How does hot tub plumbing work? (2025 Guide)

If you’ve ever wondered how your hot tub plumbing system works, then you’re not alone. Whether you’re planning a DIY build, troubleshooting some issues or are simply trying to understand your current setup. Having a solid understanding of how your hot tub plumbing system works can make your life so much easier. 

Which is why, I’ve made this guide that breaks down the essentials of hot tub plumbing in a simple and easy to follow way! 

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How Does Water Flow Through a Hot Tub Plumbing System

If you break it down to the basics, a hot tub plumbing system basically revolves around water movement. Letting water in, heating and filtering it, and sending it back into the tub.

Let’s start with the basics:

1. Suction Drains and Pump Intake
   Water leaves the tub through two suction points or drains at the bottom of your tub. These dual drains are a safety measure; if one gets blocked, the other keeps the water flowing, protecting the pump from overheating. The suction drains channel the water into the pump, which is the heart of the plumbing system.
2. The Pump: Circulation vs. Dual-Speed
   The pump in your hot tub can serve different functions depending on its type:
   • Circulation Pumps: These small pumps efficiently manage the flow for heating, filtering, and sanitization. By dedicating a steady, slower flow to these components, they operate without reducing jet power.
   • Dual-Speed Jet Pumps: These pumps serve two purposes. At low speed, they handle water circulation. At high speed, they power the jets for a more invigorating experience. 
3. Filtration and Heating
   Once the water exits the pump, it flows into the filter, which ensures clean water by trapping debris. From the filter, which has a bypass valve, water moves toward the spa pack, a central control hub that includes an electric heater.
   • The spa pack also manages cycles like filtering, jet operation, and purging.
   • Auxiliary heating options, such as air source heat pumps or propane heaters, can supplement the electric heater, but the spa pack remains essential for overall system control. While you can turn off the heater, you’ll still want the spa pack to ensure everything else works fine. 
4. Returning Water to the Tub
   After passing through the heating and filtering components, the water is returned to the tub through dedicated inlets. This completes the cycle, ensuring the water remains clean, warm, and ready for use.

Jets, Blowers, and the Venturi Effect

Hot tubs are known for their relaxing jets, but there’s more to them than meets the eye:

• Jets and Pump Power: The number and strength of your jets depend on the pump’s output. Larger tubs with more jets may require multiple pumps to maintain optimal flow. If you have multiple jets, you might need to upgrade to a bigger pump or multiple pumps. Feel free to reach out to me if you’re having issues determining your ideal pump. 
• Blowers: Acting like a giant hair dryer, the blower forces air into the tub through air-only jets. Heated blowers ensure warm air is circulated, though they don’t directly heat the water.
• The Venturi Effect: For DIY tubs made of materials like concrete or gunite, gunite jets create strong, bubbly water flows by mixing air and water. This process, known as the Venturi effect, uses water velocity to draw in air, resulting in more powerful jets.

Preventing Backflow in Your Hot Tub Plumbing

A crucial aspect of any hot tub plumbing system is protecting the components. Check valves prevent water from flowing back into the blower or other sensitive areas, which could damage heating elements or trip electrical breakers.

In a Nutshell

Hot tub plumbing might seem complex at first, but once you understand its core components and how they work together, it becomes much easier to manage. Here’s a quick recap:

• Water is drawn in through suction drains to the pump.
• Circulation or dual-speed pumps handle water movement.
• Filtration and heating systems keep water clean and warm.
• Jets and blowers add the therapeutic and relaxing touch hot tubs are known for.

Whether you’re fixing a hot tub issue, upgrading components, or building your own DIY hot tub, understanding these basics can save you time and effort. While there are differences between the different builds of hot tubs, this guide covers the basics of plumbing that apply to all kinds of hot tubs. 

For more tips and detailed guides, visit Buildahottub.com or drop your questions in the comments below. Happy hot tubbing!

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Thanks - Andi

 

Hi, Andi here. I own Buildahottub.com and also write all of the articles and info pages on the site. Some years back now, I built my own hot tub but struggled to find the information I needed. So, once my tub was complete, I started this website to help others in their own pursuit of hot tub and plunge pools DIY building information.

Fast forward to 2025, I've helped over 1400+ DIY customers just like you all over the world build hot tubs and pools. Have a good look around the site, there are lots of resources here. Please do get in touch if I can help you. - Cheers, Andi