespan of a furnace is roughly 15-20 years, the lifespan of some individual parts is much shorter. The igniter and flame sensor, for example, have lifespans of only about 5-7 years, so it stands to reason you'll need to replace these before you replace the furnace itself. Because these parts are fairly easy to install and small enough to carry a sufficient stock, many furnace cleaning technicians will replace these, with the customer's approval, if they observe much wear on the part. The replacement of these components, in addition to capacitors and contactors, are about the extent to which furnace cleaning technicians will engage in parts replacement.
One of the biggest (and most dangerous) cleaning-related repair issues is when the furnace shuts down due to a clogged furnace flue. The flue, of course, is the channel or pipe through which harmful gases produced by the combustion of your furnace are exhausted to the outside. If the flue becomes clogged with animal nests, leaves, or other debris, harmful carbon monoxide can back up into your living space and put your family at risk. Furnace flues without caps are particularly susceptible to this hazard. Our technicians are frequently called to the homes of customers whose furnaces have been red-tagged and shut down by a repair company due to a blocked flue.
A surprisingly common contributor to furnace overheating and subsequent shut-down is a clogged air filter. If the filter is choked with dirt, air flow from the return duct into the furnace is restricted and can cause the high-limit switch to detect too much warmth and shut off the burners. A blanket of dust over the evaporator coil can have a similar effect, restricting air flow from the heat exchanger to the supply duct and causing a backdraft. Because the entirety of the HVAC system is dependent upon proper air flow, any hindrance to this flow in the form of dirt or debris can wreak havoc and lead to repair issues.
When to Call it When
If your furnace is not working, or not working well, your first call should be to a repair company. It may end up that the diagnosis involves the evaporator coil needing to be cleaned, or that the furnace flue is dangerously clogged, both of which you'd likely be referred to an HVAC cleaning company for. However, the diagnosis should come from a licensed HVAC repair technician. Sometimes similar symptoms can have different causes, so to rule out any other issues, a proper evaluation should be performed.
If you are looking for a cleaning of your furnace or furnace flue as part of routine maintenance on your system, or if you are looking to improve your indoor air quality by minimizing pollutants present within, call a furnace cleaning company. During the course of their service they'll make mention of anything they see amiss and refer you to a repair company if appropriate.
Wanna dig deeper? Download our free tipsheet: 5 Questions to Ask Before Hiring a Furnace Cleaning Company.
Many thanks to our technician Roy S for lending his expertise to this article.
Or rather, some stories. Everybody loves the before and after photos some companies offer after an air duct cleaning job. Customers like to see the results of the service and the accompanying assurance that their money was well spent, not to mention the visible affirmation that they'll be breathing cleaner indoor air. HVAC cleaning companies enjoy showcasing their work, and before and after photos provide explicit testimony of the benefits of the service. Below are a few examples, with context and caveats
The images above are from a 70-year-old home in St. Paul whose ducts had never been cleaned. The duct is a standard sheet-metal return, fairly easily cleaned with a multi-tentacled air whip such as the Viper Clean Sweep, our technicians' tool of choice.
The photos were taken (as all of ours are) with the technician's cell phone—not, as many customers assume, with a scope. The reason we opt for cell-phone photos over those of borescopes is due mainly to resolution, and ease: a cell-phone photo has a much higher resolution than that of a scope, providing a high-quality and detailed image. Cell-phone photos can also be shared much more easily, quickly sent from the technician's phone to the customer's e-mail. Finally, a visual representation of the condition of the ducts can be had more easily from an access point or vent than from deep within the duct (which would require the use of a scope), with the latter providing no obvious advantage.
The images above were taken inside a Minneapolis home built in the 1960s in which the trusses (the cavity between the main-level floor and the basement ceiling) were used for return air. This building practice was relatively commonplace until recently. These kinds of duct spaces can get quite dirty, due to the porousness of wood and the tendency of dust particles to coagulate within that space. That is to say, dust particles stick more easily to wood than, for example, to metal, and once one particle sticks, subsequent particles stick more easily, resulting in quicker and more abundant buildup than inside a metal duct. This cavity was also cleaned with the Viper Clean Sweep.
In cases of newly constructed homes (above), the ducts are often dusty with drywall particles, which are ubiquitous and stubborn. At first glance this debris may not appear as voluminous as that in some of the other photos. However, because drywall dust tends to collect so densely, it can be considered equivalent to twice its amount in run-of-the-mill household dust. Drywall dust is easily disturbed, and because its particles are so small and lightweight, once rendered airborne, they create a nuisance everywhere they settle—within HVAC system components, on your furniture, in your lungs.
You may notice in the image that a few larger (relatively) pieces have been left behind inside the ducts. These are heavier bits of concrete or rubble that, because of their weight, cannot be removed by duct cleaning tools. This is of little consequence—these are too heavy to become airborne and thus are not going to compromise indoor air quality.
Flexible poly return ducts (above) are commonly found in townhomes in Minnesota. That pictured is from a townhome built in the early 2000s. Because this particular duct was located in the main living space, the dirt within was an accumulation of debris generated over several years, from the kitchen, dining, and living areas. The after photo demonstrates the subtle power of the Viper Microline, a single-tentacled air whip perfect for smaller cavities. Because it is not as forceful as multi-tentacled air whips (or brushes), it does not harm flex lines, but its gentle and swift thrashing loosens debris from every nook and cranny.
Because debris from wood-floor sanding is easily airborne, it often finds its way into a home's air ducts (above). Like drywall dust, this debris tends to cling to the walls of the ducts and its removal requires a more advanced cleaning than that which simple air-pressure provides, such as a rotary brush or tentacled air whip. Our technicians prefer the latter, especially in rectangular ducts (as rotary brushes are circular).
A final word on before and after photos: those that you see online, for obvious reasons, tend to place toward the end of the best-to-worst spectrum, the above included. Though those included here are fairly typical jobs that our techs see regularly, there are plenty of others that are not so remarkable or exemplary, especially in homes whose ducts are cleaned regularly. The salient point here is that no matter what your ducts looked like before cleaning, the top-level cleaning, utilizing an advanced agitation method as opposed to simple air pressure, will get them picture-perfect after.
Wanna dig deeper? Download our free tipsheet: 10 Questions to Ask Before Hiring an Air Duct Cleaning Company.
Many thanks to our technicians Ben S and Roy S for providing photos and lending their expertise to this article.
It's a fair question, as the two are very similar, and in one case (the fireplace flue), they're the same. The two terms are often used interchangeably, even by industry insiders, as there is much overlap. But there are distinct differences between the two as well. Let's break it down
What's the difference between a chimney and a flue?
A flue is the channel, pipe, or tube through which gases and smoke travel from a source of combustion (fireplace, furnace, boiler) to the outside environment. It is usually a vertical channel, but in some cases, as in fan-powered PVC power vents on newer, high-efficiency appliances, the flue can be horizontal. But here we are speaking of the traditional draft-style flue. That is, those that rely on natural draft—the upward movement of air as a result of differences in temperature and pressure—to safely vent the products of combustion from the home.
A chimney is, on the other hand, in its simplest definition, the housing that encases the flue. It is usually made of masonry, brick, or stone. Its exterior, extending upward beyond the roof line, is generally what we think of when we consider chimneys. It's worth noting that a chimney that does not have a flue inside it or a liner is basically serving as the flue itself.
How do chimney sweeping and flue cleaning differ?
Bearing in mind that a flue is the path through which the byproducts of combustion vent to the outside, a "fireplace flue" is the same thing as what laypeople think of as a chimney—that structure which Santa will hopefully climb down later this month, if we're lucky. So, a fireplace flue cleaning and a chimney sweeping refer to the same process. During the service, the technician generally uses a stiff-bristled brush or other chimney cleaning system to brush the inside of the flue to remove creosote buildup from its walls.
A utility flue cleaning—as opposed to a fireplace flue cleaning or chimney sweeping—would be focused on the vertical flue associated with the furnace, boiler, or water heater. Because these appliances do not generate creosote (which is a byproduct of burning wood), their flues typically do not get as dirty as fireplace flues, and the buildup they do accumulate is not as hard or caked-on, so to speak.
For that reason, the tool of choice on a flue cleaning (though every technician is different) would be a tentacled air whip. Because these are powered pneumatically by air pressure rather than manually, they are highly efficient and are quite effective at removing the scale-and-sediment buildup prevalent within utility flues, as opposed to creosote, which requires more aggressive methods.
How are they similar?
The two processes are similar in that they are both designed to remove buildup and blockages from the inside of the flue to allow free and safe passage for the gases and smoke produced by combustion. In the case of blockage removal, the process is virtually identical, as the debris that blocks both fireplace flues and utility flues is almost always of the same origin: animal nesting. To remove it, the technician will break up the nest using whatever brush or whip will work most effectively, simultaneously sucking up the debris with a vacuum attached below. He'll then complete the job by thoroughly brushing (or whipping) the sides of the flue to remove any remaining or stuck-on debris.
Finally, no body of information remotely associated with flue or chimney health would be complete without reference to the importance of chimney caps. They're vital, and without them, your roof has a gaping hole, inviting all kinds of weather damage and critter entry. It's the single easiest and most cost-effective way to maintain your chimney—or flue!
Wanna dig deeper? Our flue cleaning service page has a detailed description of the process involved and tools used, as well as links for further reading.