Generator size can be estimated by determining the major loads to be supplied and allowing some overhead for convenience appliances (television, computer, etc). Some of the most common major loads are listed below (these are average numbers and can vary):
|Furnace blower motor (propane / natural gas heat)||1,500 – 2,000 watts|
|Refrigerator / Freezer||1,500 – 2,000 watts|
|Well pump (1 horsepower)||3,500 – 5,000 watts|
|Water heater (electric)||4,000 – 5,000 watts|
|Electric furnace||11,000 +|
|Heat pump||10,00 +|
By manually switching loads off and on the owner can ensure that only one major load is running at a time. This then allows a smaller generator to be used.
- Distance from the contractor: Travel time and mileage costs money. The farther you are from the contractor the higher the cost.
- Type of transfer switch: Transfer switches come in a variety of makes, models and sizes. They can be surface mounted, flush mounted, or designed for outdoor use.
- Type of installation: Surface mounted switches take less time to install than flush mounted switches, resulting in a lower cost of installation.
- Distance from the main panel: Most manual transfer switches are designed to be installed within a couple of feet of the main panel. Additional materials and labor would be necessary to install the switch away from the main panel and would raise the installation cost.
- Remote generator receptacles: Most manual transfer switches have a receptacle to allow the generator to be plugged in to. In some cases it is more convenient to have the receptacle located closer to where the generator will be located when it is running.
- Load identification: In most cases the manual transfer switch will not be supplying all of the circuits on the main panel. The more time the electrical contractor spends identifying the circuits to be connected, the higher the installation cost.
- The national electric code and most city, state, and county ordinances require approved means of isolating generator power from utility power. These requirements are designed to protect the lives of both you and the utility workers and to protect your equipment.
- The main disconnect breakers are not designed to isolate power from two sources.
- The main disconnect breakers can fail without visible indication. The breaker may feel l like it is open but may be electrically connected internally due to a spring or other failure. This can go unnoticed until utility power returns.
- When both sources of power are available it is possible to connect both sources together. Accidentally operating the wrong breaker can have severe consequences. Approved means of isolation usually require 3-position switches or breakers that prevent connecting both sources of power.
- Common fuel source — easily obtained
- Increases portability of smaller generators
- Highly flammable
- Short shelf life (approximately 12 months)
- Storing large quantities is hazardous
- May not be available during power outages
- Long shelf life
- Clean burning
- Easily stored in both large tanks or in smaller 5 – 10 gallon cylinders
- Obtainable during localized power outages – suppliers may be unable to pump fuel during widespread outages
- Home delivery available for larger tanks
- Pressurized cylinder of flammable gas
- Fuel system is more complicated (increased possibility of failure)
- Larger tanks are not aesthetically pleasing (unsightly)
- Fuel system plumbing results in higher installation cost
- Least flammable fuel source
- Easily obtained
- On-site fuel delivery available
- 18 – 24 month shelf life
- Installing large storage tanks raises cost of system
- May not be available during power outages
This depends on the size of the tank and amount of load on the generator. Higher loads require more fuel. A conservative rule of thumb is 1 gallon of fuel per hour for a 5,000 watt generator.
Propane fueled portables use a slightly larger amount of fuel than their gasoline counterparts.
This is not recommended. Portable generators are designed for outdoor use. Running them indoors presents the following problems:
- Increased risk of carbon monoxide being admitted to living spaces.
- Potential for fire. Garages can have combustible material near the generator that can catch fire when in contact with hot exhaust components.
- Potential equipment damage. Indoor operation of the generator may restrict cooling airflow to the engine.