Start with the Envelope and Loads
Tighten the roofline (air sealing + code-level insulation) and run a room-by-room load calculation. If the main system has capacity, a short, well-sealed extension can work; but many NYC homes benefit from a dedicated variable-speed heat pump (ductless or slim-duct) for precise zoning, dehumidification, and quiet operation.
When a Dedicated Zone Wins
Choose a dedicated heat pump when the existing air handler is maxed out, duct routes are long/outside the envelope, or you want independent seasonal schedules. Keep ducts inside conditioned space, seal with mastic, and balance airflow so dormers and knee-wall niches aren’t stagnant.
Fresh Air & Humidity
Pair space conditioning with a small ERV for filtered, balanced ventilation. Target 40–50% RH year-round; use smart controls and CO₂/RH monitoring to keep comfort steady without energy waste.
Compare pros/cons and sample layouts in our energy-efficient Attic Remodeling Service guide for NYC.