Choosing a Generator

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Some common generator and electrical definitions.

Power capacity
There are many online calculators to help estimate required generator size. These assume many things and provide a reasonable guideline, but can also suggest a much larger generator than you really need. Ideally, make a list of items you will be using during an outage. Look at the label on each appliance to find its power requirement in watts or VA. Ideally you could measure the current requirement with a peak holding meter to determine maximum startup current and operating current. Startup current is important.
Many items with electric motors will have two current ratings. When they start the motor requires much higher current to begin turning than is needed after they have started to turn. A deep well pump could require over 25amps to start, but only about 6A once water is flowing. Similarly a fridge or freezer could require 15A for a very brief moment while the compressor starts but settle down to a few amps afterwards. Items such as a microwave oven or a toaster oven will usually create a steady current flow without significant peaks at startup.
If you can juggle electricity use the size of the generator can be reduced. If you insist on running the well pump in order to take a shower or fill the bath tub while cooking with the microwave and toaster ovens the total power requirement will be high. Limiting water use while cooking will solve the problem.
Generators usually have two power ratings. The lower of the numbers is usually a continuous or running power rating. When adding up all the power requirements above, this number will be the total of normal operating powers of the items being powered.
The higher number is usually labelled as surge or startup power. This is the higher of the ratings measured. It is unusual that several devices will require maximum startup current simultaneously, so consider the largest load only when determining this number.
As an example, my backup generator is rated 5500 watts continuous and 8500 watts startup. The largest startup load is the well pump which requires 27A at 240VAC or about 6480 watts. Once water is flowing the current drops to 6.2A or about 1488 watts. The generator still has an added capacity of 2000 watts available while the well pump starts up or 4000 watts while the pump is running.

Fuel source
Consider what might become scarce or difficult to get during an outage, especially if accompanied by bad weather. Most fuel stations will not be open if there is no electricity. A natural gas connection to fuel the generator may be ideal if available. Propane is a good option for longer run times if the home uses it already for cooking or heating. Gasoline will allow the generator to remain portable for camping or to loan to a neighbor. It requires stabilizer and can not be stored more than a few months before being used. Many small engines can have the carburetors modified to run on either propane, natural gas, or gasoline. Diesel fuel lasts considerably longer than gasoline but should also be used with a stabilizer. If your home uses heating oil for a furnace it can often be used as a diesel substitute fuel. Diesel engines usually cost much more.
Check fuel source vs cost page.

Engine type
Overhead valve engines typically run more efficiently and last longer than side valve engines.
Check Generac engine information page.

Noise level
Portable generators can be noisy. If you have neighbors nearby or the noise is unbearable in your house here are some ideas.

Choose an operating location as far away as possible. Note that a larger gauge wire is needed to reduce voltage drop as line length increases. Reducing line loss is required to minimize power loss and to ensure maximum power is available to the house. Lights will flicker less when heavy loads are attached.

Change the exhaust system. Noise from the portable generator systems comes primarily from two sources, the engine block and the exhaust system. With an air cooled engine there is little you can do about block noise. Some engines can have a larger muffler attached or make other changes to the exhaust system. Merely mounting exhaust pipe vertically will noticeably reduce noise.

Build a noise shielding enclosure. This could be as simple as a piece of plywood to reflect sound away from the house to a separate shed to hold the generator. Design your enclosure with safety in mind. Provide adequate air circulation and ventilation to prevent heat buildup and to remove carbon monoxide.

If the noise bothers your neighbors, invite them over for coffee or offer to run line to their home to power the freezer or a few lights. Talk to them before starting the engine, ask they let you know if the noise is bothersome before they phone the police or harbor any resentment. A little diplomacy can go a long way.

Small muffler will not reduce noise level significantly. Some come with a low tone muffler which helps, but the noise level is still very high. Honda and some Chinese clones make very low noise generators in power levels up to about 3000 watts. There are techniques to help reduce the noise level.

Last resort, shut off the engine or buy a quiet generator.