DIY Hot Tub Plumbing: How to Plan Jets, Pipe Sizes, Drains and the Skimmer

Last updated: September 2026

Plumbing is kind of essential when you’re building your own hot tub. After the structure itself, it’s the most important part of the build. Without it you don’t have a hot tub, you have a very expensive garden pond. The good news is that the concept is simple. The challenge is getting the details right before the concrete goes in, because after that, changes get expensive.

This guide covers everything I’d want you to think about at the planning stage: how the water flows, how many jets you can run, pipe sizes, drains, the skimmer, the air side and testing it all before you bury it.

How DIY hot tub plumbing works

As an overview, a hot tub is simple. The tub is full of water. Water is drawn out through the skimmer at the top and the main drains at the bottom, pulled in by the pump. The pump then pushes it through the filter, through the heater and back out through the jets.

On a typical DIY tub with a spa pack, the pump comes first and pushes water through the filter and heater. Getting the order right matters because the heater needs filtered water flowing through it under pressure to work safely.

There are actually two sets of pipes running around the tub: one for water and one for air. They’re separate and only mix in the gunite jet bodies just before the water comes out of the jets. If you want a bigger-picture explainer first, read How does hot tub plumbing work? This post is the planning detail that sits behind it.

Decide where the control room goes first

Before you draw a single pipe, decide where your pump, filter and spa pack will live. Every pipe run starts and ends there, and shorter runs mean stronger jets and fewer joints to leak.

My control room is at the front left of my tub. It’s also too small, and I’ve since had to rebuild it. Make yours bigger than you think you need, keep it close to the tub and make sure it’s dry and ventilated. There’s more in Hot tub control room design considerations.

Jets: how many, and how much flow?

How many jets you choose seems like a simple question, but it drives everything else: pump size, pipe size and the plumbing layout.

I have a 3hp pump running 15 jets and there’s plenty of power. But horsepower is the wrong way to size it. What matters is flow. Each brand and nozzle has a flow requirement, and the Waterway jets I used needed about 10 GPM each to run properly.

So the calculation is:

• Number of jets × flow per jet = the flow you need. 16 jets at 10 GPM = 160 GPM.
• Then check that the pump can deliver that flow at your system’s resistance (the “head”), using the manufacturer’s pump curve.

Nozzle size makes a big difference. For Waterway’s gunite jet internals, INYO Pools lists roughly 8 GPM for a 1/4in nozzle, 12 GPM for 3/8in, 15 GPM for 1/2in and 25 GPM for 5/8in. Fit big nozzles all round and you’ll need a lot more pump.

Once you’re into the mid-teens of jets, you’re usually looking at two jet pumps, each feeding its own set of jets. I’ve covered the maths in How to correctly size a hot tub pump and How many pumps do you need?

Where to put them

Shop-bought tubs have lots of small jets everywhere. Gunite jets in a block, ICF or concrete tub are fewer but much more powerful. I placed mine so they’d hit the middle of my back when I’m sat on the seat, in a uniform line all around the tub. The more jets and the more ambitious the layout, the harder the plumbing. There’s more on types and layouts in DIY hot tub jets: everything you need to know.

Gunite jet bodies (the bit I struggled with)

These were one of the hardest things for me to get my head around. I’d never seen them, I couldn’t find a decent diagram or video, and they’re not cheap, so ordering them felt like a gamble.

You won’t find them on plastic shell hot tubs. They’re designed to be set into sprayed concrete (“gunite” or “shotcrete”) pools, but they work just as well through block, ICF or poured concrete walls, which is why they suit a DIY build.

Each body takes water from the pump underneath and air from the blower at the back. The two mix in the body before leaving through the jet. The pump’s flow is the engine. What the air does is add volume and bubbles, which makes the jet feel much stronger. You really notice the difference when you switch the blower on.

Two lessons from my build:

• Allow for your finished surface. Some of my jets stick out slightly, and a couple were set too far back, which leaves a gap where air escapes behind the jet. Measure for render, adhesive and tile before you fix the bodies.
• Set them perpendicular to the wall. A couple of mine aren’t quite square, so the jets don’t sit perfectly flush. Nobody else notices, but I do.

I’ve written a full step-by-step in The ultimate guide to gunite jet body installation.

Pipe sizes and types

Hot tub pipe is pressure-rated, so it’s not the same as household plumbing pipe. On my build, the water lines are 2in and the air lines are 1.5in, which matches the connections on typical gunite tee bodies (2in water, 1.5in air).

The size of pipe matters more than most people think, because water can only travel so fast before friction eats your jet power and suction becomes unsafe. US pool codes set limits of 8 ft/s on return (pressure) lines and 6 ft/s on suction lines. They’re good design limits wherever you build. Here’s what that means in Schedule 40 PVC:

Pipe size	Max flow at 6 ft/s (suction)	Max flow at 8 ft/s (return)
1.5in	38 GPM	51 GPM
2in	63 GPM	84 GPM
2.5in	90 GPM	119 GPM
3in	138 GPM	184 GPM

Source: ICC CodeNotes on ISPSC velocity limits.

So a pump moving 120 GPM shouldn’t be pulling through a single 2in suction line. Split the suction across the drains and skimmer, or step up the pipe size on the suction side. There’s more on choosing and sizing pipe in Hot tub pipe: the ultimate guide.

Flexible or rigid?

There’s rigid PVC and “flexible” PVC. Don’t kid yourself here: flexible pipe isn’t very flexible. You can bend it a little, but you won’t be tying any knots in it.

I used flexible pipe because I thought it would be less likely to pop out of a joint under pressure. I have no evidence for that. It costs a little more, but it won’t break the bank.

My mistake was trying to bend it everywhere to avoid joints, because I thought more joints meant more leaks. I was wrong. Good fittings and a properly made solvent-weld joint are extremely reliable. I had one awkward joint at a funny angle in the corner of the control room that I couldn’t quite get to, and guess what? When I filled up, that was the first leak. Neat, parallel runs with proper 90° and 45° fittings are the way to go. Here’s how to make the perfect PVC solvent weld joint.

Imperial and metric don’t mix

An imperial 2in pipe is not the same as a 63mm metric pipe. It looks the same, but 2in pipe is actually 60.3mm (2.375in) on the outside. The difference is about 2.7mm, which is more than enough to ruin a joint that has to hold under pressure. Pick one system and make sure every part matches. Where you have to connect the two (for example a metric pool skimmer), use a proper adaptor. I used a couple of Waterway adaptors on my skimmer.

Manifold layout: getting even pressure to every jet

My pipe runs split almost straight off the pump and run down each side of the tub, meeting (but not connecting) in the far corner. My thinking at the time was that two shorter runs give more pressure than one long one, and I still like that approach.

That said, both split runs and closed loops can work. What matters most is that the main manifold pipe is bigger than the branches to each jet, runs are kept short and roughly equal, and the pump isn’t trying to push more flow than the pipe can carry. If the jets furthest from the pump are noticeably weaker, the manifold is usually undersized or too long.

Main drains and suction safety

This is the part I’d stress most in 2026. A single blocked suction outlet can hold a person underwater, so suction safety isn’t optional.

• Fit at least two main drains, plumbed together to the pump, so that if one is blocked, the other keeps flowing. In the USA the Virginia Graeme Baker Act sets the rules for public pools and spas: compliant covers on every drain and, for dual drains to avoid the need for extra anti-entrapment devices, a separation of more than 3ft. Residential tubs aren’t covered by that Act, but it’s exactly how I’d build a home tub too.
• Use certified anti-entrapment drain covers rated for your flow.
• Keep suction velocity low (see the table above).

More detail in Installing a main drain for your hot tub.

The skimmer

Once you know how many jets you’re having and where the pipes go, you need to position the skimmer. This is trickier than you might think.

• Keep it close to the control room to shorten the pipe run to the pump.
• Its height sets your water level. The ideal level is halfway up the skimmer mouth, so floating debris flows in. Larger bits (in my case, usually the kids’ toys) end up in the basket, and smaller bits get caught in the filter.
• Allow for its full height, including the outlet fitting. I underestimated this once I’d added a 90° bend on the bottom, and had to get the breaker out and remove another 20cm of concrete I’d laid.
• Set the lid to your finished deck height. Mine doesn’t sit flush with the deck I put in afterwards. I made a cover to fit, but in a perfect world it would be flush.

The skimmer’s size is dictated by the volume of water, so check with the manufacturer. My tub holds 2,800 litres (about 740 US gallons), so I went for a swimming pool skimmer from Certikin, a brand you’ll find in lots of UK pools. That brought two challenges. It was on metric 63mm pipe while the rest of my system was 2in, which a Waterway bush and 90° bend sorted. And then there’s what I call the “swimming pool tax”. By shopping around online for the exact model, I saved about £90, which beat even the trade price my local pool man could get.

Step-by-step fitting is in How to install a skimmer on your DIY hot tub.

The air side: blower, check valve and Hartford loop

Air can get into the jets in two ways. Venturi jets use the moving water to draw air in through a pipe open to the atmosphere, which is why some shop-bought tubs have air controls you can open and close. The other option, which I chose, is a separate blower. Think of a hair dryer on steroids, pushing air through the pipes to the jet bodies. It won’t noticeably warm your water, but it does give you lovely bubbly jets. Not sure which to choose? See Do I need an air blower or can I use venturi?

Because air and water share the jet bodies, water will find its way into the air lines when the blower is off. Fit a one-way (check) valve before the blower and a Hartford loop: the air line rises above the waterline before dropping down to the jets. Gravity then stops water reaching the blower even if a check valve sticks. Water in a blower means a tripped supply and a dead blower. There’s more in my top tip for installing an air blower.

Pressure test before you bury anything

Nine times out of ten, when a DIY tub leaks, it’s the plumbing, not the structure. Before you concrete in the jet bodies, backfill trenches or tile over anything, cap the open ends and pressure test the system. Leave it under pressure for a good while and check that the reading holds. Finding a leak now costs you a fitting. Finding it after tiling costs you a weekend and a lot of swearing. If you do end up chasing one, see How to detect and fix a hot tub leak.

Common plumbing mistakes

• Sizing the pump by horsepower rather than jet flow.
• Pulling all the suction through a single 2in pipe.
• Fitting a single main drain.
• Mixing imperial and metric pipe without adaptors.
• Bending flexible pipe into awkward shapes to avoid fittings.
• Forgetting the finished tile thickness when setting jet bodies and the skimmer.
• No Hartford loop on the blower line.
• No isolation valves or unions around the pump, so every repair means draining the tub.
• Skipping the pressure test.

Troubleshooting after you fill up

• Weak jets everywhere: dirty filter, closed valve, air lock or an undersized pump or manifold. Start with how to deal with a hot tub air lock.
• Weak jets furthest from the pump: the manifold is undersized or the runs are too long.
• Water level dropping: check the joints in the control room first, then the air lines.
• Water in the blower: the check valve has failed and there’s no Hartford loop.

Planning your own build?

Getting all of this right on paper is far easier than fixing it in concrete. My DIY hot tub plans include a full plumbing layout, pipe sizes, a parts list and the video course, so you’re not working it out as you go like I did.

If your design is custom, the Tub & Pool Designer Pro plumbing design service turns your design into a proper plumbing layout. If you want someone to go through your plumbing with you, there’s also a hot tub plumbing consultancy. For pipe, I stock 2in flexible pipe and 1.5in flexible pipe in 25ft rolls, and the Ultimate Hot Tub Control Room Guide covers the equipment end. For pumps, spa packs and spares, head to parts4tubs.co.uk in the UK or parts4tubs.com in the USA.

FAQs

What size pipe should I use for a hot tub?

For a DIY gunite-jet tub, 2in for the water lines and 1.5in for the air lines is typical. Check your flows against the velocity table above, as large pumps may need 2.5in pipe or more than one suction line.

How many jets can one pump run?

Divide the pump’s flow at your system head by the flow each jet needs. With jets needing around 10 GPM each, one pump typically runs a single bank of jets, and bigger layouts move to two pumps.

Which order do the pump, filter and heater go in?

On most DIY systems: suction (skimmer and drains), then the pump, then the filter, then the heater, then back to the jets.

Do I need two main drains?

Yes. Two drains at least 1m (3ft) apart, with anti-entrapment covers, mean a single blockage can’t trap someone.

Is 2in pipe the same as 63mm?

No. 2in pipe is 60.3mm outside diameter. Use adaptors between imperial and metric parts.

Should I use flexible or rigid PVC?

Either works. I used flexible, but don’t rely on bending it. Use proper fittings for changes of direction.

Got a question about plumbing your own build? Drop it 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