Knowing when to switch from a heat pump to a furnace can save money, improve comfort, and protect equipment. The right changeover temperature depends on energy prices, outdoor conditions, and system design. This guide explains how to set a smart switchover point, with practical rules of thumb, cost math, regional tips, and thermostat settings for a typical American home.
How Heat Pumps And Furnaces Deliver Heat
A heat pump moves heat from outdoors to indoors. Its efficiency is expressed as a coefficient of performance (COP). A COP of 3 means one unit of electricity delivers three units of heat. COP falls as outdoor temperature drops because there is less heat to capture.
A gas furnace burns fuel and is rated by AFUE, the percentage of fuel energy delivered as heat. Modern condensing furnaces reach 95–98% AFUE. Unlike heat pumps, furnace efficiency is relatively steady across temperatures.
In mild weather, heat pumps are usually cheaper to run. As it gets colder, the heat pump’s COP declines and defrost cycles increase. Below a certain temperature, a furnace can become the less expensive and more comfortable heat source, especially in a dual-fuel setup where the furnace replaces electric resistance auxiliary heat.
The Two Balance Points That Matter
Thermal balance point is the outdoor temperature where the heat pump’s maximum output equals the home’s heat loss. Below that temperature, the home needs supplemental heat. This varies by house insulation, size, and the heat pump’s capacity.
Economic balance point is where the cost per unit of delivered heat from the heat pump equals the cost from the furnace. This is the critical number for a dual-fuel system. Above this temperature, the heat pump usually costs less; below it, the furnace wins.
In many dual-fuel thermostats, this balance is managed with lockout temperatures. Compressor lockout turns off the heat pump below a chosen temperature. Furnace (or auxiliary) lockout prevents furnace or strips above a chosen temperature. Setting both creates a clean switchover band that avoids expensive overlap and short cycling.
What Temperature To Switch From Heat Pump To Furnace
There is no single “right” number, but these ranges are reliable starting points for U.S. homes with dual fuel. Refine them using your utility rates and equipment data.
- Standard heat pump + natural gas furnace: Start around 30–40°F. If electricity is cheap or gas is expensive, drop to 25–35°F.
- Cold-climate heat pump (variable-speed) + natural gas furnace: Start around 15–30°F. These systems maintain higher COPs in the 20s and often the teens.
- Any heat pump + propane or fuel oil furnace: Switch later (colder) because delivered propane/oil heat typically costs more than natural gas. Start around 15–30°F, and fine-tune with the cost method.
- Time-of-use electricity: Raise the switchover during on-peak hours and lower it off-peak. A modern thermostat can automate this.
If the alternative is electric resistance auxiliary heat, switch to the furnace earlier. Heat strips have COP ≈ 1, so they are usually the most expensive heat source in cold weather.
Calculate Your Economic Switchover Temperature
The goal is to find the outdoor temperature where your heat pump’s COP equals the break-even COP dictated by energy prices and furnace efficiency. Then use the manufacturer’s performance tables to map that COP to a temperature.
Don’t Overpay for HVAC Services – Call 888-894-0154 Now to Compare Local Quotes!
Step 1: Compute Break-Even COP From Prices
Use this relationship: Break-even COP ≈ (Electricity price × AFUE × 100,000) / (Gas price × 3,412). Electricity price is $/kWh. Gas price is $/therm. AFUE is a decimal (0.95 for 95%).
Interpretation: If the heat pump’s COP is above this number, the heat pump costs less per unit of heat. If below, the furnace costs less.
Step 2: Map COP To Temperature
Look up your model’s performance tables or extended data in the AHRI Directory or manufacturer literature. Find COP versus outdoor temperature at your indoor setpoint and fan speed. The outdoor temperature where COP ≈ break-even COP is your economic switchover temperature.
Examples
| Scenario | Electricity ($/kWh) | Gas ($/therm) | Furnace AFUE | Break-Even COP | Typical Switchover Temp |
|---|---|---|---|---|---|
| Common Midwest Rates | $0.15 | $1.50 | 95% | ≈2.8 | Standard HP: ~25–30°F; Cold-Climate: ~15–20°F |
| Cheap Gas, High Electric | $0.20 | $1.00 | 95% | ≈5.6 | Furnace nearly always cheaper below ~50°F |
| Propane Alternative | $0.25 | $2.73 (per therm equivalent) | 95% | ≈2.6 | Standard HP: ~25–30°F; Cold-Climate: ~10–20°F |
| Low Electric, Average Gas | $0.12 | $1.20 | 95% | ≈2.8 | Similar to Midwest: ~20–30°F |
Values are illustrative. Use your actual bills for accuracy. For propane, convert price per gallon to $/therm equivalent using 91,500 BTU/gal.
Emissions Break-Even (Optional)
If carbon impact matters, use a similar concept. U.S. grid average emissions are roughly ~0.4 kg CO₂ per kWh, and natural gas combustion is about 5.3 kg CO₂ per therm. With a 95% AFUE furnace, a COP around ~2.1 makes the heat pump cleaner than gas on average. Many heat pumps exceed this down into the 20s, especially cold-climate units.
COP And Outdoor Temperature: What To Expect
Manufacturer data varies, but these ranges are typical at 70°F indoor setpoint and moderate fan speeds. Use your specific model’s tables for final decisions.
| Outdoor Temp | Standard Heat Pump COP | Cold-Climate Heat Pump COP |
|---|---|---|
| 47°F | ~3.0–3.5 | ~3.5–4.2 |
| 35°F | ~2.6–3.0 | ~3.0–3.6 |
| 25°F | ~2.1–2.6 | ~2.7–3.1 |
| 17°F | ~1.8–2.2 | ~2.3–2.7 |
| 5°F | ~1.4–1.8 | ~2.0–2.3 |
| -5°F | ~1.2–1.5 | ~1.7–2.0 |
Defrost cycles and wind exposure can temporarily lower effective COP in the 20s and below. Variable-speed compressors help by maintaining output and reducing on-off losses.
Comfort, Defrost, And Humidity Considerations
Cost is not the only factor. If the home feels drafty or the heat pump struggles to maintain setpoint, switch earlier. Gas furnaces deliver higher supply air temperatures and faster recovery after setbacks.
In humid climates, heat pumps can carry moisture outdoors during defrost and may feel cooler when cycling. In very cold weather, defrost frequency rises, causing brief cool air events. A dual-fuel swap to the furnace can improve comfort during cold snaps, even if costs are similar.
All-electric homes with resistance strips should minimize strip use through tighter envelopes, smart thermostats, and staged heat settings.
Regional Guidance For The U.S.
Use these starting ranges, then fine-tune with utility rates and equipment data.
| Region (IECC Climate Zones) | Typical Dual-Fuel Switchover | Notes |
|---|---|---|
| Southeast & Gulf (Zones 2–3) | 30–40°F (standard), 20–30°F (cold-climate) | Electric rates and comfort dominate; gas may be limited. |
| Mid-Atlantic & Pacific NW (Zone 4) | 25–35°F (standard), 15–25°F (cold-climate) | Moist cold increases defrost impacts; consider comfort. |
| Midwest & Northeast (Zones 5–6) | 20–30°F (standard), 5–20°F (cold-climate) | Weather swings favor dual-fuel flexibility. |
| Northern Plains & Upper Midwest (Zone 7) | 15–30°F (standard), 0–15°F (cold-climate) | Many cold-climate models heat well below 0°F. |
| Mountain West (varies) | 20–35°F | High elevation reduces density; check capacity tables. |
Default contractor settings often use ~35°F. Modern cold-climate systems and high gas prices justify lower lockouts.
Thermostat Settings To Control Switchover
Most dual-fuel thermostats support specific lockout temperatures. The terms vary by brand. Key ideas: set a compressor lockout (heat pump off below X°F), and set an auxiliary/furnace lockout (furnace off above Y°F). This creates a clean crossover.
Ecobee (Smart, Enhanced, Premium)
- Menu → Settings → Installation Settings → Equipment.
- Set “Heat Pump” as primary and “Furnace” as backup (Dual Fuel).
- Automation → “Compressor to Furnace Min Outdoor Temp.” Choose your economic switchover temperature.
- Disable “Use Electric Heat” or set “Aux Heat Min Outdoor Temp” high to avoid strips.
Nest (3rd Gen Learning, Nest Thermostat)
- Settings → Equipment → Heat Type → Dual Fuel.
- Balance → “Heat Pump Balance” set to “Max Savings” for longer compressor run time, or “Max Comfort” to switch earlier.
- Advanced → “Compressor Lockout” and “Aux Heat Lockout” temperatures if available in your model and region.
Honeywell Home / Resideo (T6 Pro, VisionPRO)
- Installer Setup: Enable Dual Fuel and select fossil fuel backup.
- Set “Balance Point” or “Compressor Lockout” temperature.
- Set “Aux Heat Lockout” to keep strips off above your target.
Tip: Start with a conservative number (e.g., 30°F), monitor run time and bills for two weeks, then adjust by 3–5°F. Avoid frequent changes that cause short cycling.
Special Cases: Propane, Fuel Oil, Time-Of-Use, And Solar
Propane and oil: Delivered fuel prices vary widely. Convert to $/therm equivalent for apples-to-apples math. Many homes save by running the heat pump deeper into winter, then using propane for polar outbreaks.
Time-of-use rates: With peak prices triple off-peak, it can be cheapest to switch to the furnace during peak windows and revert to the heat pump off-peak. Some smart thermostats can integrate utility price signals.
Rooftop solar: Self-produced electricity effectively lowers your marginal electric cost in sunlit hours. If net metering credits are low, favor the heat pump when your array is producing.
All-electric homes: Without a furnace, focus on minimizing auxiliary strips. Tighten the envelope, raise setpoints gradually, and use weather-responsive controls.
Maintenance And System Setup That Change The Answer
Proper sizing: If the heat pump is undersized, the thermal balance point will be warmer, forcing early switchover. A right-sized or slightly oversized cold-climate heat pump can heat efficiently into the teens.
Airflow and charge: Dirty filters, iced coils, and low refrigerant reduce COP. Keep the outdoor unit clear of snow, leaves, and obstructions. Maintain 12–24 inches of clearance around the coil.
Don’t Overpay for HVAC Services – Call 888-894-0154 Now to Compare Local Quotes!
Thermostat staging: Use longer compressor run times and limit rapid temperature setbacks that trigger auxiliary heat. A 1–2°F setback is safer than deep overnight setbacks in cold weather.
Defrost strategy: Some systems allow demand defrost. Enable it to reduce unnecessary defrost cycles and improve effective COP.
Safety, Reliability, And Power Outages
Carbon monoxide safety: Any gas or oil furnace requires a working CO detector on each floor and near sleeping areas. Ensure annual combustion safety checks and proper venting.
Electrical reliability: Heat pumps and furnaces rely on fans and controls. Whole-home surge protection and a maintained condensate drain reduce nuisance shutdowns.
Backup power: If outages are common, a small generator or battery can run the furnace blower and controls more easily than a heat pump’s compressor. Plan for cold snaps accordingly.
Quick Decision Checklist
- Gather your actual $ per kWh and $ per therm (or propane/oil equivalent).
- Compute break-even COP and find the temperature where your heat pump hits that COP.
- Set compressor lockout near that temperature; set aux/furnace lockout a few degrees above it.
- Adjust 3–5°F after two weeks based on comfort and bills.
- Switch earlier during peak electric prices or heavy defrost; later with mild, dry weather.
- Keep filters clean and the outdoor unit clear to preserve COP.
FAQs About Switching From Heat Pump To Furnace
What if my heat pump keeps calling for auxiliary heat?
In a dual-fuel setup, set an aux heat lockout so the furnace handles low-temperature heating instead of electric strips. If all-electric, minimize deep setbacks and check airflow and charge to reduce strip usage.
Is it bad to run the heat pump below freezing?
No, many heat pumps are designed for it, especially cold-climate models. Economic switchover is about cost and comfort, not safety. Follow manufacturer low-temperature limits and keep coils clear.
How do I find my heat pump’s COP at different temperatures?
Check the NEEP cold-climate product list or your manufacturer’s extended performance data. The AHRI Directory also lists matched system ratings; ask your contractor for the precise model data sheet.
Can smart thermostats pick the switch point automatically?
Some do. Ecobee’s dual-fuel logic and Nest’s Balance feature estimate savings from runtime. Manual verification using your rates is still recommended for accuracy.
Real-World Tips To Dial In Your Switchover
- Start conservative: 30–35°F for standard heat pumps, 20–25°F for cold-climate models with gas backup.
- Use degree-day insights: If your winter bill spikes on colder weeks, raise the switchover a few degrees.
- Watch supply air temps: If vents blow lukewarm during cold snaps, switch earlier for comfort.
- Avoid frequent toggling: Move the lockout in small steps, then leave it for a full billing cycle.
- Coordinate with setbacks: Keep setbacks shallow in cold weather to avoid strip or furnace kicks.
Key Terms At A Glance
- Dual Fuel: A system with both a heat pump and a gas/oil furnace.
- Compressor Lockout: Temperature below which the heat pump is disabled.
- Aux/Furnace Lockout: Temperature above which the backup heat is disabled.
- Balance Point (Thermal): Heat pump output equals home load.
- Economic Balance Point: Heat cost from heat pump equals furnace cost.
- COP: Ratio of heat output to electric input; higher is better.
- AFUE: Furnace efficiency percentage as delivered heat.
Sources And Further Reading
U.S. DOE: Heat Pump Systems — Overview of performance and selection.
U.S. DOE: Furnaces and Boilers — AFUE, operation, and maintenance.
NEEP Cold-Climate Heat Pump List — Verified low-temperature performance.
AHRI Directory — Matched system ratings and data sheets.
EPA eGRID — Regional grid emissions data.
EIA: Natural Gas Prices and EIA: Electricity Data Browser — Check local energy prices to compute break-even COPs.
Don’t Overpay for HVAC Services – Call 888-894-0154 Now to Compare Local Quotes!
How to Get the Best HVAC Prices
- Firstly, keep in mind that installation quality is always the most important thing for residential HVAC project. So never sacrifice contractor quality for a lower price.
- Secondly, remember to look up the latest rebates as we talked above.
- Thirdly, ask for at least 3 bids before you make the decision. You can click here to get 3 free estimates from your local contractors, and this estimate already takes rebates and tax credit into consideration and filter unqualified contractors automatically.
Lastly, once you chose the right contractor, remember to use the tactics from this guide: Homeowners Tactics When Negotiating with HVAC Dealer to get the final best price.
