Building a house is the best time to get the electrical system right. Under-sizing service capacity, missing conduit raceways, or poor circuit planning will cost far more to fix later than a slightly larger upfront investment. This guide walks through practical, code-aware decisions to plan electrical capacity for today and future-proof for EVs, solar, batteries, smart home upgrades and changing family needs.
Quick summary: core principles
- Design for flexibility — leave spare capacity and conduit for unknown future loads.
- Plan locations now — it’s much cheaper to rough-in conduit and pulls during construction.
- Coordinate MEP systems — HVAC, plumbing and electrical routing must be planned together.
- Document everything — labeled panels, as-built drawings and load calculations simplify later upgrades.
See related topics on coordination and low-voltage wiring for more detail: HVAC, electrical and plumbing coordination: what to look out for when building a house and Low-voltage systems and home automation: what to look out for when building a house.
Understand your electrical demand (load calculation)
Start with a formal load calculation — a NEC-based estimate of expected and potential future loads. A few tips:
- Include continuous loads (HVAC, well pumps, EV chargers if on 240V constant) and diversity factors per code.
- Add planned renewable systems (solar PV) and storage – account for export limits or battery charging loads.
- Add headroom: design panels with 20–30% spare capacity beyond calculated peak to avoid full loading.
Always ask a licensed electrician or electrical engineer to perform or verify calculations. For resilience planning, review: What to look out for when building a house: backup power, EV charging and energy resilience.
Service size and main distribution: choosing the right amperage
| Main Service (Amps) | Typical home size & uses | Pros | Cons |
|---|---|---|---|
| 100 A | Small homes, limited appliances | Lower cost | May be insufficient for modern loads |
| 150 A | 1–3 bed homes with basic HVAC | Middle ground | Limited margin for EV/solar |
| 200 A | Most modern single-family homes | Good margin for EV, HVAC, kitchen loads | Slightly higher cost |
| 400 A (or >) | Large homes, multiple EVs, heavy workshop loads | Future-proof, supports subpanels and large solar | Higher installation and meter costs |
Recommendation: For new builds, 200 A service is the default modern minimum in many regions. Consider 400 A or service-ready layouts if you expect multiple EVs, large HVAC systems, high-power EV chargers, or a workshop.
Panels, subpanels and circuit planning
- Locate the main panel in a convenient, accessible location. Place subpanels near major load clusters (garage, workshop, ADU).
- Plan for dedicated circuits: HVAC units, electric water heater, oven, dryer, EV charger, and any heavy tools.
- Labeling is essential: keep a master panel directory and as-built schematics.
- Leave space for future breakers — many electricians will install a 200 A 40-space panel even if 20 are used initially.
See guidance on outlet placement and circuits: Circuit placement and outlets planning: what to look out for when building a house.
Conduit, raceways and rough-in best practices (future-proofing)
Rough-in the conduit and raceways now when walls are open:
- Run at least one 2" conduit from the main service to the garage for future EV charger wiring.
- Provide a dedicated 1¼"–1½" conduit or empty 2" reserved for solar array combiner or battery system between the roof/solar location and main panel/garage.
- Install extra empty conduits from the attic to server/AV closet for low-voltage and networking cable runs.
- Use longer-than-necessary pulls and fish tapes or pull strings.
These wiring and network strategies tie into smart home and low-voltage planning: What to look out for when building a house: smart home wiring, networks and infrastructure tips and Low-voltage systems and home automation: what to look out for when building a house.
EV charging, solar PV and battery storage — plan early
- Reserve service capacity: a single 11–22 kW EV charger can add 48–96A draw on a 240V circuit. Plan capacity accordingly.
- If adding solar later, plan conduit and combiner locations and ensure space for an inverter/charger near the main panel.
- Consider an interactive panel layout to accept a future inverter and battery system with minimal rewiring.
- For backup, install or reserve space for an automatic transfer switch and generator interlock.
For more on these topics and energy resilience, see: What to look out for when building a house: backup power, EV charging and energy resilience.
Coordination with HVAC and plumbing
Electrical routes must account for HVAC equipment and major plumbing items:
- Locate outdoor condensers and furnaces so short, dedicated circuits are possible.
- Coordinate locations of tankless water heaters, well pumps and sump pumps with electrical plans to ensure short runs and proper breaker sizing.
- Avoid running large electrical feeders through plumbing chases that will limit future access.
See more on avoiding problems in other trades here: HVAC, electrical and plumbing coordination: what to look out for when building a house and What to look out for when building a house: water supply, sewer connections and pump systems. Also check common plumbing mistakes: Plumbing layout mistakes to avoid: what to look out for when building a house.
Safety, code compliance and inspection points
- Follow NEC and local amendments — permit and inspection phases are non-negotiable.
- Ensure proper grounding, surge protection (whole-house), AFCI and GFCI protections as required.
- Install smoke and CO detectors on required circuits and with battery backup.
- Maintain clearances around panels and service equipment.
Refer to a focused checklist of MEP inspection items: What to look out for when building a house: safety, code and inspection points for MEP.
Practical checklist before drywall
- Obtain a professional load calculation and choose service ampacity.
- Reserve extra breaker spaces and install a larger panel if budget allows.
- Run conduits: garage-to-panel, roof-to-panel (solar), attic-to-closet (network/AV).
- Install subpanel locations where future loads will grow (garage, ADU).
- Pull extra low-voltage pathways for home automation and networking.
- Label all runs and keep an as-built plan in PDF and printed form for homeowners.
- Confirm locations of major appliances and HVAC with the electrician before rough-in.
Final thoughts: invest a little now to avoid expensive retrofits
The cost delta to add a larger service, a second conduit, or extra panel spaces during construction is typically small compared to chasing wiring through finished walls later. Plan with a licensed electrician and coordinate with HVAC and plumbing contractors so mechanical and electrical systems serve you now and are ready for tomorrow.
For next steps on related MEP topics and to expand your planning checklist, see these companion guides:
- Circuit placement and outlets planning: what to look out for when building a house
- Low-voltage systems and home automation: what to look out for when building a house
- Future-proof MEP decisions: what to look out for when building a house to simplify later upgrades
If you’d like, I can produce a customizable load-calculation checklist or a printable conduit-and-panel placement template for your floor plan.