How To Insulate A Ductwork Elbow [A Complete Guide] –

Ducts That Run Between Joists

Clear away clutter that blocks your access to the air ducts. Seal all duct joints with metal foil tape, instructs HVAC for Beginners. Before working with fiberglass insulation, put on eye protection, a dust mask and gloves. Wear long pants and a long-sleeved shirt.

If your ducts run between the joists, cut one standard insulation batt the length of the horizontal duct. Stand on the stepladder and push the batt into the space above the duct, with the vapor barrier side up, so it forms a sort of roof over the full horizontal length of the duct.

Cut a second length of standard insulation batt to the length of the horizontal duct to cover the duct’s underside. Direct your helper to hold the batt up to the duct with the vapor barrier side down.

Staple one end of the twine to the joist with the staple gun. Staple it close to where the duct branches off from the supply trunk. Zigzag the twine from one joist to the other, stapling it to the joists as you go. You want the twine to form a cradle that supports the bottom insulation batt. Direct your helper to hold the batt up to the duct just ahead of where you are stapling the twine.

Wrap fiberglass round duct insulation around the metal boot that connects the air duct to the rectangular supply air register serving the room. Secure the fiberglass insulation in place around the boot with foil-faced duct tape.

Ductwork Insulation – Details

Types of Ductwork Insulation

Fiberglass is the most common material used for ductwork insulation. It comes in a flexible or rigid format and has R-values that range from R-4.0 to R-11.

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Flexible fiberglass is wrapped around the air ducts. After that, the outer backing is backed by foil. On the other hand, rigid fiberglass is great for rectangular ducts. To keep the rigid board against the ductwork, experts use clamps and clasps.

Sometimes, more than one type of fiberglass can be used in a single system.

Such insulation prevents condensation, helps conserve energy, and provides temperature and acoustic control.

The second widespread type of insulation is made out of polyethylene bubbles that are located between radiant barriers (they look similar to simple foil). It is a cheaper option that is relatively easy to install. 

However, do bear in mind that in order to take advantage of the barrier, you would have to leave 2 inches of air space between the duct and the foil. And that is not always a simple thing to do. 

Foil-backed self-adhesive foam duct insulation is easy to install and can be wrapped around irregular ductwork. The material is relatively thin, but it dampens sound very well and, if you ever need to, can be used with other types of insulation.

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Warning! Make sure to use only the foam that is specially designed for insulating as a lot of foam products can become toxic when burning and are highly flammable.

Ductwork Insulation Cost

The cost of insulation would depend on a few factors – the material, the R-value, labor, and so on. Usually, duct insulation cost falls in the range between $0.95 and $2 per square foot installed.

Let’s have a closer look at what you are paying for:

  • The length of the ductwork

Of course, the longer the actual ductwork, the more expensive the insulation is going to be. The cost will also depend on the insulation ratings (R-3.5, for example, is cheaper than R-8.0).

  • The thickness of the ductwork

The thinner the ductwork, the more insulation material you would have to add to achieve the desired thickness. This is done in order to meet the recommended insulation levels.

  • Supplementary materials

Unfortunately, you can’t simply stick the material to the duct, you are going to need quite a few supplementary materials. Expect to pay $25-$50 for the supplies for every 1.000 square feet of insulation.

  • Labor costs

You can attempt doing the job yourself. It isn’t extremely challenging and won’t cost you a penny. However, if you are not used to working with such materials, you should expect to spend a wagon of time on the job.

When it comes to professionals, you will be asked to pay up to $0.80 per square foot for their services.

Tip: you can attempt completing the job on your own if it’s a small project. For larger tasks, experts recommend hiring professionals.

Even though the installation process might cost you a lot of money, in the end, it will definitely be worth it as high-quality duct insulation will help you save a small fortune on your electricity bills.

Ductwork Insulation Thickness

As a rule of thumb, the more extreme climate you live in, the more insulation you should add. People living in areas with freezing cold winters and boiling hot summers should consider going for the thickest insulation.

Moreover, it will make more sense to add a thicker layer, if you are planning on living in this particular house for decades. This will help you avoid a lot of insulation-related problems in the future.

You should plan on adding anywhere from an inch to 3 inches of insulation to your ductwork.

1-inch insulation gives you an R-value equivalent to 1.9.

1.5 inches – R 3.5

2.5 inches – R 6.0

3 inches – R 8.0


Ductwork Insulation Benefits

Ductwork insulation can be very beneficial and prevent issues with the growth of microbes such as fungus, mold, and other problems that can stem from humidity and condensation.

It Can Minimize Air Leaks

The more you can minimize air leaks within your HVAC system, the better. Air can leak down through the windows, holes in the walls, and cracks in the exterior of the building. Unsurprisingly, it can also leak through your ductwork. This actually accounts for about 25% to 30% of energy loss in most homes.

Keep in mind that these types of leaks can make your HVAC system work much harder to regulate your home’s temperature. So, if you’re looking to save on your energy bill, insulating your ductwork may be a step in the right direction. Why not maximize the efficiency of your ductwork if you can? And it doesn’t cost an arm and a leg to do so.

It Helps To Prevent Condensation Buildup

It Helps To Prevent Condensation Buildup

As cold air from outside travels through your ductwork to the interior of your home, it can cause a significant amount of condensation to build up inside of your ductwork. This is a recipe for mold and mildew growth. However, insulation can help to prevent these microbes from forming.

While dehumidifiers can also help with this, they may not be as impactful as insulating the ductwork in some cases. This is especially true if you live in an area that is relatively humid throughout the year. Also, note that breathing mold spores can be a health hazard, so it’s beneficial to minimize this as much as possible.

It Can Assist In Dampening Noises

One of the best ancillary benefits of insulation is its ability to reduce noises within your home. Sound travels easily through ductwork, bouncing off the thin metal sheets into your home’s interior. However, when there is a thick layer of insulation on top of these thin metal sheets, loud sounds such as random rattling, popping, or creaking coming from various areas of the house will be minimized.

To Sum Up

This was everything that you need to know about ductwork insulation. 

In a nutshell, if you can install insulation in your ducts – do that as there will be plenty of benefits. The main advantage is, of course, energy savings.

In case you need to insulate a small area in your house, you might be able to do that without the assistance of a professional. No matter what space you have decided to tackle, the main guidelines would be pretty much the same:

  • Find and seal the leaks
  • Clean the surface and make sure that it is dry
  • Wear personal protective equipment
  • Carefully measure and cut the insulation material
  • Wrap it around the ductwork and secure the seams or simply apply your foam insulation

Insulating your ductwork is definitely worth it if done properly. So, make sure to take your time.

The Problem with Uninsulated Ductwork

The crawl space is an unconditioned space. This means that, like an attic or unfinished basement, you don’t heat and cool it.

If you have ductwork in your crawl space, the temperature of the duct will be the same as the temperature of the crawl space.

In the winter, a crawl space can be significantly colder than the living spaces of your home. The hot air leaves your furnace at the desired temperature. When it hits the ducts in the crawlspace, that hot air is cooled by the cold ducts. It comes out of the vents at a lower temperature than desired.

This means that your furnace has to work harder to warm up your home. It has to run longer and more frequently because you have losing heat at your crawl space’s ductwork.

On a hot summer day, the opposite would be true. The unconditioned spaces that house your ductwork will likely be hotter than the living spaces. You’ll cool the air in your A/C unit and then warm it back up by sending it through hot ducts.

Leaky ducts also create indoor air quality problems. Drawing crawl space air into the air supplied to the living space can introduce allergens and other air quality issues.

This set up is inefficient, in any weather conditions. It wastes energy and money. Thankfully, efficiency can be easily restored with proper insulation.

Considering your insulation R-value

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.

Wrapping Duct Work to Prevent Condensation

Once you have the right tools and materials, follow the below steps to wrap your ducts.

Here’s how:

  • Measure your insulation. Wrap the material around your ducts and mark where you’ll need to cut for a snug fit. Make sure the fit isn’t so tight that the insulation layer will be compressed.
  • Cut the insulation. Using your straight edge or carpenter’s square as a guide, cut the insulation with a utility knife.
  • Clean and apply the insulation. Wipe down the foil edges of the insulation so that duct tape will apply cleanly later. Apply small pieces of tape as you go to hold the wrapping in place.
  • Seal insulation with tape. Remove the paper backing from the duct tape as you apply it to prevent it from sticking to itself. Seal the length of each wrapping piece with a long piece of duct tape. Seal joints by wrapping tape all the way around.
  • Inspect. Check for gaps and seal everything with tape.

Still worried about excess moisture around your HVAC ducts? Help your system out by installing a dehumidifier in your attic or crawlspace. Or have your ducts spaced out farther apart to promote airflow. And, of course, replace your air filters and get your ducts cleaned regularly.

Start Saving Money Today

Stop wasting money and energy with a leaking duct system. You’re throwing money out the window.

Invest in duct insulation today to safeguard your family’s health and your pocketbook.

To learn more tips and advice on duct insulation and other homeowner topics, check out our blog.

Contact Crawl Pros today for an estimate on upgrading your duct insulation.

Our professional estimators can see you in as little as a day.

Give us a call today at 866-673-9626


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