When not to
When heating the pool is not the right answer
Every other page on this site helps you size and price a heater. This page is the honest counterweight: five real situations where the numbers this site produces argue against buying one, or against running the one you have as hard as you were about to.
1. You are chasing shoulder-season weeks in a cold climate
Extending a season costs more per added day than the season you already have, and how much more depends entirely on climate. Widening June-through-August to April-through-October adds 122 days in Boston, MA for $2,821 on a heat pump — $23.12 per added day. The identical extension in Miami, FL adds 122 days for $710 — $5.82 per added day, about a quarter of the Boston figure. Run your own dates on the season length page before assuming a longer season is a small add-on; in a genuinely cold climate it is frequently the most expensive decision on the page.
2. You will not put the cover on
The cover page and the price drivers page both show a cover, used honestly, cutting the bill by roughly five to one on this site's default pool. That saving is conditional on the cover actually going on for most of the hours the pool is not in use. If you already know a heavy manual cover will get used for two weeks and then sit rolled up in the corner, the honest move is to size the heater for the uncovered case from the start rather than buying equipment sized around a habit you do not have.
3. The pool is wide open to wind and nothing is going to change that
Wind exposure is one of the largest free levers this site's model finds — see the price drivers page for the full ranking against cover use, season length and setpoint — spanning roughly a three-to-one range between a sheltered yard and a fully open lakeside or desert lot on its own, and compounding with every other decision that goes the expensive way. If the pool sits genuinely exposed — no fence, no hedge, no adjacent structure, and no plan to add one — that exposure is a standing cost multiplier no heater choice fixes. A bigger or more efficient unit still pays the same wind tax every hour it runs. Fixing the exposure, where that is even possible, is frequently cheaper than any heater upgrade; where it is not possible, it is honest to expect a heating bill toward the top of whatever range this site's calculators show you.
4. You are not sure you will own the pool long enough
The federal rulemaking behind current pool-heater efficiency standards used an average product lifetime in its own analysis, and it is a useful number to borrow for a different question — how long you need to own the equipment for an upfront premium to pay back at all:
For the final rule, DOE updated its methodology to include the latest data including RECS 2020, CBECS 2018, and shipment and other data from 2022 PKdata. This resulted in the same average lifetime value of 11 years.
What it settles here Eleven years is a population average, not a promise about any one unit, but it is the right order of magnitude to weigh against your own plans. If you expect to sell the house in two or three years, a heat pump's higher upfront cost has very little time to recover against a cheaper heater's lower running efficiency, whatever the payback tool says about the long-run case — the payback page's horizon is how long you own it, not how long the equipment lasts.
The same rulemaking is candid about why this decision is unusually hard to learn from directly:
The installation of a new or replacement pool heater is done infrequently, as evidenced by the mean lifetime for pool heaters. Additionally, it would take at least one full pool heating season for any impacts on operating costs to be fully apparent.
What it settles here One purchase a decade, with a full season before the running cost is even visible, means you will very likely make this decision exactly once for this pool. That is an argument for using the tools on this site before buying, not after.
5. A small, occasional-use spa does not need pool-scale equipment
The electric resistance page works through why resistance heating, generally the wrong choice for a full pool run for months, is frequently the right choice for a small spa volume heated intermittently: the total energy involved is small enough that the four-to-one efficiency gap against a heat pump is worth less than the simplicity and lower upfront cost. If what you actually have is a spa or a small plunge pool used a few times a month, sizing and pricing it as if it were a seasonal pool-heating project is very likely to overstate what you need.
The general shape of the answer
Every case above reduces to the same question: does the marginal week, the marginal degree, or the marginal square foot of exposure actually buy something you will use? This site's calculators are built to answer that with your numbers, not a rule of thumb. Run the main calculator before committing to equipment sized for the season you imagine rather than the one your habits and your climate will actually deliver.