Most modern RV air conditioners include a heat pump function — but a lot of RV owners don’t fully understand what it is, when it works, and when they should switch to the propane furnace instead. This confusion leads to cold nights and frustration that’s entirely preventable.
What Is a Heat Pump?
A heat pump isn’t a separate appliance — it’s your rooftop AC unit running in reverse. Instead of pumping heat from inside your RV to the outside (cooling), it pumps heat from the outside air into your RV (heating). It runs on electricity and uses the same components as cooling mode.
The key thing to understand: a heat pump doesn’t create heat the way a furnace does. It moves heat that already exists in the outside air into your RV.
The Big Limitation: Temperature
This is what trips up most RV owners. A heat pump can only extract heat from outside air that is above approximately 40°F (4°C). Below that temperature, there isn’t enough heat energy in the outside air to extract efficiently, and the heat pump becomes ineffective — it may run but produce barely any warmth.
Some newer heat pumps (marketed as “low ambient” or “cold climate”) can operate down to 25–30°F, but most standard RV units have the 40°F limitation.
This is why: Your heat pump seems to “stop working” or blow barely-warm air in cold weather. It isn’t broken — it’s hitting its operational limit. Switch to your propane furnace.
When to Use the Heat Pump
- Outside temps above 45°F (it works well and efficiently)
- When you’re on shore power and want to save propane
- Mild nights where you just need the chill taken off
- When propane is getting low and you need heat
When to Use the Furnace
- Outside temps below 40°F
- When you need fast, strong heat (furnaces heat up a cold RV quickly)
- When boondocking off-grid (heat pump draws significant amperage from your battery bank)
- Very humid conditions where the heat pump coils might ice over
Heat Pump vs. Furnace: Efficiency Comparison
In ideal conditions (above 45°F), a heat pump is significantly more efficient than a furnace because it moves heat rather than burning fuel to create it. A good heat pump delivers 2–3x more heat energy per watt of electricity than an electric resistance heater would.
Below 40°F, the equation flips entirely. The furnace wins. It burns propane and produces reliable heat regardless of outside temperature.
Can They Work Together?
Yes, and some RV thermostats do this automatically. The thermostat runs the heat pump as the primary heat source and automatically switches to furnace (called “auxiliary heat” or “emergency heat”) when outside temps drop too low for the heat pump to keep up. This is the most efficient way to heat an RV in variable weather.
Why Is My Heat Pump Freezing Up?
If you see ice forming on the rooftop unit while it’s in heat mode, the outdoor coil is freezing. This happens when outside temps are borderline (35–45°F) and humidity is high. Most units have a defrost cycle that handles this automatically. If yours is freezing solid and not defrosting, the defrost control or defrost sensor may have failed.
For South Mississippi winters: Our mild winters are actually ideal for heat pump use most of the time. You’ll only need the furnace on the coldest nights (below 35–40°F). Running the heat pump on most winter days will save you real propane money.
Heating System Acting Up?
Whether it’s the heat pump or furnace, Thomas can diagnose and repair it at your location. Serving Saucier MS and all of South Mississippi within 1.5 hours.
Request Heating Service