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Will 5000-watt Generator Run a Furnace? It Depends…

DISCLAIMER: AS AN AMAZON ASSOCIATE I EARN FROM QUALIFYING PURCHASES. THIS POST CONTAINS AFFILIATE LINKS THAT WILL REWARD ME MONETARILY OR OTHERWISE WHEN YOU USE THEM TO MAKE QUALIFYING PURCHASES. FOR MORE INFORMATION, PLEASE READ MY EARNINGS DISCLAIMER.

A 5000 watts generator is powerful enough to meet your basic needs during a power outage and that includes running your oil or gas furnace. If you have a forced-air electric furnace, it uses a lot more than 5,000 watts and you will NOT be able to run it on this size of a generator.

Everything else comes down to how much wattage you will require in total, meaning ALL the equipment and appliances running at EXACTLY the same time. The best way to maximize the efficiency of your generator is to manage your power usage properly.

It is NOT necessary to run your appliances during power outages all at once!

If you use a generator more efficiently, then it is possible that you will not require a lot of power and can get away with a smaller size (and cheaper) generator.

Appliance running and starting watts

Take care of your priorities first and they usually are:

  1. Refrigerator
  2. Air Conditioner or Furnace (depending on the season)
  3. Television
  4. Some lights

If those things will be running all at once, just write down their power usage and make space for some items that will NOT be used altogether (but one at a time):

  1. Microwave
  2. Electric stove
  3. Hair drier
  4. Toaster
  5. Coffee maker
  6. Etc.

How can a 5000-watt generator run a house? In addition to furnace usage, you need to know how much power you will be using in total.

By calculating your wattage use, you can know for sure if a 5000-watt generator is a proper size for you. Typical wattages of household appliances and devices are mentioned below (they are approximate, please read the label as well).

Electronics:

Devices Watts (running) Watts (surge)
TV (82” LED) 230
Computer (desktop) 80
Computer (laptop) 200

Small appliances:

Devices Watts (running) Watts (surge)
Microwave 1,450
Blender 300 900
Coffeemaker 550 1,000
Slow Cooker 200
Rice Cooker 200 500
Toaster (2-slice) 800 1,600
Toaster (4-slice) 1,150
Food Processor 350 500
Electric kettle 1,200 3,000

Large appliances:

Devices Watts (running) Watts (surge)
Refrigerator/Freezer (side-by-side) 1,120 2,200
Freezer only (12 cu. ft) 650 1,500
Electric dryer (clothes) 750 1,800
Gas dryer (clothes) 650 720
Dishwasher (cool dry) 700 1,400
Dishwasher (hot dry) 1,450
Electric stove (8” range) 2,100

Personal care:

Devices Watts (running) Watts (surge)
Hair Dryer 1,000 2,000
Iron 1,000
CPAP machine 30-60

You will probably need some water heaters:

Devices Watts (running) Watts (surge)
Water heater 4,000-4,500
Water Heater (Immersion) 3,000
Water Heater (Electric) 2,000 3,000
Water Heater (Tankless) 6,600 2,200

In a gas or oil furnace, basically, all you need to power is a blower fan, and it doesn’t require too much electricity:

Furnace fan Running watts Starting watts
1/8 HP 300 500
1/6 HP 500 750
1/4 HP 600 1000
1/3 HP 700 1400
1/2 HP 875 2350
How much electric does my gas furnace use?

Electric furnaces require a LOT more power and 5,000-generator will NOT be powerful enough to run it. Here are the ratings (again, the numbers are approximate):

Furnace fan Running watts Starting watts
Central Electric Furnace (15 kW) 15,350
Central Electric Furnace (20 kW) 20,490
Central Electric Furnace (25 kW) 25,670

Heat Pumps also use a lot of electricity:

Furnace fan Running watts Starting watts
Heat Pump 4,800 10,800

If having a big generator is NOT an option for you, the following devices can keep you nice and toasty during cold winter months:

Furnace fan Running watts Starting watts
Electric Heater 1,000 2,000
Space Heater (small) 800
Space Heater (large) 1,800
Electric Thermal Radiator 500
Electric blanket 200

** Remember! ALL the above numbers are approximate. Please consult your manufacturer’s handbook or label.

Here is an even bigger list for you! You can also download this PDF file to do your own calculations easier.

Generator running and starting watts

As you probably noticed from above, the first rating is the “Running watts” (also called “Rated watts”) and “Starting watts” (also called “Surge watts”).

Starting watts are VERY important due to the fact that they can kick in at any time and use up all your power

Surge rating usually applies to motor-driven devices like refrigerators, air conditioners, pumps, etc. If you don’t pay attention to it, it can put you in an overload situation and your generator will shut down.

The best way to control your power is to:

  1. Connect all your MAJOR appliances to the generator and leave wattage space for 1-2 MINOR appliances
  2. Use your MINOR appliance and devices one by one (NOT at the same time) and turn OFF your MAJOR appliances while using them.
  3. If you really need to use many appliances, consider SOFT STARTERS

So, how do we check appliance wattage rating? Every device has a label on it and wattage is usually mentioned:

If it doesn’t mention watts, but you have amps and volts, all you need to do is multiply amps by wattage that you use in your country (110-120v in the USA for example):

Here is a how-to figure out the size of the generator that you need:

  • Step 1. Choose your devices (that you need to run at the same time) and look up their wattage.
  • Step 2. Break down wattage by Running (or Rated) and Starting (or Surge) watts.
  • Step 3. Add all the Running (or Rated) wattage.
  • Step 4. Find the highest Starting (or Surge) wattage device on your list.
  • Step 5. Add this device to the TOTAL Running (or rated) wattage.

Here is the example for you:

Image source. Now, all you have to do is calculate to see if a 5,000-watt generator fits your needs.

VERY IMPORTANT! Generators also have SURGE WATTAGE. It is the maximum output that a generator can offer and only for a few seconds. Make sure that you are looking at the right ratings BEFORE your purchase your generator:

Very often generators are rated by SURGE WATTAGE, even though it lasts only a few seconds:

Surge wattage is important, but you need to make sure that the running wattage will accommodate your power needs as well.


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