How To Keep Chest Freezer or Fridge Running During Power Outage

Your chest freezer, or even your fridge /refrigerator freezer may have LOTS of $$ money worth of valuable food inside. The LAST thing you want is for it to spoil during a long lasting power outage! So, what about a generator for a deep freezer?

Here are a few pointers how to best deal with this situation. And a few recommended items to have on hand which will greatly help in the process.

Much of this is common sense. But it’s important.

A freezer or refrigerator will stay colder, longer, if it’s full during a power outage. The fuller it is, the more cold “mass” inside. The more mass, the longer it will stay cold. It’s simply an important concept to understand. If you know your chest freezer is full, it’s definitely going to stay frozen for a lot longer.

In my estimation, most chest freezers that are fairly full will likely stay frozen for ~ 24-48 hours. Keep reading for how to deal with this…

A freezer that’s part of a refrigerator won’t stay frozen as long compared with a chest freezer. They’re smaller. Usually less insulated too.

The first suggestion, thick, heavy, blankets! Drape blankets over the chest freezer. This provides some additional insulation. Just be aware if there are any slotted vents (don’t block them), because we’re going to intermittently power it up with a generator. Read on…

Size of Generator To Run A Chest Freezer or Refrigerator

You do not need to run a generator full time to keep your freezer or fridge cold during a power outage! Save fuel. Here’s what to know and what to do…

There’s no need for a “Super Max Turbocharged Fuel Injected 500-Horsepower Big Block” generator to get the job done! (/sarcasm)

The power consumption of a chest freezer or refrigerator is not a lot (read caveat below). Here’s how it works:

Freezers work like refrigerators, by compressing air or fluid into a small space and then letting that air or fluid expand into another space.

Compressing the fluid makes it give off heat, which happens in the back of the freezer. Letting it expand causes it to draw in heat, which happens inside the refrigerated box.

They run in cycles, triggered by a thermostat inside the freezer. Power cycles on and off

(the science behind it)

The energy used while it’s running may be in the vicinity of ~150 watts. I recommend that you do what I have done, and easily measure it yourself. Here’s an article on how to do it:

[ Read: How To Measure Power Consumption of Appliances ]

Freezer – Refrigerator | Starting Watts versus Running Watts

Caveat: When the compressor fist turns on, there is a higher power consumption (inrush surge current, or, “starting watts”). It begins high for a fraction of a second and reduces to “running watts” after a very short time (seconds or less). This inrush current may be ~5x (or more) of normal running power.

So, for generator loading, this might equate to approximately 600 to 1,200 watts, depending.

One of my portable generators is a small 2,000 watt, and it WILL run a chest freezer, even with the startup watts, no problem.

I would say a 2,000 watt or higher will be just fine.

And I strongly suspect that a 1,000 watt would be fine too.

I’ve written about a very interesting Lithium-ion generator which may be perfect for temporary operation of a deep freezer during a power outage:

[ Read: Jackery versus Gas Powered Generator ]

How Long To Run Generator For Chest Freezer or Refrigerator During Power Outage

First, you don’t need to run it all the time. That’s a waste of fuel.

There’s not a clear answer. It will depend on how much cold mass (food) is inside, how well it’s designed and insulated, the ambient temperature of the environment, and the temperature inside the fridge or freezer (see below).

I can tell you what I recommend, and what I do…

Worst, case, as the internal temperature begins to approach 32 degrees F (see below for how to know!), it’s time to run the generator. But I wouldn’t wait that long.

Most chest freezers are recommended to operate and freeze foods to zero degrees F or below. I generally set mine to cycle somewhere between 0 and -10 F. When it’s that cold, foods will stay frozen even longer. Plus it’s better for longer shelf life. However, during a power outage it’s okay if it comes up higher (as long as it stays below 32F).

Remember, less energy is required to maintain an already cold/frozen freezer temperature than it does to bring it down from a warmer temperature.

If it were me, I wouldn’t even wait until it creeps up towards 32 degrees. Rather, I would begin operating my portable generator to provide power to my chest freezers after ~ half a day has gone by. I would run it for about an hour, several times during a 24hr period. Run it more (or less) based on the internal temperature (see below).

Simply monitor the internal freezer temperature change and just keep up with it. Your times will vary.

Safety Considerations with Generator

When using a portable generator, always operate it outdoors (not in your garage!). Use high quality and proper gauge extension cord to bring power into the home (e.g. through a window).

[ Read: Best Extension Cord for your Generator ]

Monitor Freezer Temperature With Wireless Thermometer

Keep a wireless, or wired, thermometer inside your chest freezers so that you can read the temperature without opening it up during a power outage!

Wireless Freezer Thermometer is extremely helpful

And I use this method all the time to keep an eye on my freezers!

I have one in each of my chest freezers. The readout panel is mounted on the wall right above them. I always know what the temperature is inside. The internal temperature is also transmitted wirelessly to a readout panel which I keep on the window sill above the kitchen sink.

As you can see in the image below, I am monitoring three freezers. The display also shows room temperature.

This next photo shows the temperature probe inside the chest freezer. I simply use a piece of tape to hold the wire as shown. Here’s what I really like about this type of freezer thermometer sensor… The transmitter is outside the freezer. So it works better (longer range because signal is less hindered by the freezer’s shell). And the battery isn’t in the freezing cold.

>> Ambient Weather WS-10 Wireless
(view on amzn)

The unit linked above is what I purchased. It comes with three wireless sensors. The kind that will go inside (rather than outside). This may work fine for you. Use lithium batteries (much better performance in the cold).

[ Read: 2 Reasons Why Lithium AA Batteries Are Better Than Alkaline ]

However if you want the sensors with the probe, you can get those separately (they work fine with the base unit above).

>> Ambient Weather F007TP Sensor
(view on amzn)

With that said, if you’re looking for a simple 2-channel (fridge/freezer, or freezer/freezer) temperature display, I recommend this one from AcuRite:

>> AcuRite 00515M
(view on amzn)

[ Read: How To Know Your Freezer Thawed While You Were Away ]

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  1. Here a bit of background information on off grid refrig power. I have a newish garage refrig,side-by-side about 21-22 cu ft. The yellow KW usage tag says 750KW per year estimated power consumption. This 750KW annual value works out to be about 73-ish watts per hour continuously. Of course there are motor startup surges, etc, but under 75watts continuously is what I get with a kilo-watt meter. And this value have been tested in sub-freezing winter conditions, and blistering summer heat in Oklahoma – same power usage.

    For those wanting to run off golf cart batteries, I have found that eight 6v (each) 230amp/hr batteries at 95% charged will last about 10 hrs (down to 50 charge on level, or 12.2v). For total nighttime coverage of 13-14 hours you’ll want twelve 6v batts. Then you’ll need enough solar power to charge the batts while powering the refrig. I suggest 600-900 watts of solar power, depending on latitude, and sunshine levels.

  2. Ken, your generator description should have included “Binford”. I’m still using that in descriptions even though Tool Time has been off the air for years. 😂

    I have wrapped our chest freezers with 2” ridged insulation. With them in the garage, I’m sure it has helped keep them cooler. Yes, they are cut out for the fan.
    I installed a tri-fuel generator in a shed (with vents) to keep out of weather and noise lower. I hooked it up to our natural gas line with back up of propane and gasoline. Outlets are installed at all refers and freezers along with several outlets in the house, furnace and at home alarm. Haven’t had to use it, but works awesome in test.
    The one thing I don’t have are the alarms, but I need to have them to be viewed remotely.

    1. Papa J
      That reminded me of the thermal blankets folks used to use to cover their chest freezers, we had a couple that were pretty thick, wrapped around freezer secured with laces, had a fitted top that moved with the lid, pretty simple really. Could sew one up with mylar lined insulation and moving blankets

  3. I have a 12 cu. foot upright freezer, and a 4 cu. foot chest freezer. In January here in north Idaho, we lost the power for 5 days, which normally would be no big deal. However, this year was an abnormally warm Jan. I have a 2000 watt, predator generator. We plugged both freezers into it, and had no problems running them both at the same time. It ramped up when we first started them, but then calmed down and ran like a champ. We then would run a long extension cord to the house and plugged in the refridge. Other than that, looks like we’re prepared for a little grid down. (I hope) anyway, power was down long enough for us to check out and find some of our flaws.

    1. BigBad Cat, I have the next size up from yours, 3000k and I connected our frig, freezer, and woodstove blower to it with no problems. After we got power back on I went to the hardware store and got a twist lock plug(generator has a twist lock connection) and a short power strip (with HD cord), cut the plug off of the power strip and put on the twist lock connection. Now I have one cord running into the house but, about six plugs available for use inside the house.

  4. Ken I installed a generator interlock in my circuit breaker box and a generator connection outside. The interlock shuts off main before you can provide generator power to the house. My 8Kw portable generator can power essential appliances in the house. As it is portable I can roll it out and hook it up when required. We are at the end of a branch and are among the last to have power restored.

    1. Nice!
      I helped install a similar generator interlock at my dad’s house years ago. Difference being the transfer switches are on individual circuits that we selected. The obvious “essential” circuits to keep the house “alive”.

      I have a similar setup here at my home. Transfer switches on select circuit breakers. But instead of generator, it’s my solar system and associated battery bank / inverter.

  5. When sizing a generator, always use the voltage and starting amps of whatever you want to operate.
    Generators are sized in watts— volts x amps — watts
    going 10% over the load is advisable.

  6. Hey Ken,
    That acurite thermometer set is pretty cool, nice to have accurate temps, most people have no clue and wonder why everything spoils so fast when their fridge is set on the minimum setting

  7. Ken,
    Thank you for this interesting information. I have never heard of a product like this. I followed your link on Amazon and it comes with a sensor for a freezer and a refrigerator. Do you think both sensors could be used for two freezers?

  8. Sounds good – Are wifi temp sensors really good for inside a freezer?

    I’d love to try mine, got 1 spare atm.

    If anyone does get a power outage, its best, if possible, not to open the freezer at all, until the power is restored. Opening the freezer for any amount of time, will seriously reduce the time to defrost, especially stacked freezers with a side door (rather than a chest freezer with a top lid).

  9. When I suffered through long term weather related power outages in southern tenn, longest one was 14 days. I used a 2500 watt generator to keep the fridge and the chest freezer working. Learned through the the first week to run the generator two hours max one hour morning one hour in the evening…….that keeps both appliances in perfect balance. Two hours fuel per day was all that was needed. I also keep plastic bottled water in any open unused spaces in both the fridge and freezer, the mass makes it so much easier on both not having to cycle near as often and prolongs the life on these appliances.

    1. John in Nevada. That was very interesting. You used a 2500 watt generator — I assume gasoline. I wonder if you have any thoughts on using solar generators. Gasoline is starting to be a problem here where I live and I suspect that eventually it will be a major problem — especially is something tragic happens. I was just wondering if you have ever thought about solar power generators and if so, what? I’m just looking for some advice for my particular situation of having to freezer and a much needed refrigerator. Thanks.

  10. Hello. Great article, though, sad to say my 5-year old has better comprehension about these things than I do. In any case, my question is, is there a plug in “power bank” battery that would work for this application, rather than gas? Maybe it could recharge via solar? Presumably it would also recharge during rolling power-on situations (I am in a city). If so, how long could it be expected to last (used as described by you here, in high ambient temps of 100 degrees or so) without rolling or solar recharge spans. Thanks very much for a great website.

    1. Tony,
      The answer is, yes, it can be done. However, it’s going to be expensive. Why? Because the power bank (battery) needs to have enough capacity to operate the chest freezer for “a time”. The question is, how long?

      Here’s an example. I calculated one of my chest freezers to consume nearly 1 kWh of energy in a 24 hour period. So I would need a ‘power bank’ that’s rated for at least 1,000 watt hours. That would provide me with a safety margin of 24 hours off-grid.

      Here’s an example of a product that would do that:

      Jackery 1000

      The problem is, as of this post, it’s around a thousand bucks… Ouch.

      However, it is one particular solution to your question.

  11. I think a combination of generator/solar with energy storage would be the best. Running a 2000w generator( unless it is an inverter generator) to run a 100w chest freezer seem like a waste of fuel/gas expecially with rising gas prices.

    It would be better to be able to store the excess energy from the 2000w generator in a battery and use that battery for power the chest freezer for few hours without running generator.

    1. Toby,
      All the folks i know over here do that, the generator is hooked through the charge controller, some folks have them set to come on automatically when their storage system drops below a certain level, usually happens in the late evenings if there is a higher draw on the batteries or if its been cloudy, solar alone will not provide consistent supply, it just wont, there are always variables that reduce the input from the panels or the draw on the load side. Thats not saying that sometimes the generator wont come on for weeks at a time but more often than not it will pop on for an hour or two every other day.

    2. Toby,
      it’s all about your batteries. the more power you can store on sunny days the more power you will have on the cloudy days. batteries are not cheap anymore but the more you have the longer you can operate. junk cars and boats are a good source for em. ya can’t have to many.
      good luck with everything.

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