How to Use a Venturi System Instead of a Blower on a Block Hot Tub

Last updated: September 2026

A subscriber once asked me how to use a venturi system instead of an air blower on a concrete or block hot tub, and whether I could make a video on it. I love requests like that, because they’re genuinely useful for anyone tackling a DIY build. So I made the video, which you can watch below. If you’d rather read it, here’s the step-by-step version.

If you haven’t decided between the two yet, start with Hot tub air blower or venturi? Which one do you need? This post is the how-to for when you’ve chosen venturi.

How a block or concrete hot tub is normally set up

On a block, concrete or ICF hot tub, you’ll almost certainly be using gunite jet bodies. These are set into the wall before it’s rendered, with the face finishing flush with the tiles. Each tee-type body has two pipe connections:

• A 2in water connection, fed by the jet pump.
• A 1.5in air connection, which is the air line.

Waterway’s gunite jet instructions list the tee body as 1½in air by 2in water. The pump pushes water into the jet body and out through the nozzle of the jet insert at speed. The air meets the water inside the jet body, and the two leave the jet together as that fizzy, bubbly stream.

In the most common setup, the air lines all run back to an air blower in the control room. The blower pushes air down the air lines into the jets, so you get plenty of bubbles whenever you switch it on. It’s the setup I like, and it’s what most of my customers go for. But a blower isn’t for everyone. It’s noisy, it cools the water, and it needs a check valve and a Hartford loop to keep water out. That’s where venturi comes in.

How venturi works without a blower

The venturi effect is the drop in pressure you get when a moving fluid speeds up through a narrow section. In a hot tub jet, the water is squeezed through the nozzle at speed, and that drops the pressure where the air line joins. If the air line is open to the air, air gets sucked down it and into the water. No motor needed.

So instead of connecting the air lines to a blower, you bring them up to the surface and finish them with an air control: a small valve that sits on the edge of the tub. Open it and more air is drawn in, for a fizzier, stronger-feeling jet. Close it and you get water only.

Step by step: setting up venturi on a block build

1. Tee into the air lines and bring them up to the edge

Tee into the air lines from the jets and run the air line vertically up to the ledge or edge of the hot tub. On the level edge (the coping or deck), fit an air control valve, which looks something like this:

The air control is adjusted by hand, and it lets air be drawn into the system whenever the jet pump is running.

The air control must be above the water line. Water finds its own level, and the air lines are connected to the water in the jet bodies. Put an air control at or below the water line and water will pour out of it. Keep the air lines running up to the control, not dipping and rising, so they don’t trap water.

2. Fit more than one air control

You’ll want more than just one air control. On a square hot tub, I recommend one on each of the four sides. That gives you more flexibility and control over how much air each set of jets draws in, and it means the people on each side can adjust their own.

3. Keep separate air systems for each group of jets

Rather than connecting all the air lines together into one big loop, create separate systems. For example, on a 16-jet tub, split them into groups of four jets per side, each group with its own air line and its own air control. Air, like water, takes the easiest route. With one shared system, the jets nearest the air control (or with the strongest flow) take most of the air, and the rest get very little. Separate groups keep the air evenly shared and give better suction at each set of jets.

4. Balance it on high speed

Venturi relies on the speed of the water, so it works best with the jet pump on high. Once the tub’s running, open each air control a bit at a time until the jets feel right. If one side seems weak, check the water side first: the jets on that side may be getting less flow than the others. There’s more on getting the pump and jets balanced in DIY hot tub jets: everything you need to know.

What venturi can and can’t do

	Venturi	Air blower
How air gets in	Sucked in by the water flow	Pushed in by an electric air pump
Bubbles with the jet pump off?	No	Yes, with air injectors
Amount of air	Moderate, adjustable	Lots
Noise	Quiet	Noticeable
Extra kit	Air controls	Blower, check valve, Hartford loop, wiring

The full pros and cons are in Air blower or venturi? and everything about blowers is in Hot tub air blower: the ultimate guide.

A simpler alternative

If you don’t need adjustment at the tub, there’s an even simpler option. Waterway’s instructions for a no-blower setup just leave the air inlet pipe open to the air, pointing down under a vent grate. That gives you one fixed air intake. It works, but you lose the ability to turn the air up or down from the tub, which is why I prefer air controls on the edge.

Planning for a blower later

If you’re not sure, leave yourself the option. The air lines are the same size either way, so it’s mostly about leaving a capped tee on the air side and some space in the control room. If you do add a blower later, you must close or cap the venturi air controls first. A blower needs a closed air system to build pressure, and if the air controls are open, its air just escapes out of them and the jets lose power. You’ll also need a check valve and a Hartford loop, and to wire and configure the blower on your spa pack. See How to wire a hot tub blower and Configuring a Balboa spa pack.

Common mistakes

• Fitting an air control at or below the water line.
• Joining all the air lines into one system, so some jets get all the air and others get none.
• Only fitting one air control on a big tub.
• Expecting blower-level bubbles, or bubbles with the pump off.
• Running a blower into air lines that still have open air controls.
• Forgetting the air lines hold water when you winterise. See Winterizing your hot tub.

Troubleshooting

• No air at the jets: check the air control is open and the jet pump is on high. A blocked or waterlogged air line will also stop the suction.
• Water coming out of an air control: it’s at or below the water line, or the water level is too high.
• Air on one side only: the air lines are probably joined, or the water flow to that side is weak. Check the valves and the jet internals.

Planning your own build?

The air side is easy to get right on paper and a pain to change once the walls are rendered. My DIY hot tub plans include the air and water plumbing layout, a full parts list, the build guide and the video course. The Ultimate Hot Tub Control Room Guide shows where the pumps, pack and (if you go that way) the blower go.

Air controls, gunite jets and blowers are available from parts4tubs.co.uk in the UK and parts4tubs.com in the USA. For the wider plumbing picture, read my DIY hot tub plumbing guide and how to install gunite jet bodies.

FAQs

Can a hot tub work without an air blower?

Yes. Venturi jets draw air in using the flow of water through the jet, so you still get bubbles, just fewer than with a blower and only while the jet pump runs.

Where should venturi air controls go?

On the edge or deck of the tub, above the water line, where people in the tub can reach them. One per side works well on a square tub.

How many jets per air control?

I group jets by side. On a 16-jet tub, that’s four groups of four, each with its own air line and air control.

Why is water coming out of my air control?

The air control is at or below the water line, or the tub is overfilled. It needs to sit above the water level.

Can I add a blower to a venturi system later?

Yes, but close or cap the air controls first, and add a check valve and a Hartford loop to protect the blower from water.

Going venturi on your build? Tell me how you’ve laid it out in the comments below. I read them all.

Cheers,
Andi

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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