A stationary unit has a forced air or other type of cooling system that allows it to be enclosed, most typically in an outside weather housing mounted on a concrete pad similar to a central air conditioning unit.

A portable generator does not have an engine controller, which automatically replicates all the actions you subconsciously perform when starting your car. Engine controllers allow for remote control via a simple on-off switch or automatically with an automatic transfer switch (ATS). Stationary generators also have more extensive protection and safety shutdown features than do portables.

Portable generators all operate at the faster 3600-RPM speed where more engine power is produced allowing for a smaller engine, which is a benefit in reducing weight. Most stationary units use larger engines running at a slower 1800-RPM speed to achieve the same power result, but with much quieter and smoother operation. It's kind of the same thing as the difference between your lawnmower and your car at a fast idle.

Get Enough Power

Don't try to cut corners by not getting a generator with enough power. The cost per watt (the unit of electrical power) goes down considerably as the size of the generator goes up. Many people create problems of all sorts by buying too small. Only resistive loads like lights and heaters can be added directly to calculate load requirements. Others -- like motors -- require extra power of several magnitudes to start than they use to run. Most people have little idea of how much power they use in normal living or how much various loads consume.

Power Basics

Anything that makes heat with electricity (electric heat, water heaters, dryers, etc.) uses relatively huge amounts of power compared to other loads. If your house heats with electricity, consider another heat source or be prepared to buy a large generator.

A "rule of thumb": Allow 2-3 KW of generator power per horsepower of electric motor.

Electronic loads (particularly newer computers) take relatively little power, but that power must be clean and stable (well-regulated voltage and frequency with low harmonics). But computer electronics have properties that produce difficulties for the power source. If you are planning backup power for computer networks-a "rule of thumb"-the total electronic load should not exceed 50% of the generator's capacity. Besides, there's always the air conditioning that needs to keep running to keep the computers cool.

Power tips

If you're thinking of upgrading your generated power, remember that anything that makes heat with electricity (electric heat, water heaters, dryers, etc.) uses large amounts of power compared to other loads. If your house heats with electricity, consider another heat source or be prepared to buy a large generator.

Motors that start under light load (well and septic pumps, many fans) require two to three times the power to start than they do to run while those starting under heavy loads (refrigerators, compressors) may take as much as five times to start. A "rule of thumb": Allow 2-3 KW of generator power per horsepower of electric motor.

Electronic loads (particularly newer computers) take relatively little power, but that power must be clean and stable (well-regulated voltage and frequency with low harmonics). But computer electronics have properties that produce difficulties for the power source. If you are planning backup power for computer networks a "rule of thumb" the total electronic load should not exceed 50 percent of the generator's capacity. Remember to allow for the air conditioning that needs to keep running to keep the computers cool.

-- Tips courtesy of HomeAdvisor.com