How Cold Does Your Pool Get in November, and What Does It Cost to Heat It?
The sun still feels warm on the deck in November. The water is a different story.
We hear two questions a lot once the nights turn cold. Is the pool still warm enough to swim? And if it isn't, what would it cost to make it that way?
The short answers are "probably not" and "more than most people expect, unless you go about it the right way." Here is how cold an unheated pool actually gets around here, what heating it costs with gas or a heat pump, and how to get into warm water this time of year without a painful bill.
How Cold an Unheated Pool Gets in November
An unheated pool settles somewhere between the day's high and the night's low. It changes slowly, so the water reflects the last few weeks of weather more than today's forecast.
On the valley floor, November afternoons usually reach the 60s and nights drop into the low 40s. That puts most unheated pools in Lincoln and Rocklin in the low to mid 60s at the start of the month, sliding into the 50s by Thanksgiving. A warm October can buy a few extra degrees for the first week or two. It won't last.
Where your pool sits matters too. Foothill properties in Penryn and Loomis see colder nights sooner than the valley does. In Granite Bay, a pool under mature oaks loses what little afternoon sun November offers, and it will run colder than a pool in full sun a few streets over.
Is It Too Cold to Swim?
For most people, yes. Heated pools are usually kept between 78 and 82 degrees, and the Department of Energy notes that young children and older swimmers may need 80 or warmer to be comfortable.
Water in the low 70s feels brisk. Water in the 60s is a quick dip at best. Once the pool drops into the 50s, getting in can knock the wind out of you, and that is not water for long swims or for kids who stay in until their lips turn blue. If someone in the family insists on a November swim in an unheated pool, keep it short and stay close by.
So the real question isn't whether you can swim in November. It's whether warming the water is worth what it costs.
What It Costs to Warm the Pool Back Up
Here is the math in plain terms. It takes one BTU to raise one pound of water one degree. A typical 15,000-gallon pool holds about 125,000 pounds of water, so every degree you add takes about 125,000 BTUs.
Taking that pool from 62 degrees to 80 means adding 18 degrees. On a gas heater, that works out to roughly 25 to 30 therms of natural gas. At PG&E's current residential rates of roughly $3 a therm, the warm-up alone costs somewhere around $75 to $90.
That number assumes no heat escapes while you're heating. In November, a lot of it does.
Keeping the pool warm is where most of the money goes. A pool loses most of its heat at the surface, and evaporation is the biggest drain. Remember that one BTU per degree? Every pound of water that evaporates off the surface takes more than 1,000 BTUs with it. Cold, dry nights pull that heat out fast.
An uncovered pool held at 80 degrees through a typical November day and night can burn 10 to 20 therms just to stay there. That's roughly $30 to $60 a day. Run that all month and the total gets uncomfortable quickly. It is why most people around here who heat in November heat for the weekend, not for the whole month.
Gas Heater or Heat Pump in Cold Weather
The two most common heaters behave very differently once the weather turns.
A gas heater burns natural gas or propane and doesn't care what the air temperature is. On an average-size pool, a typical residential unit adds a degree or two an hour, which makes it the better tool for heating on demand. Turn it on Friday afternoon, swim Saturday, turn it off Sunday night.
A heat pump pulls warmth out of the surrounding air. That makes it efficient on a mild afternoon and much less useful on a cold night. Below roughly 50 degrees, most residential heat pumps lose most of their practical output. In November, a heat pump does its real work in the afternoon, and it can take a day or more to bring a cold pool up to swimming temperature.
What you pay for electricity changes the comparison more than most people realize. Most of our service area buys power from PG&E, where residential rates run from the mid-30s to around 40 cents per kilowatt-hour depending on your plan. At that price, the same 18-degree warm-up on a heat pump in November air costs roughly $55 to $90. That is right in line with gas, and on a cold day it can cost more.
Roseville is the exception. Roseville Electric's residential rates run roughly 12 to 16 cents per kilowatt-hour, so that same warm-up costs closer to $25 to $35. Gas in Roseville still comes from PG&E, which gives Roseville homeowners a heat pump advantage most of their neighbors don't have.
In Sheridan and parts of Penryn and Loomis, some rural properties don't have natural gas service and run their heater on propane. Propane usually costs more per unit of heat than natural gas, and a single full warm-up can pull 25 to 30 gallons from the tank. If you're on propane, check the tank level before a holiday weekend, not after.
Solar heating deserves a quick mention too. Solar panels for pools do most of their work from spring through early fall. By November the sun is low and the days are short, so solar alone usually won't keep a pool swimmable.
A Cover Does More Than the Heater
If you heat your pool at all this time of year, a cover is the best money you can spend. The Department of Energy calls covering a pool when it isn't in use the single most effective way to cut heating costs, with savings of 50 to 70 percent.
A cover works because it stops evaporation, and evaporation is where most of that heat goes. A basic solar bubble cover is fine for this. Put it on at sunset and take it off when you swim.
The catch is that a cover only saves money when it is actually on the pool. One that sits rolled up on the deck all week saves nothing. On heavily treed lots, clear the leaves off the cover before you pull it back, or you will dump them straight into warm water.
We went through the pros and cons in more detail in whether you really need a pool cover in Northern California.
Ways to Heat for Less
Heat for the swim, not the season. Turn the heater down or off between swim days. The Department of Energy is clear that reheating a pool does not use more energy than you save by letting it cool.
Pick a slightly lower target. Each degree warmer can add 10 to 30 percent to heating costs, so 80 instead of 84 makes a real difference.
Make sure the pump is running when the heater is. A heater needs good flow to fire, and a dirty filter or a pump schedule that misses the heating window wastes time and gas. If you have pool automation, set the heater and pump to run together, and schedule a heat pump for the warmest hours of the day.
Keep the inside of the heater clean. Scale on a heat exchanger makes the heater burn more gas for the same result. In Lincoln and Rocklin, municipal water carries enough calcium to build that scale over time. On well water in Loomis, Penryn, and Sheridan, the mineral load is harder to predict, which is a good reason to test before heavy use. Our heater readiness checklist walks through what to look for. If yours won't fire at all, start with why your pool or spa won't heat.
Keep an eye on chemistry when the temperature swings. Warming and cooling the water changes how chlorine and pH behave, which we covered in how pool temperature affects water chemistry.
Your Spa Is the Cheap Way Into Warm Water
If what you really want is warm water on a cold night, the spa wins on cost by a mile.
An attached spa holds a few hundred gallons, not thousands. Heating a 500-gallon spa from 60 degrees to 102 takes about 2 therms of gas, around $6 at PG&E rates, and a typical gas heater gets it there in under an hour. That is a big part of why fall and winter are spa season in Placer County.
Portable hot tubs stay warm all the time and depend on their covers to hold that heat. If the cover feels heavy or waterlogged, it has stopped insulating, and the heater is working much harder than it should. Our spa service keeps the water and filters in shape through the busy season. If the spa takes longer to heat than it used to or can't hold temperature overnight, that's a job for spa repairs.
Get Help Deciding What Makes Sense for Your Pool
There's no single right answer for every backyard. Some homeowners heat for a few weekends and keep the cover on every night. Some let the pool rest and use the spa instead, which in Placer County still means keeping the pool running through winter, not closing it. And some find out their heater costs more than it should because it's scaled, short on flow, or near the end of its life.
If you're not sure which camp you're in, we can help. American Dream Pool & Spa Service handles weekly pool service, heater diagnosis, and pool repairs across Lincoln, Rocklin, Roseville, Granite Bay, Loomis, Penryn, and Sheridan. For the rest of the season, our free Fall and Winter Pool and Spa Care Guide lays out what to do month by month.
Contact us or call or text 916-975-7370, and we'll help you figure out whether warm water this month is worth it for your pool.
