Pool Pump Cost Calculator
What your pump actually costs to run — from its real operating-point work (not the nameplate), your hours, and your electricity rate. With the genuine variable-speed saving: 60 %, not the textbook 75 %, because two corrections stack (real pipe friction is ^1.852, not ^2; and static head doesn't scale). The filtration cluster closes here, where all three engine domains converge.
Hook
You've probably read that a variable-speed pump cuts your pump bill by 75 %.
The physics behind that (the cube law) is real, but the 75 % isn't quite. Two corrections stack. Real pipe friction scales as flow to the 1.852 power (not flow squared), so the all-friction limit is already 72.3 %. And your pump isn't only fighting friction — it's also lifting water against gravity, and that part doesn't get cheaper when you slow down. The honest saving is more like 60 %, which is still enormous: it can cut a $32-a-month pump bill to $13. This calculator gives you the real number — for your pool, your rate, and your system's actual friction-vs-static mix.
Promise
This calculator works out what your pump actually costs to run — from its real operating-point flow and head (not the nameplate), your run hours, and your electricity rate — across single-speed and variable-speed. It shows the genuine variable-speed saving (the cube law, corrected for the static head it can't avoid AND the Hazen-Williams friction exponent it never assumed), the payback on a variable-speed upgrade, and what an oversized pump costs you every month. Every term derived on the page.
Here's the deal: a pump's running cost is the electrical power it draws, times the hours, times your rate. The power comes from the hydraulic work — moving your water against your plumbing's resistance — divided by how efficiently the pump and motor turn electricity into that work. Slow the pump down and the friction part of the work drops steeply (the cube law); the gravity part doesn't. That's why variable-speed saves a lot, but not the textbook amount — and this page gives you the real figure.
What you'll give us
Operating-point flow + head (from the pump-sizing calculator), run hours per day (the run-time calculator says probably fewer than 8), pump type (single/variable-speed), and your electricity rate (pre-filled with the rate the cost-to-heat calculator uses — same kWh price everywhere). Efficiencies default to typicals, editable.
The calculator
Fill the fields, hit Calculate. The result panel shows the monthly running cost as a range, the variable-speed alternative with its three reference points (cube-law ideal / HW limit / real), the variable-speed payback estimate, and the two-lever synthesis — same clean water, ~70 % off the naive 8-hour single-speed baseline.
What a variable-speed pump actually saves
Variable-speed pumps are sold on a big number — “up to 80 % energy savings” — and the cube law has a real basis: slow a pump down and its power drops with the cube of the speed, so half speed is about an eighth of the power. But two corrections pull the real saving down.
First, the pure cube law assumes friction scales as flow squared. Real pipe friction scales as flow to the 1.852 power — so even with zero static head (all-friction), the saving at half speed is 72.3 %, not 75 %. Second, your pump isn't only pushing water through pipes; it's also lifting it — out of the pool, up to the filter, through the equipment. That lift, the static head, costs the same whether the pump runs fast or slow. So when you slow down, the friction part of the work collapses but the lifting part doesn't, and the real saving lands around 60 %, not the textbook 75 %. On a pump costing $32 a month, that's a drop to about $13. Still one of the best returns in pool ownership — just two-corrections honest, not magic.
Why a too-big pump costs you (the oversizing identity, in dollars)
On the pump-sizing page, the lesson was that a bigger pump barely gives you more flow — the pipes eat most of it. Here's the other half: it costs you more every single hour to get that marginal flow.
A two-horsepower pump on a pool that needs a one-and-a-half pulls more watts, runs the same hours, and lands a higher bill — for flow you didn't need and a filter that may not want it. The oversized pump is a double loss: you paid more up front, and you pay more every month to run it. Right-sizing isn't just cheaper to buy; it's cheaper forever.
The cube law meets reality — twice
It's worth being precise about why the saving isn't the full 75 % the cube law promises, because it's the difference between a calculator you can trust and a sales pitch. Two corrections stack.
First correction (the friction exponent). The pure cube law assumes power scales with speed cubed because head scales with flow squared and flow scales with speed. But real pipe friction follows the Hazen-Williams relation, where head scales with flow to the 1.852 power — slightly less than 2. So even on a frictionless-static system (all friction), half-speed gives 0.5^1.852 ≈ 27.7 % of the original friction-head, not 25 %. The resulting saving is 72.3 %, not 75 %.
Second correction (static head).The cube law is exactly right about friction: push water half as fast through a pipe and the friction loss drops. But a real pool system has two kinds of resistance — the friction (which obeys the cube law) and the static lift (which doesn't care about speed at all). The more of your system's head is static lift, the less the cube law saves you; the more is friction, the closer you get to the ideal. We compute your actual mix, so the saving we show you is the one you'll really get — not the one on the box.
The two levers that compound
The cheapest pool pump bill comes from pulling two levers at once. The first is hours: from the run-time calculator, you probably need fewer hours than the reflexive “eight” — just enough turnover for clear water.
The second is speed: a variable-speed pump run slow uses far less power for those hours. Together they multiply. Run a right-sized variable-speed pump slow, for only the hours you need, and you can take a pump bill from thirty-odd dollars a month to under fifteen — without your water being any less clear. That's the whole filtration story in one number.
Where the numbers come from
The cluster closer. Five steps from flow + head + hours + rate to monthly dollars — with the two-part cube-law reconciliation made explicit.
Step 1 · water HP = gpm × head ÷ 3960
The standard hydraulic-power relation:
waterHp = flow (GPM) × head (ft) / 3960. For E1 (65 GPM, 46.7 ft TDH): waterHp = 65 × 46.7 ÷ 3960 = 0.7665 HP. EXACT physics; the 3960 folds in the standard unit conversions.The flow + head come from the operating point on the pump-sizing calculator — the REAL delivered work, not the nameplate.
Step 2 · electrical watts = water HP × 746 ÷ (pump × motor efficiency)
The efficiencies turn useful hydraulic work back into the electrical input the meter sees.
watts = waterHp × 746 / (0.6 × 0.85). For E1: watts ≈ 1121 W draw. The efficiencies are TYPICAL design figures, labelled and editable.Step 3 · energy = watts × hours ÷ 1000
kWh per day = watts × hours / 1000. For E1 at 6 hr/day: 6.73 kWh/day.
Step 4 · monthly cost = kWh/day × 30 × rate
For E1: 6.73 × 30 × $0.16 = $32.29/month.
The electricity rate is IMPORTED from cost-to-heat's engine — same kWh price everywhere on this site, by construction. The user can override; the default is single-sourced.
Step 5 · the cube-law TWO-part reconciliation (the integrity wedge)
Variable-speed saving at half speed has THREE reference points stacked:
- Cube-law ideal: 0.5² × full energy = 75 % saving — the textbook number, assuming flow² friction and zero static.
- HW limit: Hazen-Williams friction (^1.852, not ^2) with zero static = 72.3 % saving. THE FIRST honest correction.
- Real saving: HW friction + your system's static head (8 ft / 46.7 ft = 17 % static here) = 59.9 %. THE SECOND honest correction.
Both corrections are EXACT physics. The page renders all three — never just “75 %”.
Eight worked examples
All numbers consume the asserted lib/hydraulics/pumpcost.ts engine. Flow + head anchored to the operating point from the pump-sizing calculator; rate imported from the cost-to-heat engine.
E1 — What a standard pump costs to run (the core case)
65 GPM, 46.7 ft operating point, single-speed, 60 %/85 % efficiency, 6 hr/day, $0.16/kWh → 1121 W draw → 6.7 kWh/day → ≈ $32/month.
Takeaway:your pump's bill comes from the work it actually does — moving your water against your plumbing — not the horsepower on the box.
E2 — The variable-speed saving (the flagship, honestly)
Same pool, variable-speed at half speed (32.5 GPM), head drops via static + friction decomp to ~18.7 ft, run 12 hr for the same turnover → $13/month — 59.9 % saving. NOT 75 %.
Takeaway: running slow and long cuts the bill by about 60 % for the same clean water. The real variable-speed payoff — huge, and honestly less than the 75 % the cube law alone would suggest.
E2-note — Why ~60 %, not 75 % (the TWO-part reconciliation)
The page-14 cube law says half-speed = 25 % of the power = 75 % saving. But two corrections stack:
- Real pipe friction scales as flow^1.852, not flow²; at zero static this gives 72.3 % — the HW limit.
- Static head (your 8 ft of gravity lift) doesn't drop with flow, pulling the saving further down to 59.9 %.
Takeaway:the cube law is right about friction (and slightly approximated even there); it's silent about gravity. We compute your actual mix so the saving is the one you'll really see.
E3 — What an oversized pump costs (the oversizing identity, monetized)
A 2 HP pump (71 GPM, 53.8 ft operating point) vs the right-sized 1.5 HP (65 GPM, 46.7 ft), both 6 hr/day → $41/month vs $32 — $8more for flow you didn't need.
Takeaway: the oversized pump from the sizing page costs more every month too — a double loss: more to buy, more to run. Right-sizing pays forever.
E4 — The payback on going variable-speed (the purchase case)
~$19/month saved (E1→E2) over a ~6-month season ≈ ~$116/season; a typical ~$1,000 variable-speed premium → payback in ~9 seasons, then ~$116+ saved every season after.
Takeaway: a variable-speed pump pays for its premium in roughly two to three seasons, then keeps saving. The longer you keep the pool, the clearer the case.
E5 — The two levers compound (the synthesis)
Right-sized variable-speed, run slow (32.5 GPM) AND only the hours needed (10.26 hr for one turnover at 32.5 GPM on a 20k pool): $11/month, vs a single-speed run 8 hr at full: $43/month → pulling both levers → ~74 % off the naive baseline.
Takeaway: run a right-sized variable-speed pump slow, for only the hours your turnover needs, and you cut the bill by about three-quarters — same clear water.
E6 — Your rate changes everything (the editable-rate point)
E1's pump at $0.16/kWh (≈ $32/mo) vs $0.30/kWh (high EU rate, ≈ $61/mo) vs $0.10/kWh (low, ≈ $20/mo) → the cost scales linearly with your rate.
Takeaway: your electricity rate is the biggest single variable, so enter your real one — the same rate the heating calculator uses, because a kWh costs the same whatever it runs.
E7 — Efficiency is a lever too
E1's pump at 60 % efficiency vs a better 75 %-efficient unit, same flow/head/hours → $32/month vs $26/month — a 20 % difference from efficiency alone.
Takeaway: a more efficient pump (and variable-speed units tend to run efficiently at their sweet spot) costs less for the identical work — efficiency matters alongside speed and hours.
E8 — Per-hour and per-year framing
E1's ~$32/month → $0.18/hour run, $194/season (6 months), $388/year if run year-round.
Takeaway: however you slice it — 18 cents an hour, ~$194 a season — knowing the number lets you decide what clear water is worth to you.
Reference tables
T1 · Monthly running cost by flow × hours
ESTIMATE · at the head of the standard plumbing (46.7 ft TDH at 65 GPM), default efficiencies, default rate $0.16/kWh. Energy is exact; dollars scale linearly with your rate.
| Flow (GPM) \ hours | 4 hr | 6 hr | 8 hr | 12 hr |
|---|---|---|---|---|
| 40 | $13 | $20 | $26 | $40 |
| 60 | $20 | $30 | $40 | $60 |
| 80 | $26 | $40 | $53 | $79 |
| 100 | $33 | $50 | $66 | $99 |
T2 · Half-speed saving by static-head fraction (the integrity dataset)
EXACT physics · the cube-law two-part reconciliation. Note the 0 % row is 72.3 %, NOT 75 % — because Hazen-Williams friction is ^1.852, not ^2 (the textbook idealization). The saving drops monotonically as your system has more gravity lift.
| Static-head fraction | Real saving at half speed | vs cube-law ideal (75 %) |
|---|---|---|
| 0 % | 72.3 % | −2.7 pp |
| 10 % | 65.1 % | −9.9 pp |
| 20 % | 57.8 % | −17.2 pp |
| 30 % | 50.6 % | −24.4 pp |
| 40 % | 43.4 % | −31.6 pp |
| 60 % | 28.9 % | −46.1 pp |
| 80 % | 14.5 % | −60.5 pp |
T3 · Variable-speed payback by monthly saving × upgrade premium
ESTIMATE · seasons (6 months each) to recover the premium. Past payback, the saving continues. Real premiums and saving depend on your rate, hours, and system.
| Saving / mo \ premium | $600 | $1000 | $1500 |
|---|---|---|---|
| $10 | 10 seasons | 17 seasons | 25 seasons |
| $15 | 7 seasons | 12 seasons | 17 seasons |
| $20 | 5 seasons | 9 seasons | 13 seasons |
| $25 | 4 seasons | 7 seasons | 10 seasons |
| $30 | 4 seasons | 6 seasons | 9 seasons |
Tables released CC BY 4.0. T1 dollars are estimates at the default rate (scales linearly with your rate). T2 saving percentages are exact physics. T3 payback rounds up to whole seasons.
Methodology & sources
Cost = power × hours × rate; power = hydraulic work ÷ efficiency. The standard hydraulic relation is waterHp = flow (GPM) × head (ft) / 3960, then watts = waterHp × 746 W/HP ÷ (η_pump × η_motor). The flow and head are the OPERATING POINT (from the pump-sizing engine), not the pump's nameplate — what your pump actually delivers, not what the box says.
The electricity rate is IMPORTED from the cost-to-heat engine. ELECTRICITY_PRICE_PER_KWH_DEFAULT is single-sourced in lib/thermal/fuelcost.ts; the assertion gate proves we don't redeclare it here. The pump-cost and cost-to-heat calculators use the SAME kWh price by construction — because a kWh costs the same whatever it runs. The cross-cluster reconciliation surfaced as a user-facing trust signal.
The cube-law two-part reconciliation (the central honesty).Page 14's affinity law (idealized) says half-speed → 75 % saving. The real saving is two corrections away:
- First correction (HW exponent): real pipe friction follows the Hazen-Williams relation, where head scales with flow^1.852, not flow². Even on a zero-static system (all friction), half-speed gives 72.3 % saving, not 75 %.
- Second correction (static head): static head doesn't scale with flow. On our standard system (8 ft static / 46.7 ft total), the saving lands at ~60 %.
State the ideal-vs-real gap explicitly; we compute the user's actual friction/static mix. This is the page's integrity — don't repeat the 75 % as if it's what they'll get.
Efficiencies (60 % pump / 85 % motor) labelled typicals, editable; a real lever (F10).
State plainly (F11): doubly an estimate (operating-point model × regional rate × typical efficiencies) — ranges, editable inputs, never a hardcoded cost. The most-caveated page in the cluster, appropriately — it's making a money claim built on three layers of estimate.
This page closes the filtration cluster. It consumes the turnover hours + cube law, the operating point, the filter sibling, and the heating cluster's electricity rate from cost-to-heat — chemistry, heating, filtration, and water all backed by one coherent engine portfolio.
Reference tables T1/T2/T3 released under CC BY 4.0. Energy columns exact; dollar columns estimates at editable rate; the saving % honest about the static-head dependence.
Frequently asked questions
- How much does it cost to run a pool pump?
For a standard 1.5 HP single-speed pump at the operating point (65 GPM, 46.7 ft TDH), 6 hours/day at $0.16/kWh: about $32/month, $190/season, $384/year if run year-round. Your number scales with your rate, hours, and the operating-point power — flow × head ÷ 3960 × 746 ÷ efficiency.
- How much does a variable-speed pump really save?
About 60 %on a typical pool — NOT the textbook 75 %. Two corrections stack: real pipe friction scales as flow^1.852 not flow^2, dropping the all-friction limit to 72.3 %; and static head (the gravity lift) doesn't scale with flow, pulling the saving further to ~60 % on a typical 8 ft static, 46.7 ft total system. Both corrections are exact physics. Still enormous — about $19/month off a $32 bill.
- Why isn't the saving the full 75 % the cube law promises?
Two reasons stack. First, the pure cube law assumes pipe friction scales as flow² (flow squared). Real Hazen-Williams pipe friction scales as flow^1.852 — slightly less than 2. Even with zero static head, the saving is 72.3 %, not 75 %. Second, your pump isn't only pushing water through pipes; it's also lifting it up out of the pool. That lift (the static head) doesn't change when you slow down. So when you slow down, the friction part of the work collapses but the lifting part doesn't, and the real saving is less than the idealized ideal.
- Is a variable-speed pump worth it / what's the payback?
Typically yes, in 2–4 seasons. At ~$19/month saved (E1→E2), a $1,000 premium pays back in about 3 seasons of running (6 months per season). Past payback, the saving continues every season. The longer you keep the pool, the clearer the case — and where electricity is dear (much of California, parts of EU), payback is faster.
- Does an oversized pump cost more to run?
Yes, every hour. A 2 HP pump on a pool that needs a 1.5 HP pulls more watts (more flow × more head, both higher) and lands a higher bill — about $41/month vs $32 right-sized, for flow you didn't need. The oversized pump is a double loss: more to buy, more to run.
- What's the cheapest way to run my pool pump?
Pull two levers at once: right-sized variable-speed pump, run slow, for only the hours your turnover needs. On a standard pool that takes the bill from $43/month (naive single-speed at 8 hr) to about $11/month — ~75 % off — for the same clear water. The hours come from the run-time calculator's turnover physics; the speed savings come from the cube law (corrected). They multiply.
- How much electricity does a pool pump use?
For a typical single-speed at the standard operating point: ~1,121 W draw, ~6.7 kWh/day, ~200 kWh/month, ~2,400 kWh/yearif run year-round. That's about $32/month at $0.16/kWh, or $0.18/hour. The watts come from the cost chain: water HP × 746 W/HP ÷ pump efficiency ÷ motor efficiency.
- Why does this use the same electricity rate as the heating calculator?
Because a kWh costs the same whatever it runs. The rate (
ELECTRICITY_PRICE_PER_KWH_DEFAULT) is imported from the cost-to-heat engine — single source, never redeclared. The assertion script proves the import discipline. If we let each calculator declare its own rate, the two cost pages could silently disagree about the price of electricity — exactly the integrity failure cross-page assertions exist to prevent.
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