It all comes down to money. Who doesn’t want more money? To have more, you either have to earn more or spend less. Here’s your opportunity: The better insulated your ducts, the more money you will keep in your pocket, guaranteed. Of course, insulation isn’t free, and depending on which type you use, the cost can quickly add up. But as the old saying goes, sometimes you have to spend some to make some. When it comes to adding duct insulation, your monthly savings in utility bills will soon cover the costs, especially if you install the insulation yourself.
You need insulation – even around your ducts – no matter where you live. Insulation isn’t only about keeping heat in, after all. It also keeps the heat out of the home (or duct). In the average home, around 20 percent of the heated or cooled air flowing through the ducts is lost to leaks and uninsulated surfaces, according to the Department of Energy. The end result is higher utility bills, wear and tear on the heating and cooling system, and difficulty maintaining the temperature inside your home. In addition, uninsulated ducts can accumulate condensation, which eventually turns to rust. Once the ducts start rusting, you face having to install new ducts.
First, consider the duct location. The greater the temperature extreme between the air inside the duct and the air surrounding the ductwork, the greater your need for duct insulation. Unfortunately, so many houses – especially newer homes – end up with ductwork running through the attic. Unheated basements, crawlspaces under the home, and even garages are also typical unconditioned (neither heated nor cooled) ductwork runs. If, on the other hand, your ducts run across the ceiling of a heated basement or inside well-insulated walls and ceilings, your need for duct insulation is minimal. However, if the ducts have a lot of leaks, the air that makes it to your rooms will not be as warm or as cool as intended. So, duct loss matters no matter what.
Then there’s the duct material itself. Most heating and cooling ducts are metal. These are the bulky, gray, box-shaped ducts so common everywhere. Sometimes metal ducts are lined with duct liner, a 1-inch-thick fiberglass board that insulates the interior of the duct, rather than the exterior. Duct liner isn’t generally a DIY installation, and if your ducts already have liner, you don’t need to insulate the exterior.
Duct board, much like the duct liner, is also a fiberglass product. Made from 1- to 2-inch-thick sheets of rigid glass fiber and coated with an aluminum laminate for a moisture/air barrier, duct board comes in sections that fit together like metal ducts. Duct board’s advantage is that it is already insulated, eliminating the need for further work as long as it is structurally sound.
Another product, known as flex duct, is a round framework of wires coated with fiberglass and encased in either foil or plastic to resist moisture and air leakage. Although flexible ducts don’t require further insulation, they are vulnerable to damage, especially punctures. Since they are generally used for short runs, when working on the remainder of your ductwork, check any flex ducts as well.
Once you determine that your duct needs insulation, consider the type of insulation you want. To insulate the exterior, you have a choice between sleeve-style insulation and blanket wraps, which literally wrap around the ductwork. To install sleeves, you must either disassemble the ductwork and slide it on before reassembling the ducts or – as many homeowners find themselves doing – slit it and wrap it around like the blanket-style material. So, in the end, it’s probably best to buy the blanket insulation in the first place.
As new and innovative products arise continually, these are by no means the only types of duct insulation available, nor will they remain the main types. When evaluating any type of duct insulation, make note of the installation method, the drawbacks and advantages, as well as the insulation power, known as the R-value. Talk to others about what works for them and shop around before choosing any insulation for any part of your home.
More important than the type of insulation (provided it is installed properly) is the R-value of the insulation you use. R-value is the measure of the ability of the insulation to prevent heat from either penetrating or escaping the object insulated. The higher the R-value (literally meaning resistance value), the better the insulation works. However, there is a ceiling on the effective R-value because, at a certain level, the cost of the material becomes greater than any additional savings.
Before selecting your duct insulation, determine the optimum R-value for your region. In general, the colder your climate the higher the R-value you will need. Even then, different areas of the home may require greater or lesser insulating power. As a rule of thumb, expect to install a minimum of R-5 material. To be precise, consult the Department of Energy’s Duct Insulation R-value Chart.
When selecting your duct insulation, use the R-value you require to determine what product – or combination of products – you need. Use more than one layer if a single layer won’t give you the value you desire.
Well-meaning homeowners commonly make a couple of mistakes when insulating their ducts. First, some don’t realize that you can’t use paper-backed fiberglass insulation. Perhaps the most commonly used insulation for joists and walls, the fiberglass itself is fine, but it doesn’t take much to get the paper hot enough to burn. Never use anything not specifically intended for use with HVAC ductwork.
The second mistake is even more common: DIY-ers often do not understand they must seal the ducts first. Failing to perform this basic step will undermine your insulating efforts. No matter how well you install the insulation or how high the R-value, even with the moisture/air barrier attached to the exterior of the insulation, it won’t prevent air and temperature loss if your ducts aren’t structurally sound.
Some ducts, depending on the material and the location, are more vulnerable than others when it comes to air loss, but any duct has the potential to leak. With age, house settling, rust from moisture, animal intrusion and a variety of other hazards, your ducts may obtain anything from pinholes to gaping voids, loose and leaking connections between pieces or even potentially missing ducts. Your joists or wall studs may actually form the “duct” run if a portion of your HVAC ductwork is missing – or the air may simply pour out to the exterior.
To ensure you aren’t wasting your time, money and insulation, have a duct leak test conducted before sealing the ducts. A professional duct leak test identifies leaks inside your home’s ducts. Generally called a “duct blower door” test, the technician seals the air intake and outlet registers before blowing air through the system. With the aid of specialized tools, the technician can determine the amount of air leaking from your ductwork and where it’s occurring. Common problem areas include around the registers and vents, where they enter the room they service, and at each duct joint (connection).
Having your ducts tested adds to your expense, of course, with most professional inspections running $100 to $200. Only a professional has the equipment and knowledge required, so it’s really not a DIY-friendly task. Still, spending the money will end up paying off in the end. Also, local building codes are gradually beginning to require that new houses have a whole-house and duct blower door test performed. How does this apply to you? At any point that you make any upgrade involving your ducts that requires a building permit, you will have to follow the current code. It’s also a good selling point if you ever put your house on the market. To find a professional to perform the work, try your local utility company, HVAC service company or specialized testing companies. The Department of Energy provides excellent tips on choosing your technician. Also look for energy efficiency credits that may be available through the utility company or the state or federal government for testing and insulating your ducts. This may offset your costs significantly.
Some duct testing companies will seal the ducts for you, eliminating leaks and holes, as either part of the service or for an additional fee. Do what you’re comfortable with – if you feel confident about doing the sealing yourself, it will be messy. If you decide to proceed without testing your ducts, perform a thorough examination, looking for any rust, holes, severely damaged pieces, loose connections or missing portions, starting at the furnace and air unit and working back to the very last register in the home. Mark problem areas with a marker or chalk. After the inspection, seal your ducts, keeping a few tips in mind:
After the sealant is dry, the final step is insulating the ducts. The process is simple if you use a wrap-style insulation product. Before beginning, read the product instructions and follow wherever they deviate from general duct insulation guidelines:
Once your ducts are sealed and insulated, you can have a technician retest your ductwork if you desire. Some companies may offer the “after” test for free. Following these guidelines and installing everything properly guarantees that your second test will blow the first away – pun intended – but better yet, your utility bills will show the difference.
I’ve wrapped my ducts with duct insulation, but the heat loosens the tape and it keeps on falling down. What is the best way to secure the insulation? The way our ducts are set up I can’t wrap completely around them. And there is really nothing I can staple the insulation to. Is there a better tape? I’m just using basic duct tape. What is mastic?
Yes Ted, there is a better tape. Regular duct tape will not hold up. You need to use FOIL duct tape it is made for duct sealing and insulating ducts it is very sticky and will hold up to the heat and cold and last a long time just make sure everything is as clean as possible, this will ensure your success. Hope this helps. Good luck.
I’m sure I have a hole in an elbow that once was in contact with the ground in a crawlspace; that I have, in my old age, out-grown. The only way to it is under the main trunk, which is too close for myself to fit, and others have looked and refused to try. The only other options, as I can see, are to dig out under the main trunk, or cut a hole in the floor….neither ideas are very appealing.
Was wondering if anyone has heard of some kind of liner that could be inserted into the duct from the supplied register? Sort-of like a heart stent, that is expanded once inserted….
The thin plastic covering over the insulation on the ‘flexible’ ducts in my attic is splitting and falling off. Should I re-cover with new plastic (Ducts are around 18 yrs.)
Or would I best replace all? I also want to add one new outlet in a stagnant corner of the kitchen during the process.
Any suggestions will be appreciated.
Honestly i have just delt with this issue myself and after pondering the solution i have decided to just replace them all. if your going to do one you just do them all now so you dont have to worry later. just my 2 cents becasue if you just put new plastic… keep in mind they are 18 yrs old and bound to break again and probably or close to their end of useful life…
I have a question and I am needing help with this. I recently purchased a condo in Ft Lauderdale and the inspection revealed I needed to have the coils cleaned and a filter. When the repairmen came they recommended an electronic air filter and coating the old fiberglass duct work. Since this process. there has been an odor so toxic, I can not use the system.
If your heater is in a closet space next to your water heater (a common arrangement) both need to be well insulated. If your water heater feels warm to the touch, it needs more insulation. If your AC feels cold, more insulation there too. Pay close attention to joints where air might be leaking, even just a little. If it’a leaking around a removable panel, use metallic tape so it can be easily removed should maintenance be necessary.
Check the entire length of *cold* the copper pipe going from the outside AC unit to the inside. It may be running through the attic or under the floor. If you can find it, ensure it’s well insulated everywhere. I’ve found spray foam (such as Great Stuff) works well on the connections where it’s hard to put other sorts of insulation. (Just be careful when spraying, as the stuff sticks instantly to *everything* it touches, including you.)
I found a couple leaks in my air ducts and their not easily accessible so I was contemplating whether to use great stuff foam spray because i noticed that the ducts do get hot. I’ve never used that product, so in your professional opinion is it safe?
Another good way to check for leaks yourself is to go to where the ducts are and put your hand over potential cracks when the blower is working. If you feel any air, you need to address it. BTW, if your hand is wet, you’re more likely to notice cold air leaks in your AC during system the summertime. Also, if you feel anything near ducts which feels cold in a warm area, that is a candidate for more insulation.
A vertical furnace vent runs through an opening in a sheet of Styrofoam insulation in the roof of my attic. Do I need to apply fireproof caulk around the opening or is the furnace vent internally insulated? Is there a size requirement for the opening in the Styrofoam through which the vent passes?
Hi Sweltering in Charleston South Carolina,
I hope you have turned on your air conditioning. I used to live in the south and know just how miserable it can be in the summer!!!
I would expect it could take 3 or 4 days for the mastic to dry completely — maybe a little longer if it’s highly humid.
I do wonder how exactly the contractor applied the mastic — was it not over the seams, then the fiberglass wrapped over top? If so, it should have been dry before he wrapped it. I would also suggest calling them back and asking any questions you have. You spent good money on their time and expertise and they should be more than happy to make sure you are satisfied.
Hope you’re staying cool!
We had an A/C contractor replace all our insulated duct work under our home which is elevated 8 ft.
He used fiberglass insulation with a silver foiled outside covering. He covered much of the duct work and all seams with mastic. . We have not run the A/C for 96 hours it is still sticky wet and not dry. What is a reasonable amount of time to expect the mastic to dry? Thank you. Sweltering in Charleston SC.