# Dual Fuel Heat Pumps in Sacramento > Dual fuel heat pumps in Sacramento: a heat pump on your gas furnace, the changeover temperature set from local rates and design data, and what SMUD covers. URL: https://tulesacramentoheatpump.com/dual-fuel-heat-pump/ A heat pump added to a gas furnace that still has life in it, with the changeover point set from your utility's rates and the house's heat loss. [Tule Sacramento Heat Pump](https://tulesacramentoheatpump.com/) designs and installs dual fuel systems across the Sacramento region: an electric heat pump added to the gas furnace a house already has, with the work done by licensed and insured contractors. The heat pump cools in summer and heats through most of the winter. The furnace takes over only below an outdoor temperature you choose. The setup suits a furnace with years of life left, a house on PG&E electric rates, or an owner who wants gas heat on hand for the coldest mornings. The design decision is where to set the changeover, and the right answer depends more on your electric utility than on the equipment. ## How a dual fuel system splits the work A dual fuel system runs one heat source at a time. Above the changeover temperature the heat pump heats; below it, the controls lock out the compressor and fire the furnace. The furnace blower moves air for both, so the ducts, filter and thermostat serve one system with two ways to make heat. ### Where the heat pump coil sits The heat pump’s indoor coil mounts on the furnace, downstream of the heat exchanger. In cooling and heat pump heating the burners stay off and the coil does the work. When the furnace runs, its hot air passes through the idle coil. ### Why the two don’t run together If the compressor kept running while the furnace fired, furnace air flowing over the coil would push refrigerant pressures past what the system is built for. The control’s job is to hand off cleanly and keep the compressor off whenever the burners are lit. ## What happens on the first visit The visit checks whether the furnace can be the backup half of a matched system. - **The furnace.** Age, efficiency rating, heat exchanger condition, venting, and whether its blower is single-speed or variable-speed. - **The cabinet.** Width and height above the furnace, which decide whether a matched coil fits without major sheet-metal changes. - **The load.** A Manual J calculation and the heat pump’s rated output at low outdoor temperatures, which set the thermal balance point. - **The ducts.** Static pressure and return size, since the furnace blower must deliver heat pump airflow. - **Your rates.** SMUD, Roseville Electric or PG&E, the rate plan, and what else in the house uses gas. The scope names the heat pump, the coil, the control, the changeover setting and the permit. ## Choosing the changeover temperature ### The thermal balance point The thermal balance point is the outdoor temperature at which the heat pump’s output falls to the house’s heat loss. Below it, the heat pump alone can’t hold the setpoint. The California Energy Commission lists a 31°F heating design for Sacramento’s airport station, and NOAA’s normals there count essentially no nights at 20°F or below. A heat pump sized for the summer load may cover the house to near the design temperature; the [heat pump sizing guide](https://tulesacramentoheatpump.com/guide/heat-pump-sizing/) shows how both loads are built. ### The economic balance point The economic point is where gas becomes cheaper per unit of heat than the heat pump. It depends on the coefficient of performance, or COP, which falls as the outdoor air gets colder, and on your prices. | Winter electric rate | Price per kWh | Heat pump beats a 95% gas furnace above COP | | --- | --- | --- | | SMUD Time-of-Day, off-peak | $0.1285 | 1.41 | | SMUD Time-of-Day, 5 to 8 p.m. peak | $0.1776 | 1.95 | | Roseville Electric, Tier 2 | $0.1989 | 2.18 | | PG&E E-ELEC, off-peak | $0.28468 | 3.13 | | PG&E E-ELEC, 4 to 9 p.m. peak | $0.32063 | 3.52 | These break-even values are derived from the published tariffs and PG&E’s residential gas rate, energy charges only. On SMUD’s prices the heat pump stays ahead of gas into cold weather, so a SMUD household sets the changeover for comfort. On PG&E’s prices the bar sits above 3, so the furnace has a real economic case on the coldest mornings. ### Setting it in practice The control gets the higher of the two points. Some controls can also switch to the furnace during the utility’s peak hours, which a PG&E household may want. The setting is reviewed after the first cold snap, because the real heat loss of a house rarely matches a calculation exactly. ## Where dual fuel makes sense here ### PG&E electric territory West Sacramento, Davis, Rocklin and El Dorado Hills buy electricity from PG&E or a community choice supplier on PG&E’s wires, while gas comes from PG&E everywhere in the region. There the economic balance point sits highest, and keeping a working furnace for the coldest hours trims winter bills. ### The colder edges of the region Rocklin’s heating design is 26°F at the 0.2% level, five degrees colder than Sacramento’s airport, and the El Dorado County foothills run colder still. Across El Dorado County 27% of households heat with propane, against 2% in Sacramento County, and propane’s price shifts the balance point down. ### When a full conversion fits better In SMUD territory, with a furnace near the end of its life, dual fuel keeps a gas appliance the household may not need, and SMUD does not state whether the arrangement qualifies for its rebate. [Gas furnace to heat pump conversion](https://tulesacramentoheatpump.com/gas-furnace-to-heat-pump-conversion/) covers that path, and the [heat pump vs gas furnace guide](https://tulesacramentoheatpump.com/guide/heat-pump-vs-gas-furnace-sacramento/) compares the two. If the AC has just failed and the choice is still open, [replacing the AC with a heat pump](https://tulesacramentoheatpump.com/replace-ac-with-heat-pump/) lays out all three options. Find the changeover point for your house A load calculation and your rate plan set the temperature where the furnace takes over, so the system is configured for your bills, not a factory default. ## Defrost on tule fog mornings NOAA’s normals for Sacramento Executive Airport put the January 7 a.m. temperature at 41.6°F, with one morning in ten near 32°F and a dew point around 41°F. Fog-season air near freezing frosts the outdoor coil often, and the heat pump reverses briefly to clear it. During those minutes the indoor coil is cooling the air. An all-electric system covers defrost with strip heat. In a dual fuel system the control can fire the furnace for the defrost cycle instead, so the registers don’t blow cool air. The [aux heat and defrost guide](https://tulesacramentoheatpump.com/guide/heat-pump-aux-heat-defrost/) explains the settings and what normal frost looks like. ## Furnace, coil and controls compatibility ### The blower The heat pump needs at least 300 cfm per ton of airflow under Title 24’s charge verification. An older single-speed blower may be wired for a smaller AC, or may not reach that airflow through restrictive returns. A variable-speed furnace blower handles the job more easily, and where returns are the bottleneck, [heat pump ductwork](https://tulesacramentoheatpump.com/heat-pump-ductwork/) covers the fix. ### The coil and refrigerant New heat pumps use lower-GWP refrigerants such as R-454B or R-32, and the coil must be rated with the outdoor unit. The [R-454B guide](https://tulesacramentoheatpump.com/guide/heat-pump-refrigerant-r454b/) explains the change. The old AC coil is replaced, and the new one is sealed to the cabinet with its drain trapped and protected by an overflow switch. ### The combustion side The furnace keeps burning gas, so its venting, flue connection and combustion are checked as their own task, separate from the heat pump work. A cracked heat exchanger or a failing flue is a reason to reconsider the plan. ### Controls and testing The thermostat needs an outdoor sensor or equivalent control logic, compressor lockout and furnace staging. Title 24 treats the outdoor unit installation as an alteration that triggers duct sealing and an ECC-Rater visit, with refrigerant charge verified as on any heat pump. ## Rebates, rate plans and the gas bill SMUD’s heat pump rebate is written for systems that replace gas heating or an existing electric system, and SMUD does not state whether a heat pump added to a kept gas furnace qualifies. That is confirmed before equipment is chosen, and the [SMUD rebate guide](https://tulesacramentoheatpump.com/guide/smud-heat-pump-rebates/) lists the program terms. Roseville Electric lists no residential heat pump rebate, and no PG&E single-family rebate was found. ### What the gas account still costs PG&E’s E-ELEC rate is limited to households using a heat pump as their primary heating and cooling, so eligibility for a dual fuel home is confirmed with PG&E. On the gas side, PG&E’s residential schedule keeps a minimum transportation charge of $0.13151 a day whether or not the furnace runs. The [electric bill guide](https://tulesacramentoheatpump.com/guide/heat-pump-electric-bill-sacramento/) runs both bills together. ## What a dual fuel installation costs No local program data isolates dual fuel projects, so they are priced from the work each furnace needs. The drivers are the coil and any cabinet transition, the furnace’s blower and condition, the dual fuel control and thermostat, the line set, the outdoor circuit and any venting correction. The [installation cost guide](https://tulesacramentoheatpump.com/guide/heat-pump-installation-cost-sacramento/) covers the shared components, and the [cost estimator](https://tulesacramentoheatpump.com/tools/heat-pump-cost-estimator/) gives a range for full conversions to compare against. ## Keeping a gas furnace under California’s rules Yes. The City of Sacramento’s electrification strategy does not require immediate appliance replacement, and Title 24’s heat pump baseline applies to new homes. The [California gas furnace rules guide](https://tulesacramentoheatpump.com/guide/california-gas-furnace-ban/) separates adopted rules from proposals. ## What's included - A load calculation, and the heat pump's output at low outdoor temperatures - A furnace check: age, blower type, heat exchanger condition and venting - A heat pump coil matched to the outdoor unit and sealed to the furnace cabinet - Old condenser removed and its refrigerant recovered - Refrigerant lines replaced, or cleaned and tested for reuse - Outdoor circuit and disconnect sized to the heat pump's nameplate - A dual fuel thermostat or control with an outdoor temperature sensor - Changeover temperature, compressor lockout and defrost behavior configured - Pressure test, evacuation and charge to the manufacturer's specification - Both modes commissioned: heat pump heating and cooling, then furnace heating - The permit, inspection and ECC-Rater visit ## Dual fuel against the two all-or-nothing options | | Dual fuel (heat pump plus furnace) | All-electric heat pump | AC plus gas furnace | | --- | --- | --- | --- | | Who heats | Heat pump above the changeover point, furnace below it | Heat pump, strips as backup | Furnace all winter | | Defrost cycles | Furnace can warm the air during defrost | Strips warm the air during defrost | No defrost | | Gas service | Stays | Can close if nothing else uses gas | Stays | | SMUD heat pump rebate | Eligibility not stated by SMUD; confirmed first | Yes, on qualifying equipment | No | | Fits best | A sound furnace, PG&E electric rates or foothill cold | An aging furnace on SMUD power | A newer furnace and no interest in heat pump heating | | Check first | Furnace blower airflow and coil fit | Panel capacity and air handler location | Coil match with the new refrigerant | ## Related resources - Learn [What is heat pump aux heat, and when should it run in Sacramento?](https://tulesacramentoheatpump.com/guide/heat-pump-aux-heat-defrost/)How backup heat strips, defrost cycles and thermostat controls work together, why the valley floor rarely needs strips for capacity, what they cost to run on each utility's rates, and when a furnace makes the better backup. - Decision Guide [Is a heat pump or a gas furnace better for a Sacramento home?](https://tulesacramentoheatpump.com/guide/heat-pump-vs-gas-furnace-sacramento/)How the two compare on Sacramento's winter mornings, what each costs to run under SMUD, Roseville Electric and PG&E rates, how they differ in comfort, safety and upkeep, and which households should keep gas for now. - Learn [How much will a heat pump add to your electric bill in Sacramento?](https://tulesacramentoheatpump.com/guide/heat-pump-electric-bill-sacramento/)How heating moves from the gas bill to the electric bill, what a therm of heat costs under each local rate plan, how summer peaks and fixed charges work, and the settings that keep a heat pump's bill from creeping up. - Learn [Is California banning gas furnaces in existing Sacramento homes?](https://tulesacramentoheatpump.com/guide/california-gas-furnace-ban/)Which rules exist, which apply only to new construction, what the City of Sacramento has and has not adopted, how SB 222 treats HOAs, and why timing is usually set by the furnace and the electric rate rather than a deadline. - Learn [How is a heat pump sized for a Sacramento home?](https://tulesacramentoheatpump.com/guide/heat-pump-sizing/)How a load calculation turns your house, your town's design temperatures and your ducts into a capacity, why the old condenser's tonnage is a poor guide, and what Title 24 and the City permit allow. ## 1. Your house and your bills What you have now, what isn't working, your utility and what you want the new system to do. 2. Load, ducts and panel A room-by-room load calculation, a look at the ducts and returns, the electrical panel and where the outdoor unit can go. 3. Permit, set, braze, test Permit pulled, old equipment recovered and removed, new units set, lines brazed, pressure-tested and evacuated before charging. 4. Verified and explained Airflow, charge and backup heat checked, the ECC-Rater visit for Title 24, and the thermostat set up and walked through. ## What this work looks like Gas furnace with a heat pump coil cabinet on top and a supply plenum to the ceiling in the garage of a Sacramento-area house Slim wall thermostat with a dark screen near the stairs of a two-story Sacramento-area home, a large return air grille below it Furnace and heat pump coil cabinet in an open equipment closet in the garage of a 1970s Sacramento ranch house Heat pump outdoor unit on a pad beside the sage-green stucco wall of a Sacramento ranch house, the furnace flue vent on the roof above Keep the furnace and let the heat pump do most of the work Tell us the furnace's age, who supplies your electricity and whether a water heater or range still runs on gas. The changeover plan is built from those. ## Dual fuel heat pump questions ### At what outdoor temperature should a dual fuel system switch to the furnace? There is no universal setting. The thermal balance point comes from the house's heat loss and the heat pump's output as it gets colder; the economic point comes from your electric and gas prices. On SMUD power the heat pump only has to beat a COP of about 1.4 at off-peak prices, so the setting is usually driven by comfort. On PG&E electric rates, gas can win on the coldest mornings, and the setting moves up. ### Will a dual fuel system keep the house warm during a power outage? No. A gas furnace still needs electricity for its blower, igniter and controls, so a dual fuel system stops heating when the power goes out, just as an all-electric heat pump does. Keeping heat through an outage takes a generator or battery sized and wired for the furnace, which is separate electrical work. ### Is my furnace too old to pair with a heat pump? It depends on condition more than age. The heat exchanger has to be sound, the venting safe, and the blower able to move at least 300 cfm per ton of heat pump capacity. A furnace that needs major repairs, or a blower that can't reach that airflow, usually points to a full conversion with an air handler instead. ### Does a dual fuel system qualify for PG&E's E-ELEC rate? E-ELEC is open to households whose electric heat pump is the primary space heating and cooling system. A dual fuel system that heats mostly with the heat pump may fit that description, but PG&E decides eligibility per account, so it is confirmed with PG&E before the rate plan is counted in the operating cost comparison. ### Can a dual fuel system use a propane furnace? Yes. The heat pump and controls work the same way with a propane furnace, and propane's higher cost per unit of heat pushes the changeover point lower, so the heat pump carries more of the winter. That matters more in the El Dorado County foothills, where the Census finds propane heating far more common than on the valley floor. ## Related services Furnace to heat pump conversion One ducted heat pump in place of the gas furnace and the central AC, sized from a load calculation and tested to Title 24. AC to heat pump A heat pump in place of a failing central air conditioner, with the furnace kept as backup, removed, or replaced by the heat pump's own air handler. Variable speed heat pump An inverter-driven heat pump that runs at the output the house needs, sized and set up for Sacramento's heat and SMUD's rebate tiers.