Methodology

How we calculate heating savings

Zavepower sites state that smart heating cuts spa heating costs by up to 80 percent with the Planner on the most volatile spot days, and typically 40 to 60 percent on a spot plan. This page is the single, dated source for what those numbers mean, how they are derived, and what they depend on.

Published 2026-07-16. Reviewed when electricity market conditions or the product's heating logic change materially.

The claim, precisely stated

The savings figures refer to the heating component of a hot tub's running cost, not the total cost of ownership. Heating is the largest and the only easily movable running cost; circulation and water care are smaller and roughly constant.

"Up to 80 percent" is the upper bound, reached with the Planner active on the most volatile spot days. "Typically 40 to 60 percent" is the range we consider realistic on a spot-price plan across a season. Both figures follow from the derivation below, applied to the day-ahead price spreads observable in the public market data cited under Premise 1, they are not measurements, and this page states exactly which assumptions they rest on.

Premise 1: intra-day electricity price spread

On European day-ahead electricity markets, the price of a kilowatt hour varies through the day, and the spread between the cheapest and the most expensive hours of the same day is frequently severalfold. During volatile periods the same kilowatt hour can cost five to ten times more at the evening peak than in the cheapest overnight or midday hours.

This is publicly verifiable in the day-ahead price data published by the ENTSO-E Transparency Platform and by Nord Pool, for any bidding zone and any day.

Premise 2: a hot tub can time-shift its heating

Water stores heat. A hot tub does not need to buy its energy at the moment the bather wants warmth; it needs the water at temperature at bath time. Its thermal mass lets the heating run hours earlier, in the cheap windows, and coast through the expensive ones. That is what Spapilot automates: it never changes how warm the water is for a planned bath, only when the energy for it is bought.

The derivation

The saving on the heating component equals the difference between the average price paid per kilowatt hour with and without scheduling:

saving = 1 − (avg price paid with smart scheduling ÷ avg price paid heating on demand)

A tub that reheats blindly around the clock buys energy at roughly the daily average price, weighted toward whenever heat loss happens to trigger the heater. A tub that concentrates its heating into the cheapest quartile of hours buys close to the daily minimum. When the cheapest hours cost a fifth of the daily average, as they do on volatile days, the heating saving approaches 80 percent. On calmer days with a smaller spread, the same mechanism yields proportionally less, which is why the typical season-long figure on a spot plan is 40 to 60 percent rather than the ceiling.

A secondary saving, independent of price spread, comes from avoiding unnecessary standby reheating: not holding full bath temperature during periods when no bath is planned.

What the saving depends on

1.Your electricity plan. Spot-price and time-of-use plans (including Economy 7 type tariffs) see the full effect. On a flat tariff the price-shifting saving disappears and only the standby saving remains.
2.Market volatility. The wider the daily price spread in your bidding zone, the larger the saving. Spread varies by country and season.
3.Insulation and climate. These set how much heating energy is needed overall. They scale the absolute saving in money, not the percentage on the heating component.
4.Usage pattern. Frequent, unpredictable bathing narrows the scheduling window; planned bathing widens it.

What we do not claim

We do not claim 80 percent off your total electricity bill, only off the spa's heating component.
We do not publish fleet-measured averages yet. When we do, the measurement method will be versioned on this page.
We do not claim savings on flat tariffs beyond reduced standby heating.

Questions about the methodology? Contact us. For what this means in practice, see hot tub running costs and the energy cost guide.