A lot of Bay Area homeowners come to us wanting to install a heat pump, add an EV charger, or both. The first question they ask is: do I need to upgrade my electrical panel?
The honest answer is: it depends — and the only way to know for sure is a proper load calculation. Not a visual check. Not a guess based on the year your house was built. A calculation.
That said, there’s a lot you can understand before calling anyone. And knowing the basics means you won’t walk into a contractor conversation already convinced you need a $6,000 upgrade you might not need.
What Your Panel Actually Does — and What It Can’t
Your electrical panel is the distribution hub between the utility line coming into your home and every circuit inside it. The main breaker rating — typically 100, 150, or 200 amps — is the absolute ceiling on how much electricity your home can draw at any given moment.
That ceiling matters a lot when you start adding high-draw equipment. Here’s what the numbers look like for common home upgrades:
| Appliance | Typical amp draw | Circuit required |
| Central heat pump (3 ton) | 30–40A | 240V dedicated |
| EV charger (Level 2, 40A) | 40A | 240V dedicated |
| Heat pump water heater | 25–30A | 240V dedicated |
| Electric range | 40–50A | 240V dedicated |
| Electric dryer | 24–30A | 240V dedicated |
Add those up in a home that’s already running an electric stove, dryer, and water heater, and you can see why a 100-amp panel gets tight fast. A 200-amp panel gives you more room — but even 200 amps has limits when everything runs at once.
The key phrase there is “at once.” In most homes, not everything runs simultaneously. A load calculation accounts for that. It uses the actual expected simultaneous draw — not the theoretical maximum — to determine whether your panel has capacity.
The 100-Amp Panel Question
Many Bay Area homes built before the 1980s came with 100-amp service. At the time, that was plenty. Gas handled the heavy lifting — furnace, water heater, stove, dryer — and electrical loads were comparatively light.
When those gas appliances stay in place, a 100-amp panel can often still support a heat pump. The HVAC draw gets added, but the big gas loads haven’t converted yet, so there’s headroom.
The problem comes when you want to do multiple things at once:
- Replace the gas furnace with a heat pump (30–50A draw, dedicated circuit)
- Add a Level 2 EV charger (40A dedicated circuit)
- Switch to a heat pump water heater (25–30A dedicated circuit)
Stack those three on a 100-amp panel that’s already serving a kitchen and the rest of the house, and the math stops working. Not because any single appliance is problematic — because the combination pushes total demand past what the panel can safely deliver.
A contractor who tells you that you definitely need a panel upgrade before even looking at your current load isn’t necessarily wrong. But they haven’t done the math yet. Ask for the calculation.
When You Almost Certainly Do Need an Upgrade
There are situations where an electrical panel upgrade is predictable before anyone runs the numbers:
- Your home has a 60-amp panel — these are rarely found anymore but do exist in very old Bay Area homes. A 60-amp panel cannot support modern electrification upgrades.
- You have a Federal Pacific, Zinsco, or Sylvania Stab-Lok panel — these older brands have documented reliability and safety issues independent of capacity. Replacement is recommended regardless of what you’re adding.
- Your panel is full with no open slots — a heat pump requires a double-pole breaker taking two adjacent spaces. No space means no circuit, even if the amperage could handle it.
- You’re doing a full electrification project — heat pump HVAC + heat pump water heater + EV charger, all at once. On most 100-amp panels, this combination will require a 200-amp upgrade or a strategic subpanel.
When You Might Not Need an Upgrade
This is the part most contractors skip over, because an upgrade is a larger job. But for many homeowners, the full panel upgrade isn’t necessary.
If you’re adding just a heat pump, and your other major appliances are still gas
A load calculation will often show there’s enough headroom on a 100-amp panel. The heat pump becomes the primary high-draw addition, and the gas appliances keep the overall demand from climbing too high. In this scenario, a new dedicated circuit is all you need.
If you’re adding a single EV charger
The same logic applies. Level 2 charging at 40 amps sounds like a lot, but if your home isn’t already packed with high-draw electric appliances, a load calculation may show your existing service can handle it with a dedicated circuit and no panel replacement.
If a subpanel is the better solution
When the main panel is full on slots but not on amperage, adding a subpanel off the main is often far less expensive than a full service upgrade. A subpanel handles the new loads while the main panel continues to serve everything else. This is worth discussing with your electrician before assuming the full upgrade is the only path.
What a Load Calculation Actually Involves
A proper residential load calculation follows NEC Article 220. It accounts for your square footage, all existing major appliances and their rated draws, the new load you’re adding, and the expected simultaneous demand across all of it.
The result is a number — total estimated demand in amps — compared against your panel’s rated capacity and the 80% continuous load rule (continuous loads should not exceed 80% of the panel’s rated capacity for safe long-term operation).
If the calculated demand fits within 80% of your main breaker rating with room for the new circuit, you don’t need an upgrade. If it doesn’t, the calculation tells you by how much — and whether a subpanel or a full service upgrade makes more sense.
This calculation should happen before any equipment is ordered. It takes an electrician roughly 30–60 minutes on site, and it determines the entire scope of the electrical portion of your project.
Why HVAC and Electrical Under One Contractor Matters Here
Most HVAC contractors don’t carry an electrical license. When they scope a heat pump job that requires electrical work, they hand that portion off to a subcontractor — which means two separate bids, two separate timelines, and accountability that splits when something goes wrong.
For a project where the electrical assessment directly shapes the HVAC scope, that split creates real problems. The HVAC contractor proposes a system. The electrician assesses the panel separately. Nobody’s looking at the full picture in one conversation.
When both licenses are held by the same team, the load calculation happens as part of the HVAC scoping visit. The system selection accounts for what the panel can actually support. The electrical work and the HVAC installation happen on the same timeline, under the same warranty, with one point of contact.
That’s not just operationally convenient. It’s how the decision-making actually works correctly.
The Short Version
Your electrical panel may or may not be a barrier to the upgrade you’re planning. The only way to know is a load calculation — not an assumption, not a worst-case estimate, and not a contractor who quotes an upgrade before looking at what you actually have.
If you’re planning to add a heat pump, EV charger, or heat pump water heater in the Bay Area, start with a free estimate that includes the electrical assessment. Get the numbers first. Then decide.
About the Author
Ozone Service is a licensed HVAC and electrical contractor serving San Jose, Sunnyvale, Santa Clara, Cupertino, Mountain View, and surrounding Bay Area communities. EPA 608 Certified, BBB Accredited, EVITP Certified. Free estimates include a full electrical assessment — no separate electrician visit needed.
