Do I Need a Panel Upgrade? How to Check First

You got a quote for a heat pump, an EV charger or an induction range, and it came with a surprise: "Your panel is too small. You'll need a service upgrade first." That can add thousands of dollars and, where the utility has to get involved, weeks or months.

Sometimes that is true. Often it is not. Before you pay for an upgrade, it is worth knowing how that conclusion was reached, because there are two very different ways to reach it.

"Too small" is usually an estimate, not a measurement

When a contractor says your panel is full, they usually mean one of two things:

There are no open breaker slots. This is a space problem, not a capacity problem. It is often solved with tandem breakers or a small subpanel for a few hundred dollars. It does not require a new service.

A load calculation says your service is over capacity. This is the one that leads to expensive upgrades. The traditional calculation adds up your home's square footage and the nameplate rating of every major appliance, applies some standard percentages, and compares the total with your service size. It never looks at how much electricity your home has actually used.

That estimate is deliberately worst-case. It assumes the range, the dryer, the water heater and everything else could be running hard at once. In real homes, that almost never happens.

What homes actually use

Researchers at Lawrence Berkeley National Laboratory looked at smart-meter data from 11,940 homes. The average home's highest 15-minute peak over a year was 9.7 kW. A standard 100-amp service can deliver 24 kW.

In other words, the typical home never uses even half of a 100-amp service, even at its single busiest moment of the year. Your home may be higher or lower than average, and that is exactly the point: it can be measured rather than guessed.

The code already allows measuring

This is not a loophole. The National Electrical Code includes a section, NEC 220.87, that lets a licensed contractor base the calculation on your home's actual measured peak demand over the past twelve months instead of the worst-case estimate.

The method builds in its own safety margin: your highest measured peak is increased by 25 percent, the new equipment is added on top, and the total still has to fit within your service rating.

The data comes from the smart meter your utility already installed. You do not need any new hardware, and nobody has to monitor your panel for a month.

Questions to ask your contractor

"Is the issue breaker space or service capacity?" If it is only space, ask about tandem breakers or a subpanel.
"Which load calculation did you use?" If the answer is the standard or optional method, or a rule of thumb, ask question 3.
"Can we check my measured demand under NEC 220.87 first?" Many contractors know the section exists but have never used it, because getting and processing the utility data used to be a chore.
"If it's close, what are the options short of a new service?" A lower-amperage EV charger setting, a heat pump without large resistance backup strips, a 120-volt heat pump water heater, or a load-management device can each make the difference.

What you can do yourself

Try the panel capacity calculator for a rough sense of where you stand.
Find your interval data. Log in to your utility account and look for "Download my data," "Green Button," or "energy usage details." You want hourly or 15-minute data going back twelve months. Your contractor can also request it with your authorization. See how to get interval data from your utility.
Send this page to your contractor. The calculation has to be prepared by the licensed professional doing the work, and the local inspector has the final say. TrueLoad is the tool contractors use to run it, and their first project is free.

When you really do need the upgrade

A measured calculation is honest in both directions. You are more likely to need a larger service if:

Your panel is an old fuse box, or a model with a known safety problem. Those are worth replacing for safety regardless of load.
The home is already all-electric with resistance heat, and you are adding a lot on top.
You want several large loads at once, such as two EV chargers plus a heat pump with big backup heat strips.
Your measured peak is already close to your service rating.

If the data says you need the upgrade, you will at least know the money is being spent on a real constraint.

This page is general information, not electrical or engineering advice. Work on your electrical service must be done by a licensed professional and approved by your local permitting authority.

Do I Really Need a Panel Upgrade? What to Ask Before You Pay for One