How Much Does It Cost to Heat a Pool in LA with a Natural Gas Heater?

If you’ve ever felt a pang of guilt after switching on your pool heater and then saw your gas bill, you’re not alone! Many pool owners think heating a pool always costs a fortune, or see it as a “comfort tax.” But what if you could understand where those numbers come from, know where you can save, and actually make better choices for warmth that doesn’t blow your budget?

If you’ve ever wondered:

• “How much does it cost to heat my pool with gas?”
• “Will a bigger heater save me money?”
• “Can I warm up the pool faster without bigger bills?”

You’re exactly who this article is for.  At J Designs Pool & Spa, we help clients every day pick the right heater, size it correctly, and get more comfort with less waste. Here’s the straight talk on gas pool heating costs, sizes, and the smartest ways to save.

What Goes into Calculating Heating Costs?

* To give you real-world answers, here’s how we ran our numbers:

• 1 gallon of pool water = 8.34 lbs
• It takes 1 BTU of energy to heat 1 lb of water by 1°F
• Common heater sizes: 250,000 and 400,000 BTUs per hour (BTU/hr)
• Most heaters are about 80% efficient
• Natural gas cost used: $0.35 per therm (100,000 BTUs)
• We looked at both a quick 5°F boost and a full 20°F warm-up
• Initial heating only (not daily heat loss from wind/cold/evaporation)

Real Costs and Heating Times for Different Pools

Here’s how long it takes and what it’ll cost to heat three common pool sizes,
using both heater sizes:

Note: Using a 400,000 BTU heater gets the job done faster (almost half the time), but the total fuel cost is nearly the same. The bigger heater heats the water more quickly.

Key takeaway: Bigger heaters heat "faster". But total energy cost stays about the same.

Why Upgrading Your Pool Heater Can Pay Off

If your heater is more than 5-10 years old, it probably runs at 70–82% efficiency, or less if it’s never been serviced. That means you’re wasting up to 20% of your fuel.

Newer high-efficiency heaters (like Hayward’s H-Series or Pentair’s hybrid models) offer up to 95% efficiency and:

• Save 30–50% on fuel
• Heat the pool faster
• Lower emissions (meets demanding California standards)
• Last longer with better tech

Hybrid heaters combine a heat pump and a gas backup. They use the cheapest energy source depending on the weather, so you spend less and get steady warmth.

The Biggest Factor: Heat Loss to Evaporation

Want to cut your heating cost in half or more? Use a pool cover.

• Covers drastically slow evaporation, your #1 source of heat loss.
• A good solar or automatic cover can save 50–70% on heating costs, especially in windy or dry LA climates.
• Think of a cover as “keeping the heat you already paid for.”

How to Figure Your Own Gas Heater Cost

Here’s a quick formula:

• (Heater BTU / 100,000) x Cost Per Therm = Hourly Fuel Cost

For example, at $0.35/therm:

• 250,000 BTU heater: 2.5 x $0.35 = $0.88/hour
• 400,000 BTU heater: 4 x $0.35 = $1.40/hour
  (Fuel only – your total bill may include small delivery fees or taxes)

As of November 2025, most Los Angeles homeowners can expect to pay between $0.32 and $0.67 per therm for natural gas, depending on their provider and rate plan.

• Southern California Gas (SoCalGas): ~32 cents per therm (core residential rate, not including delivery fees or taxes)
• Long Beach Gas & Oil: ~67 cents per therm (some special-tier users may see this higher rate)

Your actual bill may include small delivery charges and taxes, but most pool owners will see the “cost per therm” fall within this range when heating their pool.

For personalized rates, always check your latest utility bill or visit your local gas provider’s website for up-to-date pricing.

Tips to Lower Pool Heating Costs

1. Always use a pool cover when not swimming
2. Heat during the day, sunlight helps!
3. Block wind with fences or hedges
4. Upgrade to a high-efficiency or hybrid heater
5. Regular heater maintenance for peak performance

Why Your Pool System Design Matters

The best heater in the world can’t fix poor water flow. If your pool has narrow pipes, a clogged filter, or an undersized pump, it’ll heat more slowly and cost more. When we install or replace a heater, we check every detail: gas lines, equipment pad, flow rate, and smart automation compatibility.

Should I Get a Bigger Heater?

If pool parties are often delayed for warm water—or if your pool never feels warm enough—a larger heater (like 400,000 BTU) can be worth it. It won’t cost more per hour to run; it simply gets your pool to the perfect temperature faster.

What’s Next?

Heating your pool doesn’t need to be a mystery or a money pit! Knowing how heater size, efficiency, installation, and the use of a cover affect your bill puts you in control of your comfort and your costs.

Curious about hybrid, electric, or solar options? Want to see model comparisons and long-term payback?
Check out our Complete Pool Heater Buying Guide for all the details.

At J Designs Pool & Spa, we’re here to help you get the most enjoyment (and value!) from your investment, so you can swim comfortably, whenever you want.

*  Note: All prices and calculations may vary from area and property specifics. In this article examples are excluded form other increases and unknown particulars not disclosed by the LADWP.