Wondering what type of generator to buy? Do you need one wired directly to the house, a portable unit or an inverter for camping? How many watts are required? Keep reading for answers to these questions and more so you make the best generator for you that won’t blow your budget.

Whole House Generators

Whole house generators are also referred to as home standby generators because they are meant to take over in the event of a power loss. They kick in within seconds of the power going out, and they are permanently installed at a site near your home. They can run on propane or natural gas and can power just a few designated circuits or your entire house.

How many watts do I need?

To decide how large of a generator you need, as in how many watts, you’ll need to figure out what you want to use it to run. Once you’ve decided the items you’d like to run with the generator, calculate the total wattage of those appliances or power needs. That’s the minimum wattage you need in a generator.

For example, if the power goes out in the summer at night, you might need lights on in the house and the refrigerator and central air running.  This is probably the bare minimum. You may want to add some other items as well like your stove, radio or furnace in the winter. Here are common wattages of many household appliances you may want to run:

Wattages for Household Equipment

Application Starting Wattage Running Wattage 240 Volts
Furnace (fuel oil or gas) 500 (1/8 Horsepower) 750 (1/6 Horsepower) 1000 (1/4 Horsepower) 1400 (1/3 Horsepower) 2350 (1/2 Horsepower) 300 (1/8 Horsepower) 500 (1/6 Horsepower) 600 (1/4 Horsepower) 700 (1/3 Horsepower) 875 (1/2 Horsepower)
Electric Range (8" Element) 2100 2100
Hot Water Heater 4500 4500
Central Air 6000 2000-4000
Electric Frying Pan 1500 1500
Dishwasher 540 216
Washing Machine 1200 1200
Clothes Dryer (Electric) 6750 5400
Microwave 1000 (650 Watts) 1300 (800 Watts) 1500 (1000 Watts) 1000 (650 Watts) 1300 (800 Watts) 1500 (1000 Watts)
Radio 50-200 50-200
Window Air Conditioner (10,000 BTU) 2200 1500
Desktop Computer 600-800 600-800
Laptop Computer 200-250 200-250
Computer Monitor 30 30
Printer 400-600 400-600
Garage Door Opener 1420 720
Coffee Maker 600 600
Sump Pump 1300 (1/3 Horsepower) 2200 (1/2 Horsepower) 800 (1/3 Horsepower) 1050 (1/2 Horsepower)
Space Heater 1250 1250
Table Lamp 150 150
Hot Plate 1250 1250
Outdoor Lighting 500-1000 500-1000

Wattages for Farm Equipment

Application Starting Wattage Running Wattage
Portable Heater (Using Diesel or Kerosene) 600 (50,000 BTU) 725 (90,000 BTU) 1000 (150,000 BTU) 400 (50,000 BTU) 500 (90,000 BTU) 625 (150,000 BTU)
Electric Fence (25 Miles Long) 250 250
Battery Charger (15 Amp) 380 380
Vacuum Pump Milker (2 Horsepower) 2300 1000
Milk Cooler 1800 1100

Basic Needs for Home Power

There are a few basic questions it helps to ask if you’re shopping for a whole house generator. Start with your water setup. Are you on city water, or do you have a well? If you have a well pump, you’ll need a 240v generator of 3800 watts or greater.

What type of heat do you use? An electric furnace or heat pump usually requires 15,000 watts or more to run. In other words, you can’t run these from a portable generator. If you have oil or gas forced air unit, you’ll probably only need about 2500 watts. This depends on the size of the furnace.

If you are on city water and have a small furnace, look for a unit that has about 3000-5000 watts. If you have a well pump or larger furnace, you’ll want at least a 5000-6500 watt unit. Most households can get by with a generator of about 6500 watts or less for normal usage.

Starting Wattage vs Running Wattage

Caterpillar_(Olympian)_Generator_Set This sounds like confusing terminology, but to put it simply, some appliances need more juice to get them started than to continue running. So for example, getting a refrigerator started and cold takes a lot more power than keeping it that way.

Appliances and equipment that take more energy to start than to run are said to have a reactive load. For these uses, it usually takes about three times more power to get it started up than to run. Some examples of reactive loads are air compressors, air conditioners, furnace fans, freezers, refrigerators, power tools and bench grinders.

Equipment that takes the same amount of energy to start as to run are called resistive loads. Most resistive loads involve creating heat. Some good examples are toasters, toaster ovens, coffee makers and light bulbs.

These numbers are important to know because you don’t want to end up buying a generator that’s powerful enough to run whatever you need but not powerful enough to start it up.

It’s also important to know that some appliances tend to draw more power at intervals, such as a refrigerator or furnace with a fan that runs intermittently. If your refrigerator has a defrosting cycle, it will need more power if that’s running as well.

Calculating Watts Needed

A lot of times you can also look on an appliance for the wattage it takes to run it, but this can be confusing as well. For instance, if you have a 1000 watt hair dryer, that means the dryer puts out 1000 watts of energy, but it actually uses more to run it as these numbers aren’t necessarily exact. The numbers in the tables on this page reflect that and should be only used as a general guideline to get an estimate of the wattage you’ll need in a new generator.

If you know the amps and volts of an appliance (sometimes you’ll see this on the sticker or tag), you can multiply those two numbers together to get the total wattage needed to run it. Most equipment is 120 volts. Exceptions are furnaces, electric ranges, electric clothes dryers, sump pumps and hot water heaters. When in doubt, take a look at the plug. Regular 120 volt appliances have a standard two or three prong plug, whereas 240 volt uses have a much larger or odd-shaped plug going into the wall.

What is Maximum vs Rated Power?

On many generators, you’ll see listings for rated and maximum power. Maximum power or load means the maximum output it can produce. This max power is generally available for up to 30 minutes.

Rated power is the amount of power that the generator can produce over long periods. It’s calculated at about 90% of the maximum power. If you’re questioning which number to use in deciding which unit to buy, it’s safest to go with the rated power number.

Using a Portable Generator for Home Use

Portable & Inverter Generators for Recreational or Contractor Use

Generac_Portable_Generators Portable generators are different than whole house generators in that while they are not lightweight, you can take them with you. Most of them run on unleaded gasoline and offer limited amounts of power for small uses.

Some come with an electric start and even have an idle control that helps them run more efficiently. Many units even have outlets so you can charge your phone or operate other electric devices.

Portable generators can be used for jobsite work, camping, tailgating or if you have a fifth wheel or RV and want to power appliances. However, if you’re in the latter category, an inverter – type generator may be a better buy for you. Inverter generators are designed to run quieter and will thus be less disruptive.

Just like with household units, when buying a portable or inverter unit, you’ll want to calculate the wattage you need.

Wattages for Contractor Equipment

Application Starting Wattage Running Wattage
Table Saw (10") 4500 1800
Rotary Hammer 1200 1200
Pressure Washer (1 Horsepower) 3600 1200
Hand Drill (1/2") 900 600
Chainsaw (Electric; 2 Horsepower) 1100 1100
Power Drill 600 (3/8"; 4 Amps) 900 (1/2"; 5.4 Amps) 440 (3/8"; 4 Amps) 600 (1/2"; 5.4 Amps)
Demolition Hammer 1260 1260
Concrete Vibrator 840 (1/2 Horsepower) 1080 (1 Horsepower) 1560 (2 Horsepower) 2400 (3 Horsepower) 840 (1/2 Horsepower) 1080 (1 Horsepower) 1560 (2 Horsepower) 2400 (3 Horsepower)
Circular Saw (7 1/4") 2300 1400
Bench Grinder (8") 2500 1400
Air Compressor 1600 (1/2 Horsepower) 4500 (1 Horsepower) 975 (1/2 Horsepower) 1600 (1 Horsepower)

Wattages for Recreational Equipment

Application Starting Wattage Running Wattage
RV Air Conditioner (11,000 BTU) 1600 1010
RV Air Conditioner (13,500 BTU) 2800 1800
RV Air Conditioner (15,000 BTU) 3300 2000
Tube Television 300 300
Flat Screen Television 120 120
Tabletop Electric Grill 1650 1650
Blender 850 400
Slow Cooker / Crockpot 170-270 170-270
Microwave (650 Watts) 1000 1000
Coffee Maker 600 600
Hair Dryer (1600 Watts) 1900 1800
Radiant Heater 1300 1300
Satellite Receiver 250 250
Laptop Computer 200-250 200-250
Portable Fan 120 40
DVD Player 350 350
Radio 50-200 50-200
2-Way Radio 360 (12 Amp) 850 (23 Amp) 960 (35 Amp) 360 (12 Amp) 850 (23 Amp) 960 (35 Amp)
One of the main things to consider if you have an RV is the size of your air conditioner. The size of generator needed to power these units can vary depending on the outside temperature and how efficient your air conditioner runs. A 3000 watt unit usually works well for a 13,500 BTU air conditioning unit. You may need a larger generator if you have a larger air conditioner.

If you have an RV or fifth wheel with dual AC units, you’ll be better off going with 7000 watts. If you’re a camper, boater or tailgater, 1000-2000 watts is usually sufficient for most needs.

No matter what type of generator you decide you need, you’ll want to consider budget and overall value. Whole house generators tend to be very pricey and run upwards of $2000 – $3000 before installation. If you decide to go that direction, you’ll want to pay close attention to the manufacturer’s warranty and user reviews of generators to make sure it’s a good investment for you.

If you decide to go with a portable or inverter generator, make sure you pay attention to its fuel efficiency. Many portable units can go through 10-15 gallons of gas or propane per day. While you may not plan on running it all day every day, you’ll need to have enough fuel on hand for your uses. Make sure to factor this into your final decision when it comes to cost and storage.