Watt Diet Calculator

Electrifying the home without upsizing the electric panel: The Watt Diet

Most people think electrical upgrades are needed if they add electric appliances, but this can be avoided with thoughtful selection of efficient products or by using load sharing devices. Homes have access to a set amount of power through the service wire from a nearby power pole. For example, a service wire may provide 24,000 Watts (100 Amps at 240V). Choosing power efficient appliances can help you avoid upgrading the utility service wire and your circuit breaker panel.

A few thoughtful selections can save you thousands of dollars and months of waiting for service upsizing.

Share amperage between major appliances to better allocate circuit panel breaker capacity. Share circuit between electric range and EV charger. Use a combined washer and dryer. Share circuit between air handler and heat pump.
Share amperage between major appliances to better allocate circuit panel breaker capacity

Below is an example of how the main electrical panel in 2,000 square foot home might look, after the home is converted from gas to all-electric.

Efficiently allocated 100-Amp electric service in 2,000 square foot home
Efficiently allocated 100-Amp electric service in 2,000 square foot home

Here is an example of an electrical panel from an even larger home that converted from gas to electric.

Efficiently allocated 100-Amp electric service in 3,000 square foot home
Efficiently allocated 100-Amp electric service in 3,000 square foot home

The Watt Diet Calculator takes information about a home and estimates the size of the electrical panel needed for that home. It can help homeowners and contractors determine if a panel must be upsized in order to electrify the home.

Watt Diet Calculator - Spreadsheet
A preview of the Watt Diet Calculator

The calculator uses a building’s characteristics and location to help size a heating product for the given home. It then calculates total power use of the home, according to methods proscribed in the National Electrical Code (NEC), and based user-defined device specifications.

This Watt Diet file requires the current version of Excel for full functionality.

Download the Watt Diet Calculator

Watt Diet Strategies

Basic strategies for avoiding an electrical panel upsize can include:

  1. Select appliances that combine two functions into one machine.  For example, the kitchen range (combining an oven and cooktop in one slide-in appliance), which lets us avoid a separate high power circuit for wall ovens.  Another example is a combined washer/condensing dryer machine that lets us avoid needing a circuit for the clothes dryer.
  2. Select power efficient versions of the appliances.  Choose the 15-amp version of a heat pump water heater instead of the 30-amp nearly identical version.  Selecting high performance, power sipping versions of heat pumps instead of lower performance versions.  Select power efficient and energy efficient heat pump dryers if you want a separate clothes dryer.
  3. Reduce heat loss and cooling loss by insulating and air sealing.
  4. Use prioritized circuit sharing devices.  These handy devices can automatically pause car charging while other appliances, like the dryer, finish. 
  5. Use EV charger pausing circuits.  These briefly pause EV charging if many devices are on at once and the main breaker is at risk of popping.
  6. Avoid overkill in your EV charger settings.  For example, pick a 20-amp or 30-amp outlet for your EV charging and avoid 50-amp chargers at home.  A 20-amp outlet can deliver 100 miles of charge overnight and more than 50,000 miles of charge in a year.  Bigger car batteries don’t require bigger circuits; they give you flexibility about when you charge.