HVAC Guide · 7 min read
Heat Pump or Gas Furnace for a Puget Sound Home?
By Alderwood Heat & Cool Pros · Published October 3, 2026
The short answer
For most Puget Sound homes, a heat pump is the stronger long-term choice: mild, damp winters let it heat efficiently, and it adds air conditioning. A gas furnace still fits when the electrical panel can't take the load or gas rates favor it. Many Lynnwood-area owners split the difference with a dual-fuel system.
How a marine climate tilts the comparison
A heat pump doesn't burn anything. It moves heat from outdoor air into the house, and it works best when that air isn't very cold. South Snohomish County's heating season, roughly October into May, is mostly 30s, 40s and rain, with only a few nights in a typical winter dropping into the teens.
Wet, near-freezing air frosts the outdoor coil, so defrost cycles are frequent here. That is normal, as our guide to heat pumps blowing cold air or icing over in winter explains. A gas furnace ignores the outdoor temperature entirely, which is its main edge during an arctic blast.
Efficiency ratings: AFUE versus COP and HSPF2
AFUE for gas furnaces
AFUE is the share of the gas's energy that becomes heat in your rooms. Many older furnaces in Lynnwood garages and crawlspace closets are non-condensing units around 80% AFUE. Condensing furnaces reach the mid-90s by pulling extra heat from the exhaust, which is why they vent through PVC and need a condensate drain. No furnace tops 100%.
COP and HSPF2 for heat pumps
COP (coefficient of performance) compares the heat a heat pump delivers with the electricity it uses. Because it moves heat rather than making it, a COP of 2 to 4 is common in mild weather, and it falls as the temperature drops. HSPF2 rolls that into one seasonal rating; higher is better.
Operating cost: how to compare PSE gas with Snohomish PUD power
Which system is cheaper to run depends on your rates, and rates change, so work it out from a few recent bills instead of trusting a rule of thumb:
- Gas: add up the delivery and supply charges on your Puget Sound Energy bill and divide by the therms used to get an all-in price per therm.
- Electricity: do the same with your Snohomish County PUD bill to get a price per kWh. Homes in the King County end of Bothell buy power from PSE, so use that bill.
- Furnace: the cost of one therm of delivered heat is the gas price divided by the AFUE as a decimal (0.80 or 0.95, for example).
- Heat pump: one therm equals about 29.3 kWh, so the cost of one therm of delivered heat is the electric price times 29.3, divided by a realistic seasonal COP.
- Fixed charges: dropping gas entirely ends the monthly gas basic charge; keeping a gas range or water heater does not.
The cooling bonus after the 2021 heat dome
A gas furnace only heats. On June 28, 2021, local stations reported 109°F in Lynnwood and about 107°F in Mill Creek, and the share of Seattle-area homes with air conditioning rose from 44% in 2019 to 53% in 2021.
Adding cooling to a furnace means installing an outdoor condenser and an indoor coil anyway. A heat pump is essentially that same outdoor unit with a reversing valve, so one footprint both heats and cools. In ducted 1980s and 1990s homes like many we see in Mill Creek, WA, that often settles the question.
Dual fuel: the middle path
A dual-fuel system pairs a heat pump with a gas furnace on the same ducts. The heat pump handles the mild, wet months, and the furnace takes over below a switchover temperature that can be set for comfort, for your PSE and PUD rates, or both.
It suits a fairly young furnace, owners who want gas heat in reserve for a cold snap, and panels that can't support large backup strips. If the furnace in your dual-fuel system runs far too often, our dual-fuel and heat pump repair service can check the switchover setting and the outdoor sensor.
What your house decides for you
Existing ducts in 1970s and 1980s homes
Heat pump air feels warm rather than hot, and it usually needs more airflow than a furnace. Many Lynnwood-area ramblers and split-levels have one small return and supply runs sized for a furnace's hotter air. A Manual J load calculation and a duct check against Manual D should come first; skipping them is how heat pumps end up noisy and drafty.
Electrical panel capacity
A heat pump needs its own circuit, and the air handler's backup heat strips draw much more. An older 100-amp panel already serving an electric range and dryer may not have room. A load calculation shows whether you need a panel upgrade, smaller strips or a dual-fuel setup.
Gas line and venting
A new condensing furnace needs PVC venting to an outside wall or the roof plus a condensate drain. If the old furnace shared a chimney with a gas water heater, removing it can leave that heater on an oversized vent, which the installer should evaluate before quoting.
Safety, lifespan, noise and where code is heading
An all-electric heat pump has no flame or flue, so the heating system stops being a carbon monoxide source. A gas furnace is safe when maintained, but it needs working CO alarms and periodic vent and heat exchanger checks. If you smell gas or a CO alarm sounds, leave the house first, then call 911 and Puget Sound Energy at 1-888-225-5773 from outside, before you call us.
Lifespan tends to favor the furnace, since a heat pump works year-round. The outdoor unit needs service clearance and shouldn't sit under a bedroom window. Washington's energy code has pushed new construction toward heat pumps; replacements in existing homes are treated differently, so ask your contractor or the permit office what applies.
Expert insight: the switchover setting that makes or breaks dual fuel
Dual fuel only saves money if the system hands off from the heat pump to the gas furnace at the right outdoor temperature. That handoff point is a setting in the thermostat or control board, and installers sometimes leave it at a conservative default. Set too high, the furnace burns gas on mild 40-degree days the heat pump could easily handle, and the heat pump barely earns its keep. Set too low, the heat pump grinds through the coldest mornings with long run times and lots of defrost.
The right number depends on the heat pump's capacity, the house's heat loss from the load calculation, and how PSE gas prices compare with Snohomish PUD power at the time. It is worth revisiting when rates change. Ask the installer what the switchover is set to and why, and have it checked on the first service visit after a full winter. Here is how the three options compare overall:
| Factor | Heat pump | Gas furnace | Dual fuel |
|---|---|---|---|
| Cooling | Yes, built in | Needs a separate AC | Yes, from the heat pump |
| Efficiency in mild, damp weather | High (COP well above 1) | Up to about 96–98% AFUE | Heat pump handles it |
| Coldest snaps | Lower output; may need backup strips | Full output | Furnace takes over |
| Fuel | Snohomish PUD electricity | PSE natural gas | Both |
| Combustion and CO risk in the house | None from the heating system | Yes; needs venting and CO alarms | Yes, from the furnace |
| Electrical panel impact | Larger | Small | Moderate |
| Rebates to check | PUD (electric-heat homes), state programs | Limited | PSE, state programs |
Making the call for your home
Old furnace, a wish for air conditioning and room in the panel: a heat pump usually fits best. Newer furnace: keep it and add a heat pump for dual fuel. Cheap gas and no interest in cooling: a condensing furnace is still sound. Before you sign, read our guide to heat pump rebates in Snohomish County and check each program's current page.
For options matched to your ducts, panel and venting, see our HVAC installation and replacement service or call (321) 478-0693. We answer 24/7, and you get a price before work starts. Every HVAC contractor we send is registered with Washington L&I, licensed where Washington requires it, and insured.
Frequently asked questions
Can a heat pump keep a Lynnwood home warm during a cold snap?
Yes, if it is sized correctly and has backup. Modern heat pumps keep producing heat well below freezing, and cold-climate models hold much of their output into the teens. On the coldest nights the system may lean on electric backup strips or, in a dual-fuel setup, the gas furnace. Those nights are few in south Snohomish County, so backup heat covers only a small share of the season when the system was sized with a proper load calculation.
Can a heat pump use the ductwork my gas furnace has now?
Usually, yes. A ducted heat pump connects to the same supply and return ducts, either through a new air handler or through a coil on top of the existing furnace in a dual-fuel setup. The real question is airflow. Heat pumps often need more air moving than a furnace, and many 1970s and 1980s homes have undersized returns. A contractor should measure static pressure and check duct sizes before the install, then add a return or resize runs if needed.
Should I replace a gas furnace that still works with a heat pump?
Not necessarily right away. If the furnace is fairly young and running well, adding a heat pump on the same ducts for dual fuel gets you cooling and efficient mild-weather heat without scrapping a good appliance. If the furnace is older, needs a major repair, or you also want air conditioning, replacing it with a heat pump at the same time usually makes more sense. Rebate rules can tip the decision too, so check the current program pages before you choose.
Still have a question, or need help right now?