Case Study · Small-Duct Retrofit · Evanston
High performance meets historic preservation.
Unico small-duct + Bosch heat pump: efficient cooling and dehumidification for a 1920s Evanston home.
Unico
Bosch IDS 2.0
Dual-Fuel System
The challenge
A landmark home. A modern comfort problem.
The Walker residence is a 1920s home in Evanston, the kind of property where every detail matters. Original woodwork, historic ceilings, and architectural character that simply cannot be compromised.
Like many North Shore homes of this era, the house lacks the ductwork to allow for conventional air conditioning. The challenge: deliver high-performance cooling to every room with minimal disruption to walls and ceilings.
The solution
A purpose-built pairing: cold-climate heat pump and small-duct delivery.
We designed a system that pairs Bosch heat pump technology with Unico small-duct high-velocity air distribution, a combination purpose-built for historic retrofits where conventional ductwork is impossible.
Heat pump
Bosch IDS 2.0
Air distribution
Unico Small-Duct System
Inverter-driven system rated for continuous operation down to −4°F. Variable-speed compressor delivers precise capacity matching for maximum efficiency and comfort.
2-inch flexible supply tubing threads through existing wall cavities and between floor joists. No soffits, no bulkheads, no visible ductwork. The home's historic character stays fully intact — not a single architectural detail compromised.
Why this pairing works
Variable-speed output. High-velocity aspiration. Perfect match.
The Bosch IDS 2.0 heat pump's variable-speed inverter compressor modulates output continuously, rather than cycling on and off like conventional systems. This delivers tighter temperature control, lower energy consumption, and near-silent operation throughout the season.
Paired with Unico's high-velocity small-duct delivery, conditioned air reaches every room through discreet 2-inch round outlets that blend into ceilings and walls. The high-velocity aspiration effect eliminates hot and cold spots by mixing room air far more effectively than conventional registers.
The process
Load calculation to commissioning. Every step documented.
1
Energy audit & load calculation
2
Envelope improvements
Comprehensive Manual J load calculation specific to the home's thermal envelope. Identified insulation opportunities and right-sized the system for actual demand — not industry rule-of-thumb oversizing.
Recommended and completed targeted insulation upgrades before system design — reducing heating load and enabling a smaller, more efficient heat pump to handle the full capacity.
3
System design & routing
4
Engineered the Unico small-duct routing through existing wall cavities and between floor joists. Every supply run planned to preserve the home's original architectural features — no compromises on routing that would require opening finished surfaces.
Installation & commissioning
Installed the Bosch outdoor unit and Unico air handler, ran all small-duct supply lines, and commissioned the system with verified performance data. Every zone tested for airflow balance and temperature delivery before sign-off.
The results
The Walker home now has quiet, whole-home comfort without visible wall units, soffits, bulky ductwork, or sacrificed living space. The Bosch heat pumps and Unico small-duct system deliver even cooling through the summer, better temperature control between floors, and discreet outlets that preserve the home's historic character.
The system also handles much of the home's heating load during spring, fall, and milder winter conditions, reducing reliance on the boiler whenever outdoor temperatures are above the homeowners' heat pump setpoint. After a one-year follow-up, we adjusted the compressor lockout settings so the heat pumps could operate at lower temperatures, improving first-floor comfort and giving the homeowners more control over when the system runs.
This is what a well-designed historic-home retrofit should look like: modern comfort, quiet operation, lower fossil-fuel reliance, and no compromise on the architecture that makes the house worth preserving.
“Next Step did a great job installing our new AC system in our older house. The installation was smooth, professional, and everything works perfectly.” — Evan Walker