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When purchasing a generator, the most important determination is the power requirements of your house and especially your large-draw electric appliances. Refrigerators, air conditioning, sump pumps, water heaters and space heaters will have some of the highest power draw in your house.
Online wattage calculators will help you find what size generator is the best fit for powering your whole house. You can also calculate this yourself by finding the wattage rating label on each of your electrical appliances.
You should multiply the total watts of your appliances by at least 1.5 to create an adequate margin of safety. You can also check with your power company or on your electric bill to find your regular power needs. In general a small to medium size U.S. house averages a minimum of 5,000 to 7,000 watts so many standby generators are sold with a minimum of 8,500 to 10,000 watt outputs.
NOTE: Some generators are listed by watt (W) and some by kilowatt (kW). A kilowatt is 1000 watts.
Air-cooled vs. Liquid Cooled
An air-cooled generator uses the surrounding air to cool the engine. This could be done passively by the surrounding air absorbing the heat and rising away from the generator, or this could be accomplished with “forced air cooling” which uses a fan to blow air across the generator’s engine. Air-cooled generators will often not work as well for longer-run, whole house applications because the cooling is not as efficient—units are more likely to overheat and shut down automatically.
A liquid-cooled generator pumps coolant through the engine block which absorbs heat from the engine before moving through a radiator where the coolant cools back off and then is cycled through again.
The advantage of liquid-cooled generators is they can operate more efficiently, without the fear of overheating in climates that regularly get above 100 degrees Fahrenheit. Liquid-cooled generators are best for whole house applications because these units are less likely to overheat.
Whole house generators are permanently installed at your home and connect to your house’s gas line, either liquid propane (LP) from a tank installed on your property or natural gas (NG) from a utility line or custom tank. Propane is a more affordable fuel and burns “clean”, meaning it leaves much less contamination.
Natural gas is advantageous because it doesn’t require refilling a tank, but a utility mainline can be a disadvantage for those who want to remain off-grid.
Many whole house generators can burn either type of fuel with a simple conversion. Make sure to purchase the correct generator for the type of fuel that you have available.
Since these generators will likely be permanently stationed aside your house, the noise level is an important consideration when choosing a generator. Generally, the Generac brand whole house generators run on the quieter side—65 dbA or less—while other manufacturers’ models may run at 69 dbA or even higher. For reference a vacuum cleaner runs at 75 dbA. Placement of your whole house generator is also important since you may not want that loud noise right next to a bedroom or office.