How long to run a generator for a freezer or fridge.

How To Keep Chest Freezer or Fridge Running During Power Outage

Your deep 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, lets talk about two things… How long to run a generator for a freezer (or refrigerator) during a power outage, and, what size generator to use.

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.

UPDATE: I’ve added a comment from a reader here on the blog who kept his freezer and refrigerator running for two weeks during a long term power outage. It’s “real world” experience. Read below to find out how long he ran his generator.

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

A freezer or refrigerator will stay colder, longer, if it’s relatively 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 than if it were only partially filled.

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. However, you can keep it all running during a power outage…

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 a compressor cycle 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 first 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.

A while back someone asked about running fridge and freezer with a generator… My power outages from storms in Tennessee (which a couple lasted over two weeks) helped establish required generator run times for both appliances.

I soon realized that keeping both the fridge and freezer full helped on maintaining correct temperaturs for both, with food or bottled water and liquids.

My minimum run times that maintained temps was 30 minutes every 15 hours depending on how well your appliances are insulated.

Use a dedicated thermometer inside both to verify safe temps which takes the guesswork out of the equation.

Some preppers over the years make the mistake of running a generator continuously during a outage…..don’t make that error. I also use a dedicated backup or just the fridge and freezer.

~ Realist

Here’s what I use to monitor my refrigerator / freezer temperature. It would be perfect during a long term power outage too… There’s a temperature display unit that magnetically sticks to the fridge. And two temperature sensors that can clip somewhere inside (and there’s a suction cup).

AcuRite Wireless Fridge – Freezer Thermometer
(view on amzn)

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 Deep 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 deep chest freezers!

I have one in each of my chest freezers. There’s also a temperature readout panel mounted on the wall right above the freezers. 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)

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

43 Comments

  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.

    1. I was thinking about getting a solar powered generator because fuel may get rationed or be unavailable. I have a 9 cu ft deep freeze and keep it fully packed. Any “air” space I fill with towels and then I put heavy detergent bottles on top so no frost gets in.
      The only other electric “need” is minimal. If I only have enough power to run EITHER the refrigerator or the deep freeze during a time period, can I use the energy to run them both by switching the power to one and then to the other. Would this work? And how many hours should be assigned to each appliance?

  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

    2. Know how your freezer or refrigerator dissipates heat before wrapping it with any kind of thermal insulation! If your unit has coils or cooling fins on the back or bottom of the unit, then go ahead and wrap the unit, of course, leaving the cooling fins or coils and fans exposed. If your unit does not have cooling coils or fins, DON’T wrap the unit with insulation, save for maybe the lid or door! These units dissipate heat through the outer walls of the unit. This is done to keep these heat transfer mechanisms from being covered with dust, dog hair, and the like.
      Covering these surfaces with insulation or blankets will keep the freezer or fridge from getting rid of heat! At best, your unit is going to run constantly. At worst, you’ll burn it out!

      I found this out when I covered the chest freezer in my barn with old sleeping bags to give it a leg up against the desert heat. After being covered a few days I went out to check on it. The side walls of the freezer were HOT. The only part that felt cold, meaning its insulation was allowing heat in, was the lid. I ended up folding the sleeping bags on top of the unit. This kept heat from getting through the lid, but allowed heat from the refrigeration process to be offloaded through the side walls.

  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?

    1. I’ve used these before. They also have an alarm you can set to go off when the freezer or fridge goes above the temp you set it for.

      I had one of these set up with the freezer sensor in my garage upright freezer and the refrigerator sensor in my garage fridge/freezer. My logic was that if the fridge was running right, the freezer, which drew its cold from the freezer coils, was as well. I might be wrong; it’s been a while since I use one of these, but I seem to remember the fridge sensor not reading low enough to use it in the freezer of the fridge/freezer. I actually put the display on the fridge in my kitchen, which was right on the other side of the wall from the garage units, and within range of the sensors. It’s always best to keep monitors like these in an occupied space, as you’re more likely to see an issue developing or will be better able to hear the alarm beep, which isn’t very loud to my aging ears. The biggest failing of these things is dying batteries.

      I’ve since moved to Sensorpush sensors and a Sensorpush WiFi gateway. It runs with an app on your phone. Once set up, the sensors will upload data to the gateway, and ultimately to the app. You can set upper and lower temp and humidity limits for each sensor. If any of these limits are breached, I get an alert on my phone, even if I’m nowhere near the rancho. Why did I blow the cash on Sensor push? I had an Accu-Rite thermometer on the barn freezer and fridge. The freezer died. I didn’t go out to the barn for a few days. By the time I did, I had lost over $300.00, pre-Biden, in meat! Never again, if I can help it! Since I installed this setup it’s “saved my bacon” three times. This kind of thing need only happen once for Sensorpush to pay for itself!!!

  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).

    1. They actually work really well. I have a Wifi extender at the rancho about 200ft from the house. The barn is another 70-80ft from the extender. The barn is also a steel building, which tends to attenuate radio signals. I had to install a second gateway in the barn, as the sensors in there couldn’t reach the one up at the house. You can install as many as you wish. I have small battery backup units (UPS) supporting the gateways, the WiFi extender, and the WiFi router. They’ll hold the powered devices for many hours if an outage occurs.

      The battery in the sensor lasts around a year, and you’ll get a low-batt alert on your phone, telling you there’s a low battery condition and on which sensor. It does so well in advance of a total failure of the sensor due to a dead battery.

      Just an FYI; the Sensorpush sensors will Bluetooth to your phone and upload to the app without the gateway. The only caveats are that the sensors will only upload when the phone is within Bluetooth range of the phone, and you won’t get alerts remotely. So… if all you’re looking to do is monitor your refrigeration locally, you can save some money. Also, if you lose power, you can keep tabs on the status of the units just by walking by them.

  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.

      1. You only need to run the generator for a short time maybe twice a day to maintain the temperature of the fridge and freezer. If you ran a chest freezer for 0.5 to 1 hour in the morning and 0.5 to 1 hour in the evening, at about 100 to 150 watts, then that is 100 to 300 watt/hours per day.

  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.

  12. There is another extremely low cost way to significantly extend the duration of keeping your food frozen without power.

    Note some food such as ice cream or meat or things with sugar can actually start thawing at temps a bit less than 32 degF or 0 degC. So, ideally we want to keep the freezer colder than their thawing points. That is easy if you have some spare room. Line the inside walls of freezer with 2 liter bottles of frozen salt water.
    One gallon of water with one pound of salt added to it is very roughly a 10% brine (those are easy numbers to remember) and it will freeze/thaw at about roughly 20 degF or -6.5 decC.
    With a bunch of these bottles in the freezer, when the power goes out, and lets say the freezer was at 0F when that happened, then it will slowly warm up to 20F then plateau there until most of the saltwater has thawed (absorbing heat that has entered the freezer) before climbing again. When the temp in the freezer starts climbing above 20 or 25F, then turn on the genset and cool it back down refreezing the water jugs.
    You will likely run the genset longer at a time, but also much longer between runnings and the food stays at a more consistent lower temp which may help reduce freezer burn or texture compromises. You can also start refreezing when the bottles are say just half thawed facilitating a schedule that might be more easy to keep.

    1. Oh yeah, it is best to fill the bottles only 75-80% full as the water expands about 10% when it freezes. Also it is good to freeze those saltwater bottles with them on their side. If they go through much thawing and refreezing monitor them to be sure they don’t bulge too much and split open. Never use glass for this, just plastic.

      1. ” ….. water expands about 10% when it freezes.”

        So true Bill. I need to remember to point this out next time I hear someone mention the ice caps melting and we are all going to drown.

  13. Lived three months without electricity in Miami after hurricane Andrew. Ran the generator in the am before going to work. Ran it again in the evening after returning home. Kept food at appropriate temperature. Every day for three months.

    Wonder if some company will ever devleope a modulating refrigerator or freezer. My Trane XV hvac normally runs on stage 1 at 30% fan speed. Don’t see those spikes in amps like the old unit.

  14. We have two side by sides stocked full pulling 120W each when the compressor runs. In preparation for blackouts, we purchased two 2000W Ecoflow Delta Max solar genies with panels. Each freezer fridge has a dedicated solar genie. If the sun doesn’t shine, I can recharge my Delta Max quietly with a duel fuel Champion inverter gennie. I also have a solar oven that reaches 200 degrees and three outdoor rocket stoves for cooking and reheat to preserve solar batteries for my two side by sides and other small appliances. Also have two solar water bladders for bathing. And a big but loud duel fuel genie with a panel box connection for my well and other big appliances for limited use.

  15. I also use a product called Temp Stick in my chest freezers. It’s the best temperature monitoring system that I’ve found. It connects to your wifi (no special gateway box needed). The monitoring service is free (U.S. company). You can set temperature alarms on their phone app for your iPhone or Android (Hi / Low setpoints). I’ve had them operational for a year so far. They have worked perfectly. Great peace of mind when you’ve got thousands $ in your chest freezers. Especially if you’re away from home for a period of time. Tip: Use Lithium batteries (they’re much better cold-tolerant).

  16. As a reminder when the power goes off turn off your big appliances at the electrical panel.
    When the power comes back on at first there will be some tremendous power surges that could destroy fridge/freezer compressor, TV’s or other electrical appliances. I saw these power surges happen when the power was restored after Hurricane Sandy….

    What power solar generator would power a 18.5 cub refrigerator/freezer? I was thinking of getting a Bluetti or Percan for that purpose.

    Will solar panels work if places in the window?

  17. For those that do not have a generator, or those that may have had a goat or two play king of the hill on the generator and bust the plastic tank, dry ice will help keep things frozen. I got the last batch from a welding supply place, some propane dealers may carry it also. You do not want to overload the freezer or refrigerator with dry ice as it may damage the thermostat. I used about 5 to 7lbs. per freezer (which are kept full, use frozen water jugs to keep full) placed on a folded towel to avoid any damage to the contents. Also insulated the units with heavy blankets. The power was only off a couple of days, but still had dry ice in the units and temps remained around 0. I do not know how long one can keep refilling the dry ice in freezers and keep the 0 temperature, but it definitely works great short term.

  18. For the last 3 months or so, I’ve been using YoLink Temperature/Humidity Sensors to monitor two freezers in a metal building about 150-200 feet from my office area. They seem to work so well, I picked up more sensors to monitor more areas (basement storage room, patio, garden shed, etc.). They also have several other types of sensors for water leaks, door/window intrusion, motion detection, etc. I haven’t tried any of those yet but am considering a couple. Available through the MSB link to the big A.

    They advertise 1/4 mile range and 2 year battery life. Works with a hub and free App on your phone, and you can set alert ranges for both temp and humidity. I don’t understand all the technical details, but I get a notification on my phone when things are outside the parameters I’ve set. It took a little while to figure out the best combination of temperature/humidity ranges and alerts, but I can access the status from my phone wherever I am whenever I want, no need to be close to the hub. You can also see a daily/weekly/monthly history of each sensor. There may be some limit to the number of alert messages but I have yet to run into it. I have one freezer in the house that is nearing it’s end of life, so it’s been interesting to monitor the swing in temperatures. I need to replace it soon!

  19. During a tornado 5 day outage we used an inexpensive 2000W peak 1000W continuous inverter hardwired to one of the cars battery( at idle) with 12g romex. Ran the freezer and Fridge intermittently for 5 days. A four cyl car sips fuel at idle. Worked well for that instance. I have since acquired a 6500w portable genset as a backup or primary and keep the vehicles full and fuel stored.

  20. I have a 10.5 cubic chest freezer that has a start up of 20 amps. I also have a 2500 inverter generator with a 20 amp T-blade plug receptacle. Can I use a 20 amp rated extension cord with a T- blade male end that would plug in to the generator? Can I then plug the freezer into female end with 3 prong cord from the freezer?

  21. While testing my freezer as a Faraday cage I discovered it was RF leaky by placing my weather station outside probe inside. If the day comes I already have a monitor solution for my frozen foods.

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