100 or 200 Amp Electrical Service?
100 or 200 Amp Electrical Service? The Ontario “Future-Proof” Answer (Without Overpaying)
If you’re building, renovating, or adding loads (EV charger, heat pump, basement suite, workshop), the 100 vs 200 amp question shows up fast. And the internet usually answers it like this: “Always go 200.” That’s not advice. That’s a bumper sticker. In Ontario, the right answer depends on your actual electrical load, your future plans, and what the Electrical Safety Authority (ESA) will accept for service sizing.
Agree: You don’t want nuisance trips, “we can’t add that circuit” problems, or a surprise service upgrade after drywall is up.
Promise: This guide will help you decide 100 amp vs 200 amp with a practical Ontario approach—loads, demand, EV charging, heat pumps, and real-world planning.
Preview: We’ll cover who needs what, the “math behind the myths,” common Ontario scenarios, cost drivers, and a 10-question FAQ you can use when talking to an electrician.
E-E-A-T line (paste your credentials): [Insert your experience/credentials here — e.g., “Licensed Ontario builder with 45 years of construction experience, coordinating mechanical/electrical design on high-performance homes.”]
Who Should Read This (and What We’re Actually Solving)
This article is for Ontario homeowners who are:
- Building new (custom, infill, rural, or subdivision)
- Renovating and adding major electrical loads (EV charger, heat pump, hot tub, induction range, suite)
- Finishing a basement or adding a secondary unit
- Upgrading from an older 60A or fused service (the “please don’t touch that” era)
The goal is simple: pick a service size that meets today’s needs and doesn’t box you in tomorrow.
100 Amp vs 200 Amp: The Difference in Plain English
Think of your electrical service like the “main highway” into your house. A 100 amp service can deliver less total power than a 200 amp service. That does not mean you can only run half as many things. It means your maximum safe simultaneous demand is lower.
The quick math (helpful, but not the whole story)
- 100A at 240V is roughly 24 kW of theoretical maximum capacity (amps × volts).
- 200A at 240V is roughly 48 kW of theoretical maximum capacity.
Ontario sizing decisions are typically based on accepted load calculation approaches and inspection requirements. If you’re touching the service, you’ll be dealing with ESA permitting/inspection requirements through your electrician and utility coordination.
Why 100 Amp Still Works in Some Ontario Homes
A 100 amp service can be perfectly acceptable when the “big loads” are not electric and your lifestyle loads are modest. Classic examples:
100A can be enough if you have:
- Gas heating and gas water heater (or other non-electric primary heating)
- Gas range or modest cooking loads
- No EV charger (or you plan to use a lower-power charging approach with load management)
- No hot tub, no large shop, no electric sauna, no electric tankless water heater
- A smaller footprint and a realistic plan to keep it that way
In short: 100A works best when your home isn’t trying to be an all-electric power station.
Why 200 Amp Is Becoming the “Ontario Default”
The modern load stack is different than it was 15–25 years ago. Even if your home is efficient, homeowners keep adding electrical demand: EV charging, heat pumps, induction cooking, home offices, server racks, workshops, finished basements, and secondary suites.
200A is strongly recommended if you want any of these:
- EV charger (especially a typical 32–48A charger)
- Air-source heat pump or electrified heating strategy
- Basement suite / second unit (more appliances, more cooking, more loads)
- Hot tub / pool equipment
- Woodworking shop or heavy tools
- Future-proof flexibility (the “we don’t know yet, but probably” category)
The Ontario “Load Calculation” Reality (Where the Right Answer Comes From)
The right way to decide between 100A and 200A is a load calculation. Not because homeowners love spreadsheets—but because electricians and inspectors need a defensible basis for service sizing.
Here’s what confuses people
Your panel can have lots of breakers. That does not mean you can run everything at full tilt at the same time. Load calculations use “demand factors” because most loads don’t run simultaneously at full power. That’s why a home can have a long list of circuits and still operate safely on a given service size.
Use a calculator to get out of the guesswork
Start with a quick reality-check here: Electrical Load & Wire Size Calculator. It helps you think in terms of loads and future plans—exactly what matters for 100 vs 200.
Common Ontario Scenarios: Pick the Service Size That Fits
These aren’t “code answers.” They’re practical planning buckets that match how Ontario homes are actually used.
Scenario A: Smaller home, gas heating, no EV
- Typical load: modest
- Best fit: 100A can work if you’re confident you won’t electrify major loads soon
Scenario B: You want an EV charger (now or soon)
- Typical added load: significant
- Best fit: 200A (unless you’re using a managed charging strategy and a calculation shows adequate capacity)
Scenario C: Heat pump (especially with electric backup) + EV
- Typical added load: high, and it can hit at the worst times (cold snaps + charging)
- Best fit: 200A (and in larger homes, you may need a deeper design conversation)
Scenario D: Basement suite / second kitchen / rental unit
- Typical added load: high and lifestyle-driven
- Best fit: 200A (or at least plan for it)
Scenario E: Rural build + well pump + workshop + future additions
- Typical added load: variable but often grows over time
- Best fit: 200A to keep options open and avoid “we can’t” moments later
EV Chargers: The #1 Reason Ontario Homes Outgrow 100 Amp
EV charging can be a big, steady load for hours. A typical Level 2 charger often needs a dedicated circuit, and adding it to a 100A home can push the service toward its limits, depending on the rest of your loads.
Ontario has specific guidance documents used by electricians when calculating service impact for EVSE (EV charging equipment). If you want to see the official direction electricians reference, review ESA’s bulletin on EV charging systems: ESA Bulletin 86-01 (EV charging systems).
Heat Pumps and Electrification: Why “Efficient” Can Still Need Capacity
High-efficiency homes often reduce total energy use, but electrification shifts demand onto electricity. In Ontario, the loads that matter for service sizing are the ones that can run simultaneously during peak conditions: cold weather heating support, cooking, laundry, and EV charging.
If you’re weighing heating system strategies in a high-performance build, these pages help you map the “comfort + electrical” relationship: Geothermal vs air-source heat pump (Ontario) and ICFPro: Is ICF worth it?.
Cost and Timing: What a Service Upgrade Really Involves in Ontario
A service upgrade isn’t just swapping a panel. Depending on your home and utility setup, it can include:
- New meter base / mast (overhead) or new service conductors (underground)
- Panel replacement and breaker rework
- Bonding/grounding upgrades
- Coordination with the utility (disconnect/reconnect)
- ESA permit and inspection
Utilities and ESA coordination matters. For a clear, Ontario-typical utility note on the process, see Hydro One’s service upgrade overview: Hydro One: Service Upgrade.
Permit timing matters too. If you’re in design/planning, don’t ignore the broader permit path: How to get a building permit in Ontario.
The Builder’s Decision Framework (Fast, Practical, and Usually Right)
If you want the “builder version” of the decision—here it is:
If you’re building high-performance and want a broader education hub (ICF, comfort, mechanical planning), browse: ICFPro.ca.
What to Ask Your Electrician (So You Get Real Answers)
When you ask “Do I need 200 amps?” the best electricians don’t answer with a guess. They ask questions. Here are the questions you should ask them:
- What load calculation method are you using, and can I see the assumptions?
- Are you including EV charging now—or planning for it later?
- Are you assuming gas or electric cooking, drying, and water heating?
- Are you planning for a heat pump (and what backup heat assumptions)?
- Do you expect any limitations from the utility infrastructure in this area?
- What’s included in your upgrade scope (mast, meter base, grounding, permit, utility coordination)?
If you also want the “code and compliance” context around the building process, here’s your Ontario overview: Ontario Building Code overview (2026 guide).
People Also Ask: 100 or 200 Amp Electrical Service (Ontario FAQ)
Click a question to expand the answer. (10 common questions.)
1) Is 100 amp service enough for a house in Ontario?
It can be—especially in smaller homes with gas heating and no large future electrical plans. The issue is that “enough” changes quickly when you add an EV charger, a heat pump, a hot tub, or a basement suite. The correct way to decide is a load calculation that reflects your appliances and your future plans, not just the current state of the home.
2) When should I upgrade from 100 amps to 200 amps?
Upgrade is commonly triggered by adding high, steady loads like EV charging or electrified heating/cooling strategies, or by renovations that add a secondary unit, workshop equipment, or major new circuits. If you’re already close to capacity and you want to avoid future limitations, upgrading during a renovation is often smarter than waiting until you’re forced into it later.
3) Can I install an EV charger on 100 amp service?
Sometimes, yes—but it depends on your other loads and the results of a proper calculation. Some homes can support lower-power charging or managed charging strategies, while others will require a service upgrade to stay compliant and avoid overloading. The safest approach is to have a qualified electrician run the calculation and confirm what ESA will accept for the final configuration.
4) Does a 200 amp panel mean I can run everything at once?
Not “everything,” but it gives you much more headroom for simultaneous use. The bigger point is flexibility: 200A makes it far easier to add new circuits without playing a constant “what can we turn off?” game. It also reduces the chance that future electrification upgrades force a second round of construction later.
5) What’s the difference between a panel upgrade and a service upgrade?
A panel upgrade is replacing the distribution panel (breaker panel) inside the home. A service upgrade usually means increasing the capacity of the supply coming into the home (meter base, service conductors, possibly mast/underground conductors) and coordinating with the utility and ESA inspection. Many 100A-to-200A jobs are service upgrades, not just panel swaps.
6) Does a heat pump require 200 amp service in Ontario?
Not always. Some heat pump systems and well-designed homes can work on 100A, but the risk rises when you add electric backup heat, additional loads, or EV charging. The deciding factor is the total calculated demand and how loads coincide during peak conditions. If you’re planning electrification, 200A is often the safer “future-proof” choice.
7) Will upgrading to 200 amps increase my hydro bill?
The service size itself doesn’t make you use more electricity—your appliances and habits do. A bigger service is like a bigger driveway: it allows more vehicles, but it doesn’t force you to buy them. That said, many people upgrade because they’re adding loads (EV, heat pump, suite), and those loads can increase consumption depending on how they’re used.
8) Do I need a permit to upgrade electrical service in Ontario?
Yes—service changes and most significant electrical work require proper permitting/inspection through ESA processes handled by a licensed electrical contractor. Your electrician typically pulls the permit and coordinates inspection and utility reconnection. Plan this early in a renovation or new build so it doesn’t become a schedule bottleneck.
9) What are signs my 100 amp service is already maxed out?
Common signs include frequently tripped breakers when multiple loads run, no physical panel space for additional breakers, “we can’t add that circuit” feedback from electricians, and renovations that keep pushing you into subpanels or workarounds. The most reliable sign is a load calculation showing limited remaining capacity for future additions.
10) If I’m building new in Ontario, should I just choose 200 amps?
In many cases, yes—especially if you want EV charging, heat pumps, a suite, or any meaningful future flexibility. New construction is the easiest time to make the decision, and upgrading later can be more disruptive. If your design is clearly modest and gas-heavy with no electrification plans, 100A can still be reasonable—but be honest about future upgrades.
Final Word
The “best” service size isn’t a one-size-fits-all number. It’s the service that supports your life today and your upgrades tomorrow without forcing expensive do-overs. If you’re adding EV charging or electrified heating, 200 amps is often the practical Ontario answer. If your loads are modest and you’re staying that way, 100 amps can still work—just confirm it with a proper load calculation and a real plan.
Hey, great article on the differences between 100 and 200 Amp.
Lilly Jones | http://www.copperheadelectric.ca/
Service load calculations 3va per sq ft according to nec sq ft/240v
Adding appliances @ 1500va each stoves 8 or12 kw and dryer at 5000va
Water heater 4500va total the load
Sizes the service for a single family dwelling
Really great info 100 or 200 amp service. Thanks!
How much does it cost in Ontario to go from 100 to say 125 Circuit
Anywhere from $500 to $1000 depending on service.
Will there be a difference in monthly Hydro One charges?
Families today tend to need much more electrical power than previous generations. As technology grows, so does the load on domestic electrical systems, which results in the need for an electrical panel upgrade in many older properties.
I recently came across your article on 100-amp or 200-amp service and wanted to share my appreciation for the valuable information you provided.
Your article does an excellent job of explaining the differences between a 100-amp and a 200-amp electrical service and the factors to consider when choosing the appropriate service for a residential property. The detailed breakdown of the electrical requirements and load calculations helps readers understand the capacity and capabilities of each service.
I particularly appreciate how you highlighted the importance of assessing the electrical needs of a home and considering future expansions or upgrades. The information you provided on the benefits of a 200-amp service, such as increased capacity and flexibility, is valuable for homeowners who may be contemplating electrical system upgrades.
Additionally, your article discusses the role of a qualified electrician in assessing and determining the appropriate service size based on the specific requirements of a property. This emphasis on professional expertise underscores the importance of consulting with a licensed electrician to ensure the electrical system meets safety and functionality standards.
The inclusion of common appliances and their electrical demands as examples helps readers visualize the electrical load and better understand the implications of choosing a 100-amp or 200-amp service.
Overall, your article provides a comprehensive overview of the factors involved in deciding between a 100-amp or 200-amp service, enabling homeowners to make informed decisions about their electrical needs.