Most of us would class our refrigerator as an essential item to keep running during a power outage. When calculating what size home generator you need, you may assume you need to keep your refrigerator and freezer constantly running.
But that doesn’t have to be the case. If the power goes off for thirty minutes, the food in your fridge won’t spoil. Depending on various conditions, you may only need to run your refrigerator intermittently to keep your food cool.
This is important for three reasons:
- It means you may be able to buy a smaller generator.
- You won’t need to run your generator 24/7.
- You will use less fuel, so your fuel stores will last longer.
In this article, we look at how to keep the contents of your refrigerator cool while minimizing your generator use and conserving fuel.
Let’s get started.
How Much Power Does a Refrigerator Need?
A standard refrigerator uses around 1200 starting watts and 200 running watts. These figures will vary depending on the size, make and model, and age of the appliance.
You can calculate the exact power usage for your refrigerator using the following equation:
Power (watts) = volts x amps
You should be able to find the volts and amps on the manufacturer’s sticker on your refrigerator.
This will give you the running watts.
Refrigerators also need an extra jolt of power to start the compressor motor. This is usually 2-3 times the running watts, but to be on the safe side, we suggest taking a conservative assumption of up to 6 times the running power.
So, for a 200-watt refrigerator, you want to allow 1200 watts for starting the appliance.
As is often the case, things are not quite this simple. Depending on the operating conditions and environment, the refrigerator may need to draw on extra power while it’s in use. For example, if the refrigerator is in a warm room and you leave the door open, the compressor will kick in to keep the contents of the refrigerator cool.
When calculating the size of generator that you need for your home, it’s always best to allow for some contingency in your calculations for situations such as this.
Related: What can a 3000-watt generator run?
Why Shouldn’t You Keep Your Refrigerator Running Constantly?
There’s no reason why you shouldn’t keep your fridge running constantly if you have the fuel and generator capacity to do so.
That said, most portable generators are not designed to be run nonstop for 24 hours a day. At the very least, you need to stop the engine to run maintenance checks and refuel. The more you run the generator, the more frequently it will require maintenance and the shorter its lifespan.
Running your generator constantly will also use a lot of fuel. This might not be an issue for a short-term power outage, but in a lot of disaster situations, you don’t know how long the power will be out and how long you’ll need to keep running your generator.
There’s also a security implication to running a generator. Even “quiet” models create a lot of noise and make it clear to anyone passing that someone’s home.
Assuming you want to conserve fuel and generator power as much as possible, how often should you power up your refrigerator and for how long?
How Long Do You Need to Run a Generator for a Refrigerator?
Let’s start with a couple of basic principles:
- It uses less power to keep a cold refrigerator at the same temperature than it does to cool it down.
- You don’t want to leave the power off for too long, otherwise, you’ll end up using extra energy (and fuel) to get it back to the optimum temperature.
- You don’t want to be constantly switching your fridge on and off. Because refrigerators use a lot of power starting up, regular surges could mean you use more fuel than keeping it running constantly.
The first thing you need to know is how long your refrigerator can keep food cool when the power goes out.
To figure this out, you’ll need a wireless thermometer (this one on Amazon would work well) that allows you to see the internal temperature of the fridge without having to open the door. Turn the power off and see how long it takes for the temperature to rise.
As a general rule, an average refrigerator will keep food cold for around four hours if the door is unopened.
Pro Tip – a wireless thermometer will help you determine how long and how often you need to run your appliance to keep food cool.
Once the internal temperature has begun to rise, turn the power back on. This is when you can open the refrigerator to take out any food or drinks you may want over the next four hours. (If you’re running a test, don’t forget to simulate this!) You can then time how long it takes for the fridge temperature to return to its stable level.
We’d suggest running power to your refrigerator for about an hour before turning it off again. This gives plenty of time for the food inside to cool and allows for you to open the fridge a few times to put things in and out.
Put these two figures together and you end up with a 1:4 ratio. Run a generator for an hour to cool your refrigerator for four hours.
This is a general guide as various factors affect how quickly the temperature in a fridge changes and how much power you’ll need to cool it down. These include:
- How old your refrigerator is. Newer models are more efficient at keeping food cold and will use less power.
- What condition the refrigerator is in, in particular, whether the door seals are still effective.
- The temperature of the room where the fridge is located.
- How full the refrigerator is.
How to Conserve Refrigerator Power Use
The less heat you let escape, the less power your refrigerator will need to stay cool. Many of these tips are energy-saving common sense, but they become even more important when you have limited power.
Here’s how to reduce the amount of power your fridge needs:
- Store your refrigerator in a cool room. This is particularly important if you live in a hot climate and won’t be running your air conditioning during a power outage. A cold basement is ideal, as long as it won’t get flooded.
- Make sure the fridge isn’t located next to a heat source, such as an oven or dishwasher.
- Keep the refrigerator door closed as much as possible. Plan to only access the fridge when the generator is running.
- The greater the thermal mass in your refrigerator (i.e. the more stuff that’s in it!), the easier it is to keep cool. If you haven’t got much food in there, fill your fridge up with jugs of water.
- Keep the condenser coils on the back of the fridge clean and if necessary, replace the rubber seal around the door.
How to Stop Food Spoiling During a Power Outage
Using the method above, your refrigerator should stay cool enough that food won’t spoil. However, if you’re short on fuel or you live in a hot climate, you may not be able to keep the temperature in your refrigerator as low as you’d like.
The FDA (Food and Drug Administration) recommends storing perishable food below 40ºF. Above this temperature, bacteria such as E.coli and salmonella grow more quickly. These bacteria can make you sick and may even kill you.
The “safe time” for food once the ambient temperature rises above 40ºF is two hours. Food should be eaten or cooked within this time.
If you’ve got a fridge full of food and you’re worried you won’t be able to keep it all cool, there are some ways to prevent food spoiling or being wasted.
1) Freeze Anything You Don’t Immediately Need
Freezers require powering up less frequently, so if you have spare freezer capacity, it may make sense to freeze extra meat, milk and other items that won’t be consumed immediately.
2) Store Food in the Right Place
The fridge door and top shelf will be the warmest parts of the refrigerator and most susceptible to temperature fluctuations when the door is opened. The coolest part of the fridge will be at the back of the lower shelves – this is the best place to store meat, fish, seafood and other perishables that are breeding grounds for bacteria.
3) Use a Rotomolded Cooler
If you don’t have a generator or you need to conserve generator power, consider using a rotomolded cooler with ice packs that you can refreeze in your freezer. The advantage of using a cooler box is that you can store it in the coolest place in your house, whereas it’s not as easy to move a large refrigerator.
4) Cook the Most Perishable Food First
Eating the most perishable food first means it won’t have time to spoil. You could also cook raw meat, fish and vegetables into meals that can be frozen for later consumption.
Read more about how to keep your fridge cold without power.
What About Freezers?
The same principle of using intermittent power applies to freezers, but as they’re even more efficient at retaining heat and you’re unlikely to be accessing it as much, you can leave it off for longer. If your freezer is packed full, it may be up to 48 hours before the internal temperature rises above freezing.
Chest freezers are better at retaining heat when the door is opened and as with refrigerators, they operate most efficiently when full. Having a half-full freezer halves the time you can leave it without power before food begins to defrost.
As with your refrigerator, fitting a digital thermometer that allows you to read the temperature from outside the freezer is useful. You could also pack ice cubes at the top of the freezer – if these have melted and refrozen, you know the temperature rose above freezing.
How Do I Choose The Right Generator?
You should check out our generator buying guides here:
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A less messy method to check if your freezer melted and refroze items is to put a clear soup container filled most of the way to the top with ice and then place a quarter on top of it. If the freezer starts to melt them the quarter will sink from the top of the ice.
If it’s at the bottom you know things defrosted completely. If it’s stuck partway down the container then you had a partial defrost event.
A mug with ice is another option, but I prefer the sealed clear container so it’s easy to view from any angle and no risk of spillage when melting.
Trying to understand your calculator for a battery stand-by generator, where the claculator says I need 3,530 Wh running and 4,580 Wh starting and recommends a unit with less capacity?
Can you give me some more information, it should only recommend units that exceed your given power needs. You can email us at [email protected] if that is easier.
Thank you for the information.