Your pool is getting chilly, summer is fading, and you’re not ready to cover it up yet. So you started shopping for a gas pool heater… and got buried in BTUs, efficiency ratings, and metal types. Sound familiar?
Here’s the good news: picking the right heater comes down to 5 simple questions. Get them right and you’ll be swimming into October and soaking in a hot spa on cold nights. Get them wrong and you’ll be waiting an hour for warm water and wincing at your gas bill. Let’s make sure that doesn’t happen.
How Efficient Should a Gas Pool Heater Be?
Short answer: Look for a thermal efficiency rating of 82% or higher.
Why it matters to you: efficiency decides how much of your gas actually heats your water and how much just disappears into your monthly bill. A higher-efficiency gas pool heater might cost more up front, but if you swim a lot, it pays you back every single month.
Pro tip: Call your local utility company before you buy. Some offer rebates when you replace an old heater with a high-efficiency one.
What Size Gas Pool Heater Do I Need?
Short answer: For a 20,000-gallon pool with no spa, go with 250,000 to 400,000 BTUs.
Heater power is measured in BTUs, and the bigger the number, the faster your pool warms up. Any size will get there eventually. The real question is how long you’re willing to wait before you jump in.
To narrow it down, start with your pool’s gallons, then think about:
- Your local climate
- How windy your yard gets
- How many months a year you want to swim
- Whether you use a pool cover (it keeps the heat in and saves you money)
Good to know: Size only affects how fast the water heats up. Once you hit your temperature, a smaller heater keeps it there just as well.
What Size Heater Do I Need for a Pool and Spa?
Short answer: 400,000 BTUs. That’s what most pool and spa owners choose.
Picture this: you get home after a long day, you want to sink into your spa, and then you wait… and wait. Here’s how long it takes to heat a 700-gallon spa from 70° to 100°:
- 250,000 BTUs: about 51 minutes
- 400,000 BTUs: about 32 minutes
The bigger heater gets you into hot water 19 minutes sooner. Your back will thank you.
Copper or Cupro-Nickel: Which Heat Exchanger Lasts Longer?
Short answer: Cupro-nickel. It outlasts copper.
The heat exchanger is the heart of your heater and the most expensive part to replace. Many heaters use copper, but cupro-nickel holds up better against corrosion, strong pumps, and tricky water chemistry. That means fewer repairs and a heater that lasts longer.
Have a saltwater pool? Make cupro-nickel a must. Salt is tough on metal.
Can I Install a Gas Pool Heater Myself?
Short answer: Leave it to a licensed pro.
You’re working with gas lines, so this isn’t a weekend DIY project. A licensed install also protects your wallet: some manufacturers cut warranty coverage to parts only, with no labor, if anyone else installs the heater.
Before you buy, check the warranty for:
- How long it lasts
- Whether it covers parts only, or parts and labor
Replacing your pump, filter, and heater at the same time? Ask about equipment bundles. Some manufacturers extend parts and labor coverage when you buy all three together.
Your Gas Pool Heater Cheat Sheet
Save this for when you’re shopping:
- Efficiency: 82% or higher
- Size (pool only): 250,000 to 400,000 BTUs for a 20,000-gallon pool
- Size (pool + spa): 400,000 BTUs
- Heat exchanger: cupro-nickel
- Install: licensed pro
- Warranty: parts and labor
Ready to Keep Swimming?
You don’t have to give up your pool just because the weather cools off. The right gas pool heater keeps the fun going for months longer. And if you’re still not sure which one fits your backyard, we’ll help you sort it out. Our team helps pool owners match heaters to their pool size, climate, and budget every day.
Want more ways to enjoy your backyard all year long? Join Backyard Blueprint, our email full of fun backyard ideas.
