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TECHNICAL INFORMATION
COMMUNICATION
Quality and Continuous Improvement
N
umber: TIC2023-0012
Title: ULN90 Combustion Air Filter
Product Category: Residential Furnaces
Products Affected:
Condensing Ultra-Low NOx Gas Furnaces
MODELS AFFECTED:
Situation:
Carrier has found that airborne fiberglass insulation in attics can be pulled into the burner box on the
Ultra-Low NOx, condensing gas furnaces. Fine fibers of fiberglass insulation remain airborne in
attics well after insulation installation. The fiberglass insulation causes a restriction in the burner box
that can lead to undesirable combustion tone/noise during operation, increased burner box
temperatures and BTS (Burner Thermal Switch) trips. The destructive analysis of failed burner
boxes has clearly shown glass fibers entrapped in the burner mesh and diffuser plate as the root
cause of restricted burner boxes.
Solution:
Carrier engineering has tested and approved three field installed solution for preventing airborne
glass fibers and other debris from being pulled into the furnace burner box.
Solution 1 (Recommended):
Install the combustion air/vent system as a direct-vent, two pipe system. Drawing combustion air
from a space outside the attic will greatly reduce the chance of noncombustible material being drawn
into the burner box and burner mesh.
Only trained and qualified personnel should design, install, repair and service HVAC systems and equipment. All national standards and
safety codes must be followed when designing, installing, repairing and servicing HVAC systems and equipment. It is the responsibility of
the Dealer to ensure local codes, standards, and ordinances are met.
Carrier
59CU5
59SU5
1
Date: 09/26/2023
Revision
Bryant
935C
935S
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Summary of Contents for Carrier 59CU5
- Page 1 935S Situation: Carrier has found that airborne fiberglass insulation in attics can be pulled into the burner box on the Ultra-Low NOx, condensing gas furnaces. Fine fibers of fiberglass insulation remain airborne in attics well after insulation installation. The fiberglass insulation causes a restriction in the burner box that can lead to undesirable combustion tone/noise during operation, increased burner box temperatures and BTS (Burner Thermal Switch) trips.
- Page 2 TECHNICAL INFORMATION COMMUNICATION Solution 2: If unable or unwilling to orient the combustion air pipe to pull fresh air from outside of the attic space, create an intake filter using a PVC increaser (2x4 if using 2” intake piping, 3x4 if using 3” intake piping), a 4”...
- Page 3 TECHNICAL INFORMATION COMMUNICATION Fig. 2 Assembled intake air filter Solution 3: Utilize an inline filtration box to filter intake combustion air. These intake air filter boxes are available from multiple third-party suppliers in various sizes to fit space constraints. Only trained and qualified personnel should design, install, repair and service HVAC systems and equipment. All national standards and safety codes must be followed when designing, installing, repairing and servicing HVAC systems and equipment.
- Page 4 Replace this filter only if filter is damaged or excessively dirty. Expected filter life is 2-5 years in most attic applications. See Carrier Informational Bulletin TIC2023-0012 for additional information. NOTICE This furnace is equipped with a semi-permanent combustion air filter. This filter has been installed per manufacturer recommendations to prevent airborne debris from entering the furnace.
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