Here at Kuhlman Electric we are big fans of using portable generators as emergency power. They have one huge advantage over whole house generators, cost! Portable generator systems are a fraction the cost of the whole house systems, both upfront and yearly running cost. The downside is the portable generator takes some manual effort to turn it on / plug it in and in some cases it cannot power as many things in the home as a whole house generator. Click here to see the pros and cons of the portable and whole house generator systems.
Portable generators come in a wide variety of sizes which can make picking one out a bit overwhelming. First step is to decide what you want to power within your house. Do you want to power your heat only? Do you want to power your refrigerator too? How about some general lights and outlets? Microwave? Put some thought into this. The more things you want to power the larger generator you will need.
Generators are rated in watts. Really small portable generators may be only 1000 watts and larger ones will be 12,000 watts. A really easy way to calculate your generator needs is to add up the wattage of the items in your home you want to power.
Let’s look at the most common requests we get from customers and their corresponding wattages:
- Heat, air handler with fan (gas or oil) 500 watts
- Gas range / oven 100 watts (only powers the clock / timer, igniter)
- Microwave 1500 watts
- Refrigerator 750 watts
- Window air conditioner 1400 watts
- General outlet and lights 1500 watts (TV, internet modem, LED lights), (this is general number and probably a little on the high side to be safe)
- Garage door opener(s) 1200 watts
Keep in mind you would not run the heat and window air conditioner at the same time. For the purposes of the exercise, we will use the larger air conditioner load.
The total wattage of the above is 6,450 watts. We need to remember though that this calculation assumes everything is running at the same time. It’s probably unlikely for this to be the case. Items like microwaves and garage door openers will only be used shortly. Even a refrigerator is not always cooling.
Even though you know everything won’t be used at once it’s a good idea to still add them all up and size the generator based on that total wattage. When doing it this way you can substitute other appliances when one it not being used. For example, if you are not using the microwave, the dishwasher or disposal can be used. You could even use your washing machine or gas dryer!
Going back to our total amperage of 6,450 we’ll want to find a generator that has at least this amount of “running amperage”. Fortunately, a very common generator size is 7500 watts (running) and 9500 watts (peak). The difference between peak and running is simple. The generator can supply up to 9500 watts briefly, meant to absorb motors starting up. When any motor turns on (disposal, fan, a/c etc.) it draws more amperage during “start up” then falls back to its running watts.
For the loads outlined I would recommend a 7000 – 7500 watt running portable generator. This size is by far the most popular portable generator we install and for good reason. It covers most customer’s needs!
But I only I want to run my heat!
We have many customers who are only concerned with running their heat. No problem here at all! If we look at the example before we can see the average air handler draws about 500 watts. If you have a forced hot water system, the wattage may be even less. This will depend on your heating system, and I recommend looking at it to add up the wattages.
There are plenty of inexpensive 1000 watt (running) portable generators to choose from. If you only want to run your oil/gas heat, this small generator should be all you need. Again, do you due diligence and add up the wattage on your heating system!
How about large loads like electric dryer, electric range, and central air conditioners?
For the most part, if you are choosing to go the portable generator direction you may need to make some concessions. Big loads like these may need to not be used during power outage. Having said that, could you get a portable generator large enough to power them? Probably.
Let’s start with the electric dryer. These draw on average 5000 watts. Add that to the previous example and we get 11,450 watts. There are reasonably priced generators with 12,000 running watts. We still need to keep in mind that we can still manage the loads. Meaning while using the dryer we won’t use the microwave and garage door opener etc.
Next is the electric range. These draw on average 10,000 watts. This will only happen if every burner is ON and the oven is ON. If only one burner is being used the wattage will be a fraction of that 10,000. Even in the first example we used, if you have an electric range you will probably be OK using a single burner. Using all the burners / oven at once? No way.
Finally, we have central air conditioner. Some homes have 2 systems or more, others have one. You would need to add up the wattage of your system(s) and see where you are at. Using my own house as an example I have 2 central air conditioners for a total of 10,000 watts combined. I went with a 7500 watt generator knowing that I cannot use the central air while power is out. Most customers will have to make this same decision to keep the cost of the portable generator reasonable. Is there a generator out there that will power the central air? Sure, but it’s very expensive!
If you live an area where power outages can last days, you may want to invest in a larger unit if you have electric cooking and/or heating. Once you get to a BIG portable generator you get into the price point of the whole house generators. At that point you may want to give the whole house system some serious consideration.
Gas vs Propane Portable Generators
There are two types of portable generators to choose from. Gas and Propane. Most of the propane generators are “dual-fuel” meaning they can run on either fuel buy turning a switch! I really recommend the dual-fuel generators.
Gas Generator Pros
- Gas is readily available
- More wattage when compared to propane. A popular dual-fuel generator customers of ours use is rated at 7500 watts using gas and 6750 watts using propane.
- Gas only generator may be a little less expensive
- No tanks to swap, just add more gas during long outages
Gas Generator Cons
- Gas can be messy! Storing gas can be smelly and difficult
- Generator carburetor may need to be cleaned more often
Propane Generator Pros
- Clean! Storing propane is clean and easy. No need to worry about spilling gas.
- Generator carburetor will not need to be cleaned as often as propane burns very clean
Propane Generator Cons
- More expensive upfront cost for the generator
- Added expense of purchasing propane tanks
- Will need to swap tanks if running for a long time
We can combine the best of the gas and best of the propane (other than upfront cost!) in one unit which is the dual-fuel generator. Looking at the most popular portable generator our customers use as an example. The gas only 7500 watt unit it $850 where as the dual-fuel unit is $1,125.00. For many of our customers, the additional $275 is worth the convenience of propane.
I recommend getting 2 propane tanks to keep on hand. You know the normal grill size tanks you probably already have? Well propane dealers sell larger tanks, 2 and 3 times as tall as the grill tank. I recommend getting 2 of these tanks (largest you can handle on your own) and keep them filled and ready for when the time comes. When on generator power and one tank runs out, you can switch tanks and take the empty one to refill. If you are in a pinch and run out of propane you can always switch to gas!
Recap
- Add up the wattages of the things around your house you want to power. Take the larger of the two coincidental loads (AC vs Heat Example). Don’t forget you can substitute loads! A good example of this was the microwave. When the microwave is not being used, you can use other appliances of similar wattage or less.
- Look for a portable generator with running watts that meets or exceeds your needs
- Decide on gas or dual-fuel
I choose a portable generator; how do I connect it to my house?
Great question! Click here to find another article we wrote about choosing between a generator panel and interlock kit.
