Generator Sizing Tool

generator sizing tool

Generator Sizing for Home Use

» Essential Load Generator Sizing Calculator

Essential Loads are the specific circuits to be powered during a utility outage. An essential load solution keeps you protected and secure.

» Whole House Generator Sizing Calculator

Calculate the total load of your home for whole house protection. Find out how a load management* solution can keep you comfortable while saving your money.

Tutorial Video: Generator Calculator Guide


What size generator do we need? I want to power my whole house but I don't want to spend a fortune! What options are there for whole and partial house automatic back-up generators? This article will address those questions and get you started towards better understanding the issues surrounding standby generator sizing. Our approach is based upon the National Electric Code and local municipalities may vary - ask an expert to help size your generator system!

Sizing a generator can be a daunting and dangerous task for the typical homeowner. Assurance Power Systems specializes in designing and installing standby generator packages to meet your needs. There are three basic approaches to sizing an automatic standby generator: 1.) Whole house protection, 2.) Whole house protection with automatic load shedding, and 3.) Partial house protection.  Our GenSizer TM tool can assist you sizing your generator for all these approaches.

Whole house protection is for those homeowners who want uninterrupted back-up power with the ability to power all loads simultaneously. This is, naturally, the most expensive option, but it can give you peace of mind that you will live without interruptions. Sizing a generator for whole house protection involves calculating all general loads, motor and low power factor loads, and heating and cooling loads. Other factors to consider for whole house protection are fuel supply and spacial constraints. You need to ensure you have adequate space to meet local setback requirements as well as space for fuel storage if you don't have access to a natural gas service line.

Whole house protection with automatic load management is quickly becoming the way ahead for residential standby generator systems. There are great solutions from leading generator manufacturers that offer fantastic value propositions. This technology monitors the output of the generator lower priority loads until the generator output is able to handle these loads. This new technology maximizes your investment and allows you to power more with less. For example, many houses that would require a 35kW or even a 45kW generator can be powered with a 20kW or smaller generator! Not only is the total installation cost roughly 30% less than a whole house solution, operating costs are significantly less because the smaller generators burn much less fuel (approximately 2 gallons of propane vapor per hour versus 4 gallons per hour). With the plethora of new products on the market, Assurance Power System can customize a managed load whole house solution for you that will be sure to meet your needs and budget.

Partial house solutions are the most affordable solutions, but limit your protected circuits to a dedicated emergency panel. The codes surrounding these installations are also very strict because it is assumed that the dedicated emergency circuits will be running simultaneously, and, therefore, the generator must be sized to handle all simultaneously loads. This is contrary to whole house and managed whole house solutions because the National Electric Code allows for discounts on whole house load calculations because the loads are not all being used simultaneously. 

There are several variables involved in designing and installing a home standby system.  Generator installations should be performed by professionals! Assurance Power Systems has installed thousands of standby generators. We are there for our customers from the design phase to the preventative maintenance and upkeep of their chosen generator system. Call Assurance Power Systems (877) 499-9500 and find out how we can customize a solution for you.

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Note: The results of the tool are not valid without the signature of a representative of Assurance Power Systems.

*Load System: This is the process of managing loads so the generator won't overload the output rating of the generator.