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How Does Hot Tub Plumbing Work?

Ever since humans realized how enjoyable it is to relax in hot springs they’ve been devising novel ways of bringing the experience a little closer to home. In fact, the first mention in recorded history of people using hot tubs goes back to the ancient Egyptians, some 4,000 years ago. But, it was those early masters of plumbing, the Romans, that really kicked hot tub action into high-gear. (Of course, the ancient Romans’ hot baths were absolutely filthy by today’s standards since they hadn’t yet perfect the art of circulation, filtration, and chlorine.) So now that we’ve gone back in time, let’s just to the present day to answer the question, “How does hot tub plumbing work?”

Without Plumbing Your Hot Tub Would Be Just a Big Bucket

To say plumbing is important to how hot tubs function is like stating the importance of roads to driving; proper plumbing is essential to a hot tub’s performance and your own satisfaction while using a hot tub. Since much of a hot tub’s plumbing is tucked away behind the shell, most are probably unaware of how many pipes, fittings, plugs, valves, clamps, hoses, reducers, nuts, and connections are necessary for a hot tub to work. First off, the plumbing in your hot tub is different than most types of plumbing in that a hot tub’s pipes form a closed loop, meaning the water circulates non-stop while the hot tub is turned on. Since a hot tub's plumbing forms a loop, there really is no beginning or end to the system, so let's start with the water being sucked out of the tub then work our way around to the jet nozzles.

  • Suction line — To keep water clean and circulating throughout your hot tub's network of pipes and fittings mean that the water needs to be continuously removed, filtered, and returned to the tub. The part responsible for sucking water out of the hot tub is the suction line, which is powered by the pump.
  • Skimmer — Leaves and other debris can really clog up the works, which is why all hot tubs and swimming pools use some form of a skimmer. A skimmer uses the suction force from the pump to draw in leaves, hair ties, and everything else that incidentally falls into hot tub water.
  • Pump — The same pump that pushes water back into the hot tub is responsible for drawing water out of the hot tub. Both the skimmer and suction lines lead to the pump, where the water is then pushed to the filtration stage.
  • Filter — Hot tub filters are comprised of a fine mesh and/or fabric to actively remove smaller bits of debris, moss, algae, and smaller particles that are not captured by the skimmer.
  • Heater — Once water passes through the filter it then goes through another PVC pipe until it reaches the heater. The heater (as you probably guessed) carries the huge responsibility of heating the water as it passes over the heating element. We may be glossing over the details of the heater assembly in this article, but this unit can have anywhere from 20 to 30 parts, including sensors, the housing, heating element, and bulkhead nuts.
  • Hot return line — While it’s commonly referred to as just the “return line,” we refer to it as the “hot return line” in this article to avoid confusion with the suction line. The hot return line includes the PVC pipes and fittings that branch off of the heater and on toward the manifolds in order to deliver a fresh supply of hot water to the tub.
  • Venturi air control — While the Venturi air control doesn’t fit the textbook definition of being a plumbing component, it is worth noting since it plays a crucial role in creating that whooshing message action from the jets. Not to go too far into the physics, but the rush of water creates a passive suction that allows air to be pulled in through the air control and out through the jet nozzle. (This should not be confused with the air blower, which creates bubbles at the bottom of the tub basin.)
  • Manifolds — All depending on the layout of your hot tub, you may have one central manifold or a network of manifolds. Manifolds are essentially water line distributors, sort of like power strips, but for water pipes.
  • Flexible PVC tubes — Each jet in a hot tub has at least one flexible PVC tube to deliver the water-air mixture. Now that we’ve reached the flexible PVC tubes, we’re getting really close to completing the cycle of your hot tub’s closed loop plumbing system.
  • Jets — Years ago, a dozen jets in a hot tub was considered optimal, nowadays, the standard hot tub has 70 or more jets. The jet nozzle, with its tapered end, is responsible for created that fast stream of water-air mix that feels good on the skin and soothes achy muscles after a long day of work.

No Wait, There’s More

While we’ve outlined the various components of a hot tub’s plumbing, we didn’t go too far into the hydraulic science of how hot tubs operate. For the water to mix with air and create that jetting action present in the many nozzles, the pipes need to become narrower as they approach the jets. While you might assume this is to increase pressure, the exact opposite is true; when water passes through a series of pipes that gradually decrease in circumference, water velocity actually increases, but water pressure actually decreases. This sudden drop in water pressure forces outside are in through the air control and into the hot return line. In physics, this induction force is known as the Venturi effect.

Have a Leak in Your Hot Tub?

Because hot tubs have such a vast plumbing network, it’s only a matter of time before a gasket, seal, or fitting gives way. Fortunately, there’s Master Spa Parts®. Master Spa Parts carries all you will ever need in the way of hot tub plumbing supplies — all those caps, plugs, elbows, check valves, hoses, clamps, manifolds, reducers, unions, nuts, and drains that we didn’t have time to cover in this article. Since we are a centralized operation, we can also offer these products at greatly reduced prices. Here’s to many happy days and nights spent in your leak-free hot tub!