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.
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.