A Taylorsville customer in a 1986-built two-story home contacted us about replacing their original 80% AFUE atmospheric-vent furnace. They had two specific goals: efficiency improvement to reduce gas bills, and addressing the chronic upstairs/downstairs comfort imbalance their home had experienced since construction. The customer had received quotes from other contractors for furnace replacement only, with prices ranging from $5,500 to $8,500, but none had specifically addressed the comfort imbalance issue. This case study documents an integrated furnace upgrade plus two-zone system installation that addressed both efficiency and comfort goals.
Customer Situation
- Home: 1986-built Taylorsville two-story, approximately 2,250 sq ft (1,250 sq ft main level, 1,000 sq ft upper bedroom level)
- Existing equipment: 38-year-old 80% AFUE Carrier atmospheric-vent furnace, original installation; 14-year-old R-410A AC (not being replaced)
- Symptom: Upstairs consistently 6–8°F warmer than downstairs in summer, 5–7°F cooler than downstairs in winter; high gas bills; furnace approaching end of service life
- Customer priorities: Address comfort imbalance, efficiency upgrade, reasonable budget
- Prior quotes: $5,500–$8,500 from other contractors for furnace replacement only
Comfort Imbalance Assessment
We performed comfort imbalance assessment alongside the furnace evaluation:
Measurements during initial visit (cool spring day):
– Outdoor temperature: 52°F
– Main level temperature: 70°F (at thermostat)
– Upper level temperature: 65°F
– Differential: 5°F
Causes of imbalance:
– Single-zone HVAC with thermostat on main level
– Heat distribution provides equal supply to both levels
– Stack effect during cooling pulls warm air upstairs; during heating pulls cold air downstairs
– Two-story home requires per-floor temperature management for optimal comfort
Why furnace replacement alone wouldn’t solve this:
– New furnace would still operate as single zone
– Distribution problem fundamentally requires zoning, not equipment replacement
– More efficient equipment would still produce same comfort imbalance
Integrated Project Recommendation
We recommended addressing both goals together rather than sequential projects:
Combined project scope:
- Modulating condensing furnace replacement — addresses efficiency and equipment age
- Two-zone system installation — addresses comfort imbalance with per-floor temperature control
- Variable-speed equipment selection — works properly with zoning (single-stage doesn’t modulate adequately across zone demand variations)
Why combined project costs less than sequential:
– Single installation visit (vs. coming back later for zoning)
– Ductwork access already available during furnace work
– Commissioning happens once across complete system
– Customer saves approximately $1,500–$2,000 vs. sequential approach
Manual J Load Calculation
- Total conditioned area: 2,250 sq ft
- Insulation: R-13 walls, R-30 attic (1986 construction)
- Windows: 285 sq ft vinyl double-pane (replaced 2008)
- Salt Lake design conditions: 14°F heating / 96°F cooling
Manual J results:
– Total heating load: 56,000 BTU/h
– Total cooling load: 30,000 BTU/h (2.5 tons)
Per-zone analysis:
– Main level zone: 28,000 BTU/h heating / 15,500 BTU/h cooling
– Upper level zone: 28,000 BTU/h heating / 14,500 BTU/h cooling
Equipment sizing: 60,000 BTU furnace (existing was 100,000 BTU — 67% oversized for actual load)
Equipment Selection
Modulating condensing furnace:
– Trane S9V2-VS, 60,000 BTU input, 97% AFUE
– Modulating gas valve provides 40–100% capacity range
– Variable-speed ECM blower for zoning compatibility
– 12-year parts warranty, lifetime heat exchanger warranty (registered)
Zoning system:
– Honeywell HZ322 zone control panel (2-zone)
– Zone dampers in main supply trunk (one per zone)
– Bypass damper for excess airflow management
– Two Ecobee Smart thermostats (one per zone)
Combined project price: $13,800
Installation
Crew: Travis Hollings (lead installer), Mike Reyes, Cole Bennett
Duration: 2 days
Day 1 — Old equipment removal and rough-in:
– Old atmospheric-vent furnace removal
– Old chimney evaluation and decommissioning
– Water heater venting resolution (chimney liner installed for water heater)
– New furnace placement
– PVC venting installation (sidewall)
– Combustion air intake
– Condensate drainage with neutralizer
– Gas line connection
– Electrical connections
Day 2 — Zoning installation and commissioning:
– Zone damper installation in supply trunk (cut openings, install dampers, seal with mastic)
– Bypass damper installation in supply trunk
– Zone control panel installation in equipment area
– Thermostat installations (one main level, one upper level)
– Low-voltage wiring between zone panel and thermostats
– Equipment commissioning across both zones
– Zone operation verification
Commissioning Measurements
Furnace (altitude-corrected for 4,350 ft Taylorsville elevation):
– CO ppm air-free: 9 ppm ✓
– O2: 7.6% ✓
– Combustion efficiency: 96.4% ✓
– Gas inlet pressure: 7.1″ wc ✓
– Manifold pressure low-fire: 1.4″ wc, high-fire: 3.5″ wc ✓
– Temperature rise: 38°F (target 35–65°F) ✓
– Static pressure: 0.44″ wc with bypass open ✓
– Blower amp draw: 4.8 amps (nameplate 6.5 amps) ✓
– Flame sensor microamps: 7.4 µA ✓
Zoning operation:
– Main level only call: zone 1 damper open, zone 2 closed, bypass partially open
– Upper level only call: zone 2 damper open, zone 1 closed, bypass partially open
– Both zones calling: both dampers open, bypass closed
– Modulation observed: furnace fires at low capacity during single-zone calls, ramping up for both-zone calls
– Indoor CO: 0 ppm ✓
Final Cost and Rebate Filing
Customer’s project cost:
– Furnace, zoning system, water heater venting: $13,800
– Less maintenance plan enrollment: -$100
– Net invoice: $13,700
Rebates filed on customer’s behalf:
– Federal 25C tax credit: $600 (furnace)
– Dominion Energy Therm-Wise furnace rebate: $200
Total incentives: $800
Effective net cost after incentives: $12,900
Comparison to alternatives:
– Other contractor quotes for furnace only: $5,500–$8,500
– Adding zoning later as separate project: estimated $4,500–$6,000 with additional commissioning
– Combined project total cost (~$13,000–$14,500 estimated for sequential): $1,500–$2,000 more than our integrated approach
Customer Outcome
Winter performance (first heating season):
Comfort:
– Main level temperature: 70°F at thermostat
– Upper level temperature: 70°F at thermostat (vs. 65°F previously)
– Differential between zones: 0–1°F (customer-controlled by setpoint preferences)
– Modulating furnace provides quieter, more consistent heating
Energy:
– Gas usage compared to prior winter: 41% lower (controlling for weather)
– Annual gas cost reduction: approximately $580/year vs. old 80% AFUE equipment
– Modulating operation runs at lower capacity for longer periods rather than short-cycling
Summer performance:
– Existing AC works with new zoning (variable-speed blower compatible)
– Main level temperature: 74°F at thermostat
– Upper level temperature: 75°F at thermostat (vs. 80°F+ previously)
– AC operates more efficiently with zoning since cooling is delivered where needed
Customer assessment: “The comfort difference is dramatic. We can finally sleep upstairs in summer without having to crank the thermostat way down. The energy savings are an added bonus.”
What This Case Study Demonstrates
- Integrated project approach — addressed both stated goals (efficiency + comfort) together rather than treating them as separate problems
- Zoning is the actual solution to two-story comfort imbalance — equipment efficiency improvement alone doesn’t solve distribution problems
- Manual J right-sizing — original 100,000 BTU furnace replaced with 60,000 BTU (40% smaller) for proper operation
- Variable-speed equipment selection matters for zoning compatibility
- Combined project economics — sequential approach would have cost $1,500–$2,000 more
- Realistic improvements documented — 41% gas usage reduction is significant from 80% to 97% AFUE conversion; zoning eliminated 5–8°F temperature differential between floors
- Water heater venting included — proper atmospheric-vent furnace replacement addresses water heater venting issue
Considering Similar Project?
If you have a Taylorsville two-story home with comfort imbalance issues plus aging furnace, contact us or call (385) 250-0687. We provide integrated project scoping that addresses comfort and efficiency goals together rather than treating them as separate projects.
- Phone: (385) 250-0687
- Address: 4454 Manhattan Ct, West Valley City, UT 84120