Your Electrical Panel

Volts, Amps, and Watts - a quick refresher

It is useful to use an analogy to water flowing in a pipe when explaining electricity.  

Voltage is analogous to water pressure.  The higher the voltage the more force is pushing the electrons through your appliance.  Most household wiring is 120 Volts but some high-power appliances, such as ovens and level 2 EV charging stations, use 240 Volts.

Amps (Amperes) are a measure of electrical current and are analogous to the number of gallons of water per second flowing in a pipe.  One Amp is equivalent to about 6,240,000,000,000,000,000 electrons flowing through your circuit each second.

Watts are a measure of power, how fast something can be done.  The more Watts you have the faster you can charge your EV or boil water on an induction stove.  To calculate Watts, multiply the Volts times the Amps.

Why Your Panel's Capacity Matters 

All modern electrical panels have 2 separate 120 Volt lines coming in from the utility.  These can be combined to produce 240 Volts for high-power circuits.

Newer homes (typically 1980's and later) have panels rated at 200 Amps or more.  If you have a 200 Amp panel your home can draw 48,000 Watts (48 kilowatts) from your utility and you should easily be able to electrify your whole home unless you have some unusually large loads.  You should still plan your electrification ahead of time to avoid overloading your panel.

Most older homes were built with panels rated at 100 Amps, allowing 24 kilowatts to be used at one time.  It is more challenging to electrify a home with a 100 Amp panel, but it usually can be done if you plan ahead to avoid "painting yourself into a corner."  You may need to use energy management devices or a smart panel - see below for the details.

Some older homes have panels rated at less than 100 Amps, with 65 Amps being common.  If your panel is rated at less than 100 Amps you will likely need a panel upgrade to completely electrify your home.

Regardless of the rating of your panel, if it contains fuses instead of circuit breakers you should consider upgrading.

Panel upgrades can be expensive and time consuming.  If your neighborhood has above-ground wiring (wires running above ground from the utility pole to your home) it can cost several thousand dollars for a panel upgrade.  A panel upgrade can cost well over $10,000 if you have below-ground wiring.

How to Avoid a Panel Upgrade and Save Money

Many electricians will tell you that you need to upgrade to a 200 Amp panel to electrify your home.  However, this is usually not true!  Most homes can be electrified with only a 100 Amp panel but you may need to make your home leak less heat, select power-conserving appliances (a little different than energy-efficient appliances), use energy management or circuit sharing devices, or as a last resort replace your panel with a smart panel.

For a detailed discussion of this topic, see the Watt-Diet in Redwood Energy's Pocket Guide to Electrification.  

For more information see this video Electrical Panels: How to avoid a panel upgrade from Electrify Now and San Diego Learn.

For a less detailed introduction, read the following document from Electrify Now and the additional comments below.

Insulating and Air-sealing your Home

If you home leaks heat you will need a larger heat pump to maintain comfortable temperatures inside.  The larger heat pump will cost more to buy, cost more to run as it keeps up with the leaks, and use more electricity from your Amps-budget.

Heat can leak out of, or into, your home through holes in your building envelope or through poorly insulated walls and windows.

Air-sealing consists of finding places where air can flow from outside to inside and sealing those holes.  This can include weather stripping around doors and windows and holes in your ceiling or walls where the wires for lighting and electrical outlets penetrate.

Older, single-pane windows offer very poor insulation.  Replacing these with modern double or triple pane windows can save a lot of power.

Poorly insulated walls are more difficult to fix.  You may be able to hire a contractor to cut holes in the drywall and blow additional insulation into the wall.  Two or three holes will need to be cut between each pair of studs, about every 16 inches horizontally.  This can leave an expensive drywall repair job.  You may want to concentrate on the south and west facing exterior walls as these can let a lot of heat into your home on hot summer days.

Power-Conserving Appliances

Power-conserving appliances use less power than normal appliances of the same type.  This is different than energy-efficient or energy-conserving appliances which waste very little energy but may still draw a lot of power.  A power-conserving appliance will likely do its task slower than a normal appliance.

1. EV charging stations: Many car dealers will tell you to install a 50-Amp level 2 (240 Volt) charger in your garage so you can charge your car's battery from zero to 100% overnight.  However, this is half of the power an entire 100 Amp panel can supply.  A power-conserving alternative is to install a 16 Amp to 20 Amp level 2 charger.  This will still add 80 to 100 miles of range to your EV overnight.  Most people will find this sufficient.
   
   

2. Heat pumps for heating and cooling your home: Modern, inverter-driven heat pumps can use less power than older designs.  Talk to your HVAC contractor about low-power solutions.
   
   Some contractors will try to sell you a "backup duct heater" that uses electrical resistance elements (like a giant toaster) in your ducts "in case the outside temperature gets too low."  These backup heaters are very inefficient and use a lot of electricity (up to 50 Amps at 240 Volts).  Modern heat pumps should not need this in San Diego County as they should be able to work at all temperatures we are likely to see.
   
   Some contractors may want to sell you a hybrid system that has a backup gas furnace.  Again, these are not needed in San Diego County and defeat full electrification of your home.
   
   

3. Heat pump water heaters:  Most heat pump water heaters (HPWH) require a 240 Volt, 30 Amp circuit.  This is because they contain resistive heating elements, just like a regular electric water heater.  These resistive heating elements will be used if all of the hot water in the tank is used and there is demand for more hot water.  (Using the heat pump only, without the resistive heaters, can take several hours to heat up a tank full of cold water.)
   
   Several manufacturers have developed 120 Volt HPWH that can plug into a normal 15 Amp circuit.  Some of these contain no resistive heaters while others contain small, low-power resistive heaters. 
   
   It is highly recommended that you switch to a larger tank than you currently use if you are installing a 120 Volt HPWH so that you are less likely to run out of hot water.  If your existing gas water heater has a 40 gallon tank, you should get a HPWH with around 65 gallons.  If you are replacing a 50 gallon water heater, your new HPWH should have an 80 gallon tank.
   
   The 120 Volt water heaters may also come with a thermostatic mixing valve (smart valve).  This allows the water in the tank to be heated to a high temperature and then be mixed with cold water in just the right ratio to produce normal-temperature hot water.  The additional cold water adds to the total volume that can be used before the tank runs out of hot water.  If your 120 Volt HPWH does not have an internal thermostatic mixing value, you can ask your installer to put an external valve on the unit.
   
   

4. Clothes Dryers: A standard electric clothes dryer uses resistance heaters to heat and dry the clothing and typically need a 240 Volt, 30 Amp circuit.  An alternative is a Ventless Washer-Dryer Combo.  These combine the washer and dryer in a single appliance that plugs into a standard 120 Volt, 15 Amp outlet.
   
   It will take longer to wash and dry a single load, but on the other hand you don't have to remember to move the clothes from the washer to the dryer.  Put in the dirty clothes and take out the clean and dry clothes.