Hot Tub Heating Cost Calculator
Estimate monthly electricity costs to keep your hot tub at temperature.
Safety
Hot tubs lose heat 24/7 from cover, sides, and pipework. A well-fitted, well-insulated cover is by far the biggest cost lever — a worn or loose cover can triple operating costs. Heat pumps cut electric resistance heating bills by ~60% but cost $1,500–3,000 to add and are less effective below 45°F ambient.
A 400-gallon hot tub held at 102°F in mild weather costs about $31 a month to heat on a new R-12 cover, around $99 on a worn one, and roughly $176 with no cover at all. Cover condition moves the bill more than climate or heater type do. Enter your tub above for a figure at your own electricity rate.
What It Costs to Keep a Hot Tub Warm
A hot tub is a constant 24/7 heat loss problem — water is held 40–80°F above ambient air, with heat escaping through the cover, the cabinet sides, and the plumbing. The single biggest variable is the cover. A new, properly fitted R-12 cover keeps a 400-gallon tub running on $25–40 per month in a mild climate. The same tub with a five-year-old sagging cover can cost $80–120 per month for identical use, because the heater is running far more hours to fight evaporative loss through the worn foam. This calculator models heat loss as the product of volume, temperature difference, and a calibrated cover-quality factor — the inputs that actually matter.
Typical Monthly Cost by Setup (400 gal, 102°F water)
| Cover | Mild (55°F) | Cold (30°F) | Warm (75°F) |
|---|---|---|---|
| Good (new, R-12+) | ~$31/mo | ~$47/mo | ~$18/mo |
| Fair (3–5 yrs) | ~$55/mo | ~$84/mo | ~$31/mo |
| Poor (worn/loose) | ~$99/mo | ~$151/mo | ~$57/mo |
| No cover (open) | ~$176/mo | ~$269/mo | ~$101/mo |
Where the Heat Actually Leaks
For a typical foam-insulated portable spa with a quality cover, roughly 60–70% of heat loss is upward through the cover (evaporation + conduction), 20–25% through the cabinet sides and bottom, and 10–15% through plumbing penetrations and the equipment bay. That's why cover quality dominates the bill — fix the biggest leak first. A folded thermal blanket placed on the water surface under the rigid cover adds another R-4 and is the single cheapest upgrade ($30–60). Replacing a fully waterlogged cover is the next biggest win — a cover that absorbs water loses most of its R-value because water conducts heat 25× faster than dry foam.