Size circuits for heaters, pumps, and lights. Compare copper or aluminum, distance, and derating effects. Export results as files and share with installers easily.
Sample inputs and typical outputs for a common setup.
| Item | Example input | Example output |
|---|---|---|
| Voltage | 240 V | Lower current than 120 V |
| Heater | 5.5 kW | 5,500 W |
| Pump | 1,500 W | Included in total watts |
| Blower | 700 W | Included in total watts |
| Diversity | 1.00 | No reduction applied |
| Distance | 50 ft | Voltage drop computed |
| Typical result | — | ~32 A running, ~40 A sized |
Safety note: verify bonding, GFCI protection, and disconnect requirements with a qualified electrician and local authority.
Accurate inputs start with the equipment nameplates. Enter heater kilowatts and motor data as installed, not brochure peaks. If you only know pump horsepower, convert using realistic efficiency so current is not underestimated. Include blowers, lighting, ozone or UV, and any added accessories. Use the diversity factor when controls prevent full simultaneous operation, then review the resulting connected wattage for plausibility.
For planning, size overcurrent protection from the calculated sizing current. Many hot tubs require dedicated protection and ground‑fault protection appropriate to wet locations. Choose the next standard breaker rating above the sizing amps, and confirm the disconnecting means location and working clearance. A slightly larger breaker does not fix undersized conductors, so evaluate breaker and wire together rather than separately.
Conductor ampacity depends on material, insulation temperature rating, ambient heat, and the number of current‑carrying conductors sharing a raceway. This calculator applies simple derating multipliers to reflect those effects and then selects the smallest wire meeting the derated amp requirement. Use copper or aluminum consistently with your terminals and lugs. Treat the suggested gauge as a starting point for a qualified review.
Long runs can cause voltage drop that reduces heater output and increases motor heating. The calculator estimates drop from conductor resistance, current, and one‑way distance with a round‑trip assumption. Keep drop near common planning limits by shortening the run, upsizing wire, or moving the panel or disconnect. If the drop exceeds your limit, prioritize wire upsizing before increasing breaker size.
Operating cost depends more on runtime than nameplate power. The energy section multiplies each load by your estimated daily hours to produce kWh per day and a monthly approximation. Heater hours vary with outdoor temperature, cover quality, wind exposure, and setpoint. Use seasonal runtimes for better budgeting. Re‑run scenarios after insulation upgrades or circulation scheduling changes. To compare options, adjust heater hours, then export results for discussion with an electrician. Small changes in voltage drop and wire material can noticeably shift both installation cost and performance overall.
Use the nameplate values on the installed equipment. If you only have horsepower, convert using the efficiency field. Avoid brochure “peak” values that can overstate normal running current.
Some loads run for long periods, so planning often uses a multiplier to size conductors and protection. Adjust the factor to match your local practice and the expected duty cycle.
It derates the base ampacity using ambient temperature and current‑carrying conductor count. Then it picks the smallest gauge that meets the derated amp requirement for your sizing current.
It estimates round‑trip drop along the conductors at your sizing current and distance. If the percent is high, heater output can fall and motors can run hotter, especially on long runs.
Aluminum can be used where allowed, but terminations must be rated for it and installed correctly. Always use listed lugs, proper anti‑oxidant practices when required, and torque to specification.
It is a planning estimate based on your entered runtime. In colder weather, heater hours usually increase. Run separate scenarios for summer and winter to budget more realistically.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.