It’s 6:15 on a weekday evening in August. The pump on the pad is running flat out, because the pins on the old mechanical time clock say noon to 8 p.m., and nobody has touched them since the house was sold. Every minute of that is being billed at Edison’s most expensive rate of the day. Is it better to run the pool pump at night or day? Neither, at that hour, and fixing it is a small job under our pool repairs and upgrades list: move the pins, or better, reprogram the pump.

Type “run pool pump at night or day” into a search bar and most of what comes back is written for utilities that charge less at night. Southern California Edison doesn’t work that way anymore. Its time-of-use plans price power by what the grid is doing, and at noon the grid is full of solar. So the answer here is different from the answer in a lot of the country, and the water has opinions too.

What SCE charges for each hour of the day

SCE’s residential time-of-use rate page lists three plans. These are the prices it shows as of September 2026, rounded to the cent the way SCE rounds them. Summer is June through September, winter is October through May.

A few footnotes from the same page. Summer weekends swap on-peak for a cheaper mid-peak (46 cents on the 4-9PM plan, 54 on the 5-8PM plan). The 4-9PM and 5-8PM plans take a baseline credit of 10 cents a kWh off usage up to your monthly baseline allocation. All three plans carry a $0.79 a day base charge that your pump schedule can’t touch. TOU-D-PRIME is only open to households with an EV, a home battery or an electric heat pump system.

For context, SCE’s June 2026 rate advisory puts the average residential rate at 34.4 cents a kWh. Expensive power is the local constant. When you buy it is the variable.

Why noon beats midnight for eight months a year

Most people assume night is the cheap time because it used to be. SCE’s own help center now says the 4-9PM and 5-8PM plans “offer low prices while the sun is shining and solar power is contributing to the power grid.” Look at the winter column again. From October through May, 8 a.m. to 4 p.m. is the cheapest block on the 4-9PM plan, and overnight costs about 12% more.

In summer, off-peak is a flat 34 cents from midnight to 4 p.m. and again after 9. So a pump running at 2 a.m. and a pump running at 11 a.m. cost exactly the same. Nobody wins by staying up late.

The math on a real pump

Pacific Northwest National Laboratory’s Building America guide to variable speed pool pumps supplies the wattage. A typical 1.5 HP pump draws about 2,000 watts at 3,450 RPM, the speed a single-speed pump runs all day. Slow it to 2,400 RPM and the draw falls to 593 watts: 30% less speed, 70% less power.

Here is eight hours at each speed on the TOU-D-4-9PM plan, before the baseline credit. (How many hours your pool actually needs is a separate post.)

The noon-to-8 time clock from the first paragraph costs a full-speed pump about $50 a month more in summer than the same eight hours in the morning (22 weekdays with four on-peak hours, 8 weekend days at mid-peak). And the slow pump at its worst hours still costs less than the full-speed pump at its cheapest.

Slower also moves less water, so the fair comparison runs it longer. Flow drops in step with speed under the pump affinity laws, so 2,400 RPM needs about 11.5 hours to match eight at full speed. That’s about $2.32 on a summer day, against $5.44.

ENERGY STAR explains why: cutting pump speed in half lets it use about one-eighth the energy. Moving a single-speed pump’s hours helps, but California’s rules mean its replacement has to be variable speed anyway. Our post on California’s variable speed pump rule covers what qualifies and how to program one so it actually saves money.

What the water wants

The power bill says daytime or overnight, just not 4 to 9. The water breaks the tie, and it votes for daytime.

Start with chlorine. NSW Health’s fact sheet on pool stabiliser says about 35% of free chlorine can be destroyed every hour it’s exposed to UV in an outdoor pool with no cyanuric acid. At 30 mg/L of cyanuric acid, that loss drops to about 3% an hour, and more stabilizer past that adds little. Leslie’s makes the case for night running on exactly this point: chlorine does its job more easily when the sun is down. Fair, but in a pool with stabilizer in range, the sun isn’t the chlorine thief it’s made out to be.

Algae is the stronger argument. AQUA Magazine, the service trade publication, puts it plainly: algae absorb light and use photosynthesis to turn nitrates and phosphates into energy, and they “thrive in still waters.” Daylight is when algae is working. Moving, filtered, chlorinated water during those hours is the opposite of what it wants. If you have been fighting it already, our pool algae removal guide covers what the schedule can’t fix.

Then there are swimmers. Sunscreen, sweat and body oils go in during the afternoon, and Leslie’s lists removing them as a reason to filter when the pool is actually in use. A pool that sits still from 9 a.m. to 9 p.m. and gets filtered after everyone is asleep is cleaning up yesterday. When that goes wrong, it looks like a green pool by Friday.

Debris, wind and the skimmer

Leaves and blossoms that land while the skimmer is pulling get caught at the surface, in the basket, where they belong. Leaves that land while the pump is off float around, soak up water and sink, and then they’re a stain on the plaster and a job for the cleaner. Around here that matters most when the Santa Anas blow and half the neighborhood’s landscaping ends up in the deep end. Run the pump while the wind is up, and empty the basket after.

Noise, neighbors and the bedroom window

Pentair’s IntelliFlo brochure puts a typical single-speed pump at 67 decibels and its variable speed pump at 45, next to a library at 50. Pool equipment tends to live on the side yard, a few feet from somebody’s bedroom. A single-speed pump running at 2 a.m. gets noticed. A variable speed pump at low RPM usually doesn’t, but if the pad is under a neighbor’s window, it’s one more reason to do the heavy filtering in daylight.

If you have solar panels

This is where daytime stops being a close call. SCE’s Solar Billing Plan page says its export credits are “less than what you pay for electricity from SCE’s grid,” and it names the pool pump specifically: running larger appliances “such as a dishwasher, dryer or pool pump during sunny daytime hours is one of the easiest ways to use more of your solar energy.” Solar Billing Plan customers are on TOU-D-PRIME, and NEM 2.0 customers have to be on a time-of-use rate, per SCE.

So if the panels are on the roof, the pump runs while they’re making power. A pool pump running at midnight on a solar house is buying 24 to 26 cent grid power while the panels sell the afternoon back for less.

The same logic applies to a heat pump pool heater, which draws far more than the pump does. If you are weighing one, our heater repair or replace guide runs the SCE numbers against gas.

Is it better to run the pool pump at night or day? Our default schedule

For most variable speed pumps on an SCE time-of-use plan, this is where we start:

Main filtration block in the morning through early afternoon, done by 4 p.m. (5 p.m. on the 5-8PM plan). That lines up with winter super off-peak and with solar production, which is also when algae is busiest.

Pump off, or at its lowest speed, from 4 to 9 p.m. on weekdays. Summer weekends are mid-peak: cheaper, not cheap.

A short low-speed block after 9 p.m. only if the pool needs more hours than the day block covers, or a cleaner runs off the pump. Summer off-peak is the same price at night as at noon, so this costs nothing extra in summer and a little extra in winter.

Then adjust for the pool, not the calendar. A pool under a pepper tree needs the skimmer at different hours than a pool in an open backyard in Camarillo. That’s the kind of thing a tech on weekly maintenance notices by the second visit.

Asked at the pad, every week

Should I just run the pump 24 hours to be safe? No. Leslie’s says 24-hour running is for algae treatment until the water clears. The rest of the year it’s running through the 4 to 9 p.m. window for nothing.

My pump is on a mechanical time clock. Does daylight saving matter? Yes. A mechanical clock doesn’t change itself, and it stops during a power outage. SCE’s peak hours follow the real clock, so a dial that’s an hour off pushes a schedule ending at 4 into the peak. Check it every March and November, and after every outage.

Does the baseline credit change the answer? No. It takes the same 10 cents off every hour until you use up your allocation, so the cheapest hour stays the cheapest hour.

Is night ever the better choice? If the pool is being shocked and nobody swims until morning, running the pump overnight to circulate that chlorine makes sense. It’s a day, not a schedule.

Find your rate plan name before you touch the timer

Pull up your last SCE bill and find the rate plan name. It will say TOU-D-4-9PM, TOU-D-5-8PM or TOU-D-PRIME. Then look at the pump’s schedule and answer one question: is anything running between 4 and 9 p.m. on a weekday? If yes, that’s the change to make this week, before the day or night question even comes up.

If the schedule lives on a pump keypad or an automation panel nobody in the house knows how to use, send us the pump brand and model through the site along with your rate plan name. We service Pentair, Jandy, Zodiac, Hayward and Sta-Rite equipment, and reprogramming a pump is a short visit. Call (805) 586-2055 and we’ll get a tech out to the pad.