What Size Generator To Run A Heat Pump

Frequently Asked Questions: What Size Generator Do I Need to Run My Heat Pump?

Power outages can be disruptive, especially when they happen during extreme weather. If you rely on a heat pump for heating and cooling, ensuring you have a generator that can handle its power needs is crucial. This FAQ provides answers to common questions about sizing a generator for your heat pump.

Q1: What's so special about heat pumps that requires specific generator sizing considerations?

Heat pumps are efficient, but they require a significant amount of power during startup, also known as the "starting surge". This surge is often several times higher than the heat pump's running wattage. A generator needs to be powerful enough to handle this initial surge, or the heat pump simply won't start. Ignoring this starting surge is the most common mistake people make when sizing a generator for a heat pump.

Q2: How do I find out the wattage requirements for my heat pump? Where do I look?

There are several places to find this information:

• The Heat Pump's Nameplate: This is usually a metal plate attached to the unit itself, either on the outdoor condenser or the indoor air handler. Look for labels such as "Minimum Circuit Ampacity (MCA)" and "Maximum Overcurrent Protection (MOCP)". These will give you clues about the amperage draw.
• The Owner's Manual: This document should provide detailed specifications, including the running watts and the starting surge watts (or Locked Rotor Amps – LRA, which can be used to calculate surge watts).
• The Manufacturer's Website: Often, you can find the specifications for your specific model on the manufacturer's website by searching for the model number.
• Consult a Qualified HVAC Technician: If you're having trouble finding the information, a qualified HVAC technician can help you determine the wattage requirements for your heat pump.

Once you have the amperage, you can calculate the wattage using the formula: Watts = Volts x Amps. In the US, residential voltage is typically 240 volts for heat pumps.

Q3: What's the difference between "running watts" and "starting watts" (or surge watts), and why does it matter?

These are critical distinctions when choosing a generator:

• Running Watts: This is the continuous power your heat pump needs to operate after it has started. This is the wattage it consumes while maintaining a constant temperature.
• Starting Watts (Surge Watts): This is the brief, high power required to start the heat pump's compressor. This surge can last for a few seconds, but it's crucial to accommodate it. The generator must be able to deliver this much power, even if only for a short time.

Your generator must be capable of supplying both the running watts and the starting watts of your heat pump, plus any other appliances you plan to run simultaneously.

Q4: How do I calculate the right size generator, taking into account the heat pump's surge wattage and other appliances?

Here's a step-by-step approach:

1. Determine the Heat Pump's Running Watts: Find this on the nameplate, owner's manual, or manufacturer's website. Let's say it's 3000 watts.
2. Determine the Heat Pump's Starting Watts: This is often harder to find directly. If you only see the Locked Rotor Amps (LRA), multiply that by the voltage (usually 240V) to get the starting watts. For example, if LRA is 30 amps, then starting watts = 30 amps x 240 volts = 7200 watts.
3. Calculate the Total Starting Watts: This is the highest starting wattage of any device you plan to run. In our case, it's the heat pump's 7200 watts.
4. Calculate the Total Running Watts: Add up the running watts of all the appliances you want to run at the same time, including the heat pump. Let's say you also want to run a refrigerator (200 running watts), some lights (100 watts), and a TV (150 watts). The total running watts would be 3000 (heat pump) + 200 + 100 + 150 = 3450 watts.
5. Choose a Generator: The generator needs to meet both of these requirements:
   • Starting Wattage Requirement: The generator's starting wattage should be at least the total starting watts (7200 watts in our example). It's generally recommended to add a safety margin of 10-20% to this figure. So, 7200 watts + 10% = 7920 watts.
   • Running Wattage Requirement: The generator's running wattage should be at least the total running watts (3450 watts in our example). Again, adding a safety margin is wise. So, 3450 watts + 10% = 3795 watts.
6. Select the Generator Size: Based on these calculations, you'd need a generator with a starting wattage of around 8000 watts and a running wattage of around 4000 watts (rounding up for safety). Look for a generator with at least these specifications.

Important Considerations:

• Generator Type: Inverter generators provide cleaner power and are generally quieter, but they may be more expensive and have lower wattage outputs. Conventional generators are often more powerful and more affordable.
• Fuel Type: Generators run on gasoline, propane, or natural gas. Consider the availability and cost of each fuel type in your area.
• Automatic Transfer Switch (ATS): An ATS automatically switches the power source from the utility grid to the generator when the power goes out. This provides seamless power and prevents backfeeding into the grid, which is dangerous. This is highly recommended for permanently installed generators.
• Professional Installation: For larger generators, it's best to have a qualified electrician install the generator and any necessary wiring or transfer switches.

Q5: Can I use a smaller generator if I stagger the startup of my appliances?

While this is theoretically possible, it's not recommended for a heat pump. The heat pump's starting surge is so significant that it will likely still overload a smaller generator, even if you turn off other appliances. Furthermore, constantly manually managing the load on the generator during a power outage can be inconvenient and potentially lead to problems. It's much safer and more reliable to choose a generator that can handle the heat pump's surge wattage comfortably.

Q6: What happens if I try to run my heat pump on a generator that's too small?

Several things can happen, none of them good:

• The Heat Pump Won't Start: The most likely scenario is that the generator simply won't be able to provide enough power to overcome the starting surge, and the heat pump won't start at all.
• Generator Overload: The generator could overload, causing it to shut down automatically or even damage the generator itself.
• Damage to the Heat Pump: Repeated attempts to start the heat pump with insufficient power can potentially damage the compressor or other components.
• Reduced Lifespan of Both Heat Pump and Generator: Continuously pushing the generator to its limits will shorten its lifespan, and the same applies to your heat pump if it's struggling to start due to insufficient power.

It's always better to err on the side of caution and choose a generator that's slightly larger than you think you need.

Q7: Are there any devices I can use to reduce the starting surge of my heat pump?

Yes, there are devices called "soft starters" that can reduce the inrush current (starting surge) of your heat pump's compressor. These devices gradually increase the voltage to the compressor motor, reducing the spike in power demand. Installing a soft starter can significantly reduce the size of the generator you need.
Benefits of using Soft Starters:

• Reduced Starting Surge: Soft starters significantly decrease the inrush current, making it easier for generators to start and run the heat pump.
• Smaller Generator: With a reduced surge, you can potentially use a smaller and less expensive generator.
• Extended Equipment Life: Gradual starting reduces stress on the compressor motor and other components, potentially extending their lifespan.
• Reduced Voltage Dip: Soft starters minimize voltage fluctuations, which can improve the performance of other electrical devices in your home.

• Cost: Soft starters add to the overall cost of the system.
• Installation: Professional installation by a qualified HVAC technician is recommended.
• Compatibility: Ensure the soft starter is compatible with your specific heat pump model.

Disclaimer: This information is for general guidance only. Always consult with a qualified electrician or HVAC technician for specific recommendations tailored to your situation and equipment.