When you're planning a home addition—a new bedroom, home office, or garage—your electrical panel often becomes the hidden bottleneck. If your main panel doesn't have available breaker slots or sufficient amperage capacity, you won't get power to those new spaces without a rewiring project first. Here's what you need to know before calling an electrician.
Why Your Panel Matters for Additions
Your electrical panel is the central hub distributing power throughout your home. Older homes typically have 100-amp service; newer homes often run 150 or 200 amps. A modest home addition like a bedroom might draw 20–40 amps in new circuits. If your panel is already maxed out—or close to it—you'll need either a panel upgrade (bumping service from 100 to 150 or 200 amps) or a sub-panel installation in your addition.
Running out of breaker slots is equally common. A full panel leaves no room to add the 2–3 new circuits your addition requires.
Assess Your Current Capacity
Before paying for a site visit, gather basic information:
- Find your main panel. It's usually in the basement, garage, or utility room. Look at the main breaker—it shows your current amperage (100, 150, or 200 amps).
- Count available slots. Open the panel door (safely) and see how many empty breaker spaces exist. Tandem breakers can double capacity but aren't always code-compliant in all jurisdictions.
- Check your age and condition. Panels older than 25–30 years, or those with visible rust or damage, may need replacement regardless of capacity.
- Review your load. If you're adding high-demand equipment (hot tub, electric vehicle charger, mini-split HVAC), that's amperage you'll lose to the addition.
A qualified electrician can do this assessment in 30–60 minutes for $100–$300.
Panel Upgrade vs. Sub-Panel: Cost Trade-Offs
Panel upgrades replace your entire service entrance, including the meter, main breaker, and panel itself. This is the gold-standard solution if you're adding significant square footage, but it's pricey: $2,000–$5,000+ depending on your location and local utility requirements.
Sub-panels are smaller panels fed from your main panel via a heavy-gauge wire run. They install closer to your addition and cost $1,200–$2,500 installed. The downside: a main panel upgrade is eventually inevitable if you keep adding circuits.
For a modest single-room addition, a sub-panel often makes financial sense. For major expansions or if you already have limited capacity, a full upgrade is the cleaner choice.
Permits, Inspections, and Timeline
Never skip permits. Unpermitted electrical work voids homeowner's insurance claims and creates liability if something fails.
- Permit cost: $50–$300 (varies by municipality).
- Inspection timeline: 1–2 weeks for approval after application.
- Actual work: A sub-panel installation takes 1–2 days. A full service upgrade can stretch 2–5 days, especially if the utility company needs to swap the meter.
- Final inspection: Scheduled after work completes, typically within a week.
Plan 3–4 weeks total from permit application to final approval.
What to Ask Electricians
When comparing providers, don't just ask for price. Request these specifics:
- Do they pull permits and handle all inspections, or is that on you?
- What's the amperage upgrade—100 to 150? 150 to 200?
- Is the cost quoted all-inclusive, or are there add-on fees for conduit, disconnect switches, or meter work?
- Do they handle utility company coordination, or do you contact them directly?
- What's their warranty on the panel installation itself?
If you're weighing multiple providers, Mercoly lets you compare licensed electricians specializing in panel upgrades and rewiring, view their rates, and check reviews all in one place.
Code and Utility Requirements
Your local electrical code dictates what's allowed. Some jurisdictions limit sub-panels to specific amperage or distance from the main panel. Your utility company may charge a fee to upgrade service, and some require their own contractor to handle the meter swap.
Call your utility before finalizing your plan—surprises at that stage can derail timelines and budgets.
Frequently Asked Questions
Q: Can I add a sub-panel without upgrading my main service? Yes, as long as your main panel has capacity and your local code permits it. A sub-panel is fed from a breaker in the main panel, so you're limited by your total amperage, not individual breaker slots.
Q: Will upgrading my panel increase my electric bill? No. A panel upgrade only expands your capacity—what you actually pay depends on how much power you use. Adding circuits doesn't cost more unless your new appliances and HVAC draw significantly more energy.
Q: How do I know if I need a full 200-amp service or 150-amp? 150 amps covers most residential additions. Choose 200 amps if you're adding electric heating, an EV charger, or large AC units, or if your addition exceeds 1,500 square feet.
Start with a professional assessment, compare licensed providers, and get permits in writing before any work begins.