What Size Generator Do I Need?

People buy generators for a number of reasons.  Regardless of the reason, you need to have an idea what you are going to supply power to, and how much current is required by those things.  When I was looking into getting a generator, I asked myself the question, “What size generator do I need?”

Luckily, there are a few resources to help you determine the size generator you will need to power the things you want to plug in:

Westinghouse Wattage Calculator

Honda Wattage Estimation Guide

I found both of these tools very useful for deciding what size generator I needed to power my house.   When looking at the guides, you will notice something that is important.   Many devices, especially ones with electric motors, require more electric current to start than it takes to run.

That makes sense to me.  Newton’s Law states that objects in motion tend to stay in motion.  Object stopped tend to stay stopped.    So, it takes extra energy to take a stopped motor and start it then it takes to keep it running after it is started.

When looking at the charts, you will see the term Surge or Starting watts.   Notice that the difference could be significant.   I never realized how many things have electric motors in them, like the refrigerator.   There is a compressor in it that has a motor.    The circulator  pumps that are part of your heating system are motors, too.   When I thought about what size generator do I need, I got confused.   Do I need to add up all of the surge numbers or the running numbers?

In addition, I started to ask myself, “Do I really have to power everything?”   The answer to that was no.   There are a few things I don’t need to have and others are essential.   So, when thinking about choosing a generator, ask yourself these questions:

1. What do I want to power?
   1. What are the essentials to power?
      1. For me, this was my refrigerator, heater, hot water, some lights and the coffee pot 🙂   Although I have Oil heat, the boiler still requires electricity.   This was something I didn’t even think about until it was gone.  If you have electric heat, you have to think big, when it comes to generator size, or more likely, look to alternate ways to heat your home.Cold showers get old really quickly.   Do you have a gas or electric hot water heater?    What about your washer and dryer?Do you have a pump that need to be powered?   Think about all of these things and write them down.
   2. What is nice to have power?
      1. More lights, the television, DVD player, hair dryer, etc.
   3. What can I live without?
      1. Things like the oven and stove.   I have an electric oven and stove and this takes up a lot of power.   Although I can use it with the generator I purchased, I don’t have to.  For example, I can use the gas barbeque with stove on the side.   If you have a gas stove, you are in luck.

After evaluating all of the things you want to power, you can then have to do a little math.   Add up all of the running watts of each category.   Back to our main question, which was “What size generator do I need?”   Choose a generator that will at least take care of your essential items and some of your nice to have items.    Add in some buffer wattage for surge and you are half way there with your low number.

Next, you will need to look at your options and your budget to come up with the next.   For instance, I bought the 7500E portable generator.    After doing the math as I described above, I could have gotten by with a 5000 watt generator.   Why did I get the 7500E?

I did a lot of looking and reading of reviews.    I  saw that some brands of generators caught on fire and was recalled! Yikes!   I saw some that got ok review and some that got excellent reviews.    The Westinghouse got excellent reviews, so I choose to get that brand of generator.    The difference in price between the 5500 watt model and the 7500 watt model was under $300 dollars.   I also thought it would be better to run the 7500 watt model, running it at half its load, then the 5500 watt model running it closer to its capacity.

1. I decided the $300 was a small enough difference for me, so I went for that one.    In addition, you never know when a neighbor may ask you if they can run an extension cord, so that they don’t loose all of the food in their refrigerator.

One last thing I want to write about here is the surge watts.   The key here is you need to start your generator.   After it is warmed up and running smoothly, you need to apply power to a few things at a time.    For instance, first plug in your refrigerator, then after that is running, plug in the next device.

Running a lot of extension cords is not the best idea, although it will work in an emergency.   A better idea would be to plan for hooking the generator up to your home a neater way.    An electrician is needed for professional and safe installation of either a transfer switch or interlock kit.

If you have the generator hooked up to your house with a transfer switch or interlock kit, follow this plan:

1. Turn off all the breakers
2. Safely connect the generator to your house.
3. Supply power to the devices one breaker at a time.

That should help you get past the surge watts.    Choose the device that draw the most current to be the first you provide power to.

I hope this article helped you to answer “What size generator do I need?”   It was a learning experience for me when I was figuring it out.