Case Study: High-Velocity Small-Duct AC Retrofit for a 1925 New Britain Colonial Revival
This case study documents a 2025 project adding whole-home central cooling to a 1925 Colonial Revival in New Britain's West End neighborhood. The home had original hot-water boiler heating but no cooling system; the homeowners wanted whole-home cooling that preserved their substantial original interior architecture while providing traditional supply registers throughout rather than visible ductless indoor units. The project used SpacePak high-velocity small-duct technology to route 2-inch flex tubing through wall cavities and ceiling chases.
Customer Situation
The homeowners had lived in the 2,800 square foot Colonial Revival for 16 years before deciding to add cooling:
- Original cooling approach: Window AC units in 4 primary rooms during summer; oscillating fans in other spaces; uncomfortable second-floor bedrooms during heat waves; no cooling in finished basement office.
- Aesthetic priorities: Strong preference for traditional supply registers rather than visible ductless wall units; homeowners didn't want any visible cooling equipment in primary living spaces; preserved early-20th-century Colonial Revival character important.
- Interior features to preserve: Original oak hardwood floors throughout; plaster walls with picture rails and crown molding; original built-in shelving in library; ornate plaster ceiling medallion in dining room; tile fireplace surrounds in living room and library.
- Heating system: 2019 modulating condensing boiler with cast iron radiator distribution; 18 radiators across 3 floors; preserved and working well.
- Customer preference: Whole-home cooling solution with traditional appearance; willing to invest premium for solution matching architectural character; long-term home retention planned.
- Initial consultation: Customer specifically requested high-velocity small-duct system after researching options; previous neighbor installation in similar 1920s home provided positive reference.
Diagnostic Visit and System Design
April 2025 consultation visit and system design:
- Manual J cooling load calculation: 33,000 BTU/hr (2.75 ton) whole-home cooling load at Hartford 88°F/73°F summer design; load distribution favoring west and south exposures.
- System selection: SpacePak SPS Series small-duct high-velocity system; 36,000 BTU/hr nominal cooling capacity (3 ton); R-410A refrigerant; matched to home load with reasonable margin.
- Indoor unit placement: Air handler placement in third-floor attic space; access via existing attic stairs; sufficient clearance for installation and future service.
- Outdoor unit placement: Side yard location away from primary outdoor living areas; 30 inches from exterior wall; vegetation screening preserved with placement coordination.
- Distribution design: Route 2-inch flex tubing supply runs through wall cavities, closet chases, and accessible ceiling spaces; 14 supply outlets total throughout home; return air centrally located.
- Wall and ceiling access: Identified access points minimizing visual disruption; some closet ceiling penetrations; supply outlets in inconspicuous locations.
- Electrical service: Existing 200A service adequate; dedicated 240V circuit required for outdoor unit and air handler.
- Refrigerant lineset routing: Through attic from outdoor unit to indoor air handler; standard lineset run.
Solution Scope and Equipment Selection
Equipment Selected
- SpacePak SPS Series 3-ton outdoor condenser: R-410A refrigerant, variable-speed inverter compressor; SEER2 18.5 efficiency rating; matched to indoor air handler.
- SpacePak SPS Series air handler: Mounted in third-floor attic; ECM blower motor; designed for high-velocity small-duct distribution; integrated supplementary electric heating coil for future heat pump conversion capability.
- 2-inch flex tubing distribution: Sound-attenuating insulated flex tubing routed through wall cavities and ceiling chases; small diameter allows routing through spaces conventional ductwork cannot reach.
- 14 supply outlets total: 5-inch round supply outlets at ceiling locations in primary living spaces; 4-inch outlets in smaller spaces; outlets located inconspicuously in corners or near walls to minimize visual impact.
- Central return air: Wall-mounted return grille in upstairs hallway; routes to air handler via ceiling chase.
- Honeywell programmable thermostat: Mounted in centrally-located hallway; provides whole-home temperature control.
- Condensate drainage: From air handler through attic to existing plumbing; coordinates with bathroom drain stack.
- Filter housing: Filter access point in attic adjacent to air handler; standard pleated filter (changes every 2-3 months).
Installation Process
Project completed June 2025 over 5 working days:
- Day 1: Outdoor unit pad preparation and equipment placement; electrical disconnect installation; dedicated 240V circuit run.
- Day 2: Attic preparation; air handler placement and mounting; condensate drainage installation; structural supports and vibration isolation.
- Day 3: Refrigerant lineset routing from outdoor unit through attic to indoor air handler; pressure testing for leak verification.
- Day 4: Distribution flex tubing installation through wall cavities and ceiling chases; supply outlet cutting and installation at 14 locations.
- Day 5: System fill and refrigerant charging; commissioning with airflow verification at all supply outlets; thermostat installation and configuration; customer walkthrough and operating instruction.
Results
Project commissioned June 30, 2025. First full summer 2025 results:
- Whole-home cooling achieved: All living spaces reach setpoint reliably during 88°F+ outdoor conditions; substantial comfort improvement vs. previous window AC arrangement.
- Aesthetic outcome: Traditional supply outlets at ceiling locations; no visible indoor cooling equipment in primary living spaces; preserved Colonial Revival interior character.
- Even temperature distribution: High-velocity small-duct produces more even temperature distribution than typical residential AC; small-diameter tubing creates higher air velocity from outlets, improving mixing.
- Quiet operation: Indoor air handler operates at low audible level (44 dBA at supply outlets); outdoor unit operates at 56 dBA; substantial acoustic improvement vs. previous window AC arrangement.
- Cooling-season energy use: Estimated $480 cooling-season electrical cost for summer 2025 (vs. estimated $640-$720 with previous 4-unit window AC arrangement); 30-40% reduction.
- Customer satisfaction: Homeowners report substantial comfort improvement with no compromise to interior architectural character; “best home improvement we've done” feedback.
Investment Summary
- SpacePak SPS Series 3-ton outdoor condenser: $5,200
- SpacePak SPS Series air handler with supplementary heating coil: $4,800
- 2-inch insulated flex tubing distribution materials: $1,840
- 14 supply outlets and return grille: $1,640
- Refrigerant linesets, insulation, fittings: $840
- Electrical work (dedicated 240V circuit, disconnect): $1,240
- Honeywell programmable thermostat: $285
- Installation labor (5 days, 2 technicians): $7,400
- Permit and inspection coordination: $320
- Outdoor pad and miscellaneous: $440
- Total project cost: $24,005
- Eversource rebate (high-efficiency AC eligible): −$450
- Net customer investment: $23,555
Lessons Applicable to Other Pre-WWII Homes
- High-velocity small-duct preserves traditional appearance: For homeowners specifically wanting traditional supply registers rather than ductless wall units, high-velocity systems provide hidden distribution with conventional outlet appearance.
- 2-inch flex tubing accesses spaces conventional ductwork cannot: Smaller diameter allows routing through wall cavities, closet chases, and ceiling spaces where conventional ductwork doesn't fit.
- Cost premium over ductless or conventional AC: High-velocity systems typically cost 15-25% more than equivalent ductless capacity; cost reflects specialized equipment, tubing, and installation labor.
- Aesthetic priority justifies premium cost for some customers: Homeowners with strong architectural preservation priorities frequently choose high-velocity systems; cost reflects priority rather than necessary inefficiency.
- Even temperature distribution benefit: Small-diameter high-velocity outlets produce excellent room mixing; sometimes better even temperatures than conventional 6-8 inch supply registers.
- Supply outlet placement matters: Inconspicuous outlet placement in corners or near walls minimizes visual impact; coordinate with homeowner during design phase.
- Future heat pump conversion possible: Including supplementary heating coil in air handler allows future heat pump conversion; provides flexibility for electrification path.
Frequently Asked Questions
- What's the difference between high-velocity small-duct and ductless mini-split systems?
- Substantially different approaches. (1) Visible equipment: ductless has wall-mounted or ceiling cassette indoor heads visible in each conditioned room; high-velocity has only small supply outlets (4-5 inch round) at ceiling locations — no visible indoor units. (2) Distribution: ductless uses individual refrigerant linesets to each indoor head; high-velocity uses single air handler distributing through 2-inch flex tubing to supply outlets. (3) Control: ductless provides individual room control per zone; high-velocity provides whole-home control via single thermostat (zoning possible but adds complexity). (4) Cost: high-velocity typically 15-25% more expensive than ductless for equivalent capacity. (5) Aesthetics: high-velocity preserves traditional supply register appearance; ductless has visible modern indoor equipment. (6) Installation: high-velocity simpler conceptually (single air handler) but requires routing access for flex tubing; ductless requires individual indoor head locations and routing. Choice depends on customer aesthetic priorities, budget, and zoning needs.
- How does the SpacePak system differ from conventional central AC?
- Several key differences. (1) Distribution: SpacePak uses 2-inch insulated flex tubing vs. conventional 6-12 inch rigid metal ductwork; allows routing through smaller spaces. (2) Supply outlets: SpacePak uses 4-5 inch round outlets vs. conventional 4×10 or 6×14 inch rectangular registers. (3) Velocity: SpacePak supplies air at higher velocity from smaller outlets vs. conventional lower-velocity larger registers; both achieve similar room temperature outcomes through different mixing patterns. (4) Sound: high-velocity outlets sometimes more audible than conventional registers; modern systems include sound-attenuating tubing reducing this concern. (5) Installation: SpacePak typically easier to install in retrofit applications where conventional ductwork can't fit; conventional easier in new construction or open ceiling configurations. (6) Equipment: SpacePak uses specialized equipment optimized for high-velocity operation; conventional uses standard residential AC equipment. (7) Cost: SpacePak typically 30-50% more expensive than equivalent conventional central AC; the premium reflects specialized equipment and installation. Best fit: retrofit applications in pre-WWII homes without existing ductwork where aesthetic priorities favor traditional supply outlets.
- Can high-velocity small-duct systems be added to homes with hot-water boiler heat?
- Yes, this is one of their primary applications. Common scenario: pre-WWII home with hot-water boiler heating and no cooling; homeowner wants central AC without disrupting boiler system. (1) Independent systems: high-velocity AC operates entirely independently of existing boiler; air handler in attic or basement, distribution through walls/ceilings, no interaction with hydronic system. (2) Preservation of boiler: existing hot-water boiler and radiator distribution untouched; HVAC modernization happens through completely separate AC system. (3) Sometimes combined: if home plans future electrification, high-velocity air handler with electric heating coil could provide both cooling and supplementary heating; boiler retained as primary heat for severe cold. (4) Distribution coordination: existing radiator distribution doesn't interfere with high-velocity tubing; both systems operate independently. This case study's home had recent (2019) modulating condensing boiler that was preserved entirely; high-velocity AC added as completely separate system.
- What's the installation timeline for high-velocity small-duct AC?
- Variable based on home size and complexity; typical 3-7 days for whole-home installation. This case study's 5-day timeline typical for 2,800 sq ft Colonial Revival. Factors affecting timeline: (1) Home size: larger homes with more supply outlets take longer; small homes (1,500-2,000 sq ft) sometimes 3-4 days. (2) Access challenges: homes with finished basements, multiple floor levels, or limited attic access take longer than easily-accessed installations. (3) Outlet count: more supply outlets requires more individual installation time. (4) Distribution complexity: routing through challenging spaces (walls without easy access, around obstructions) takes more time. (5) Concurrent work: combining with other home improvement (electrical work, renovation) sometimes extends timeline. (6) Customer involvement: customer preferences about supply outlet placement may require iterative consultation during installation. Most projects complete within 5-7 days; rarely exceed 10 days even for complex installations.
- How does cooling-season energy use compare to conventional AC?
- Similar to conventional variable-speed AC of equivalent SEER rating. SpacePak Variable-speed inverter equipment SEER2 18.5 vs. conventional residential AC SEER2 ratings ranging 13.4 to 26 depending on equipment tier. Operating cost factors: (1) Equipment SEER: higher SEER = lower operating cost for equivalent cooling. (2) Variable-speed operation: modulates capacity to match load; better part-load efficiency than single-stage. (3) Distribution losses: small-duct systems have similar distribution efficiency to well-designed conventional ductwork; sometimes better than poorly-designed conventional systems. (4) Right-sizing: high-velocity equipment available in narrow capacity range (typically 2.5-5 ton); right-sizing important for efficiency. (5) Operating pattern: customer behavior affects operating cost as much as equipment selection. For this case study, projected $480 cooling-season cost represents typical performance for the equipment tier and home characteristics.
Contact Biozura Heating and Air
For high-velocity small-duct AC installation in pre-WWII New Britain and surrounding area homes, contact us for consultation. Connecticut DCP Unlimited HVAC License #S1-0414829.
- Emergency Line (24/7): (860) 955-4428
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