TL;DR. For Seattle homes built before 1985 without modern forced-air ductwork, ductless mini-splits typically win. New ductwork costs $8,000-$14,000, which kills the math for central AC. A 3-zone ductless system runs $13,200 vs $21,600 for central AC + new ductwork. For most older homes, a heat pump (heating + cooling) beats AC alone because of rebates.

Direct answer, ductless wins for most older homes

For Seattle homes built before 1985 without existing modern ductwork, ductless mini-splits are typically the right answer. The cost savings vs running new ductwork ($6,000 to $14,000 of avoided ductwork), the comfort improvement of zone-level control, and the install simplicity (1 to 3 days vs 4 to 10 days) all favor ductless.

The exceptions where central AC still wins: homes with existing functional ductwork from a forced-air furnace, larger homes (3,000+ sq ft) where 6+ mini-split heads gets expensive, and homes where aesthetic concerns rule out wall-mounted indoor units.

Why ductwork is the dealbreaker

Most pre-1985 Seattle homes have one of three heating configurations:

Radiant or boiler heat (no ducts). Old craftsmans and some mid-century homes use radiators or in-floor radiant. Zero ductwork to work with. Adding central AC means installing complete ductwork from scratch, which costs $8,000 to $14,000 and requires opening walls, ceilings, and floors.

Single forced-air system with undersized or leaky ducts. Common in 1955-1985 homes. The ducts technically exist but aren’t sized for the higher airflow modern AC requires. We can sometimes work with them (with significant modifications, $3,500 to $7,000); often we can’t.

Wall furnaces or floor furnaces. Older craftsmans sometimes have these. Ductwork is nonexistent.

In each case, ductless mini-splits skip the ductwork problem entirely. Each indoor unit serves one room or zone. No ductwork required.

Cost comparison, real Seattle numbers

For a typical 1,800 sq ft 1960s rambler that doesn’t have functional ductwork:

Option A: Add central AC (requires new ductwork)

  • New ductwork installation: $8,500
  • Central AC condenser and air handler: $9,500
  • Electrical work (240V circuit, sometimes panel upgrade): $1,800
  • Drywall patch and texture from ductwork install: $1,800
  • Total: $21,600 over 6 to 10 days

Option B: Ductless multi-zone mini-split (3 zones)

  • 3-zone outdoor compressor: $4,200
  • 3 indoor wall-mounted heads: $2,400
  • Refrigerant line and electrical: $2,400
  • Install labor: $4,200
  • Total: $13,200 over 2 to 3 days

Option C: Ductless multi-zone mini-split (5 zones, whole-home)

  • 5-zone outdoor compressor: $5,400
  • 5 indoor heads (mix of wall and ceiling cassette): $4,200
  • Refrigerant line and electrical: $3,200
  • Install labor: $5,800
  • Total: $18,600 over 3 to 5 days

For most older Seattle homes, the 3-zone ductless option ($13,200) saves $8,400 vs central AC with new ductwork.

The comfort difference

This is the part most people don’t think about until after install.

Central AC cools the entire home to one thermostat setpoint. If you set it to 72°F, every room targets 72°F. Some rooms run cooler (rooms near the air handler), some run warmer (rooms at the end of long duct runs). Older homes with thermal mass differences make this worse.

Ductless multi-zone cools each zone to its own setpoint. Bedroom at 68°F for sleeping. Kitchen at 74°F because it’s empty during the day. Living room at 72°F when occupied, off when empty. Each zone has its own remote control or app.

Real-world energy implications: a 3-zone ductless system in a 1,800 sq ft home typically uses 20 to 35% less energy than central AC cooling the same space to the same average comfort level. Zone-level setpoint control plus only running compressors when zones call for cooling.

When central AC wins for older homes

Three scenarios:

Existing functional ductwork. If you have a relatively recent (post-1990) gas furnace with adequate ductwork, adding central AC is straightforward and cost-effective. $7,500 to $12,000 vs ductless multi-zone $13,000 to $19,000.

Larger homes (3,000+ sq ft). Beyond 6 mini-split heads, the cost stacking gets uncomfortable. Central AC pulls ahead.

Aesthetic concerns. Ductless indoor units mount on walls (or ceilings, or recessed in floors for high-end installs). Some homeowners don’t want visible indoor units. Concealed ducted mini-split systems exist but cost more than standard ductless.

The heat pump alternative (most older Seattle homes)

For older Seattle homes considering AC, the actual best path is often heat pump installation rather than dedicated AC.

A multi-zone ductless heat pump system:

  • Provides both heating AND cooling
  • Qualifies for the $1,200 PSE Trade Ally instant rebate
  • Qualifies for the federal 25C tax credit (up to $2,000)
  • Replaces the aging gas furnace, radiator system, or wall furnace

Real example: 1,800 sq ft 1960s rambler with aging gas furnace, considering AC:

  • Add ductless AC: $13,200 (and you still have aging gas furnace, no rebates)
  • Add ductless heat pump (heating + cooling): $14,200 - $1,200 PSE - $2,000 federal = $11,000 net (and the gas furnace can be removed)

For $1,800 less than dedicated AC, you get a system that handles both heating and cooling. This is why most of our older-home AC consults end up as heat pump installs.