Ductless Mini-Splits decisions
Honest ductless mini-splits decision guides for Greater Seattle — the trade-offs, sourced local cost context, and the questions to ask any bidder before you sign.
Evaluate
Ductless or ducted: which retrofit fits your house?
This is the retrofit decision framework — not the side-by-side hardware table on our compare page. The fork is really about your ducts: homes with sound (or repairable) ductwork usually do best reusing it with a ducted heat pump; homes without ducts — or with ducts not worth saving — usually do best going ductless. Building new ductwork into a finished house is the expensive third path that rarely wins. Add Seattle inputs: pre-war housing stock, panel capacity for ducted vs ductless electrical draw, SCL vs PSE rebate mechanics, and how long you'll stay once you've paid for distribution.
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Single-zone or multi-zone ductless: how many heads do I need?
Start from the problem, not the floor plan — this page is the sizing/occupancy framework; use the comparison table when you want cost columns side by side. One space that's never comfortable wants a single-zone; whole-home heating/cooling without ducts wants multi-zone — but zones should follow loads and doors, not room counts. The most common design error is more, bigger heads than the house can load. Panel capacity and stay horizon belong here too: multi-zone wants a larger dedicated circuit; incremental single-zone often fits tight 100-amp pre-war service when you're solving one room at a time.
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Evaluate
Should I repair or replace my ductless mini-split?
This is the ductless repair-or-replace framework — not the install-cost comparison table. Ductless systems run the same math as any heat pump — 12–15-year typical lifespan, electronics are repair-tier, compressor/refrigerant-circuit failures on old units are replacement-tier — with one wrinkle: on multi-zone systems, diagnose whether the problem is one head, one zone's circuit, or the outdoor unit before any replacement conversation. Add local inputs: SCL instant discounts and PSE conversion rebates attach to qualifying replacements; pre-war homes often choose ductless precisely because line sets avoid duct demolition; stay horizon decides whether head-level repair on a 13-year system is a bridge or a trap.
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Need the fundamentals first?
Learn
How do ductless mini-splits actually work?
A ductless mini-split is a heat pump that skips ductwork entirely: an outdoor unit connects to one or more wall-mounted indoor heads through a small line set — refrigerant lines, power, and a drain bundled through a penetration needing only a three-inch wall opening. Each head heats and cools its own zone with its own remote, and because refrigerant carries heat directly to the room instead of through leaky ducts, ductless systems avoid the 20–30% distribution losses typical of older forced-air homes in Greater Seattle.
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Why is ductless the go-to for Seattle's older homes?
Seattle's pre-war housing stock — Craftsmans, Tudors, foursquares across neighborhoods from Ballard to Burien — was built with radiators, gravity furnaces, or nothing at all, and retrofitting ducts through plaster walls and balloon framing is invasive and expensive. Ductless heads need a three-inch wall opening each, which is why they've become the standard comfort retrofit for this stock: heating and cooling without tearing the plaster, trim, and floor plan that make these houses worth owning.
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How should a multi-zone mini-split be laid out?
A multi-zone system runs several indoor heads from one outdoor unit — and the design question isn't 'how many rooms' but 'how many zones': which spaces genuinely need independent control, what heating and cooling load each carries, and how line sets route across the floor plan. Good multi-zone design is a layout exercise before it's an equipment order, and in Seattle's mix of ramblers, two-stories, and pre-war layouts, the routing often matters as much as the head count.
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What's the right heating and cooling for an ADU or backyard cottage?
For Seattle ADUs, DADUs, and garage conversions, a single-zone ductless heat pump is the de-facto standard: one compact outdoor unit, one indoor head, full heating and cooling, no ducts, and no load added to the main house's system. Extending the main house's ductwork to a detached backyard cottage almost never pencils out — the runs are long, the balance is wrong, and code expects each dwelling unit to have its own heat source anyway.
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