Service capacity
Panel headroom
Check whether a Level 2 charger, heat pump, or other new load appears to fit a 100, 150, or 200 amp service — using measured utility demand or a simplified optional-method estimate.
Open the calculatorIndependent calculators for U.S. homeowners
Will your panel take the charger, the heat pump, or the generator — and what will it cost to run?
Panel Headroom is a tool site, not a utility and not a contractor. Use the calculators to walk through headroom and operating cost with published methods and dated public data, then take the result to a licensed electrician or HVAC contractor.
Three calculators
Backup power
Generator size
Add running watts for the loads that may run at once, then add only the largest starting increment. Default wattages come from Honda’s published estimation table.
Open the calculatorOperating cost
Heat pump vs gas furnace
Compare dollars per million Btu of delivered heat using AFUE, HSPF2, and EIA 2025 state-average electricity and gas prices — or type the rates on your bill.
Open the calculatorGuides, then specific questions
The overviews explain the decision. The question pages answer the way homeowners actually ask — 100-amp vs 200-amp, charger plus dryer, interlock vs transfer switch, heat-pump cost in a high-rate state.
Panel, EV charging, and service upgrades
Headroom, 40- vs 50-amp circuits, load management, and what a 200-amp upgrade actually includes.
Backup power and transfer equipment
Interlock kits, manual and automatic transfer switches, inlet size, and essential-load generator sizing.
Heat pumps and operating cost
HSPF2 vs AFUE, cold-climate COP at 5°F, mini-split vs window unit, and state-average running cost.
Start with a specific question
- Can a 100-amp panel support a Level 2 EV charger?
- Can I add an EV charger and a heat pump to a 100-amp panel?
- Does my panel support an EV charger and a dryer at the same time?
- 40 amp vs 50 amp EV charger: which circuit do I need?
- Interlock kit vs transfer switch
- What size generator for a fridge, furnace, and lights?
- Heat pump vs gas furnace: which costs less to run?
- How much does a 200-amp panel upgrade cost?
See all first-edition questions (53 published, with a larger inventory behind them).
This is not a permit calculation, a utility approval, or a substitute for a licensed electrician, HVAC contractor, or the authority having jurisdiction. Panel Headroom is an independent educational site. It is not a utility, a certification body, or a contractor. Electrical and generator work that is done incorrectly can cause fire, shock, or carbon monoxide poisoning. Use the adopted electrical code and manufacturer instructions; pull permits where required.