South Salt Lake Two-Story Home Three-Zone HVAC Installation

Customer:

Brennan and Sage T. (consent for documentation given)

Address area:

South Salt Lake, near 4500 South and 700 East — established two-story residential subdivision

Home characteristics:

2004 two-story home, approximately 2,840 sq ft. Main floor (1,420 sq ft) includes living areas, kitchen, dining room, and home office. Second floor (1,200 sq ft) includes primary bedroom suite, two secondary bedrooms, and laundry room. Daylight basement (220 sq ft conditioned space, balance unfinished). Vinyl siding with brick accents. Vinyl double-pane windows throughout. Forced-air HVAC with 2004 original ductwork. Standard 2004 South Salt Lake construction representative of the residential subdivisions along the 4500 South corridor.

Project type:

Three-zone retrofit on existing single-zone HVAC system to address inter-floor temperature variation common in two-story homes with single central thermostat

Project completion date:

October 14, 2024

Total cost:

$5,200 installed. No rebates available for zoning retrofit work.

Background

Brennan and Sage T. purchased this home in 2018 (6 years at time of project). The 2004 HVAC system was original at their purchase. Both spouses worked remotely from home offices on different floors — Brennan on the main floor, Sage in the upstairs primary bedroom suite repurposed as office. Inter-floor temperature variation created daily conflict: Brennan’s main floor office often ran 71-73°F while Sage’s upstairs office reached 77-80°F during cooling and 65-68°F during heating. Single thermostat located in main floor hallway couldn’t address the variation. They had been working with a single thermostat setpoint compromise of 73°F that left both offices uncomfortable. The 2024 project addressed this through three-zone retrofit, dividing the home into independent setpoint zones.

Existing Equipment (Retained)

Furnace:

2004 Carrier 58STA050 furnace, 80,000 BTU/hr input, 80% AFUE. 20 years service at time of project. Operating well within manufacturer specifications. Atmospheric venting through dedicated B-vent stack. Located in basement utility area. Approaching end of expected service life; customers noted likely replacement within 2-3 years. Decision to retain existing equipment during zoning retrofit: equipment functional, replacement decision separate. Zoning retrofit compatible with future equipment replacement.

AC:

2004 Carrier 38ACA AC, 3-ton, 12 SEER (pre-SEER2 rating), R-22 refrigerant. 20 years service. Operating well. R-22 charge maintained. Approaching end of service life; replacement timing aligned with future furnace replacement decision.

Ductwork:

2004 sheet metal trunk and branch ductwork. Round trunk descending from basement equipment through floor system to main level central trunk; branches to room registers via short flex transitions. Second floor branches accessed through stair chase from main floor trunk. Standard 2004 residential ductwork.

Thermostat (replaced):

2004 Honeywell Round mechanical thermostat in main floor hallway. Single zone control across entire home. Replaced during this project with three communicating zone thermostats.

Filtration:

1-inch MERV 8 filter at return air. Standard residential filtration. Retained for this project.

Pre-Project Diagnostic Assessment

Initial consultation (September 2024):

90-minute on-site consultation. Detailed assessment of: ductwork configuration for zoning feasibility, electrical compatibility for zone control wiring, equipment compatibility with zone control board, customer priorities for setpoint preferences and operating patterns.

Temperature variation documentation:

Customers had been tracking temperature variation across zones for 3 months prior to consultation. Documented patterns:

• Cooling season (summer 2024): Main floor 72-74°F when set to 73°F; second floor 77-80°F at same setpoint; basement 68-71°F at same setpoint
• Heating season (winter 2023-2024): Main floor 70-72°F when set to 71°F; second floor 65-68°F at same setpoint; basement 62-64°F at same setpoint
• Pattern consistent with typical two-story home: hot air rises (cooling problem upstairs) and falls (heating problem upstairs)

Ductwork analysis (Manual D):

• Supply plenum static pressure: 0.54″ WC (within acceptable range)
• Main floor branches: 720 CFM total airflow (designed for main floor load)
• Second floor branches: 580 CFM total airflow
• Basement branch: 130 CFM
• Total system airflow: 1,430 CFM (appropriate for 3-ton AC at altitude derate)
• Trunk locations adequate for damper actuator installation at three points: main floor branch, second floor branch, basement branch

Zoning feasibility verification:

Three-zone configuration feasible based on:

• Adequate airflow per zone (minimum 300 CFM required for damper modulation)
• Equipment capacity adequate for zone-call-driven operation
• Ductwork access at trunk-to-branch transitions allows damper actuator installation without major ductwork modifications
• Existing electrical adequate for zone control wiring (24V control circuits)

Alternative configurations evaluated:

• Two-zone (main floor + upstairs): Simpler installation, $4,200 estimated. Adequate for primary inter-floor variation. Basement remained part of main floor zone. Trade-off: basement would still be over-conditioned when main floor reached setpoint.
• Three-zone (main floor + upstairs + basement): Slightly more complex, $5,200 actual. Addresses basement over-conditioning issue. Selected option.
• Four-zone (with primary bedroom suite as separate zone): Estimated $7,400. Sage’s primary office is the upstairs primary bedroom suite; separating it from secondary bedrooms could address her specific setpoint needs more precisely. However, four-zone added complexity with marginal additional benefit; three-zone determined adequate.
• Mini-split addition for upstairs primary suite: Estimated $8,800 installed. Standalone solution rather than zoning retrofit. Rejected because customer wanted whole-home solution rather than supplemental equipment.

Decision Framework

Customer selection:

Brennan and Sage selected three-zone configuration. Reasoning: (a) three-zone addresses both inter-floor variation and basement over-conditioning; (b) cost premium over two-zone ($5,200 vs $4,200) reasonable for additional zone independence; (c) compatible with future equipment replacement when furnace and AC reach end of life; (d) standard residential thermostats (not smart) acceptable given customers’ preference for simple operation.

Thermostat selection considerations:

Customers evaluated smart vs. standard programmable thermostats. Smart thermostats (ecobee, Nest) offer remote control and energy reporting. Standard programmable (Honeywell T6 Pro) offers schedule-based operation. Customers selected Honeywell T6 Pro standard programmable for all three zones — simpler operation, no Wi-Fi configuration required, no recurring concerns about smart home cloud connectivity.

Equipment Specifications

Zone control board:

• Honeywell Truezone HZ432 zone control board (3-zone capable, expandable to 4-zone if future requirement)
• Compatible with Honeywell T6 Pro communicating thermostats
• Built-in damper actuator power supply (24V)
• System protection logic (prevents short-cycling on zone-only calls)
• 5-year manufacturer warranty

Damper actuators (3 units):

• Belimo TruZone CCV24-MFT actuators (24V proportional, normally-open)
• Round damper bodies for 8-inch trunk transitions (main floor zone: 8-inch, upstairs zone: 8-inch, basement zone: 6-inch — downsized actuator)
• Belimo TruZone CCV24-MFT actuators rated for residential duty cycle
• 5-year manufacturer warranty

Thermostats (3 units):

• Honeywell T6 Pro communicating thermostats (programmable, non-Wi-Fi)
• Located in:
  • Main floor central hallway (replacing original Honeywell Round)
  • Upstairs hallway central to bedroom area (new location, drywall penetration)
  • Basement utility area (close to existing equipment)
• Standard 5-2 day programming capability
• 2-year manufacturer warranty

Control wiring:

24V thermostat wiring from zone control board to each thermostat location. Damper actuator wiring from zone control board to each actuator location. Total wiring runs: approximately 85 feet across the home. Routing through existing electrical chases and behind drywall to minimize visible runs.

Bypass damper:

Honeywell ARD bypass damper installed in supply trunk to manage airflow when only one zone is calling. Prevents excessive static pressure when single small zone (basement) is the only zone with a call. Standard practice for single-equipment multi-zone systems.

Installation Scope and Timeline

Day 1 (October 13, 2024):

• 8:00 AM: Marcus Halverson and Eli Tran arrived. Equipment delivered.
• 8:30 AM: System shutdown. Power confirmed off at HVAC equipment.
• 9:00 AM: Zone control board installation in basement utility area near existing equipment. Wired to 24V transformer source.
• 10:00 AM: First damper actuator installation (main floor branch). Trunk cut for damper body insertion. Belimo actuator mounted and wired to zone control board.
• 11:30 AM: Second damper actuator installation (upstairs branch).
• 1:00 PM: Lunch break.
• 1:45 PM: Third damper actuator installation (basement branch). Smaller 6-inch damper required.
• 2:30 PM: Honeywell ARD bypass damper installation in supply trunk.
• 3:30 PM: System restart and basic operation verification across all three zones.
• 5:00 PM: Day 1 completion. System operational with default zone parameters.

Day 2 (October 14, 2024):

• 8:00 AM: Marcus Halverson on-site for thermostat installation and zone calibration.
• 8:30 AM: Main floor thermostat installation (replacing original Honeywell Round in hallway). Wiring connection to zone control board.
• 9:30 AM: Upstairs thermostat installation. Drywall penetration for new wiring location in upstairs hallway. Patched with paint-matching texturing.
• 11:00 AM: Basement thermostat installation.
• 12:00 PM: Lunch break.
• 1:00 PM: Zone calibration. Testing each zone’s response to thermostat call across heating and cooling modes. Verifying damper actuator response times and full close/open functionality.
• 2:30 PM: Bypass damper calibration to address static pressure during single-zone operation.
• 3:30 PM: System verification: full system operation across all three zones with various combinations of zone calls.
• 4:30 PM: Customer education on thermostat programming, zone interaction, expected operating patterns.
• 5:00 PM: Day 2 completion. Customer signed off on installation acceptance.

Commissioning measurements (after installation):

• Static pressure (all zones calling): 0.51″ WC (improved slightly from baseline 0.54″ due to bypass damper management)
• Static pressure (single small zone calling, basement): 0.55″ WC with bypass operating — well within acceptable range
• Main floor zone airflow: 720 CFM (matches design)
• Upstairs zone airflow: 580 CFM
• Basement zone airflow: 130 CFM
• Zone response time: Damper actuators reaching full close/open within 35-45 seconds (Belimo TruZone manufacturer spec: 30-60 seconds)
• Operation across zone combinations: All 7 possible zone-call combinations tested and verified

AHJ inspection:

Not required for zoning retrofit on existing system in South Salt Lake jurisdiction. Maintenance/upgrade scope, not equipment installation.

Cost Breakdown

Itemized project cost:

• Honeywell Truezone HZ432 zone control board: $480
• Belimo TruZone CCV24-MFT damper actuators (3 units): $945 ($315 each)
• 8-inch damper bodies (2 units): $245
• 6-inch damper body (1 unit): $145
• Honeywell ARD bypass damper: $185
• Honeywell T6 Pro communicating thermostats (3 units): $585 ($195 each)
• Control wiring (approximately 85 ft): $185
• Drywall penetration for upstairs thermostat + patching/texturing: $185
• Trunk modifications for damper insertion: $485
• Installation labor (Marcus Halverson + Eli Tran, 17 hours combined across 2 days): $1,485
• Zone calibration and commissioning: $385
• Subtotal: $5,320
• Existing customer discount (Brennan and Sage customers since 2019): -$120
• Total customer cost: $5,200 installed

Rebates and incentives:

• Rocky Mountain Power Wattsmart: not applicable to zoning retrofit (covers equipment installation only)
• Dominion Energy ThermWise: not applicable
• Federal IRA 25C: not applicable to zoning retrofit (covers high-efficiency equipment installation)

Comparison to alternative approaches:

• Two-zone retrofit (would not address basement variation): $4,200 estimated
• Mini-split addition for primary bedroom suite: $8,800 installed
• Full equipment replacement with built-in zoning (during eventual furnace replacement): zoning component cost estimated at $2,400-$2,800 incremental to equipment replacement, vs $5,200 as standalone retrofit. Trade-off: zoning retrofit value during current equipment service life is immediate; bundling with equipment replacement defers improvement.

Post-Project Outcomes

Winter 2024-2025 heating season performance:

• Main floor zone setpoint: 70°F. Actual temperatures: 69-71°F consistently.
• Upstairs zone setpoint: 70°F. Actual temperatures: 69-71°F (previously 65-68°F at single thermostat setpoint).
• Basement zone setpoint: 65°F. Actual temperatures: 64-66°F (previously 62-64°F under-conditioning).
• Sage’s upstairs office: Maintained 70°F consistently throughout winter, eliminating the previous 65-68°F variation that had been her primary complaint.
• Gas bill comparison winter 2023-2024 vs. 2024-2025: -$45/month average (basement under-heating and upstairs over-heating both eliminated, more efficient distribution).

Summer 2025 cooling season performance:

• Main floor zone setpoint: 73°F. Actual temperatures: 72-74°F consistently.
• Upstairs zone setpoint: 73°F. Actual temperatures: 72-74°F (previously 77-80°F at single thermostat setpoint).
• Basement zone setpoint: 76°F. Actual temperatures: 75-77°F (previously 68-71°F over-conditioning).
• Sage’s upstairs office: Maintained 73°F consistently throughout summer.
• Electric bill comparison summer 2024 vs. summer 2025: -$28/month average July-August (basement over-conditioning eliminated, more efficient distribution).

Customer-reported assessment:

Brennan: “We bought this house knowing the temperature variation was a problem, but we underestimated how much it affected our daily work-from-home routine. The zoning retrofit was the single biggest quality-of-life improvement we’ve made to the house.” Sage: “Being able to set my office at 70°F in winter and 73°F in summer, independent of what’s happening on the main floor, has eliminated a daily source of stress. I should have done this years ago.”

Daily operating pattern:

• Weekdays: All three zones at active setpoints during work hours (Brennan main floor, Sage upstairs); basement at reduced setpoint (heating) or elevated setpoint (cooling)
• Evenings: Main floor and upstairs active setpoints; basement reduced
• Overnight: All zones at moderate setpoint (saving energy)
• Weekends: Variable patterns based on home use

Annual energy bill changes:

• Winter heating: -$45/month average across 5-month heating season = -$225/year
• Summer cooling: -$28/month average across 2-month peak cooling season = -$56/year
• Combined annual savings: -$281/year
• Payback period on $5,200 investment: 18.5 years on energy savings alone
• Customer-reported comfort improvement value: significant (not captured in payback calculation)

System integration with future equipment replacement:

Existing zoning system is compatible with future furnace and AC replacement when 2004 equipment reaches end of life. Zone control board, damper actuators, and thermostats all work with replacement equipment. When customers eventually replace equipment (estimated 2026-2028), zoning continues without additional cost.

Ongoing service relationship:

Brennan and Sage continued as customers post-project. Annual tune-ups continue. Plan benefits applied to ongoing service. Service relationship continues smoothly.

Why This Case Study Illustrates Important Patterns

Two-story home temperature variation root cause:

Inter-floor temperature variation in two-story homes is the inevitable result of: convection (hot air rises, cold air falls), solar gain differences between exposures, distribution patterns from central single-thermostat HVAC systems, and equipment cycling patterns. Zoning addresses the symptom directly by allowing independent setpoints per floor. Ductwork modifications could address some convection issues but not all; zoning is the comprehensive solution.

Existing equipment vs. equipment replacement timing:

Some customers consider postponing zoning retrofit until equipment replacement (bundling the costs). Trade-off: zoning value during remaining equipment service life is immediate; bundling defers improvement. For Brennan and Sage, 2-3 years estimated remaining equipment service life meant zoning value during that period justified standalone retrofit. For customers with newer equipment (5+ years remaining service life), bundling may make more sense.

Two-zone vs. three-zone vs. four-zone trade-offs:

Each zone added increases cost and complexity. Two-zone (main + upstairs) addresses primary inter-floor variation but leaves basement as part of one zone. Three-zone adds basement independence. Four-zone adds room-level granularity (typically separating primary bedroom suite). Cost increment per zone: approximately $1,000-$1,500. Marginal benefit per additional zone decreases — first zone separation provides most value, additional zones provide diminishing returns.

Bypass damper necessity:

Multi-zone systems with single equipment require bypass damper management when zone calls don’t match equipment capacity. When only the small basement zone calls, the equipment’s full capacity must go somewhere; bypass damper allows excess airflow to recirculate through the equipment cabinet, preventing excessive static pressure. Skipping bypass damper installation in single-zone-call scenarios stresses equipment and reduces efficiency.

Smart vs. standard thermostat selection:

Brennan and Sage chose standard programmable thermostats. Standard programmable adequate for set-and-forget operation. Smart thermostats provide remote control, energy reporting, smart scheduling, and home automation integration — valuable for some customers, not necessary for others. The thermostat choice is independent of zoning equipment; zoning works with either type.

Customer-reported value beyond energy savings:

Energy savings of $281/year produce 18.5-year payback on $5,200 investment — relatively long payback period. The actual customer value came from daily comfort improvement and elimination of household climate-related conflict. Quality-of-life improvements are real economic value even if difficult to capture in payback calculation.

Code and Standards Compliance Documentation

Applicable codes and standards:

• ACCA Manual D: Ductwork analysis (existing ductwork verified adequate for zoning configuration)
• ACCA Manual N: Zoning system design protocol (3-zone system designed per protocol)
• 2024 IMC with Utah amendments: Mechanical systems modifications
• Utah DOPL HVAC contractor licensing: #11567823-5501 active and current
• NEC Article 725: Class 2 control circuits (24V zoning control wiring compliant)

Documentation provided to customer:

• Zone configuration diagram
• Damper actuator locations and wiring schematic
• Thermostat installation locations
• Pre and post-project static pressure measurements
• Zone calibration results
• Warranty registration for zone control board, damper actuators, thermostats

Frequently Asked Questions

Can any two-story home benefit from zoning retrofit?

Most two-story homes do experience inter-floor temperature variation that zoning addresses. Eligibility for retrofit depends on: ductwork accessibility for damper installation, adequate airflow per zone, equipment capacity for zone-call-driven operation, electrical capacity for control wiring. Ducted homes are universally compatible; specific feasibility analysis during consultation identifies any constraints.

Why not just install separate equipment per floor?

Cost. Separate equipment per floor (two furnaces, two AC condensers, two air handlers) costs $14,000-$20,000+ additional vs. zoning retrofit at $4,200-$7,400. Zoning retrofit achieves 90% of the comfort benefit at 30-40% of the cost. Separate equipment makes sense for very large homes (4,000+ sq ft) or homes with complex layouts that exceed single-equipment zoning capability. For typical two-story homes under 3,500 sq ft, zoning retrofit is the better economic choice.

How long does the zoning equipment last?

Honeywell Truezone zone control boards typically have 10-15 year service life. Belimo TruZone damper actuators have 10-12 year service life. Honeywell T6 Pro thermostats have 8-10 year service life. Damper bodies themselves (sheet metal) last 20+ years. Components are replaceable individually as they reach end of life. Total zoning system service life often matches or exceeds underlying HVAC equipment service life.

Will zoning affect my equipment warranty?

No. Zoning retrofit is compatible with all major HVAC manufacturer equipment. Bryant, Carrier, Trane, Lennox, Goodman, and other manufacturers all allow zoning systems with their equipment. The zone control board interfaces with equipment via thermostat connection — same connection method as single-zone thermostats. No equipment modification required, no warranty implications.

What if my equipment needs replacement during zoning system life?

Existing zoning equipment is compatible with replacement HVAC equipment. Zone control board, damper actuators, thermostats remain in service. Replacement equipment installs with same thermostat connection as original. Zoning continues without additional cost. This is what makes standalone zoning retrofit economical — the investment carries forward through equipment replacement.

Project Details Summary

Customer:

Brennan and Sage T. (consent for documentation given; customers since 2019)

Property:

South Salt Lake 2004 two-story home, 2,840 sq ft with daylight basement, work-from-home dual office configuration

Project:

Three-zone HVAC retrofit on existing 2004 single-zone Carrier equipment

Completion date:

October 14, 2024 (two-day installation)

Total cost:

$5,200 installed (with customer loyalty discount)

Equipment installed:

Honeywell Truezone HZ432 zone control board, Belimo TruZone CCV24-MFT damper actuators (3 units with 8-inch, 8-inch, and 6-inch damper bodies), Honeywell ARD bypass damper, Honeywell T6 Pro communicating thermostats (3 units)

Outcome:

Independent setpoint capability across main floor, upstairs, and basement zones. Sage’s upstairs office maintained 70°F winter / 73°F summer consistently. Combined annual energy savings $281/year. 18.5-year payback on energy savings; significant customer-reported quality-of-life improvement.

Ongoing service relationship:

Comfort Care plan member continuing. Annual tune-ups scheduled. Equipment replacement decision deferred to 2026-2028 with zoning system carrying forward.

Schedule HVAC Zoning Consultation

• Phone: (385) 300-1867
• Address: 756 E Winchester St #322, Salt Lake City, UT 84107
• Email: info@saltlakecityheatingairconditioning.xyz
• Utah DOPL HVAC Contractor License: #11567823-5501
• EPA Section 608 Universal (Lead Tech): #608U-2009-447129

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