Arkansas HVACR NewsMagazine November 2025

HVACR NewsMagazine November 2025

State National Chapter News

around the appliance using thermal barrier materials.

ensure occupant safety, SPF must be separated from living spaces by a 15 minute thermal barrier (TB) — typically ½" gypsum board as prescribed by the building code or an approved intumescent coating as an alternative TB. In some attics and crawlspaces with limited access and not used for storage, where direct occupancy is rare, an ignition barrier (IB) covering or coating may suffice. The detailed requirements for TB and IB are covered in Technical Document SPFA-126. But when HVAC systems enter the picture, the rules change. Attics and crawlspaces are common locations for gas-fired heating systems, and when these spaces are insulated with SPF, several precautions are essential: • Dedicated Makeup Air : SPF creates an extremely airtight enclosure. Combustion appliances need a reliable source of fresh air to operate safely. Without it, negative pressure can lead to back drafting and dangerous carbon monoxide buildup. High temperature exhaust from gas appliances must maintain safe distances from SPF and other combustibles. This isn’t just good practice —it’s code . Around Equipment : If SPF is present near combustion equipment, it must be protected. When direct application of a TB is impractical (as in large attics), contractors should build an enclosure Exhaust Clearance : Thermal Barriers

Not all heating systems pose the same risk. High-efficiency furnaces with PVC exhaust systems are generally safe to install in contact with SPF, thanks to their lower exhaust temperatures and sealed combustion design. In unvented attics and crawlspaces with limited access where spray polyurethane foam (SPF) is not protected by a prescriptive ignition barrier (IB), air should not be circulated into these spaces from occupiable space. As a result, these areas cannot be actively conditioned using supply and return airflow. Open ventilation between the floor below an unvented attic and the occupied space beneath — or between the floor above an unvented crawlspace and the space above — can allow smoke to enter occupied areas during a fire. However, when SPF is protected by a thermal barrier (TB) in these locations, active conditioning and open-air exchange with occupied spaces is allowed. Ductwork located in unconditioned spaces is frequently under-insulated and poorly sealed. Spray polyurethane foam (SPF) offers an effective solution for both insulation and air sealing of ducts; however, its use is subject to specific limitations: • Metal Ducts: SPF may be applied to the exterior of metal ducts in accordance with ICC guidelines. When used in this manner, the foam must be protected with the same fire-rated SPF and Ductwork

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