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REF_07 / UTILITIES & SYSTEMS

Heat Pump

Also known as: Mini-split · Air-source heat pump · HPWH

An electrified HVAC unit that's now effectively required for new ADUs under Washington's energy code.

DEFINITION

A heat pump is an electrified HVAC system that moves heat rather than burning fuel — a single outdoor unit pairs with one or more indoor heads to deliver both heating and cooling at 2–4× the efficiency of resistance heat. For ADUs, mini-split heat pumps (1–2 tons) and heat pump water heaters (50–80 gallon) are the default specification under WSEC 2021. Pierce and Snohomish PUDs offer $800–$2,400 rebates for heat pump installations in qualifying ADU projects.

NAV_GRAPH / Local data
FAQ

Frequently asked

  • What does Heat Pump mean in the context of an ADU?

    Heat Pump is part of the regulatory and technical vocabulary you encounter when permitting and building an accessory dwelling unit in Washington. Knowing the term matters because reviewers, inspectors, and your lender will use it without explanation. We define Heat Pump in plain English and connect it to the specific code citation, fee, or construction detail that affects your project. Use the related-terms section to navigate adjacent concepts you'll need on the same plan set.

    Go deeper: Open the Washington ADU Energy Code Guide 2026

  • Where does Heat Pump apply in the WA ADU process?

    Heat Pump typically shows up in either the design phase (when the architect or designer is laying out plans against zoning), the permit phase (when reviewers check the submittal against code), or the construction phase (when inspectors verify built conditions match the approved set). The same term can appear in your loan documents if it affects valuation or risk. Each glossary entry maps the term to the exact phase where it matters most.

    Go deeper: Open the Washington ADU Energy Code Guide 2026

  • Why should I care about Heat Pump for my project?

    Misunderstanding Heat Pump is one of the most common reasons ADU projects hit avoidable cost overruns or permit delays. A clear shared vocabulary between you, your designer, and your builder shortens decision time and reduces change orders. Bookmark this glossary and refer back as you progress from feasibility through final inspection.

    Go deeper: Glossary: Washington State Energy Code (WSEC)

  • How does Heat Pump affect my ADU budget?

    Most glossary terms map to either a cost line, a review timeline, or a permit fee. Where Heat Pump drives cost, the impact is itemized in our standard fee schedule and itemized at feasibility — so by contract time, Heat Pump is a known number, not a discovered surprise. Click through to the related cost or permit page for the current Heat Pump-specific dollar range and timeline.

    Go deeper: Read the Five hidden ADU costs that wreck Puget Sound budgets guide

  • Is Heat Pump regulated under RCW 36.70A.681?

    WA statewide ADU preemption (RCW 36.70A.681 / HB 1337) covers many ADU-adjacent topics: size caps, setbacks, owner-occupancy, parking, height, lot-size minimums. Whether Heat Pump falls under preemption depends on its specific scope — design review, side-sewer permitting, drainage review, and tree-protection rules are generally NOT preempted, while size/setback/parking generally ARE. Each glossary entry flags the preemption status.

    Go deeper: Read: Bellevue ADU rules — what changed under HB 1337

TERM_HEAT PUMP

Need "Heat Pump" explained for YOUR lot? Get it in plain English.

Definitions help. Applying them to your specific property is what matters. Send the address and we'll explain how Heat Pump plays out on your build.

  • Plain-English read of "Heat Pump" on your lot
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WA Lic. GOLDESA747LZBuilding since 2012
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