IECC climate zone
Zone 4C — Mixed – Marine
Seattle, Portland, western Washington and Oregon.
Winter design temp
27°F
Heating degree days
4,700
Cooling degree days
300
Summer design temp
83°F
What to install here
Ideal heat pump territory: long mild heating season, almost no cooling load, and rarely severe cold. Standard heat pumps perform excellently and the payback against electric resistance heat is fast.
What "winter design temperature" means
It is the temperature that only about 1% of winter hours fall below — not the record low. Engineers size equipment to it, and it is the number to compare a heat pump's low-temperature rating against. A unit rated to 27°F in this zone has no margin; one rated 10-15 degrees below it does.
States predominantly in this zone
Oregon, Washington.
Large states span several zones — elevation and latitude shift this locally. Use your county's designation if you are near a boundary.
Heat pumps that work in zone 4C
Ranked by cold-weather capability against this zone's design temperature. Products rated above 27°F are shown with a warning rather than hidden.
Carrier Infinity 24 Heat Pump with Greenspeed Intelligence (25VNA4)
- Enough heat for an average house, roughly 1,400-2,000 sq ft Rated capacity: 36,000 BTU/h
- Still puts out full heat when it's 5°F outside, so your backup heater stays off Capacity retained at 5°F: 100%
- Its cold-weather performance has been independently measured and published, not just claimed in a brochure NEEP cold-climate listed: Yes
- Communicating - full features on the brand's own thermostat, but you're tied to that brand's dealer when a control board fails Thermostat compatibility: communicating
$8,900 – $10,100
equipment only · est. — install labour backed out of an observed installed price
Gree Sapphire Ultra SAP12HP230V1AO Single-Zone Ductless System
- Still puts out full heat when it's 5°F outside, so backup heat stays off Capacity retained at 5°F: 98%
- On a 5°F night it still delivers about twice the heat of a plain electric heater for the same electricity COP at 5°F: 2.11
- Scores 9 on the official heating efficiency test — closer to the legal minimum HSPF2: 9
$2,984 – $4,484
equipment only · est. — outdoor unit from 1 seller, indoor air handler added
Mitsubishi MSZ-FS09NA / MUZ-FS09NA Single-Zone Ductless System
- Keeps 89% of its heat when it's 5°F outside — backup heat only steps in occasionally Capacity retained at 5°F: 89%
- On a 5°F night it still delivers about twice the heat of a plain electric heater for the same electricity COP at 5°F: 2.21
- Scores 10 on the official heating efficiency test — solidly above the legal minimum HSPF2: 10
$2,143 – $2,143
equipment only · 1 seller · seen 2026-08-16
Mitsubishi P-series PUZ-AK48NLHZ Hyper-Heat Ducted System
- Enough heat for a mid-to-large house, roughly 2,000-2,800 sq ft Rated capacity: 48,000 BTU/h
- Keeps 87% of its heat when it's 5°F outside - backup heat only steps in occasionally Capacity retained at 5°F: 87%
- Its cold-weather performance has been independently measured and published, not just claimed in a brochure NEEP cold-climate listed: Yes
- Open 24V - works with any standard thermostat, and any competent tech can service it Thermostat compatibility: open
$7,428 – $8,928
equipment only · est. — outdoor unit from 1 seller, indoor air handler added
Mitsubishi M-Series SUZ-AK36NLHZ Hyper-Heating
- Enough heat for an average house, roughly 1,400-2,000 sq ft Rated capacity: 36,000 BTU/h
- Keeps 85% of its heat when it's 5°F outside - backup heat only steps in occasionally Capacity retained at 5°F: 85%
- Its cold-weather performance has been independently measured and published, not just claimed in a brochure NEEP cold-climate listed: Yes
- Open 24V - works with any standard thermostat, and any competent tech can service it Thermostat compatibility: open
$6,043 – $8,008
equipment only · est. — outdoor unit from 1 seller, indoor air handler added
Fujitsu Halcyon XLTH Extra Low Temperature Heating
- Keeps 80% of its heat when it's 5°F outside — backup heat only steps in occasionally Capacity retained at 5°F: 80%
- Its cold-weather performance has been independently measured and published, not just claimed in a brochure NEEP cold-climate listed: Yes
- On a 5°F night it delivers a modest efficiency edge over plain electric heat COP at 5°F: 2
- Scores 12 on the official heating efficiency test — solidly above the legal minimum HSPF2: 12
$3,669 – $5,169
equipment only · est. — outdoor unit from 1 seller, indoor air handler added
Bosch IDS Ultra Inverter Ducted Split
- Enough heat for an average house, roughly 1,400-2,000 sq ft Rated capacity: 36,000 BTU/h
- Drops to 78% of its heat at 5°F, so backup heat does part of the work on cold nights Capacity retained at 5°F: 78%
- Open 24V - works with any standard thermostat, and any competent tech can service it Thermostat compatibility: open
$6,616 – $10,685
equipment only · 2 sellers · seen 2026-08-16
Daikin Fit Aurora DH9VS
- Enough heat for an average house, roughly 1,400-2,000 sq ft Rated capacity: 36,000 BTU/h
- Drops to 75% of its heat at 5°F, so backup heat does part of the work on cold nights Capacity retained at 5°F: 75%
- Communicating - full features on the brand's own thermostat, but you're tied to that brand's dealer when a control board fails Thermostat compatibility: communicating
$5,500 – $8,000
equipment only · rough estimate, no seller data yet
LG LGRED° Single-Zone Ductless Heat Pump
- Drops to 72% of its heat at 5°F, so backup heat does part of the work on cold nights Capacity retained at 5°F: 72%
- On a 5°F night it delivers a modest efficiency edge over plain electric heat COP at 5°F: 1.9
- Scores 11 on the official heating efficiency test — solidly above the legal minimum HSPF2: 11
$2,440 – $2,440
equipment only · 1 seller · seen 2026-08-16
Daikin Aurora Multi-Zone Ductless System
- Drops to 70% of its heat at 5°F, so backup heat does part of the work on cold nights Capacity retained at 5°F: 70%
- On a 5°F night it delivers a modest efficiency edge over plain electric heat COP at 5°F: 1.85
- Scores 10.5 on the official heating efficiency test — solidly above the legal minimum HSPF2: 10.5
$7,005 – $9,077
equipment only · est. — outdoor unit from 1 seller, indoor air handler added
Mitsubishi FX Deluxe Single-Zone Hyper-Heating (MUZ-FX)
- Drops to 70% of its heat at 5°F, so backup heat does part of the work on cold nights Capacity retained at 5°F: 70%
- Its cold-weather performance has been independently measured and published, not just claimed in a brochure NEEP cold-climate listed: Yes
- On a 5°F night it still delivers about twice the heat of a plain electric heater for the same electricity COP at 5°F: 2.2
- Scores 13.3 on the official heating efficiency test — among the highest in this catalog HSPF2: 13.3
$3,990 – $3,990
equipment only · 1 seller · seen 2026-08-16
Trane 19 Multi-Speed Low Profile Cold Climate Heat Pump
- Enough heat for an average house, roughly 1,400-2,000 sq ft Rated capacity: 36,000 BTU/h
- Drops to 68% of its heat at 5°F, so backup heat does part of the work on cold nights Capacity retained at 5°F: 68%
- Open 24V - works with any standard thermostat, and any competent tech can service it Thermostat compatibility: open
$6,000 – $9,000
equipment only · rough estimate, no seller data yet
Fujitsu Airstage Ducted Single-Zone Heat Pump
- Enough heat for an average house, roughly 1,400-2,000 sq ft Rated capacity: 36,000 BTU/h
- Open 24V - works with any standard thermostat, and any competent tech can service it Thermostat compatibility: open
$5,404 – $6,904
equipment only · est. — outdoor unit from 1 seller, indoor air handler added
Lennox SL25XPV Variable-Capacity Heat Pump
- Enough heat for a mid-to-large house, roughly 2,000-2,800 sq ft Rated capacity: 48,000 BTU/h
- Its cold-weather performance has been independently measured and published, not just claimed in a brochure NEEP cold-climate listed: No
- Communicating - full features on the brand's own thermostat, but you're tied to that brand's dealer when a control board fails Thermostat compatibility: communicating
$23,496 – $23,496
equipment only · est. — install labour backed out of an observed installed price
Bosch Climate 5000 Single-Zone Ductless System
- Scores 9.5 on the official heating efficiency test — closer to the legal minimum HSPF2: 9.5
Price not yet sourced
we haven't found a defensible price
Carrier Performance 26 37MARA Single-Zone Ductless System
- Scores 13.6 on the official heating efficiency test — among the highest in this catalog HSPF2: 13.6
Price not yet sourced
we haven't found a defensible price
Samsung WindFree RXX12AMD / RNX12AMD Single-Zone Ductless System
- On a 5°F night the efficiency advantage over plain electric heat is largely gone COP at 5°F: 1.76
- Scores 9 on the official heating efficiency test — closer to the legal minimum HSPF2: 9
$1,749 – $1,749
equipment only · 1 seller · seen 2026-08-16
Get a recommendation for your specific house
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