Hot Tub Pool Combo: The Complete DIY Design Guide

Last updated: September 2026

Hot tub and pool combos are a fixture at hotels and resorts. So can you build one yourself, in your own garden or backyard? The simple answer is yes. Let’s face it, it doesn’t get much better than having both. But a combo is two projects that have to work together, and the decisions you make at the design stage decide whether it works well or fights you forever.

In this guide I’ll go through the key design elements, the choices that matter, and the mistakes I see people make.

What is a hot tub pool combo?

A hot tub pool combo (or spa pool combo) is a heated hot tub, with jets, built alongside or into a swimming pool so the two work as one space. The hot tub is small and hot, and the pool is bigger and cooler. Most people use them for the contrast: a swim, then a soak.

It’s not the same as a spool, which is a small pool with jets that does both jobs in one body of water. If that’s what you’re after, see What is a spool? If you already have a pool and want to add a tub, see Can I add a hot tub to my existing swimming pool?

Layout and shape

So what’s the first thing to think about? Shape is definitely one of them. Square and rectangular pools and hot tubs are much easier to build, but a kidney-shaped pool with a round hot tub looks so cool.

You need to choose a layout you can actually build. Laying bricks to create a round tub is a real skill, and not something to try on your first rodeo. Be honest about your skills, or budget for someone who does curved work.

Layout	How it works	Good for
Raised spa spilling into the pool	The tub sits above the pool water and overflows into it	The classic resort look
Attached, separate water	They share a wall but no water	Different temperatures and chemistry, with a joined-up look
Faux spillover	Separate water, with a water feature on its own pump that looks like an overflow	The look of a spillover without sharing water
Detached	Two separate structures, linked by a deck or patio	Simplest to build and to add later

Size matters too. The bigger the pool and tub, the more they cost to build and heat. Think about where the control room goes as well. It has to reach both, and shorter pipe runs are always better. See Hot tub control room position.

Water flow: spillover or separate?

Once you’ve decided on the layout, the next step is deciding how the water will flow. Is the hot tub going to overflow into the pool? If so, the considerations and the plumbing are quite different from keeping the waters separate.

Spillover (shared water)

In a typical spillover, the pool’s pump draws water from the pool, pushes it through the filter and heater, and returns it into the hot tub. The hot tub fills and spills back into the pool. The hot tub’s jets run on their own pump, drawing from the tub’s own drains.

It looks amazing, but think it through. If you have a return line from the pool to the hot tub and you want different temperatures, you’re constantly topping the tub up with cooler pool water, which is counter-productive to say the least. The way round it is to design the valves so you can put the system into “spa mode”: the suction switches to the tub’s drains, the tub circulates and heats on its own, and the spill stops. When the tub’s up to temperature, you can switch back. As I explained in Can I add a hot tub to my existing pool?, you shut off the overflow while the hot tub heats.

Separate water

Keep the waters totally separate and each one gets its own pump, filter and heater. The hot tub can sit at 38–40°C (100–104°F) while the pool stays cooler, and you manage the chemistry for each separately.

If you still want the look of an overflow, you can add a water feature or waterfall on its own pump, spilling from the tub area into the pool. It looks connected, but the waters stay separate.

Plumbing: keep the hot tub jets on their own system

Pools and hot tubs do different jobs. As I explained in Why pool and hot tub plumbing should remain separate, pool plumbing is designed for a large volume of slow-moving water, and hot tub plumbing is designed to move a small amount of water quickly. In practice that means:

• A dedicated jet pump for the hot tub. A pool pump won’t give you enough flow for proper jets. As a rule of thumb, one jet pump runs up to about 16 jets at around 10 GPM each. See How many pumps do you need?
• At least two main drains in the tub, plumbed together with compliant anti-entrapment covers. See Installing a main drain.
• Water features on their own pump, never teed off the jets.
• Filters sized for each job. A sand filter that’s fine for the pool’s circulation can’t take the flow of a multi-jet system.
• Check the pool filtration can cope if the tub shares its water, because you’re adding volume to be filtered.

Heating your hot tub and pool combo

How will you heat it: together, or independently? This is a big decision, and you need a clear plan before anything is built. The main options are:

• Independent heaters. Run the pool on gas, propane or an air source heat pump, and give the hot tub a spa pack with its own electric heater (or its own heat pump). This is the simplest to control.
• One heater, diverted. Use a pool heater for both, with manual gate valves or actuated valves to divert its output to the tub when you want to raise it to 39–40°C (102–104°F). It saves buying two heaters, but you’re heating one or the other, not both at full tilt.
• Heaters or controls designed for pool and spa at different set points do exist, but they cost more up front.

A few facts to design around:

• Gas and propane heat fastest but cost the most to run.
• Air source heat pumps are the cheapest to run. The US Department of Energy puts pool heat pumps at a COP of 3 to 7, but they’re slower and lose efficiency below about 10°C (50°F).
• Cover both. The DOE says a pool cover can cut pool heating costs by 50–70%, because evaporation is the biggest heat loss. A spillover that’s running also loses heat and water as it falls, so switch it off when you’re not using it.
• Don’t overheat the tub. The US Consumer Product Safety Commission says hot tub water should never exceed 104°F (40°C).

Chemistry: one set of levels or two?

Hot tubs need higher sanitiser levels than pools. The CDC recommends at least 1 ppm of free chlorine in pools (2 ppm if you use stabiliser) and at least 3 ppm in hot tubs, with pH between 7.0 and 7.8. It also recommends not using cyanuric acid (stabiliser) in hot tubs at all.

• Separate water: you maintain two sets of levels. Treat the hot tub as a hot tub, using the ranges in my hot tub chemical levels guide, and the pool as a pool.
• Shared water (spillover): you’ll run one set of chemistry through both. It’s tempting to set it for the pool, but when the tub is running in spa mode, it’s a hot tub, so make sure it has at least the 3 ppm a hot tub needs. Keep stabiliser as low as you can, because it ends up in the hot water too. See Cyanuric acid in hot tubs.

Permits and safety

• UK: In England, an outdoor pool is often permitted development, within the outbuildings limits, but check with your council if you’re in a conservation area, national park or green belt, or at a listed building. The electrics must meet Building Regulations (Part P) and be installed by a registered electrician.
• USA: Expect a permit for an in-ground pool and spa. The CPSC’s safety barrier guidelines recommend a barrier at least 48in high with self-closing, self-latching gates, and they count spas and hot tubs as pools. Local codes set the actual rules. See Do I need a permit for my hot tub?
• Everywhere: supervise children, use a lockable cover on the hot tub, and fit compliant drain covers. The RLSS UK recommends secure fencing at least 4ft high around home pools too.
• Electrics: both need dedicated, RCD- or GFCI-protected supplies, and in the USA, bonding. See Hot tub wiring explained

Common mistakes with combos

• Choosing spillover, then wanting a hot tub at a different temperature, with no valves to isolate it.
• Running jets off the pool pump. They’ll be weak and disappointing.
• Returning cold pool water into the tub while it’s trying to heat.
• Forgetting the chemistry in a shared-water design.
• A control room that can’t reach both, or is too small for two sets of equipment.
• Curves beyond your skills, especially in blockwork.
• No covers, which means big heating bills.

Real combo builds

For inspiration, have a look at Danny’s pool and spa combo, Scott’s hot tub added to a pool in Arizona, a hot tub and plunge pool combo built from scratch, and Adding a spill-over hot tub to an existing swimming pool. For more layout ideas, see Spa pool combo: backyard ideas.

Planning a hot tub and pool combo?

Getting the design right from the start is key to any successful project, and a combo is no different. The key, as I see it, is the plumbing layout and working out exactly how you want it to function. Everything is possible. We just have to plan and design for it.

• Designing both from scratch? My custom hot tub and pool combo design consultancy ($2,997) takes your rough sketch of both and turns it into a 3D model, a 3D plumbing layout showing every pipe, jet and filter run, an architectural CAD drawing, a 6,000+ word build guide and a parts quotation. Pool filtration design is handled separately from the hot tub control room. I’ve explained how the design process works step by step.
• Structures already built or designed? The hot tub and pool combo plumbing consultancy ($2,497) gives you 3D plumbing schematics for both systems, a parts specification and quotation, and email support through your build. It doesn’t include structural design or CAD.
• Want to sketch it yourself first? Try the free Tub & Pool Designer Pro software, then I can turn your design into architectural CAD and a 3D plumbing design.
• Just the hot tub? My DIY hot tub plans cover a standard tub in full.

FAQs

Can I build a hot tub and pool combo myself?

Yes, if you plan it properly. Keep the shapes within your skills, get the plumbing designed before you build, and use a qualified electrician for the supply.

Can the hot tub and pool be different temperatures?

Yes. With separate water it’s easy. With a spillover, you need valves that let the tub circulate and heat on its own while the spill is stopped.

Should my hot tub spill into the pool?

Only if you’re happy to share water and chemistry, and to switch into spa mode to heat the tub. If you want independent temperatures all the time, keep them separate and add a water feature for the look.

Can one pump run the pool and the hot tub jets?

Not well. Pool pumps are designed for slow, high-volume flow. Hot tub jets need a dedicated jet pump, roughly one for every 16 jets.

Do a pool and hot tub need different chemical levels?

Yes. The CDC recommends at least 1 ppm of free chlorine for pools and at least 3 ppm for hot tubs. With shared water, make sure the tub has hot tub levels when it’s in use.

Do I need planning permission for a pool and hot tub in the UK?

Often not, as they can fall under permitted development, but check with your council if you’re in a conservation area, national park, green belt or listed building. The electrics must meet Building Regulations.

Planning a combo? Tell me about 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