DUCTWORK REPAIR & RETROFIT IN SALT LAKE CITY

Ductwork in Salt Lake City is fundamentally different from ductwork in West Jordan or Lehi. Most of SLC's housing stock is older than the concept of central forced-air HVAC. Avenues, Sugar House, Marmalade, and Liberty Wells homes were built between 1890 and 1940 with hydronic boilers and radiators — or with massive gravity-fed octopus furnaces in the basement that pushed warm air upward through huge trunk lines. When forced-air HVAC was retrofitted into these homes in the 50s, 60s, and 70s, the ductwork was almost always undersized, poorly sealed, run through unconditioned attics, and balanced by guess. Most of those systems are still in service.

Our SLC ductwork crew spends most of its time on three categories of work. First, sealing leaky existing ductwork — most pre-1990 ductwork in SLC homes leaks 25-40% of conditioned air into attics, crawlspaces, and wall cavities. Second, converting old octopus-furnace ductwork to modern forced-air supply and return — the original 16-inch round trunks that fed gravity-fed warm air don't work right with a high-efficiency variable-speed blower. Third, retrofitting ductwork into 1920s Avenues homes that are 16-18 feet wide and have nowhere obvious to run trunks — usually the right answer is single-zone ductless mini-split heat pumps, but sometimes we make it work with creative routing through closets and soffits.

What duct problems cost in real dollars and air quality

A typical SLC home with leaky ductwork (25-35% loss is common in pre-1990 systems) is paying an extra $400 to $800 per year on heating and cooling — gas bills run higher in SLC than in newer suburbs because of the older equipment cohort. Worse, on January inversion days when outdoor PM2.5 spikes, leaky attic-run ductwork actively pulls polluted attic air into the supply stream and circulates it through the house. Sealing the ducts cuts utility bills 15-25% AND meaningfully improves indoor air quality on the worst inversion weeks. Payback runs 3 to 6 years on utility savings; the air quality benefit is immediate.

Common duct problems in SLC neighborhoods

• Octopus furnace conversion mismatch — original 16-18" round trunks that don't match modern furnace plenum sizing
• Unconditioned attic flex duct — joints disconnected at plenum, R-2 insulation that's degraded, hot in summer, frozen condensate in winter
• Undersized return air — single small return in a hallway feeding the whole house, blower starves for air
• Crushed flex duct in tight spaces — common in narrow Avenues homes where ducts squeeze through joist bays
• Leaky sheet metal joints — original 50s and 60s rigid metal trunks where mastic has dried and fallen off
• No insulation in unconditioned spaces — attic and crawlspace ducts in old SLC homes often have R-4 or nothing
• Single-zone heat distribution — original gravity systems have no zone control; some rooms always too hot, others too cold

Diagnostic — what's actually happening in your ducts

Two tools do most of the work. A pressure-based blower door and duct blaster test measures total leakage in cubic feet per minute at 25 pascals — this is the standard energy-code metric and tells us objectively how much your system leaks. Then we visually inspect with a lighted probe and camera, pulling insulation to look at joints, checking flex duct runs, measuring trunk sizes against load calculations. SLC homes typically test at 25-45 CFM25 per 100 sqft of conditioned space; Utah energy code targets 8 CFM25 on new construction. Lots of room to improve.

Sealing options for old SLC homes

Manual sealing with mastic and foil tape — works where we can access joints. Mastic adhesive brushed onto every seam, foil-backed butyl tape on major connections, strap-and-screw on flex-to-rigid transitions. Effective in homes with accessible attics and basements. $1,500 to $3,500 for a typical SLC home.

Aeroseal interior sealing — a polymer aerosol pushed through the duct system under pressure; as it hits leaks, it accumulates and seals from the inside without needing to access the exterior. Works on attic flex inside finished walls — exactly the situation in narrow Avenues and Sugar House homes where you can't easily get to the ducts. $2,500 to $4,500 for most homes. Often the only practical option in homes with finished basements and fully-trimmed-out attic spaces.

Replacement of bad sections — if flex duct is collapsed, crushed, or just too old to seal, we replace runs with new insulated flex or rigid sheet metal. $15-$35 per foot installed.

Octopus furnace conversion — SLC specialty

When we replace a 1940s gravity octopus furnace with a modern 95% AFUE condensing unit, the original ductwork almost always needs significant modification. The 16-18" round trunks designed for natural-convection airflow are now massively oversized for a small modern furnace's CFM output, which causes airflow velocity problems. The original branch runs to second-floor registers might be too restrictive for modern airflow. The original return path — usually a single grille at the bottom of the basement stairs — is way undersized. We resize the supply plenum, often add a new return air, and balance the system as part of any octopus replacement. Plan for $1,500-$3,500 in ductwork modification on top of the furnace install.

Single-zone retrofit in narrow Avenues homes

Some Avenues bungalows are 16-18 feet wide. There's no room to run new trunks through the house without massive interior surgery. In these cases the right answer is usually a multi-zone Mitsubishi Hyper-Heat ductless mini-split system — wall-mount or ceiling-cassette indoor units in each zone, slim refrigerant lines instead of ductwork, no significant remodeling. Install runs $12,500 to $22,000 for a 3-5 zone system, more if you need cassette mounts in every room. Way less expensive and more comfortable than running ductwork through plaster walls.

Registers, grilles, and balancing

Final step on most ductwork projects is room-by-room airflow balancing. Registers have dampers; we adjust them to deliver the right volume to each room based on heat load. Bigger south-facing rooms get more air in summer; colder north-facing rooms more in winter. On systems with zone dampers, we calibrate damper positions and confirm the bypass works. A well-balanced system feels even across the house and the equipment cycles properly.