Planning a DIY Hot Tub in 2026: 10 Key Decisions to Make Before You Dig

Last updated: September 2026

So, you’re thinking about building your own hot tub? Good. It’s one of the best projects you’ll ever do. I built mine in my back garden, and since then I’ve helped more than 1,500 people build theirs, from simple block tubs to infinity-edge spas and plunge pool combos.

What I’ve learned from all those builds is that the tubs that go well are decided before a spade goes in the ground. Size, position, control room, walls, jets, heating and finish: get those decisions right and the build is just work. Get them wrong and you’re fighting them for years. This guide goes through each one, in the order I’d think about them.

First, decide how you want to build it

Before the technical decisions, there’s a bigger one: how much help do you want? Over the years I’ve seen three routes work.

Route	Who it suits	Where to start
Do it yourself, unaided	Confident DIYers who enjoy working out the design	The free guides on this blog and my YouTube channel. I want to build a hot tub: where do I start? is a good first read.
Follow a proven plan	Most people. You want certainty that it’ll work without designing it from scratch.	DIY hot tub plans in a range of sizes, with the video course included
Have it designed for you	Odd-shaped spaces, special features, combos, or you just want it done properly	Custom architectural CAD and plumbing design, or full design consultancy

Whichever route you choose, the decisions below are the same. The difference is how much of the thinking you do yourself.

I’ll be honest about one thing I see every year: plenty of people make a start and never get past it. The ones who finish are the ones who plan properly first. The number of “halfway through” rescue projects I get asked to pick up, with pipes through the walls and no idea what comes next, tells you how much planning matters.

1. Size: how big should your hot tub be?

Size seems simple, but it’s the decision that affects everything else. Think about three things together:

• How many people will realistically use it at once, and how much room each person needs.
• How much space you actually have, including room around it for steps, decking, the cover and the control room.
• Whether you can heat that volume of water. More water takes more energy and longer to heat, which means planning your soaks rather than jumping in when you feel like it.

Find the happy medium between those three. My own first design was far bigger than it needed to be, and I scaled it back to suit the heater I was planning to use. I’ve written that story up in Avoid these 7 DIY hot tub mistakes.

That said, the builds I help with have been getting bigger. Where 6ft x 6ft or 7ft x 7ft (roughly 1.8–2.1m square) used to be common, most people now go for 8ft x 8ft (2.44m) or larger. Part of that is people wanting one space to do several jobs: a hot tub in winter, a small pool in summer, or even a swim spa with a counter current swim jet. A swim spa needs more thought, because there are minimum dimensions and the seating layout changes. If you’re torn between a tub and a pool, read Hot tub vs plunge pool: which should you build?

To estimate the water volume, multiply the internal length by the width by the water depth, then take off an allowance for the seats and steps. A metre (40in) of water in a 2.44m (8ft) square tub is about 6,000 litres (1,570 US gallons) before you allow for seats, so seats and steps make a big difference.

2. Location: where will you build it?

You might have several possible spots, or there may be only one place it could go. Either way, think about:

• The control room. The tub’s position decides where the pumps, filter and heater can go. More on that next.
• Access. Can a micro digger get in, and where will the spoil go? My garden had no access, so I dug mine by hand. I’ve covered the dig itself in my in-ground build guide.
• Buried services. In the UK, run a free search on LinesearchbeforeUdig. In the USA, call 811 before you dig. It’s free.
• Water and power. You need a tap nearby for filling and topping up, somewhere to drain it, and a route for a dedicated electrical supply.
• The view and privacy. Face a view rather than a fence if you can, and think about who can see in.
• Where the cover goes. When you’re in the tub, where does the cover live? You don’t want to throw it on the lawn every time.

Do you need permission?

In England, the Planning Portal says you typically won’t need planning permission for a garden hot tub, unless you’re in a listed building or a conservation area. The electrics still have to meet Building Regulations. In the USA, many cities and counties want a permit for an in-ground spa, and safety barrier rules may apply. See Do I need a permit for my hot tub?

3. The control room: close and below the water line

This is one of my favourite topics, because it’s where so many builds go wrong. Two rules:

Keep it close. Ideally, the control room is within 15–20ft (4.5–6m) of the tub. Every extra length of pipe and every bend adds friction, and friction costs you jet pressure. If it has to be further away, upsize the pipe on the long runs.

Keep it below the water line. Hot tub pumps are centrifugal pumps. They’re built to move a lot of water quickly, but they can’t suck air, so they need water to flow into them. Below the water line, gravity keeps them primed.

If the control room is above the water line, you need a self-priming pump, and that’s where things get more expensive. Self-priming pumps are generally swimming pool pumps. They cost more, and they’re designed to move water efficiently and slowly through a filter rather than drive a set of hot tub jets. There are workarounds, such as a priming circuit on a centrifugal pump or a self-priming hot tub pump, but below the water line is simpler, cheaper and gives you more power at the jets.

And make it bigger than you think. Mine was too small, and changing a filter was a pain for years until I rebuilt it. There’s more, including the workarounds, in Hot tub control room position.

4. Materials: what will you build it with?

There are three main ways to build the shell, and they all work. Choose the one that best suits your skills, your site and your budget.

Wall system	Pros	Watch out for
Hollow concrete block (CMU)	Cheap, widely available and easy to work with	Needs vertical rebar and core-filling, render, and separate insulation
Formed and poured concrete	Very strong, with no mortar joints	Formwork is a big job, and plumbing has to be set before the pour
ICF (insulated concrete forms)	Light, easy to cut and plumb through, with insulation built into the wall	Needs bracing when you fill it, and a pour done in one go

Mine is block, and it’s been fine. But if I built it again, I’d use ICF. I call it Lego for adults. Insulation has become one of the biggest questions people ask me about, because it keeps running costs down, and with ICF you get the wall and the insulation in one. See the best ICF blocks for a hot tub and my TubBlox kits.

Whatever you choose, the structure needs a reinforced slab, rebar tied into the walls and a hydrostatic relief valve in the floor. The in-ground build guide covers all three. Insulate under the slab and behind the walls while you can. It’s cheap now and almost impossible to add later. See DIY hot tub insulation.

5. Jets: how many do you need?

A built hot tub is very different from a plastic shell tub. Shell tubs are marketed with dozens of jets and air nozzles. What we build has fewer jets, but much bigger ones, and they feel far better for it.

My rule of thumb is a maximum of 16 jets per pump. Each jet needs a certain flow to work properly, and a pump only delivers so much. So you can’t just keep adding jets to one pump. If you want more than 16, you need a multiple-pump system. For most 8ft x 8ft or 10ft x 10ft tubs, 16 is plenty.

There’s a calculation behind this, and it depends on the jets, the pipe sizes and the length of the runs. See How many pumps do you need? You’ll also want to decide on bubbles: an air blower or a venturi system?

6. Water features: keep them separate

Planning a waterfall, a water blade or a spillway? Keep it on its own system, with its own suction and its own pump.

That gives you control of the flow, so you can get the water feature looking exactly right, and you can run it when you want. If you tie it into the spa pack, you’re limited by the pack. All the spa packs I use switch the jet pumps off automatically after a set time, and your waterfall goes off with them.

On its own supply, you can even put it on a timer or a smart switch and control it by voice. That supply still needs to be part of a properly designed outdoor installation, RCD protected in the UK or GFCI protected in the USA, and fitted by your electrician. There’s more in the ultimate guide to adding a water feature.

7. Heating: probably your most important decision

How you heat the tub drives the plumbing, the electrics and, most of all, your running costs. The main options are:

• Electric, using the heater in the spa pack. It’s simple and cheap to buy, but with UK electricity at around 26p per kWh under the October–December 2026 price cap, it’s the most expensive to run.
• Air source heat pump. Almost every European build I design now has one. See the ultimate guide to air source heat pumps for hot tubs and how to choose the right air source heat pump.
• Gas or propane. The most popular choice with my US customers.
• Solar, wood and the rest. I’ve yet to see a solar thermal setup that heats a hot tub well on its own, but I know several customers who run their heat pumps from solar panels.

I compare them all in What is the best method to heat my DIY hot tub?

One top tip: if you’re using an external heater (a heat pump, a gas heater or an extra electric heater), give it a dedicated circulation pump. That way the heating circuit doesn’t steal flow from the jets, and the heater gets steady flow whenever it needs it. It’s why a dual-pump layout, with a circulation pump plus a separate heat source, is now standard in my plans. See how to add a circulation pump.

8. Electrics: plan the supply now

Your electrician will connect it at the end, but the supply needs planning now, before you pour concrete across the cable route.

• UK: a dedicated circuit with 30mA RCD protection and a local isolator, installed by a registered electrician. It’s notifiable work under Part P.
• USA: a dedicated 240V GFCI-protected circuit with a disconnect in sight of the tub, under NEC Article 680. Most areas need a permit and an inspection.

The size of the circuit depends on your spa pack, heater and pumps. See A guide to hot tub electrics.

9. Water treatment: decide how you’ll look after it

Chlorine or bromine are the standard choices, and the CDC recommends at least 3ppm free chlorine in a hot tub, with pH between 7.0 and 7.8. I’ve also been asked more and more about salt systems. People tell me they like the feel of the water on their skin and don’t like the smell of chlorine. I get it, although I’m sticking with chlorine in my own tub.

If you want salt, plan the chlorinator into the plumbing from the start. See Considering a saltwater hot tub? and my guide to hot tub chemical levels.

10. Finishing: the final touch

The main finishes are:

• Painted epoxy pool paint
• Tiles, especially mosaic pool tiles
• Modern cement and microcement finishes
• Natural stone

Here’s the important principle: don’t let the finish be part of the structure. If you want a natural stone look, don’t build the walls out of that stone. Build the structure from block, ICF or poured concrete, waterproof it with a proper membrane and flood test it, then treat the stone just like a tile, a finishing surface that’s independent of the structure and the waterproofing. It’s far easier to get right, and far easier to fix. See Waterproofing, grout and tile adhesive.

Don’t forget time and budget

A DIY hot tub takes longer than you think. Depending on the time and help you have, 10–12 weeks is typical. See How long does a DIY hot tub build take? for a real example. On budget, the plumbing kit, heating and finish are where the money goes. If money’s tight, What is the cheapest hot tub to build? covers the budget options.

Decision	What I’d recommend for most builds
Size	Balance people, space and heating. 8ft x 8ft (2.44m) is a popular sweet spot.
Control room	Within 15–20ft (4.5–6m), below the water line, bigger than you think
Walls	ICF, or core-filled block with insulation
Jets	Up to 16 per pump
Water features	Own suction, own pump, own control
Heating	Heat pump (UK/Europe) or gas (common in the USA), on a dedicated circulation pump
Finish	Independent of the structure, over a proper waterproof membrane

Planning your own build? Here’s how I can help

If one of the standard sizes fits your space, my DIY hot tub plans make every decision above for you. You get CAD drawings with every dimension, the plumbing layout (including the dual-pump heating circuit), a full parts list and the video course. There are also infinity hot tub plans, swim spa plans and plunge pool plans.

If what you want isn’t quite standard (an odd-shaped garden, a feature you’ve seen on Pinterest, a hot tub and pool combo), start with the free Tub & Pool Designer Pro software. I can then turn your design into architectural CAD and a 3D plumbing design you can build from, hand to a builder or use for permits. Here’s how the custom design process works.

If you want me involved beyond the drawings, there’s custom hot tub design consultancy, plumbing consultancy for your build, and design consultancy for hot tub and pool combos.

For parts, I’d always rather you bought a set that’s been checked to work together than a basket of bargains that don’t. My stores are parts4tubs.co.uk in the UK and parts4tubs.com in the USA.

FAQs

What should I decide first when planning a DIY hot tub?

Size and location, because they decide everything else: the control room position, the pipe runs, the heating and the budget. Then choose your wall system, jet layout and heating method before you dig.

How far can the control room be from the hot tub?

Ideally within 15–20ft (4.5–6m). Further than that and you lose jet pressure to friction unless you upsize the pipe or the pumps. Keep it below the water line so standard hot tub pumps stay primed.

How many jets can one hot tub pump run?

As a rule of thumb, up to 16. Above that, you need a second jet pump. The exact number depends on the jets, pipe sizes and run lengths.

What’s the cheapest way to heat a DIY hot tub?

For most people in the UK and Europe, an air source heat pump on a dedicated circulation pump, combined with good insulation and a good cover. In the USA, gas or propane is popular, depending on local fuel prices.

Can I use natural stone for my hot tub walls?

Use it as a finish, not as the structure. Build the shell from block, ICF or poured concrete, waterproof it, then fix the stone like a tile.

How long does it take to build a DIY hot tub?

Typically 10–12 weeks, depending on how much time and help you have. Don’t rush the plumbing.

Got a question about planning 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