Heat Pumps in Seattle: The Complete Homeowner's Guide

A heat pump in Seattle is an electric system that heats your house in winter and cools it in summer by moving heat between the indoor air and the outdoor air, rather than burning fuel. For most Seattle houses it works well: the city’s design temperature is a mild 24°F, City Light’s electricity is relatively cheap, and a properly sized system carries the house through nearly every winter hour.

That short answer hides the decisions that actually determine whether a heat pump works in your house. This guide walks through them in the order a careful project would: how the machine works, how it behaves in Seattle’s weather, how it gets sized, what your ducts and electrical panel need to handle, what the city requires, and what it costs to buy and to run. The Seattle Heat Pump Company wrote it for homeowners comparing options, whether or not you end up working with us.

How a heat pump works

A heat pump is a refrigeration system that can run in both directions. In summer it works exactly like a central air conditioner: refrigerant absorbs heat from the indoor air at the indoor coil, a compressor raises its pressure and temperature, and the outdoor coil releases that heat outside. In winter a reversing valve flips the flow. The outdoor coil becomes the cold side, pulling heat out of outdoor air even when it is below freezing, and the indoor coil releases it into the house.

The parts are the same in every ducted system:

• The outdoor unit holds the compressor, the outdoor coil, a fan and the reversing valve.
• The indoor coil sits either on top of a gas furnace or inside an electric air handler, which also contains the blower that moves air through your ducts.
• The refrigerant line set is a pair of insulated copper lines connecting the two.
• An expansion device controls how much refrigerant enters the coil.
• The thermostat and controls decide when the system heats, cools, defrosts or calls for backup heat.
• A condensate drain carries away the water the indoor coil pulls out of the air in cooling mode.

Because a heat pump moves heat instead of making it, it delivers more heat energy than the electricity it uses. That ratio is the coefficient of performance, or COP. A COP of 3 means three units of heat for each unit of electricity. Electric baseboard and the resistance heat strips in an air handler have a COP of 1.

Single-stage and variable-speed

Older and entry-level heat pumps run their compressor at one speed, on or off. Variable-speed models, often called inverter heat pumps, change their output continuously to match the load. In Seattle, where the weather spends months between about 35°F and 55°F, a variable-speed unit spends most of its time running gently at low output. That means steadier temperatures, quieter operation and fewer of the on-off cycles that waste energy and wear parts. Single-stage equipment costs less up front and is still a reasonable choice when the budget is tight and the ducts are good. The comparison guide covers the tradeoff in detail.

Efficiency ratings

Two ratings appear on every heat pump. SEER2 measures seasonal cooling efficiency and HSPF2 measures seasonal heating efficiency, both under the current federal test procedure. For a Seattle home, HSPF2 matters more, because heating is most of the work. City Light’s contractor discounts use these ratings: $300 for systems at SEER2 15.2 and HSPF2 8.1 or above in retrofits, and $600 at SEER2 16.0 and HSPF2 9.5 or above. The ratings guide explains how to read them on a quote.

How heat pumps handle a Seattle winter

The fear behind most heat pump questions is simple: will it keep the house warm when it is cold out? In Seattle, the numbers are reassuring.

The city’s energy code sets the heating design temperature for Seattle at 24°F, the outdoor condition a system is sized to handle. Over the 1991 to 2020 climate normals, Sea-Tac averaged about 25 nights a year at or below freezing and about one night a year at 20°F or below. The coldest night from 1991 through 2025 was 14°F. Snow is light, averaging about 6 inches a year, with snow on the ground for only a few days.

Modern heat pumps keep producing heat well below those temperatures, though their capacity drops as it gets colder. That is why sizing to the design temperature matters, and why the code requires backup heat controls. Seattle’s energy code requires heat pump thermostats to minimize supplemental heat, prohibits it from running above 40°F, and requires the lockout to be set at 35°F or lower at final inspection. On a well-designed system, the backup strips or gas furnace only help on the handful of hours when the heat pump alone falls short.

What Seattle has a lot of is damp weather in the 30s. At those temperatures, moisture freezes onto the outdoor coil, and the heat pump periodically runs a defrost cycle: it briefly reverses to warm the coil, often with a cloud of steam and a whoosh of the fan stopping and starting. That is normal. A coil that stays encased in ice is not, and usually points to an airflow, defrost control or refrigerant problem worth a service call.

Do you need a cold-climate heat pump?

Cold-climate heat pumps are designed to hold more of their capacity at low temperatures; ENERGY STAR’s cold-climate designation requires tested performance at 5°F. Inside Seattle, most houses do not need one: a standard variable-speed unit sized for 24°F carries the load. The calculation changes for houses with unusually high heat loss, for some foothill sites, and for Redmond, whose code design temperature is 17°F. The load calculation tells you whether a standard unit keeps up at your design temperature. The Seattle winter guide goes deeper.

Summers have changed

For decades many Seattle houses had no air conditioning at all. That is changing quickly. Sea-Tac’s cooling degree days roughly doubled from the 1990s to the last decade, and the June 2021 heat dome set an all-time record of 108°F. The American Housing Survey found that about 53% of Seattle-area homes had a primary air conditioning source in 2021, up from about 31% in 2013. A heat pump on the existing ducts provides whole-house cooling, so many homeowners now buy one for summer and discover it also replaces most of their heating bill.

Sizing: why the old furnace is the wrong guide

Most heat pump comfort complaints trace back to sizing. A system that is too small runs constantly on cold days and leans on electric backup heat. A system that is too large reaches the set temperature quickly and shuts off, over and over. Those short cycles waste energy, wear the compressor, and in summer leave the house clammy, because the system never runs long enough to pull moisture out of the air.

The right size comes from a load calculation, not from the size of the furnace or air conditioner you have now. Seattle’s energy code requires heating and cooling loads calculated with ACCA Manual J and equipment selected with Manual S, no larger than the smallest size that meets the load. A Manual J calculation works room by room: wall, window and ceiling areas, insulation levels, window performance, orientation, air leakage and the design temperatures, 24°F for heating and 83°F for cooling in Seattle.

The old equipment is a poor guide for a simple reason. Many Seattle furnaces were oversized when installed, and many houses have since gained new windows, attic insulation or air sealing. Replacing a 100,000 BTU furnace with a heat pump of the “same size” can produce exactly the oversizing problem described above. The sizing guide shows how the calculation works and what to ask a contractor.

Your ducts: the part most quotes skip

A gas furnace heats air to well above body temperature, so it can deliver a lot of heat with modest airflow. A heat pump delivers warm air at a lower temperature, so it needs to move more air to deliver the same heat. That single fact explains most heat pump problems in older Seattle houses.

When the ducts cannot carry the airflow, the symptoms are rooms at the end of long runs that never warm up, a loud blower, long run times and backup heat that comes on more than it should. The usual culprits:

• A small or single return. Many Seattle systems were built with one central return that worked for a hot furnace but chokes a heat pump.
• Leaky ducts. Joints and boots in crawlspaces and attics leak heated air into spaces you don’t live in.
• Undersized runs. Branch ducts to added rooms or second floors are often too small.

The test is straightforward. With the blower running, a technician measures static pressure across the system and compares it with the equipment’s rated limits, then looks at the return path and the condition of exposed ducts. The result tells you whether the ducts work as they are, need targeted fixes such as an added return and sealing, or need replacement. That test belongs before equipment is chosen, because it changes what equipment makes sense.

Some older Seattle houses have no usable ducts at all, or only the large round ducts of an early gravity furnace. In those houses, a ducted heat pump may need new ductwork, and ductless mini-split systems become a real alternative. The Seattle Heat Pump Company focuses on ducted systems; the ducted vs ductless guide explains when each approach fits. For houses with ducts, using a heat pump with existing ductwork covers the measurements.

Electrical capacity

Every heat pump needs a dedicated circuit and an outdoor disconnect. The question is whether your panel and service can carry it alongside everything else.

A heat pump’s compressor draws less than many people expect. The bigger electrical question is backup heat. Electric resistance strips in an air handler can draw far more current than the heat pump, and a house that also has an electric range, dryer, water heater or car charger can run out of capacity. A load calculation for the electrical service answers whether a new circuit is enough or a panel or service upgrade is needed.

When a 100 to 200 amp upgrade is needed, Seattle-area projects typically budget about $1,333 to $4,500 for the panel work, plus the electrical permit. A dual fuel design that keeps a gas furnace as backup can avoid resistance strips entirely, which sometimes avoids the upgrade. The panel guide covers the options.

Backup heat and controls

Every heat pump design needs an answer to the coldest hours. There are two common answers.

Electric backup. An electric air handler includes resistance heat strips. Seattle’s code requires controls that keep them off above 40°F, with the lockout set to 35°F or lower at final inspection. On a properly sized system they run rarely. On an undersized system or one with a poorly configured thermostat, they run often and drive up the bill.

Dual fuel. The heat pump’s coil sits on a gas furnace. The heat pump heats the house until the outdoor temperature drops below a changeover point, and then the furnace takes over. Choosing that point is an economic decision as much as a comfort one: it depends on the heat pump’s capacity at low temperatures, your electric rate and your gas rate.

Thermostat setup is where good equipment often goes wrong. A thermostat left on furnace settings can call for backup heat every time you raise the setpoint a few degrees in the morning. Commissioning should set heat pump staging, the outdoor lockouts and recovery behavior, and someone should explain them to you. The backup heat guide walks through the settings.

Permits and who can do the work in Seattle

Seattle treats a split heat pump as refrigeration work. The Seattle Department of Construction and Inspections requires a refrigeration permit for any split-system heat pump or air conditioner, and only a licensed refrigeration contractor can obtain it. An electrical permit covers the circuit, and a furnace or mechanical permit applies when the indoor equipment is replaced or altered. Inspections include a cover inspection before anything is concealed and a final inspection.

That licensing requirement has a practical effect: homeowners report that some smaller firms working in the suburbs decline jobs inside Seattle city limits, and the refrigeration license is a common reason given. It is also why it is worth asking every bidder who will pull the refrigeration permit.

Outside the city, the rules shift. Bellevue requires a mechanical permit for a heat pump and an electrical permit for wiring or service work. Shoreline and Lake Forest Park electrical permits go through Washington Labor & Industries. Seattle’s fees for a typical job run about $192 to $556 depending on the scope. The permit guide lists each fee and inspection.

Noise rules and where the outdoor unit goes

Seattle’s noise code limits residential sound at the property line to 55 dBA during the day and 45 dBA at night. For heat pumps, the city adds a practical step: equipment in a side yard needs a noise review, and a predicted property-line level of 47 dBA or less on the heating rating passes. Above that, the design needs a sound barrier, a compressor blanket or a different location. Bellevue applies the same 55 and 45 dBA limits.

That rule is why outdoor-unit siting is often the first design decision on a narrow Seattle lot. It is also why you may hear claims about setbacks that do not exist. One homeowner was told a heat pump needed to sit 30 feet from the property line; Seattle’s rule is a noise limit, not a fixed setback. The noise guide explains how the review works.

The refrigerant change

Since January 1, 2026, Washington’s Department of Ecology rules require newly installed residential heat pumps and air conditioners to use refrigerants with a global warming potential under 750. R-410A, the refrigerant in most systems installed over the past 15 years, no longer qualifies for new equipment. The replacements, such as R-454B and R-32, are mildly flammable and come with updated handling and equipment rules. For a new installation this is mostly invisible. For a replacement, it can mean a new indoor coil and a closer look at the existing line set. The refrigerant guide covers what it means for older systems.

What a heat pump costs

For a ducted system on existing ducts in usable shape, Seattle-area projects typically fall between about $6,700 and $20,000, based on published cost data. A like-for-like replacement of an existing heat pump typically runs about $6,700 to $15,000. The spread comes from equipment size and efficiency tier, whether a coil goes on the furnace or a new air handler replaces it, duct work, electrical work, and access.

Incentives lower the net price:

• Seattle City Light offers contractor discounts of $300 or $600 on qualifying heat pumps, by efficiency tier, one system per home.
• Seattle Clean Heat takes $2,000 off an oil-to-heat-pump conversion with a qualifying Mitsubishi Electric system installed by a participating contractor. Moderate-income households can get $4,000 more on installs completed within the program’s current funding period, and income-eligible households can get a free conversion through the Office of Housing.
• PSE offers rebates in its electric territory, including $1,500 for adding a heat pump to a gas furnace when you buy both gas and electricity from PSE. That last condition excludes Seattle, where City Light sells the electricity.
• The federal 25C tax credit ended for equipment placed in service after December 31, 2025.

The cost guide breaks down each driver, and the rebate guide keeps the incentives current. For a range specific to your house, the cost estimator asks a few questions and gives a number without asking for contact details.

What it costs to run: City Light versus PSE

The economics of a heat pump in the Seattle area depend heavily on who sells you electricity.

Inside Seattle, City Light’s current residential rate is 13.38 cents per kWh, and PSE sells gas at about $1.67 per therm. At those rates, a heat pump costs less to run than a 95% efficient gas furnace whenever its COP is above about 2.2. A modern heat pump clears that through most Seattle winter weather. Shoreline, Lake Forest Park, Burien and parts of Renton also buy City Light power, at slightly higher suburban rates.

On the Eastside and in most other suburbs, PSE sells both electricity and gas. At PSE’s current electric rate of about 20.6 cents per kWh, the break-even COP rises to about 3.4. A heat pump still wins in mild weather, but the furnace can be cheaper to run on the coldest days. That is the case for dual fuel: let the heat pump work when it is cheapest and switch to gas when it is not. PSE has also filed for significant rate increases, which are not yet approved, so the comparison may shift.

Oil is harder to price, because there is no official weekly heating oil price series for Washington. What is certain is that oil heat carries a buried or basement tank as a long-term liability, and the city aims to move every oil-heated home off oil by 2030. The operating cost guide works through each fuel.

Converting from oil or gas

Most Seattle heat pump projects replace something.

From oil. The city estimates that roughly 7,000 to 10,000 Seattle homes still heat with oil, down from about 18,000 in 2018. A conversion replaces the oil furnace with an air handler, or adds a heat pump coil to a new or existing furnace, connects a new outdoor unit, and decommissions the tank. Seattle Fire Department rules require a tank out of service for a year to be decommissioned, either removed or filled in place, under a permit, by an ICC-certified decommissioner. Fire Department records show roughly 1,000 to 1,400 of those permits a year since 2021. See oil to heat pump conversion and oil tank decommissioning.

From gas. About a third of Seattle households heat with gas. You can retire the furnace and go all-electric, or keep it as backup in a dual fuel system. The decision usually turns on the furnace’s age and your electric utility. See furnace to heat pump conversion and dual fuel heat pumps.

From an old heat pump. Replacements now involve the refrigerant change described above, and often an indoor coil or air handler. See heat pump replacement.

Comparing quotes without getting played

Seattle homeowners regularly report quotes for the same house that differ by many thousands of dollars, deadline discounts that expire the same day, and conflicting advice about whether their house can have a heat pump at all. Much of that confusion comes from quotes that describe different scopes.

Put every quote on the same footing by asking for:

• the load calculation, including the design temperature used
• model numbers for the outdoor and indoor equipment, and the matched system rating
• whether ducts were tested, and exactly what duct work is included
• the electrical scope: a circuit, or a panel or service upgrade
• whether the line set is new or reused, and how a reused one will be tested
• who pulls the refrigeration permit
• which rebates will appear on the invoice
• what commissioning includes

A price far below the range usually leaves something out. A price far above it may include work you need or a tier you don’t. A “today only” price on a system that will run for many years is a reason to slow down. The quote comparison guide goes line by line.

What happens during installation

A ducted installation on usable ducts usually takes one to three days of work once permits and equipment are in hand. The sequence:

1. The old equipment is removed, and any refrigerant is recovered.
2. The outdoor unit goes on a level pad or wall bracket, with clearances for airflow and service.
3. The indoor coil or air handler is installed and connected to the ducts, with any duct changes made.
4. The line set is run, brazed with nitrogen flowing to keep the inside of the copper clean, then pressure tested with nitrogen.
5. A vacuum pump pulls the system down to a deep vacuum, verified with a micron gauge, before refrigerant is released.
6. Electrical work, the condensate drain and the thermostat are completed.
7. Commissioning sets and checks airflow, charge, defrost and backup heat lockout, and records temperatures and pressures.

Commissioning is the step that separates an installation that performs from one that merely runs. The installation process guide describes each step and what to look for.

Living with a heat pump

A heat pump behaves differently from a furnace, and knowing what is normal saves worry.

• Steadier, cooler air. Supply air feels warm rather than hot. Variable-speed systems run long and gently instead of blasting heat and shutting off.
• Defrost. In wet weather near freezing, expect periodic defrost cycles with steam from the outdoor unit.
• Setbacks. Deep nighttime setbacks can trigger backup heat during morning recovery. Small setbacks or none often cost less.
• Maintenance. Change or clean filters regularly, keep plants and debris a couple of feet from the outdoor unit, and keep the condensate drain clear. Near Puget Sound, salt air corrodes outdoor coils; one major manufacturer recommends washing coastal units about every three months, and some models offer coated coils for coastal sites.

The maintenance guide covers seasonal checks.

Where to start

If you are early in the process, start with three numbers: your utility, your current heating fuel and the approximate age of your furnace or air conditioner. Those decide most of what follows. Then get the house measured. A load calculation, a duct test and a look at the panel and yard turn a general idea into a specific plan.

The Seattle Heat Pump Company plans ducted heat pump installations across Seattle and King County, carried out by licensed and insured contractors. Call the number on this page or send a few details about your house to get started.