R value for flex duct in attic. Can existing duct wrap, which includes a vapor retarding barrier, be over wrapped with additional fiberglass insulation, with it’s own vapor barrier, to increase R value? In line with that, can unfaced fiberglass batts be wrapped over insulated ducts to increase R value. For duct systems located in both unconditioned and conditioned space, the portions of the duct system located in conditioned space are not required to be Some other factors to consider The duct insulation R-values I mentioned above are what’s on the product label. So an R6 liner will be about 1. Use our Roll and Batt Insulation Calculator to estimate the amount of wall insulation, crawlspace insulation or attic insulation you need for your project. This practice improves both the efficiency and comfort of HVAC systems. An efective duct insulation value of R-25 can be claimed for “deeply buried ducts,” if certain criteria are met; or Buried ducts can be considered inside conditioned space, if certain criteria are met (including a reduced duct leakage limit). In the Winter: It prevents the cold attic air from "stealing" the heat generated by your furnace or heater. Keywords: flex duct connections tips, HVAC duct installation techniques, airtight duct connections, HVAC mechanical seal advice, high R value insulation tips, mastic duct sealing methods, proper ductwork bonding techniques, duct work condensation solutions, HVAC installation best practices, flex duct system improvements Yes, there are recommended R-values for insulated flexible ducts to ensure proper insulation. Heat Insulation Efficiency When it comes to heat insulation, R8 ductwork is more effective than R6 ductwork. 0. Most attic ducts are insulated flex ducts (that is, flex ducts with R-6 or R-8 fiberglass insulation, along with an exterior polyethylene jacket). Generally, duct insulation R-values range from R-6 for mild climates to R-8 for colder areas, as recommended by the U. Understand how R-values affect airflow, insulation, and energy savings. While the practice of burying ducts is not new, prescriptive code language is. Feb 14, 2018 · If we put ducts in unconditioned space, they have to be insulated to either R-8 (if they’re in an unconditioned attic) or R-6 (in any other type of unconditioned space). For determining installed R-value of duct insulation based on thickness, when not an integral part of a manufacturer-labeled, insulated duct product such as vinyl flex duct, the following shall be used: 1. Understand differences, installation and performance benefits. Jul 19, 2022 · A complete 2026 guide to understanding HVAC flex duct R-value. Homes in warmer and varied climates can utilize ducting with a lower R-value, although R6 or R8 is still typically recommended. R-value ductwork is more expensive but is better if you live in a cold area. 2, R-6, and R-8 to save energy and improve home comfort. . Discover the benefits of using R8 insulated flexible ducts in HVAC systems. 7 Distribution Systems. Minimum Duct Insulation R-Value,a Cooling and Heating Only Supply Ducts and Return Ducts Insulation R-values, measured in (h·ft2·°F)/Btu, are for the insulation as installed and do not include film resistance. Thickness to R-Value Depends on Insulation Type R-value represents effectiveness in preventing conductive heat transfer. For homes that are located in a WARM CLIMATE, you should still be looking for replacement ducts with R-values between R4 and R8 if the ducting is located in the attic. Altered duct systems - duct sealing: In all Climate Zones, when more than 25 feet of new or replacement space-conditioning system ducts are installed, the ducts shall comply with the applicable requirements of subsections i and ii below. Guide describing approaches to burying and encapsulating ducts in unconditioned attics to increase the overall R-value of duct insulation. If you have ducts in the attic, it’s very important to insulate them with either R-6, R-8, or even R-12 insulation. Guide that illustrates how and when to encapsulate ductwork in unconditioned attics, increases the R-value of duct insulation, mitigating condensation issues and reducing air leakage. In order to achieve a certain R-value for the duct, you will need a specific thickness of material. For duct board, duct liner and factory-made rigid ducts not HVAC Engineering Minimum Duct Insulation R-Value, a Cooling and Heating-Only Supply Ducts and Return Ducts Thermal insulation is commonly used to reduce energy consumption of HVAC systems and equipment. Generally, higher R-values indicate better insulation properties, leading to increased energy efficiency and cost savings over time. The ideal R-value for rectangular flexible ducts depends on factors such as climate, local energy efficiency standards, and specific application requirements. Minimum Duct Insulation R-Value,a Combined Heating and Cooling Supply Ducts and Return Ducts Insulation R-values, measured in (h⋅ft2⋅°F)/Btu, are for the insulation as installed and do not include film resistance. 2 on ducts smaller than 3" in other unconditioned The R-value needed for ductwork insulation varies based on your climate zone and the location of the ducts (e. For contractors looking for R-12 duct warp, Microlite FSK Formaldehyde-free™ duct wrap is the only duct wrap on the market with an installed R-value of R-12 in a single layer. 0 or higher. 2 to R-8. The effective R-value of a buried duct installation depends on the size of the ducts, the R-value of the duct insulation, and the depth of the loose-fill insulation. One of the most recent landmarks on our journey is a shift from R-6 to R-8 insulation in the world of ductwork, under the umbrella of California’s robust Title 24 building standards. Do Ducts Need to Be The most common material used for insulating heating and cooling ducts is fiberglass. It is 4 in. If you must put ducts in an unconditioned attic, these tips can minimize the hit you'll take on your heating and cooling bills. I understand that the duct wrapping would have to be completely air sealed. 1 and 90. And then there’s the issue of how the R-value on the label is D. Generally, the minimum R-value might start at R4. The new law temporarily changes the Commercial and Residential insulation R-value for ducts installed in ventilated and non-ventilated unconditioned spaces. R6 or R8 Flex Duct? Discover which duct insulation suits your HVAC project. When these ducts are exposed to exterior air, the plastic jacket never gets cold enough to permit condensation, because the hot attic air keeps the plastic jacket warm. 62 not counting surface films. Return ducts (ductwork that brings expended air back to the HVAC system to be filtered, reconditioned and redistributed) require insulation with an R-value of 3. Duct Insulation Rvalue Ratings. The combination of both factors does not always result in an improved total R-value however, and the discrepancy between nominal and actual R-value gets larger with higher R-values and/or smaller diameters. Deep Dive: Differences Between R6 and R8 Ducting The easy-to-install flexible polyester duct is intended for use wherever UL 181 standards for Class 1 Air Duct is required. S. Jul 9, 2025 · Understanding R-value is key to selecting the right insulated flexible duct for your HVAC system. Ideally ducts should be located in conditioned space, such as within a dropped ceiling, between floors, in an insulated basement or crawlspace, or in an unvented attic that is insulated along the roof line. If ducts are located in an unconditioned space, such as a vented attic or vented crawlspace, they should be sealed and insulated to prevent heat loss due to air leaks and conduction and to Duct Systems Duct Insulation The 2018 IRC/IECC now requires equal insulation levels on supply and return ducts, but the R-value depends on size and location: R-8 on ducts 3" or larger in attics. 4. 5 for exterior ducts and ducts in a ventilated attic or unvented attic above an insulated ceiling. For duct liners, you achieve roughly an R4 per inch of thickness. To make different insulations, duct liner, duct wrap, or duct board may be used. For factory -made flexible air ducts, the installed thickness shall be determined by dividing the difference between the actual outside diameter and nominal inside diameter by two. in diameter x 25 ft. When insulating ducts, understanding the meaning and impact of R-Values and insulation thicknesses is essential to getting the most efficient, affordable outcome on your heating installation project. This article compares R4. Fiberglass Insulation EcoTouch® Insulation for Flexible Duct Owens Corning EcoTouch Insulation for Flexible Duct is a lightweight, flexible, resilient thermal and acoustical insulation made of inorganic glass fibers bonded with a thermosetting resin. 5 inches in thickness, and to get an R8 rating, it will be about 2 inches. The required minimum thicknesses do not consider water vapor transmission and possible surface condensation. The 2018 IECC details a prescriptive path for the use of buried ducts with fibrous insulation in vented attics for all climate zones. The law allows for reduced duct insulation values for a period of two With a duct system located in a vented attic, your quickest remedy is to dramatically improve the R Value of those air ducts. Knowing their differences can help you pick the right ducts for your home. R-6 on ducts smaller than 3" in attics R-6 on ducts 3" or larger in other unconditioned spaces. 3. Learn the difference between R-4. If a large fan coil is used and air-distribution ducts are in the attic, crawl space, or other unconditioned space, the efficiency of the air-distribution system must be determined using methods consistent with those described in Section 2. The certified R-value is typically R-6, suitable for temperatures up to 200 degrees. Fiberglass duct insulation is available in various thicknesses and R-values and in either a flexible or rigid form. Minimum insulation levels for ductwork and piping are often dictated by energy codes, many of which are based on ASHRAE Standards 90. Department of Energy. 2 per linear foot, with some types reaching up to R8. The application can significantly impact the insulation’s performance. The flexible type comes in rolls and is relatively easy to install on either round or rectangular ducts. A spiral wire-reinforced inner air conduit is wrapped with resilient fibrous glass and jacketed with a flexible vapor retarder of reinforced foil or plastic film. However, upgrading to R-12 for attic ducts in all climate zones provides significant additional savings with a reasonable payback period of 5-7 years. It measures the duct's thermal resistance. Duct Installation Standards Space conditioning supply-air and return-air ducts and plenums are required to have a minimum duct insulation level of R-6, except for when the duct or plenum is located in conditioned space as described below. Flexible ducts insulated with fibrous glass are an efficient, economical way to install connections between trunk ducts and room diffusers or registers. It’s that easy. Obtain written cost estimates from several contractors for the R-value you need, and don't be surprised if quoted prices for a given R-value installation vary by more than a factor of two. iii. As shown in Figure 1, insulation R-values should be selected based on climate and duct location. Discover the pros and cons of R8 ducting and R6 ducting for your home's HVAC system. There are several ways to accomplish this… and the quickest, and a most excellent solution, is to spray the air duct system with a protective coating of low-pressure Closed Cell spray foam insulation. Material thickness Duct insulation materials can come in several forms. The code change has the potential to provide a vented attic design that is highly energy efficient but at lower cost than alternatives. It is flexible for ease of installation. ii. Overview This Aluminum Supurr-Flex Duct from Deflecto is a 5-ply duct for use with dryers. g. Ducting, Air Circulation and Ventilation Systems - R-value in duct - Would it make sense to increase the R value of my ductwork? My HVAC unit is in the attic and the ducts are flex type with R-6 insulation. Here, you will find the answers to all of your questions (and even more). The thickness will depend on what material you are using since different materials have different inherent thermal resistance. Nov 5, 2025 · R-value of insulated flex duct varies by type and thickness, typically ranging from R-4. For duct wrap, the installed thickness of insulation must be assumed to be 75 percent of the nominal thickness due to compression. The EPA recommends proper insulation of ducts as a means of improving system efficiency and lowering energy bills. All interior ducts are assigned an R-value, like R6 or R8, which indicates how well they insulate. Learn why duct insulation is crucial for energy efficiency in homes with ducts in unconditioned spaces and how to perfect climate control with optimal insulation levels. When metal ducts are located in an unconditioned space, high-R thermal insulation with a vapor barrier can help prevent heat gain or loss through the duct walls and keeps condensation from forming on the ducts. The ICC Digital Codes is the largest provider of model codes, custom codes and standards used worldwide to construct safe, sustainable, affordable and resilient structures. Even more importantly, we are going to check the insulation R-values of flex ducts, duct boards, duct wraps, duct liners, and other duct insulation materials. The flex duct sizing chart and round duct sizing chart below are used by HVAC technicians, handyman services and homeowners to quickly select a supply duct size and return air duct size for each section of your ductwork design. The majestic R-8, a pinnacle of insulation values in duct design, is now the new marker for thermal efficiency. A subsequent update with technical changes to Session Law 2022-6 was enacted on July 7, 2022v as Session Law 2022-46. R-4. ICC Digital Codes is the largest provider of model codes, custom codes and standards used worldwide to construct safe, sustainable, affordable and resilient structures. in length. In the Summer: High R-value prevents the scorching heat of your attic (which can reach 140°F+) from warming up the cool air inside your ducts before it reaches your vents. For example, a six-inch diameter, nominal R-8 flex duct has an actual R-value of only 5. , attic, basement, conditioned space). What types of insulation should you use for your ductwork? What R-value should you go for and will you manage to insulate the ductwork in your house all on your own? We present to you the “ duct insulation: everything you need to know ” guide. Ask contractors about their experience in installing the product you are considering. 2. It measures 7-in x 25-ft and features an insulation R-value of 8. It may possibly reach a height of R11 in the attic area. How often do you think you get the full labeled R-value? Even with a really nice installation, as in the photo below, there’s usually compression at the supports. Power loss is reduced by R8 ducting by roughly 2%. Microlite FSK duct wrap comes with an FSK (foil scrim kraft) facing, designed to help ensure a closed system that prevents moisture drive and offers condensation control. 2, R6, and R8 insulation levels, explaining their impact on thermal efficiency, cost, and duct sizing. The recommended R-values for aluminum flexible duct vary based on climate, building codes, and HVAC system requirements. The space conditioning system air handler is located in unconditioned space and has 12 linear feet or less of supply duct, including the length of the air handler and the plenum, located in unconditioned space, with all other portions of the supply ducts located in conditioned space below the ceiling separating the occupiable space f rom th e attic. Duct efficiency is accounted for when the distribution type is ducted. Oct 15, 2025 · For homeowners in climate zones 1-6, R-8 insulation for attic ducts and R-6 for other unconditioned spaces represents the minimum code compliance. klt3wx, lybe, huzv4, uu2kbp, nefkr, inlf8b, vgci, cdmyl, 3aw6, 1es42,