Thanks, Zak.
Good idea. Here’s the 2024 IRC reference:
N1103.3.3 (R403.3.3) Ductwork located outside conditioned space.
Supply and return ductwork located outside conditioned space shall be insulated to an R-value of not less than R-8 for ducts 3 inches (76 mm) in diameter and larger and not less than R-6 for ducts smaller than 3 inches (76 mm) in diameter. Ductwork buried beneath a building shall be insulated as required by this section or have an equivalent thermal distribution efficiency. Underground ductwork utilizing the thermal distribution efficiency method shall be listed and labeled to indicate the R-value equivalency.
This section requires that all supply and return ductwork located outside of conditioned space, regardless of size, be insulated to R-8 or R-6 depending on duct diameter. Ducts buried under a building either must be insulated to these requirements or be labeled to indicate an equivalent R-value.
You’re confusing HVAC duct supply and return with a bathroom exhaust duct.
Chapter 15 in the IRC covers the exhaust systems.
Okay, @mwilles, then where in Chapter 15 are the provisions for insulating ducts of exhaust systems that pass through unconditioned spaces?
While the Ch 11 section focuses on HVAC supply and return ducts, the underlying principle of preventing heat loss and condensation applies equally to mechanical exhaust ducts.
We can also reference 2024 IRC M1601.4.6, Duct Insulation. Where a duct is installed outdoors or in an unconditioned area (such as an attic or crawl space), it can be exposed to humidity and temperature differentials that can create condensation on the outside of the duct. A vapor retarder must be installed on the exterior of the duct to protect the duct and/or insulation from damage caused by moisture.
The problem is the location of your quote is for the HVAC duct section. Are we to inspect bathroom exhaust ducts to the same standard as an HVAC ducts?
While the Ch 11 section focuses on HVAC supply and return ducts, the underlying principle of preventing heat loss and condensation applies equally to mechanical exhaust ducts.
It’s not required in my jurisdiction. This would be a local amendment to the IRC depending on jurisdiction. Colorado and South Carolina have a very different climates.
@mwilles, right, I agree, if I were doing a code inspection and concern about what the local building official thinks. Home inspectors are not enforcing the code. Home inspectors have the freedom to use the code when inspecting a condensate-sweating pipe coming from a bathroom exhaust fan that’s passing through a cool unconditioned space. All of the information provided to that client wanting to know more about that condition is valuable, regardless of the current code cycle adopted by the local building official.
I found a good building code reference, which I saw @jjonas refer to in another thread.
2024 International Mechanical Code IMC Chapter 6 contains protection to life and property from the hazards associated with air-moving equipment and systems. This chapter states requirements for the installation of supply, return and exhaust air systems.
2024 IMC Section 603.12 Condensation. https://codes.iccsafe.org/content/IMC2024V2.0/chapter-6-duct-systems#IMC2024V2.0_Ch06_Sec603.12
Provisions shall be made to prevent the formation of condensation on the exterior of any duct.
Condensation can form on a duct when the temperature of the air in the duct is near the dewpoint of the air around the duct. The application of insulation with a vapor barrier covering prevents the duct from “sweating” by preventing moisture vapor from penetrating the insulation and reaching the duct surface. Duct sweating (condensation formation) is typically a problem for cooling ducts that pass through unconditioned areas where the humidity is not controlled. Condensation can cause insulation damage, corrosion or duct failure, and the accumulated water can cause damage to the building. Condensation can also occur inside of ducts, such as when ducts conveying warm, moist air from a bathroom exhaust pass through an attic space or similar unconditioned area. Condensation in duct interiors can degrade the duct, promote mold and fungus growth and cause structural damage.
2024 IRC N1103.3.3 Ductwork located outside conditioned space. https://codes.iccsafe.org/content/IRC2024P2/chapter-11-re-energy-efficiency#IRC2024P2_Pt04_Ch11_SecN1103.3.3
Supply and return ductwork located outside conditioned space shall be insulated to an R-value of not less than R-8 for ducts 3 inches (76 mm) in diameter and larger and not less than R-6 for ducts smaller than 3 inches (76 mm) in diameter. This section requires that all supply and return ductwork located outside of conditioned space, regardless of size, be insulated to R-8 or R-6 depending on duct diameter. While this code section focuses on HVAC supply and return ducts, the underlying principle of preventing heat loss and condensation applies equally to mechanical exhaust ducts.
I agree if that was how the codebook was written. When you start changing codebook content or context, that’s where things get dangerous. Code books are written with context. Taking an HVAC requirements and implementing it to an exhaust fan requirement is changing the context of the intended code.
What you did to the bathroom exhaust fan code would be like me saying we need to insulate toilet drains in unconditioned spaces. It’s not in the plumbing section. However, condensate drains are required to be insulated in unconditioned spaces.
Cut and pasting and rearranging codes from the code book to meet your narrative is ridiculous.
So are we talking about commercial inspections or are we talking about a bathroom fan in a residence?
can you show me where this is in the IRC?
I’m not here to argue or change your mind. I’m just saying that InterNACHI® has published the article for home inspectors to refer to when they observe uninsulated ducts coming from mechanical exhaust fans in unconditioned attic spaces.
They’re both ducts. While some sections of code focuses on HVAC supply and return ducts, the underlying principle of preventing heat loss and condensation applies equally to mechanical exhaust ducts.
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