For most San Mateo homes under 2,000 square feet with gas heat, gas cooking, and no EV charger, a 100 amp panel is still enough - and a straight replacement runs $1,800 to $3,200 in 2026. You need a 200 amp upgrade the moment you add a Level 2 EV charger, switch to a heat pump or induction range, or add an ADU, because those loads push a 100 amp service past its 80 amp continuous limit. Everything below is how we actually make that call on site, with the numbers we use.
We do this walkthrough several times a week across San Mateo, and the answer almost never comes down to panel brand. It comes down to what you plug in, how old the service entrance is, and what your utility feed can support.
The short answer: 100 amps is usually enough until it isn't
A 200 amp vs 100 amp panel upgrade San Mateo CA decision is really a load calculation question, not a preference question. The National Electrical Code (NEC 220.82) lets us calculate your existing load, and a 100 amp service can carry roughly 80 amps continuously - about 19,200 watts at 240 volts.
That sounds like a lot until you stack real appliances. A Level 2 EV charger pulls 32 to 48 amps on its own. A heat pump with backup electric strips can pull 40 to 60 amps. An induction range adds 40. Add a tankless electric water heater and you have already blown past 100 amps before the dryer turns on.
If your home is all-gas and you are not adding anything major, 100 amps is fine. If you are electrifying anything, plan for 200.
What 100 amps actually powers in a San Mateo home
Here is what a typical 100 amp service comfortably handles in a San Mateo house built between 1945 and 1975:
- Gas furnace, gas water heater, gas range and oven
- Central air conditioning up to about 3 tons
- Electric dryer (30 amps)
- Dishwasher, disposal, microwave, refrigerator
- Lighting, outlets, and a few kitchen circuits
That is a real, working house. We replace 100 amp panels all the time and leave the service size alone when the load calculation supports it. If your panel is a 1960s Zinsco or a Federal Pacific Stab-Lok, the issue is the panel itself, not the amperage - that is a electrical panel replacement San Mateo CA job regardless of size, because those breakers have a documented failure rate and most insurers in San Mateo County now flag them.
What 100 amps does not handle well: two EVs, an EV plus a heat pump, an ADU on the same meter, or a full kitchen remodel with induction and a tankless water heater. Any one of those pushes you into 200 amp territory.
What changes when you move to 200 amps
A 200 amp service gives you roughly 160 amps of continuous capacity - about 38,400 watts - plus physical space for 40 to 42 breaker slots instead of 20 to 24. That second part matters more than people expect.
When we do a 200 amp panel upgrade San Mateo CA, here is what actually changes:
- Service entrance conductors get upsized from 1/0 aluminum or 2 AWG copper to 2/0 copper or 4/0 aluminum.
- The meter socket is replaced - PG&E will not reconnect a 200 amp panel to a 100 amp meter base.
- The grounding electrode system is brought up to current code: two ground rods, a continuous grounding electrode conductor, and bonding to the water and gas lines.
- Available fault current goes up, so the main breaker's AIC rating has to match - usually 22,000 AIC in this area.
We handle the PG&E coordination, the permit with San Mateo's Building Division, and the inspection. Typical project runs one to two days of on-site work, with a permit turnaround of 5 to 10 business days before that.
Do I need 200 amp or 100 amp panel San Mateo CA?
You need 200 amps if any of these are true: you own or plan to buy an EV, you are replacing a gas furnace or water heater with electric, you are adding an ADU or a second kitchen, or your panel has fewer than four open breaker slots. Otherwise, 100 amps is often the right call.
Run through this list honestly:
- EV charger in the next three years? 200 amp. A 48 amp charger alone is 60% of a 100 amp service's usable capacity.
- Heat pump or mini-split conversion? 200 amp if there are electric backup strips. A cold-climate heat pump without strips can sometimes stay on 100.
- Induction range or electric tankless water heater? 200 amp. Both are 40 to 60 amp loads.
- Adding a junior ADU or in-law unit? 200 amp minimum, sometimes 320 amp with a split service.
- Panel full, no open slots, no plans to electrify? 100 amp replacement is fine - or a subpanel installation San Mateo CA if you just need more circuits.
If you are on the fence, the load calculation settles it. We run it on site, in writing, before you commit to anything.
Cost difference: 100 amp vs 200 amp panel San Mateo CA
In 2026, a 100 amp panel replacement in San Mateo typically runs $1,800 to $3,200 installed. A 200 amp upgrade runs $3,200 to $6,500, and can hit $8,000 or more if the service mast, meter location, or underground feed has to be rebuilt.
Where the money goes on a 200 amp job:
- Panel and breakers: $600 to $1,400 depending on brand and circuit count
- Service entrance conductors and meter socket: $500 to $1,200
- Grounding and bonding: $200 to $500
- Permit and inspection: $250 to $600 in San Mateo
- Labor: one to two days for a crew of two
The gap between the two is real, but it is not the place to save $1,500. If you are going to need 200 amps within five years, doing it once is cheaper than doing 100 now and 200 later - you pay for the permit, the inspection, and the PG&E disconnect twice.
How San Mateo's housing stock shapes the decision
San Mateo's panel question is really an age-of-house question. The 1940s to 1960s tracts in Hayward Park, Baywood, and the streets off Alameda de las Pulgas were built with 60 amp fuse boxes. The 1960s and 70s ranch homes in Beresford and Shoreview mostly got 100 amp panels. Very few homes west of El Camino were built with 200 amps from the start.
That matters because the utility feed to those older homes is often undersized too. If you are in one of those neighborhoods and your service drop is 100 amp overhead, we may need to coordinate a service upgrade with PG&E before the panel swap - that adds two to four weeks to the schedule. We see the same pattern in the older housing stock across Burlingame Electrical Panel Upgrade territory, where 1950s capes and bungalows sit on the same vintage 100 amp feeds.
If your home still has a fuse box, the size question comes second. A fuse box replacement San Mateo CA is the first step, and we usually recommend going straight to 200 amps at that point because the labor overlap is nearly total.
Common mistakes we see on panel size decisions
The most expensive mistake is sizing to today's loads instead of the next ten years. Here is what we run into most often:
- Adding an EV charger to a 100 amp panel without a load calc. The charger works fine until the dryer, oven, and AC all run at once. Then the main trips - or worse, the breaker does not trip when it should.
- Assuming a bigger panel fixes a bad panel. A 200 amp Zinsco is still a Zinsco. Brand and condition matter as much as amperage.
- Skipping the permit to save time. Unpermitted panel work in San Mateo County surfaces at sale, at insurance renewal, and at the next inspection. It always costs more to fix later.
- Reusing the old meter socket. PG&E will fail the reconnect. We replace it every time on a 200 amp job.
- Ignoring the grounding system. Older San Mateo homes often have a single ground rod or a water-pipe ground that no longer meets code. That is part of the upgrade, not an add-on.
When to call a professional
Call us when your main breaker trips more than twice a month, when your lights dim every time the AC kicks on, when you smell hot plastic near the panel, or when you are planning any of the electrification projects above. Those are not DIY problems - a 200 amp service carries enough current to kill you, and the permit and utility coordination are not something a homeowner can pull off alone.
Our team runs the load calculation, pulls the San Mateo permit, coordinates the PG&E disconnect and reconnect, and leaves you with a labeled panel and a passed inspection. We do same-day consultations across the Peninsula, and we will tell you honestly if 100 amps is still the right answer for your house.
Frequently Asked Questions
Should I get a 200 amp or 100 amp panel in San Mateo CA?
Get 200 amps if you plan to add an EV charger, heat pump, induction range, or ADU - those loads exceed a 100 amp service's 80 amp continuous limit. Stay at 100 amps if your home is all-gas and you have no electrification plans. A load calculation confirms it either way.
How do I choose between 200 amp and 100 amp in San Mateo California?
Count your large 240-volt loads and add 20% for future growth. One EV charger plus a heat pump means 200 amps. Gas appliances and no EV usually mean 100 amps is enough. We run the NEC 220.82 calculation on site before recommending either.
Is 100 amp enough for my home in San Mateo CA?
Yes for most homes under 2,000 square feet with gas heat, gas cooking, and no EV - roughly 80 amps of usable capacity covers those loads. It is not enough once you add a 32 to 48 amp EV charger or electric backup heat.
Who can advise on panel size in San Mateo?
A licensed electrical contractor who pulls San Mateo permits regularly and coordinates with PG&E. We do this daily, run the load calculation in writing, and handle the permit, inspection, and utility reconnect as one job.
How long does a 200 amp upgrade take in San Mateo?
One to two days of on-site work, plus 5 to 10 business days for the permit and two to four weeks if PG&E has to upgrade the service drop. We schedule the disconnect window with PG&E before we start.
Get help with Electrical Panel Upgrade in San Mateo
If you are weighing a 100 amp replacement against a full 200 amp service upgrade, we will run the numbers for your specific house and give you a straight answer. Call San Mateo Panel Pros at +1 (650) 372-5030 to book a same-day consultation.