What Makes a Good DIY Hot Tub Design? Sizes, Seats, Heating and More

Last updated: September 2026

Designing your own hot tub is fun. But it’s also the most important stage of the whole project. Before you even think about breaking ground, you should have a design and a plan. I think the saying goes “fail to plan, then plan to fail”, and in hot tub building it’s absolutely true. An hour spent planning saves ten hours of doing.

Since I built my own tub, I’ve helped more than 1,500 people with theirs, so I’ve seen what makes a design work and what causes problems years later. This guide walks through the decisions that make a good DIY hot tub design.

Start with what you want the hot tub to do

What do you want from your hot tub? Yes, you want it hot, and yes, you want jets. But what about lighting, audio, a waterfall or a water blade? All of the above?

There’s a common misconception that you can just tee a water feature off your jets. You can’t. It never works well that way, and one always starves the other. A water feature should always have its own pump and its own lower drain. That’s why these things need planning at the design stage, not added later. There’s more in Adding a water feature to your DIY hot tub.

The same goes for jets. As a rule of thumb, one jet pump runs up to about 16 jets, because each jet needs around 10 GPM. Go beyond that and you need a second pump, and that has to be in the design. See How many pumps do you need for your DIY hot tub?.

Make it yours: unique features

What unique features will you include? Why would you need them? You don’t. But you’re designing this yourself, so why not add some of your own personality? Creating something that’s just for you is one of the reasons we build our own hot tubs in the first place.

Some ideas I’ve seen work well: a lounger seat, an infinity or overflow edge, a stainless water blade, underwater lighting, a swim jet, or a cold plunge alongside. Just remember each one needs to be in the plan before the concrete goes in.

Materials and finish

How are you going to build it? The main choices for the walls are concrete block, poured concrete and ICF (insulated concrete form) blocks. Mine is block, but if I built again I’d use ICF, because the insulation is built into the wall. There’s a full comparison in Hot tub wall construction: what are the options?

Then there’s the finish. Personally, I like small mosaic pool tiles, and having seen so many customer builds, I’d choose them over large tiles every time. They follow curves and seat edges far better. You can also paint the surface with a pool-grade coating. Whatever you choose, it goes on top of a proper waterproofing system, so decide at the design stage. See Waterproofing, grout and tile adhesive.

Size, layout and depth

Size matters, but not in the way you might think. The bigger the tub, the more water you have to heat. That means a bigger heater and higher running costs. The most common DIY size I see is 8ft x 8ft, which seats a family comfortably without being expensive to run.

The dimensions I design to

Make a tub too deep and it’s hard to sit on the seats without floating off them. Make it too shallow and it doesn’t feel like a soak at all. It’s a fine balance. As a rule of thumb, here’s what I use:

Dimension	Metric	Imperial
Water height (floor to the centre of the skimmer)	90cm	about 35.5in
Seat height (from the floor)	45cm	about 17.75in
Seat depth (front to back)	50–55cm	about 19.75–21.75in
Water over the seat	about 45cm	about 17.75in

These are my starting point, not a law. Taller people like deeper seats, and a mix of seat heights around the tub suits everyone. Your plans set the final figures.

Steps, and where the cover goes

When you’re designing the layout, think about where the steps go, because you’ll definitely need a way in. Steps inside the tub take up seating space, and steps outside take up garden. Either way, keep treads non-slip and consider a handrail. See Hot tub steps: the ultimate guide.

Also, where does the cover go when you’re in the tub? Covers are big and heavy, so you don’t want to carry them far. Plan a spot for a cover lifter or somewhere to slide it. If your tub is an unusual shape, remember the cover will need to be made to measure. See The ultimate guide to hot tub covers.

Plan the control room properly

If you’ve read other posts on this blog or watched my YouTube channel, you’ll know I talk a lot about the control room. That’s because it’s the part I got wrong on my own build.

My advice is to leave far more space than you think you’ll need. Having too much space is never a problem. Not having enough certainly is. Making plumbing connections in a tight space is hard, and so is routine maintenance. Before I rebuilt my control room, changing and cleaning the filter took about an hour. I had to physically remove the filter from the plumbing, so there was a good chance it would leak when I put it back. Total mess. After I redesigned it with more space, it takes about 10 minutes. Do yourself a favour and give yourself plenty of room. See My hot tub control room remodel.

Position matters as much as size. Keep it close to the tub, and decide early whether it sits above or below the water line, because that decides whether you need self-priming pumps. See Hot tub control room position.

Choose the heating method at the design stage

The heating method should be decided during the design, not after. The things to think about are the volume of water, how quickly you want to heat it and the running costs.

There’s no point designing a huge tub and then trying to heat it with a 3kW electric heater. It’ll struggle to get up to temperature, especially in winter, and it’ll cost you the earth.

• If you want to decide an hour before that you fancy a soak, you need gas or propane. It’s the fastest.
• If running costs matter most, look at an air source heat pump. It’s still the most economical way to heat a pool or hot tub. The US Department of Energy puts pool heat pumps at a COP of 3 to 7, meaning 3 to 7 units of heat for each unit of electricity. They’re slower than gas, and their efficiency drops in colder weather, but when I fitted one to my own tub, I cut my running costs by 66%.
• Electric through the spa pack is the simplest to install, and it’s fine for smaller tubs or as a top-up alongside a heat pump.

There’s more in What is the best method to heat my DIY hot tub? and How I reduced the running costs of my hot tub by 66%.

Insulation: design it in

An in-ground tub loses heat into the ground all year round. The time to deal with that is in the design, with rigid insulation under the slab, insulated walls (ICF makes this easy) and a good, well-fitting cover. It’s very hard to add afterwards. See DIY hot tub insulation.

Safety features to design in

• Two main drains, plumbed together and with compliant anti-entrapment covers, so a single blocked drain can’t trap anyone. In the USA, drain covers for public pools and spas must meet the ASME/ANSI A112.19.8 standard under the Virginia Graeme Baker Act. It’s good practice for a home tub too. See Installing a main drain.
• Temperature. The US Consumer Product Safety Commission says hot tub water should never exceed 104°F (40°C). Make sure your controller and heater are set up to respect that.
• Non-slip steps and coping, and a handrail if anyone older will be using it.
• A lockable cover, especially if you have children or visitors. In the USA, many areas also require a barrier around a spa. See Do I need a permit for my hot tub?
• Electrics: a dedicated, RCD- or GFCI-protected circuit with an isolator or disconnect within sight of the tub, installed by a qualified electrician. See Hot tub wiring explained.

A quick design checklist

1. Location, access for materials, and where the water goes when you drain it.
2. Internal size, shape and water depth.
3. Seats, loungers and steps.
4. Wall construction and finish.
5. Jets, pumps, blower and any water features.
6. Control room size and position (above or below the water line).
7. Heating method and power supply.
8. Insulation and cover.
9. Lighting and extras.
10. Permits and safety.

Common design mistakes

• Going too big and then paying to heat it.
• Seats too shallow or too deep for the people using them.
• A control room that’s too small (my mistake).
• Water features on the jet pump.
• Forgetting the steps and the cover until the tub is built.
• Undersized heating for the volume and the climate.
• No insulation under or behind the shell.
• Curves you can’t build. Square and rectangular tubs are far easier for a first build.

Want help with your design?

It might seem daunting to design your own tub, but you don’t have to start from scratch. I know what works and what doesn’t.

• A standard size: my DIY hot tub plans have all of the above worked out: CAD drawings, plumbing diagrams, a parts list, the build guide and the video course.
• Your own layout: design it in the free Tub & Pool Designer Pro software, then I can turn it into architectural CAD and a 3D plumbing design.
• Something truly custom: if you’re still weighing it up, read Custom hot tub: should you build one? My custom hot tub design consultancy goes from your rough sketch to a 3D model, plumbing, CAD, build guide and parts quotation. If there’s a pool too, there’s the hot tub and pool combo design consultancy. I’ve explained how the custom design process works step by step.

FAQs

How deep should a DIY hot tub be?

I design for about 90cm (35.5in) of water from the floor to the centre of the skimmer. Most tubs sit somewhere around 90cm–1m (36–40in) of water.

How high should hot tub seats be?

I usually make seats 45cm (about 17.75in) high and 50–55cm (about 19.75–21.75in) deep. That leaves about 45cm of water over the seat. A mix of seat heights suits people of different sizes.

What is the best size for a DIY hot tub?

The most popular size I see is 8ft x 8ft. It’s big enough for a family and not too costly to heat. Go bigger only if you’ll use the space.

Can I put a waterfall on the same pump as the jets?

No. Give it its own pump and lower drain, or neither will work properly.

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

Gas or propane if you want fast heat-ups, and an air source heat pump if you want the lowest running costs. Electric through the spa pack is the simplest to install.

What is the best material for a DIY hot tub?

Block, poured concrete and ICF all work. I’d choose ICF today for its built-in insulation and ease of building.

Designing your own tub? Share your ideas or questions in the comments below. I read them all.

Cheers,
Andi

You can also find me on my socials;

Can I Help You?

If I can help you in any way I would love to hear from you. You can get in touch using the form below.

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