R6 vs R8 Duct Insulation: 5 Differences You Need to Know

Ducts are a part of our home’s HVAC (heating, ventilation, and air conditioning) system. They act as passages to deliver hot or cold air to various places around the house.

One of the factors we have to accommodate for when purchasing ducting for installation is how well-insulated it is. Because if it’s not insulated well, you will lose some of that hot or cold air through the ducting before it can reach its destination, which results in wasted energy, costing you more money for electricity.

We judge how well insulted a piece of duct is by giving it an R rating, ranging from R1.9 (not well insulted) to R12 (very well insulated).

In some very rare cases, insulation is not required at all. But that only applies to the hottest of climates. So for most of us in typical Western climates, we need to figure out which kind of R-value ducting we need and why so we can save the most money.

So today, we’re looking at two of the most common R-ratings you will encounter, which are r6 and r8.

Their main difference is how well they insulate hot/cold air. R6 is less efficient at insulating than r8 ducting, but it’s also a fair bit cheaper because it uses less insulation material.

So depending on the climate of where you live, what kind of purpose the ducting is for, and where it needs to be installed (i.e., indoors or outdoors), you may find that r8 is unnecessary and can opt for the cheaper r6.

What is R6 duct insulation

R6 ducting is more affordable but has a lower thermal efficiency than R8. 

It also comes in a thinner diameter than r8 due to having less insulation which gives it additional flexibility and means it can be installed in tighter spots.

The insulation is usually made from bulky fibrous material such as slag wool or fiberglass insulation board wrapped around aluminum foil.

R6 is the more commonly used kind of duct of the two and is appropriate for the widest variety of climates and applications.

What is R8 duct insulation?

R8 is a little more expensive than R6 ducting but has better insulation for hot and cold air.

Depending on your climate and use case, this increased insulation will often offset the increased price of the ducting resulting in better long-term money savings. R8 can reduce energy loss by an additional 2% over R6, which results in a 3% increase in energy efficiency.

Although this might not sound like a lot, this can add up after years or even decades.

Because of its increased thermal insulation qualities, it’s thicker than R6, which also makes it less flexible. Therefore, it’s not as ideal for tight spots and might not be able to install correctly into places R6 can.

What is the difference between R6 and R8 duct insulation?

Even when you understand their differences in thermal efficiency, it can be tough to know which one’s going to be the most cost-effective for your particular use case.

So let’s take a deeper look at their differences to help you get a better overview.

1. Cost

The cost of these can be a difficult thing to work out. Regarding the duct insulation itself, r8 is the most expensive.

However, in colder climates where more excellent insulation will lower energy consumption by up to 3%, you may find that r8 is the cheaper option.

However, if your climate does not benefit from the increased thermal insulation, r6 will be the more cost-effective option.

2. Which R-value for which climate

There are a total of 8 climate zones across the United States which are rated from 0-8.

Zone 1 is exceptionally humid and warm, including places such as Hawaii and Puerto Rico. And zone 7 includes the coldest of climates, including all of Alaska.

Whether your duct is intended for heating, cooling, or both will indicate whether R6 or R8 is most appropriate for that area.

Ducting is used for both heating and cooling:

  • R8 is appropriate for climate zones 0 through 4 for exterior ducts as cool air will need to pass through it while being protected from the hot exterior climate.
  • R6 can be used for all climate zones in unconditioned space or buried ducts.

Ducting is used for heating only:

  • Climate zones 0-1 do not need insulation as it’s already so hot.
  • Climate zones 2-4 require R6 ducting for exterior ducts to prevent heat loss.
  • Unconditioned space ducts can use R6 ducting for zones 2 through 8.

Ducting is used for cooling only:

  • Climate zones 0-6 need R8 insulation to protect the high eat from leeching the cold air through the ducting.
  • Unconditioned space ducts can use R6 instead.

As you can see, your climate and whether it’s used for hot air, cold air, or both will dramatically affect the effectiveness of your duct insulation. Be sure to research this aspect thoroughly before purchasing!

3. Material thickness

Duct insulation materials can come in several forms. To make different insulations, duct liner, duct wrap, or duct board may be used.

For duct liners, you achieve roughly an R4 per inch of thickness. So an R6 liner will be about 1.5 inches in thickness, and to get an R8 rating, it will be about 2 inches.

Duct wrap is quite similar but achieves an R4.2 per inch of thickness. THis puts an R6 at just under 1.5 inches of thickness and an R8 at just under 2 inches of thickness.

Duct board is rated at R4.34 per inch of thickness, making a 2-inch duct board (2 layers of 1 inch placed on top of each other) rate at about R7.

Using this information, you can get a good idea of whether you will be able to fit R8 ducting in your intended spot, or if it’s too tight, you may have to settle for R6.

Whether liner, wrap, or board is better – they are all very similar, and you won’t find any real, quantifiable difference in their performance.

4. Flexibility

Because of its thickness, R8 is less flexible than R6, so depending on what kind of corners it needs to take, you may be unable to use R8 ducting for the entirety of the duct run.

This can also make it more difficult if you originally installed R6 and wish to upgrade to R8 later on, as it may not fit around the construction. So be mindful of tight spaces when choosing the best one for your home.

5. Building codes

In specific scenarios, you may not choose which ducting rating you select as some local building codes will have requirement standards for new HVAC system installations.

For example, in colder climates, you may be required to use R8 ducting as a minimum. So be sure to research this thoroughly before planning your building and making a purchase!

R6 vs R8 Duct Insulation: Are they the same?

Even though these are both made from the same materials and essentially serve the same purpose, the difference in their price, efficiency, and thickness means they require proper consideration when planning your build.

  • Because R8 ducting uses more material and is thicker, it costs a bit more than R6 ducting. Depending on your environment and intended use (i.e., for hot air, cold air, or both), it can save you more money in the long run because of its better thermal insulation.
  • Different rating ducting may become more or less efficient depending on your climate zone and what kind of ducting is used. Check the information detailed above under ‘Which R-Value for which climate’ to determine your climate zone and R rating.
  • R8 has greater thermal insulation but, as a result, is quite a bit thicker than R6, meaning you may have difficulty installing it into a place intended for R6 ducting. So you will need to determine the thickness and ensure enough room for it before purchasing.
  • Because R6 is a thinner material, it’s much more flexible, allowing it to be installed into tighter spots and fit around tighter corners.
  • Some locations will have building codes requiring you to use a specific R-rating duct regardless of what you deem best for your application. Be sure to research the local building codes in your area to ensure you adhere to the requirements correctly.
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