# 100-Amp vs 200-Amp Service: How To Decide | Boise Electrician Experts

> How to tell whether 100-amp service still covers your Boise home. The load calculation, the honest test, and what each costs.

URL: https://boiseelectricianexperts.com/guide/100-vs-200-amp/

100-amp service covers most homes running gas heat, gas water heating and one AC system. You need 200 amps when the NEC Article 220 load calculation exceeds 100 amps — typically at three or more large electric loads.

## The honest test

Count your large electric loads: heat pump or electric furnace, central air,
electric range, electric dryer, electric water heater, EV charger, hot tub,
shop, ADU, well pump.

**Two of those on 100 amps** is usually fine. **Four or more** almost never is.
**Three** is where the calculation has to be done rather than guessed.

Gas appliances change the answer completely. A house with gas heat, a gas range
and a gas water heater has far more headroom than an all-electric house of the
same size — which is why the electrification decision and the panel decision are
really one decision.

## What the calculation does

Under NEC Article 220 a dwelling load calculation totals general lighting load
by square footage, small-appliance and laundry circuits, fixed appliances, the
larger of heating or cooling, then applies demand factors that account for the
fact you never run everything at once. The result is a number in amps, compared
with your service rating.

This is why square footage alone is a bad proxy. A 1,600 square foot Bench ranch
that has gone all-electric does not need the same service as a 1,600 square foot
house still on gas. Any contractor quoting 200 amps without asking what is in
the house is quoting a part number rather than a design.

## The Treasure Valley version of this question

Locally, the decision is usually forced by one of three additions.

**A heat pump conversion.** The load that most often turns an adequate 100-amp
service into an inadequate one, because cold-climate units with electric
resistance backup draw heavily in a real winter.

**An EV charger.** A 48-amp unit is a continuous load sized at 125 percent under
NEC 625.

**A shop or ADU.** Common on the valley's larger lots. A shop with a welder or
compressor is a genuine load needing its own subpanel and feeder, not a circuit
borrowed from the house.

If two or three of those are in your plans, do the calculation once against the
finished picture. Upgrading twice is the expensive path.

## When 100 amps is genuinely fine

- Gas heat, gas water heater, gas range
- One AC system
- No EV, no hot tub, no shop
- Panel in sound condition with open slots

If that is you and the panel is not a Federal Pacific or Zinsco, leave it alone.
A service upgrade you do not need is $1,500 to $4,000 of nothing.

## The middle options people skip

**A subpanel.** Solves "no open slots" when the service has capacity.
Frequently the right answer.

**A single dedicated circuit.** If one appliance is tripping one circuit.

**Load management.** For EV charging, devices that shed or throttle the charger
during household peaks can avoid an upgrade entirely.

**Panel replacement without a service change.** If the issue is an obsolete
panel rather than capacity.

## What each costs in Boise

| Job | Range |
| --- | --- |
| 100A to 200A service upgrade | $1,500 - $4,000 |
| Licensed electrician, hourly | $80 - $140 |
| Trip charge | $50 - $100 |
| DOPL permit | Scaled to declared job value |

## What about 400 amps?

Rare in residential and usually the wrong answer — but it comes up in Eagle and
on larger custom builds with multiple HVAC zones, a shop, a pool and two EVs. It
is a materially bigger job involving different service equipment. If someone
proposes it for an ordinary house, ask to see the load calculation.

## Bottom line

Do not buy amperage by intuition. Count your large electric loads, and if the
answer is three or more — or if a heat pump or EV is in your plans — have the
NEC 220 calculation done before you take bids. Call 208-856-4826.

## FAQ

### Will 200-amp service lower my bill?
No. A panel distributes power, it does not consume or save it. What an upgrade buys is capacity, modern overcurrent protection, current GFCI and AFCI coverage, and a system your insurer will write.

### How do I find out what service I have?
Open the panel door and read the rating on the main breaker: it will say 100, 125, 150 or 200. If there is no main breaker and you see screw-in fuses, you likely have 60 amps, and that is a replacement conversation regardless of load.

### Can I upgrade later when I actually need it?
Yes, and often you should. The exception is when you are already opening the service for another reason — doing the meter base, grounding and panel in one visit is meaningfully cheaper than doing them twice.