# Furnace to Heat Pump Conversion in Seattle

> Furnace to heat pump conversion in Seattle: retire or keep the gas furnace, City Light vs PSE economics, air handler, panel and gas cap. Start planning yours.

URL: https://seattleheatpumpco.com/furnace-to-heat-pump-conversion/

Updated: 2026-10-21

Furnace to heat pump conversion swaps a gas furnace's heat for an electric heat pump on the same ducts, either replacing the furnace outright or keeping it as backup. [The Seattle Heat Pump Company](https://seattleheatpumpco.com/) plans furnace to heat pump conversions for houses across Seattle and King County, and licensed and insured contractors carry out the work. The decision that shapes everything else is what happens to the furnace.

That decision depends on the furnace's age, on which utility sells your electricity, and on the house's ducts and electrical panel. Two neighbors with identical furnaces can sensibly choose differently. This page covers gas furnaces; oil-heated homes have a different sequence with a tank and their own rebates, covered on the [oil to heat pump conversion](https://seattleheatpumpco.com/oil-to-heat-pump-conversion/) page.

## What happens on the first visit

A conversion visit looks at the furnace as closely as the house, because the furnace may stay.

**The house.** A Manual J load calculation sets the heat pump's size. A gas furnace's input rating is a poor guide: many were oversized when installed, and insulation or window upgrades since have shrunk the load further.

**The furnace.** Its age, condition and blower decide whether keeping it is an option. A heat pump coil adds resistance to airflow, and the furnace's blower has to move enough air across that coil for the heat pump to work. Variable-speed blowers handle that better than older single-speed ones. A furnace near the end of its life is usually not worth building around.

**The ducts.** A static pressure reading shows whether the ducts can carry a heat pump's higher airflow. Gas furnaces deliver hot air at modest volume; a heat pump delivers warm air at higher volume, so return-side restrictions that never bothered the furnace can starve the heat pump. The [existing ductwork page](https://seattleheatpumpco.com/heat-pump-existing-ductwork/) explains the measurements.

**The electrical service and gas appliances.** The panel's capacity decides whether electric backup heat fits without an upgrade. The visit also notes every other gas appliance in the house, because they decide whether gas service stays, and whether one of them shares the furnace's vent.

## Retire the furnace or keep it

There are three workable paths, and the right one depends on the house, not on a preference for one technology.

**Retire it and go all-electric.** An electric air handler replaces the furnace, holding the indoor coil, the blower and backup heat strips. This is the usual choice when the furnace is old, when City Light sells your electricity, or when the goal is to drop gas heat. The furnace's gas line is capped by a qualified gas fitter, and the job closes with commissioning of the heat pump and the backup heat lockout.

**Keep it as backup.** The heat pump's coil sits on the furnace, and controls switch between them based on outdoor temperature or cost. This is dual fuel, and it makes the most economic sense where electricity is expensive relative to gas, which in this region means PSE territory. The [dual fuel heat pump](https://seattleheatpumpco.com/dual-fuel-heat-pump/) page covers the changeover settings.

**Coil now, retire later.** A newer furnace with a capable blower can carry a heat pump coil for now and give way to an air handler when it wears out. The catch is planning: the coil and line set chosen today should suit the future air handler, or the later step costs more than it should.

Some homeowners are told a heat pump always needs a furnace behind it. That is not true of a properly sized ducted system in Seattle's climate, where the design temperature is 24°F and Sea-Tac sees about one night a year at 20°F or colder. Backup heat is still part of the design, for defrost and the rare coldest hours, but it does not have to be gas. The [heat pump versus gas furnace guide](https://seattleheatpumpco.com/guide/heat-pump-vs-gas-furnace-seattle/) compares the two in full.

## Your electric utility changes the math

Inside Seattle, City Light sells the electricity and PSE sells the gas. That split is the main reason conversion advice differs across the region.

| Electric utility | Electricity per kWh | COP a heat pump needs to beat a 95% gas furnace |
|---|---|---|
| City Light, Seattle | 13.38¢ | about 2.2 |
| City Light, suburban areas such as Shoreline and Burien | 14.64¢ | about 2.4 |
| PSE, Eastside and most suburbs | about 20.6¢ | about 3.4 |

Those break-evens compare energy charges only, using PSE gas at about $1.67 per therm. The coefficient of performance, or COP, is the heat delivered per unit of electricity, and it falls as the outdoor temperature drops. A modern heat pump clears 2.2 through most of a Seattle winter, so on City Light the all-electric case is strong. On PSE electricity, 3.4 is a higher bar on cold days, which is where keeping a newer furnace as backup starts to earn its place.

Rates move. PSE has requested further increases of 17.75% for electricity and 12.93% for gas; those requests had not been approved. The [operating cost guide](https://seattleheatpumpco.com/guide/heat-pump-operating-cost-seattle/) works through the numbers for each utility.

## The air handler, the panel and the gas cap

When the furnace leaves, three pieces of work come with it.

### The air handler and backup heat

The air handler usually goes where the furnace stood, so the duct connections stay short. Its backup heat strips are sized to the house's load at design conditions, not to the largest strip that fits. Seattle's energy code keeps supplemental heat off above 40°F and requires the lockout set to 35°F or lower at final inspection, so the strips should run only in defrost and the coldest hours. The [backup heat settings guide](https://seattleheatpumpco.com/guide/heat-pump-backup-heat-settings/) explains the controls, and the [air handler replacement](https://seattleheatpumpco.com/air-handler-replacement/) page covers placement and coil matching.

### Electrical capacity

A gas furnace runs on a small circuit for its blower and controls. A heat pump needs its own circuit and an outdoor disconnect, and electric backup strips can draw more current than the heat pump itself. Panel size and existing loads decide whether that fits. In Seattle, an electrical permit covering a 200-amp service runs $410.84 under current fees, compared with $110.38 for a circuit alone. The [panel requirements guide](https://seattleheatpumpco.com/guide/heat-pump-electrical-panel-requirements/) explains how capacity is worked out.

### Capping gas and checking the vent

The gas line to the furnace is shut off and capped by a qualified gas fitter. If a gas water heater shared the furnace's vent or chimney, removing the furnace changes how that vent performs, because a flue sized for two appliances can be too large for one. The remaining appliance's venting is checked before the job closes, and corrected if needed. If the water heater, range and fireplace all leave too, the gas service can be closed, ending PSE's $14 monthly basic charge.

## What it costs, and what comes off

A furnace conversion follows the ducted installation range: about $6,700 to $20,000 for Seattle-area projects on usable ducts, as, a budgeting range, not a quote. There is no published figure for gas conversion specifically, so the conversion items are drivers rather than prices:

- a new air handler, which alone runs about $1,500 to $4,200 in national figures (HomeGuide and Carrier)
- a panel upgrade from 100 to 200 amps, typically about $1,333 to $4,500 in the Seattle area
- capping the gas line and any venting correction for appliances left behind
- duct changes where the return or trunks are too small

City Light offers a contractor discount of $300 or $600 on qualifying heat pumps, one system per home. PSE offers $4,000 to income-qualified PSE gas customers who replace gas heat with a heat pump and remove or cap the gas equipment; because PSE sells gas inside Seattle, Seattle households may qualify, which PSE should confirm. Since April 2, 2026, PSE rebates require a PSE Trade Ally installer. PSE's hybrid rebate for keeping the furnace needs both PSE gas and PSE electric, so it does not apply inside Seattle. The federal 25C credit ended for equipment placed in service after December 31, 2025. The [PSE rebate guide](https://seattleheatpumpco.com/guide/pse-heat-pump-rebates/) and the [installation cost guide](https://seattleheatpumpco.com/guide/heat-pump-installation-cost-seattle/) cover the details.

Permits close the loop. In Seattle, the split system needs a refrigeration permit that only a licensed refrigeration contractor can obtain, plus electrical and mechanical permits when the circuit and indoor equipment change. The [Seattle permit guide](https://seattleheatpumpco.com/guide/seattle-heat-pump-permit/) covers each one.

## What's included

- Load calculation and duct static pressure test
- Furnace condition and blower capacity review
- Recommendation to retire the furnace, keep it as backup, or stage the change
- Electric air handler or coil on the furnace, matched to the outdoor unit
- Electrical service review and dedicated circuits
- Gas line to the furnace capped by a qualified gas fitter when the furnace leaves
- Venting check for any gas appliance that stays
- Thermostat configured for heat pump staging and backup lockout
- Permits, inspections and startup commissioning

## Three ways to convert from a gas furnace

|  | Retire the furnace (all-electric) | Keep the furnace as backup (dual fuel) | Coil now, retire later |
| --- | --- | --- | --- |
| What changes | Air handler with backup heat strips replaces the furnace; gas line capped | Heat pump coil added to the furnace; controls switch between them | Coil on the furnace today, air handler when the furnace wears out |
| Typical situation | Older furnace, City Light electricity, interest in dropping gas heat | Furnace with years left, PSE electricity on the Eastside | Newer furnace, plan to go all-electric eventually |
| What the assessment checks | Panel capacity, backup heat size, venting of gas appliances left behind | Blower capacity, coil fit, changeover setting | Whether the coil and line set will suit a future air handler |

## Questions

### Will a heat pump keep my house warm without the gas furnace?

In Seattle, a heat pump sized to a load calculation carries most houses through the whole winter. The city's design temperature is 24°F and Sea-Tac averages about one night a year at 20°F or colder. Electric backup heat covers defrost and the rare coldest hours, and Seattle's code keeps it locked out in milder weather.

### Does a heat pump still need a separate furnace?

No. A ducted heat pump can be the only heating system, with an electric air handler and backup heat strips in place of the furnace. Keeping a gas furnace as backup is a choice called dual fuel, which makes the most economic sense where electricity is expensive relative to gas, such as PSE territory.

### Will I need an electrical panel upgrade to convert from gas?

Not always. A gas furnace draws little electricity, while a heat pump and electric backup heat draw much more. Whether the existing panel can carry that depends on its size and what else runs on it. When an upgrade from 100 to 200 amps is needed, it typically runs about $1,333 to $4,500 in the Seattle area.

### What happens to my gas service after the furnace comes out?

The furnace's gas line is capped by a qualified gas fitter. If a water heater, range or fireplace still uses gas, the service stays and PSE's monthly basic charge continues. If every gas appliance goes, you can close the account. A water heater that shared the furnace's vent may need its venting changed.

### Will my heating bill go up if I switch from gas to a heat pump?

It depends mostly on your electric utility. On City Light's current Seattle rate, a heat pump beats a 95% efficient gas furnace once its efficiency averages a COP of about 2.2, which modern units clear most of the winter. On PSE electricity the break-even is about 3.4, so savings are narrower. No honest estimate can guarantee a number.