Reference setup
The national index models a covered, insulated 100-gallon outdoor plunge maintained at 50°F. It assumes 0.84 kWh/day of baseline circulation/filtration power, an effective thermal conductance of 11 BTU/hour/°F, and a chiller coefficient of performance of 2.2. Those assumptions are deliberately held constant for every city.
Climate data
The automated updater requests the National Centers for Environmental Information's 1991–2020 U.S. Monthly Climate Normals for stations near each indexed city. It also attempts to obtain a recent 30-day temperature average from NOAA/NCEI Daily Summaries. If NOAA data cannot be fetched during a refresh, the last successful NOAA value is retained; the bundled first-run dataset contains approximate seed values.
NOAA/NCEI Monthly Normals · NOAA/NCEI Daily Summaries
Electricity prices
The updater uses the U.S. Energy Information Administration API route for electricity sales to ultimate customers by state and sector, selecting the residential sector and latest available monthly average retail price. EIA publishes this series in cents per kilowatt-hour. A free EIA API key is recommended for automatic refreshes.
EIA Retail Electricity Sales & Prices
Energy calculation
For each month, ArcticSoak calculates an approximate temperature-holding load from the positive difference between monthly average ambient temperature and the 50°F target. That load is divided by the assumed chiller COP and added to baseline circulation consumption. Monthly energy is multiplied by the state's electricity rate.
ArcticSoak Score
The score is a 0–100 comparative index. Seventy-five percent reflects climate cooling burden and twenty-five percent reflects estimated annual electricity cost. It is intentionally relative: a score of 85 means the reference setup is easier/cheaper to cool than a city scoring 30 under the same assumptions.
Important limitations
- Ambient air temperature is not identical to equilibrium tub-water temperature.
- Solar exposure, wind, humidity, plumbing length, tub color, insulation and cover quality matter.
- Chiller efficiency changes with load and ambient conditions.
- Very cold climates may require freeze protection or winterization; ArcticSoak models cooling demand, not winter heating.
- Electricity prices are state averages, not your utility tariff.
- These are not medical recommendations.
Reuse and attribution
The downloadable ArcticSoak CSV may be cited in articles, research and reporting with attribution and a link to ArcticSoak.com. Please describe outputs as estimates from the ArcticSoak reference model rather than measured appliance energy consumption.