Facebook tracking pixel
(707) 539-4533 |  Sonoma Napa and Marin Counties

updated 4/18/23

If you’re a homeowner in Santa Rosa, your HVAC system’s ductwork plays a vital role in keeping your home comfortable. While your air conditioning or heating unit may get all the attention, the ducts running through your house are just as essential. Without ductwork, your HVAC system would not be able to distribute air to every room, rendering it useless. Maintaining your ductwork is crucial to the efficiency and longevity of your system, and neglecting it can lead to increased energy bills and decreased airflow.

Diligent care keeps your furnace doing what it’s supposed to do best: warming your building and keeping you toasty during chilly weather. However, several problems can prevent your furnace from operating as it should, and the more you learn about them, the better prepared you will be to identify them and find solutions should they ever occur. One of the most common troubles that plague furnace owners throughout the United States and beyond is that of a furnace that leaks air from the ducts. Leaking ducts can stop your furnace from warming the air in your home adequately—although they will not prevent it from running and wasting energy. As a result, leaks can cost you a lot of money over time and still leave you shivering. One questions our clients often ask us is whether they should use mastic or furnace tape to fix leaks. The answer may surprise you.

What Are Mastic and Furnace Tape?

Firstly, let’s take a more in-depth look at what mastic and furnace tape are so that we can compare them. Those of you who do not yet possess detailed HVAC knowledge might never have heard of either of these tools before, so it’s important to start with the basics. Here they are:

  • Mastic is a form of construction adhesive used in a wide variety of home improvement tasks. It is typically found holding tiles together in floors, walls, and ceilings. Mastic may also be used to join panels made of plywood, concrete, or even leather and certain textiles. There is a specific form of mastic known as duct mastic that is commonly used to seal ducts in HVAC systems.
  • Furnace tape is a term referring to several different varieties of foil and metal tapes coated with adhesive on one side. This tape is almost exclusively used for sealing ducts. Depending on the quality of the tape, it can last for long periods of time.

You can use each of these tools in certain cases, but choosing between them depends on specific circumstances. In the following paragraphs, we will examine several considerations that can (and should) affect your choice.

Wait a Second—What about Duct Tape?

Hang on, did we hear you right? You want to use duct tape to fix leaks in your ductwork? Wait for a second—it sounds reasonable when you put it like that. Too bad “duct tape” is a misnomer. It turns out that duct tape is actually the last thing you should use to try sealing your ducts. It isn’t even approved for use on them. Whoever came up with the name for it probably just had a cruel sense of humor.

Don’t get us wrong: duct tape can be exceptionally useful in a wide variety of tough home improvement projects. However, it isn’t designed to withstand the heat and dust that tend to be present in an HVAC system for long periods of time. In fact, duct tape will probably only solve your problem for a couple of days, tops. Of course, that’s utterly hypothetical since you should never use an unapproved project on your ducts in the first place. If you did, the duct tape would probably melt and could even become a safety hazard—just trust us and don’t try it.

So—Mastic or Furnace Tape?

Let’s return to the matter at hand—the big showdown; the battle royale. Two home improvement products enter, and one home improvement product leaves! Just kidding. This isn’t life or death. Both mastic and furnace tape are specifically designed to seal leaks in HVAC ducts. You can use either one without courting disaster. However, just as we said before: either product may serve you better in specific scenarios. Here’s how to know which one you should choose for the leaks in your ducts:

  • How much do you care about appearances? Mastic is reliable, but it can also look a little bit sloppy to have gobs of paste holding your ducts together. Tape, on the other hand, can provide a clean aesthetic and give your ducts some class—assuming you’re worried about visitors judging your ducts.
  • How much can you afford to spend? Here’s the thing about furnace tape: it’s cheaper than mastic, but only on the low end. High quality furnace tape tends to be more expensive than mastic. That said, most licensed contractors advise against using low-quality furnace tape because it rarely lasts longer than a few years. If you want to avoid replacing it on a semi-regular basis, either go with mastic or invest in some primo furnace tape that will stand the test of time.
  • What materials are you most comfortable handling? You might not be the kind of person who likes to get their hands dirty—in which case, mastic is probably not for you. Then again, if you’re into arts and crafts, you can consider it a creative project. It’s really up to you.

Mastic and furnace tape each have unique properties that can make them better for some HVAC owners than for others. Review the above information before you hit up the hardware store, and you should be able to select the tool that best fits your style and budget.

How (and When) to Repair Your Ductwork at Home

While your air conditioner or furnace might be the star of your HVAC system, the ducts running through your house are at least as important – if not more so! Without the ductwork, your heating and cooling units would have no way to actually transfer air into every part of the house, making them useless. Besides, while air conditioners, heat pumps, and furnaces only last about 15 years or so, your ducts will continue to be usable indefinitely as long as you make sure they’re taken care of.


Ductwork doesn’t require nearly as much maintenance as HVAC units since there are no moving parts inside, just the big metal pathways running through the ceiling. However, that doesn’t mean you can just leave them alone forever. Ducts still need a little care and attention every once in a while, and letting problems build up in your ducts can have a significant effect on the efficiency of your system. Even the smallest leak in your ductwork can allow air to escape, cutting the airflow of the HVAC system and reducing its efficiency. Heating and cooling systems also rely on the pressure in your ducts to keep the air moving quickly, and a hole can cause that pressure to drop. If you notice a sudden spike in your monthly power bills, the culprit could very well be a leak in your ductwork.


In this post, we’ll go over a few things you need to know before attempting to repair your ducts. We’ll also talk about when you should just get professional help instead of trying to handle it all by yourself since ducts can be pretty fragile.


How to Tell if Your Ductwork Has a Hole

It’s safe to assume that most of us have better things to do than conduct full inspections of our ductwork every once in a while, so you’ll have to analyze the performance of your HVAC system to recognize when the ducts have a leak. Here are a few different signs that could mean you have a hole somewhere in your ductwork:


Increased Energy Bills – This is one of the most common signs that something is wrong with your heating and cooling system. When your air conditioner or furnace loses efficiency, it’s forced to work harder, turning on more frequently and staying on for much longer. That means it needs to use more electricity every month, leading to sudden spikes in your energy bill. Unfortunately, increased power bills are a symptom of quite a few HVAC-related issues, including a hole in the ducts. It can be difficult to tell where the problem is coming from, so we recommend hiring an HVAC professional to inspect the whole system and identify what exactly is going wrong.


Warm or Cold Spots – If your HVAC system is working properly, every room in your house should be more or less the same temperature. There are a few other factors that affect the temperature in a room, including the elevation, insulation, or the number of windows, but you shouldn’t see a significant difference when walking from room to room. If you notice that a certain section of your house is abnormally warm or cold, the culprit could be a leak in your ducts preventing temperature-controlled air from reaching the vents.


Dust – Keeping the house clean from dust is a constant battle, but it should be a winnable one. If you notice that your home seems to be dusty all the time, even if you’re cleaning it consistently, then you could have a problem with your ductwork. Holes in the ducts don’t just allow air to escape, they also can cause dust and dirt to be sucked into the ductwork. That dust is then blown out into your house through the vents when you turn the HVAC system on. Too much dust can also reduce the airflow through the ducts, which is why we recommend having your ductwork cleaned every three to five years.


Dirty Air Filter – Checking the air filters in your HVAC units is one of the most important things you can do to keep your system running smoothly. The frequency depends on which filters you buy, but you should be cleaning or replacing them about once a month or so. If you notice that your air filter seems to be a lot dustier than usual, that could be caused by a hole in your ducts sucking more dust up from the crawlspace or from under your home.


Visible Damage – You don’t have to inspect every inch of your ductwork by yourself, but it’s a good idea to take a look at your ducts every once in a while and check for any visible damage. That’s especially true if you have metal ducts, which can be surprisingly fragile and easy to dent. If any sections of your ductwork look crushed or deformed, there’s a very good chance that air is escaping through a small hole somewhere in that damaged section. Unfortunately, you won’t be able to repair a dented section of ductwork, but the replacements aren’t too expensive if the damage is limited to a small area.


Finding Holes in Your Ducts

If you think there might be a leak somewhere in your ductwork, the next step is to find out where it is. There are a few things you can do to find the holes.


First, inspect the ducts yourself. This can be a bit of a pain, but you’ll have to climb into the attic, crawlspace, or basement to look over every section of ductwork individually. If there are sections that are not visible or otherwise hard to reach, don’t strain yourself trying to access them. HVAC professionals have plenty of tech they can use to check for leaks, so you can just hire one if you can’t find the hole yourself. Take an especially close look at any sections that already have tape on them, as they’ve probably been repaired once already and are more likely to spring a leak again.


Next, turn the HVAC system on in fan mode. As the blower fan is running, return to the accessible ducts and run your hand along them, feeling for any air escaping. Make sure you pay special attention to the joints in between the ducts, since this is the most common place for a leak to appear. You can also detect leaks by holding a candle up to the ductwork and watching the smoke. If you notice movement, then there’s air either escaping through a leak or getting sucked in through one. When you find a leak, mark the spot with a pen or marker so you can return to it later. Even if you end up hiring a professional to handle the repairs for you, it’ll still be helpful if they know where exactly the holes are.


Sealing a Small Leak in Your Ductwork

If you notice a small pinhole leak in your ducts, then you might want to just fix it yourself before getting a professional involved. You should make sure to be careful, however, even when just fixing a tiny hole. Ductwork is very delicate and even the smallest dent can cause another leak to spring.


You have a few options when sealing a leak in the ductwork. The first is to just cover it up with some tape. There are several varieties of HVAC tape that you can use to cover a small leak, and which one you use will depend on the material your ducts are made of. Make sure you only use proper HVAC tape to make these repairs – other kinds of tape won’t be able to hold up to the temperature of the air in the ducts, potentially becoming a fire hazard. As a general rule, using HVAC tape to cover up a leak is going to be the cheapest way to handle it by yourself, but it won’t last as long as other methods. High-end furnace tape can last for significantly longer, but you’ll be looking at a higher price tag if you go in that direction. If you do use tape, make sure you thoroughly clean the outside of the duct before making the repair, as any grease left under the tape can prevent it from attaching properly.


This might seem backward, but one thing that you absolutely should never use to repair your ducts is duct tape. Despite the name, regular duct tape is not intended for use on ducts and doesn’t have enough heat resistance to handle the hot air inside the ducts themselves. Using duct tape on your ductwork can actually create a serious fire hazard, so we can’t stress enough that you should only use tape specifically designed to be used in HVAC systems. If you’re unsure, look for tape marked with the Underwriters Laboratory logo. UL is a non-profit organization that identifies safe and effective products for trade work, and you can trust any tape that bears their seal.


One alternative to tape is a kind of sealant called mastic. Water-based mastic can be applied directly to the leak with a paintbrush and hardens when it comes into contact with the metal, forming a tight seal. While it’s a little more expensive than most HVAC tape and leaves your ducts looking a little less clean, mastic will last for much longer than tape and is generally a better solution. You can also use a caulk gun to apply the mastic instead of a paintbrush if you prefer. This might sound a little confusing, but make sure any product you buy is labeled as duct mastic sealant instead of just regular duct seal, which is used for sealing leaks on the outside of your house. For a leaky duct, look for the word “mastic” before you buy.

Ask us for your Air Duct Cleaning needs

Repairing a Large Hole in Your Ducts

If you have a hole in your ductwork that’s too large for the sealants mentioned in the section above, you’ll have to either replace the section or patch the hole with a piece of metal. This is a bit more difficult than just putting some tape over the leak, so don’t be afraid to call an HVAC professional if you’re not confident in your ability to do it yourself. Accidentally damaging your own ducts can be an expensive mistake, so we recommend thinking twice before patching up the leak on your own. That being said, you should be able to cover the leak with a piece of sheet metal and some tools that most homeowners have around the house, including a drill, aviation snips, and a caulk gun. Here are some step-by-step instructions you can follow to patch up a leak in the ducts:


 Step 1 – Start by switching off any HVAC units that you have attached to the ductwork. Air blowing through the ducts can make the work more difficult so make sure you don’t forget this step. Any time you’re doing any work on the HVAC system, you should always start by turning off the units themselves. If you’re not sure how to do that, you can just find the fusebox and flip the switch controlling that circuit.


Step 2 – Put on safety glasses and any other personal protective equipment that you have. This might seem a little bit like overkill, but any home handyman or DIYer knows how suddenly things can go wrong with even the simplest jobs. The ducts should be cool as long as you keep the furnace turned off, but you can always wear work gloves if you want to be extra safe.


Step 3 – Thoroughly clean the area around the leak with a clean cloth, making sure there’s no grease or dust left behind. If dirt or grease ends up underneath the patch, it can prevent the sealant from properly taking hold and cause small leaks to occur, undermining the whole repair project. You don’t need to make it spotless, but make sure to give it a good once-over before moving on.


Step 4 – Measure the height and width of the hole with a tape measure, then add one inch to each measurement and mark them on a piece of sheet metal. For the most part, we recommend using 26 gauge galvanized metal when working with ducts since that’s thick enough to hold up to wear and tear without being too heavy or difficult to cut to size. The extra inch you added to the measurements gives you enough space to secure the sheet metal to the ducts without getting too close to the tear itself.


Step 5 – Use the marker to draw straight lines between the four corners you marked on the sheet metal. You can use a ruler if that’s all you have, but we’d recommend something a little sturdier like a combination square. Use aviation snips to cut along the lines until you have a piece of metal just bigger than the leak. Make sure you wear gloves when you’re cutting the sheet metal so you don’t accidentally catch a sharp edge with your hand. If you don’t have snips, you can use a circular saw to cut the metal, although the edge will be a little rougher.


Step 6 – If you’re patching metal ductwork, then use screws to attach the cut metal sheet to the duct, covering up the hole. We recommend using a sheet metal screw, #10 size. Using the wrong screw could cause the duct to tear further, so make sure you have something designed to be used with sheet metal. If you’re patching up ducts made of fiberboard, then don’t bother with the screws. Instead, just attach the metal sheet to the duct with some HVAC metal foil tape to keep it in place.


Step 7 – Use a tube of silicon caulk to make a seal around the outside of the patch. Try to apply it in a single continuous bead all the way around if you can to prevent any small holes. If you’re fixing a fiberboard duct then you don’t need to use the caulk either, just make sure that you smooth out the tape with a plastic squeegee so there are no air bubbles caught underneath. Give the caulk some time to set before turning the HVAC system back on. Just follow the instructions on the tube, since set time can vary. If you secured the patch with tape, you can turn the HVAC units back on immediately after you finish.


Once you’ve turned the HVAC system back on, make sure you check to make sure that there isn’t any more air escaping through the leak. If you finish patching the leak but you’re still experiencing problems, then we’d recommend just getting in touch with an HVAC professional to replace the section of ductwork. Working with ducts can be a little tricky and it’s easy to make a mistake, so don’t be afraid to get professional help if you feel that you’re getting out of your depth.


Should I Repair My Own Ducts?

The HVAC field is one that requires a lot of fairly specialized knowledge, which is why there usually aren’t too many homeowners performing maintenance on their own air conditioners or ductwork. Despite the information offered in this blog post, we do generally recommend that you let an HVAC contractor handle any heating or cooling related issues that you might have, including problems with the ducts. Not only are ducts fragile and easy to damage, but they also tend to run through some cramped and sometimes inaccessible parts of your house, making them difficult to work with.


We also recommend contacting an HVAC contractor or technician if you continue to experience problems like increased electricity bills after fixing the ducts. It’s possible that there could be other leaks that you missed during the process or holes in a section of the ductwork that you couldn’t access by yourself. There also might be something going wrong with another part of the HVAC system, including an air conditioner or furnace that’s in need of repair. Issues that pop up in one part of the system often create more problems in other parts, which is why it’s so important to keep up with maintenance.


Even if you’re confident in your ability to patch or otherwise repair your ductwork on your own, there is one thing that we recommend you always get professional help with: cleaning the ducts. Every three to five years, you need to have your ducts cleaned to make sure there’s no dust building up in there and cutting the airflow through the system. Cleaning your ducts also stops mold from growing inside them and releasing spores into the air you breathe. This is a very difficult and complex process and is best left to the professionals. Not only is it easy to accidentally damage the ductwork, but missing even the smallest patch of mold in your ducts can lead to a whole new infestation in a matter of weeks.


Duct Repair in Santa Rosa

If you’re in Sonoma, Marin, or Napa County and you need help with your ducts, Valley Comfort Heating & Air is here to help. We can offer advice on which products to buy and how to make repairs yourself, or we’re more than happy to come out and handle the problem ourselves. We also offer regular maintenance appointments so you can feel confident that every part of your HVAC system is running smoothly, ducts included.

You can get in touch with us through our website here, by visiting our physical location in Santa Rosa, or by giving us a call at (707) 539-4533 today.