How to Build a DIY Exercise Pool (Swim Spa with a Counter Current Jet)

Last updated: September 2026

Fancy swimming every morning without driving to the leisure centre? An exercise pool (a swim spa, or a short pool with a counter current swim jet) lets you swim “endlessly” against a current in a space not much bigger than a large hot tub. And yes, you can build one yourself.

I need to be straight with you first. The build I describe here is my own, and what I actually built is my hot tub: about 2,800 litres, heated to 39°C, with jets and a blower. You can’t swim laps in it. Everything I learned building it applies to an exercise pool, though (the planning, the dig, the blockwork, the plumbing, the leaks), so I’ve included my experiences alongside the bits that are different when you scale up to something you can swim in.

What counts as an exercise pool?

“Exercise pool” gets used for a few different things. Here’s how I’d split them:

Type	Typical size	How you exercise	Water temperature
Swim spa / exercise pool	14–20ft x 8–10ft (4.3–6m x 2.4–3m)	Swim against a counter current jet, aqua jog, water aerobics	Pool temperature, around 25–30°C
Plunge or cocktail pool with a swim jet	From about 14ft x 7ft (4.2m x 2.1m)	Swim jet at one end, lounging the rest of the time	Pool temperature
Lap pool	Long and narrow	Swim real lengths, no jet needed	Pool temperature
Hot tub (like mine)	7–12ft square	You don’t really. It’s for soaking and hydrotherapy	37–40°C

This guide is about the first two: a built-in pool you swim in against a current. If you’d rather swim real lengths and have the garden for it, read Can you build a DIY lap pool? If you’re wondering whether a big hot tub will do, I answered that in Can I use my hot tub as a swimming pool? For the bigger picture on swim spas, see Can I build a DIY swim spa? and Backyard swim spa: everything you need to know.

Plan first (this is where my build went wrong)

Planning is the most important part, full stop. I went through it myself and there were places where my planning wasn’t quite right. The big one: I didn’t leave enough space for the control room, where the pumps, filter and electrics live. I’ve since had to rebuild it. On an exercise pool the control room has more in it (a swim jet pump as well as the filtration and heating), so make it bigger than you think.

Location

Before you fall in love with a spot, think about:

• Space around it. You’ll want a deck or paving, steps in and out, and somewhere for the cover to go when it’s off.
• What you’ll look at. It sounds daft, but if you have a view, use it rather than staring at a fence. Remember you’ll be facing the swim jet when you swim.
• Access for a digger. A pool this size is a lot more soil than a hot tub (more on that below).
• Where the control room goes. It needs to be close to the pool and low enough for the jet pump to sit below the waterline. See Hot tub control room design considerations. The same rules apply to a pool.
• The electrics. There are no plugs. The pool is hard-wired from your consumer unit (fuse board) or panel, so plan the cable route before you pour concrete across it.

How will you fill it and top it up?

You’ll lose water to evaporation, splashing and backwashing, so you want an outside tap nearby. Running a hose across the garden every week gets old fast. An auto top-up valve is worth considering on a pool this size.

My hot tub took about three hours to fill from a garden hose. A 12,000-litre exercise pool is four or more times that, so check your tap’s flow with a bucket and a stopwatch and plan a full day.

How will you empty it?

You won’t drain a pool as often as a hot tub, but you will for repairs. Use a submersible pump and hose, or design a drain-down route into the plumbing. Check where the water can legally go (chlorinated water shouldn’t go into a stream or surface water drain), and decide it now rather than when the pool is full.

Roof, pergola or indoors?

If you want a roof, a pergola or a full building over the pool, design it now. Footings for posts are far easier to put in before the pool than to squeeze in afterwards. An enclosure also cuts heat loss and lets you swim year-round, which matters more on a pool than on a hot tub. Indoors, ventilation is the big issue, because a warm pool puts a lot of moisture into the air.

Above ground or in-ground?

I’d go in-ground every time. It keeps the garden looking good, it’s easier to get in and out of, and you’re not on show to the whole neighbourhood when you’re in it. It’s also structurally easier: the ground supports the walls, and you can backfill behind the blockwork with concrete so the walls have nowhere to go.

A raised or partly sunken pool works too, but then the walls resist the full water pressure on their own and need engineering for it.

Size, depth and shape

Length and width

A counter current swim jet needs at least 4m (about 14ft) of length to work properly. Any shorter and the water bounces off the back wall and you swim in waves. A longer pool gives you more room to kick without catching the far wall, and a calmer current.

My swim spa plans come in sizes from 14ft x 8ft up to 20ft x 10ft for exactly this reason. According to my swim spa guide, the average backyard swim spa is about 14ft x 8ft.

Depth

You need enough depth that your hands don’t hit the floor when you swim. Commercial swim spas give you a useful benchmark. For example, H2X’s standard model holds about 42in of water and its deep model about 51in, so roughly 1.1–1.3m. Deeper is better for aqua jogging. Remember the hole is deeper than the water: add the slab, sub-base, membrane, tiles and freeboard. I’ve broken down that build-up in my in-ground hot tub groundwork guide, and it works the same way for a pool.

Seats and steps

Steps, a bench seat or a baja (tanning) ledge all eat into your swim length, so keep them out of the swim lane and draw it all out before you commit.

Shape

Keep it rectangular. Blocks and ICF are square, so a rectangle is easy, and a swim jet wants a straight run of water anyway. You can build curves or angles (blocks are easy to cut with the right saw), but remember you’ll be tiling it. The fancier the shape, the harder the tiling. Think, and think again, before you start.

Permissions and safety rules

UK

In England, the Planning Portal says outdoor domestic swimming pools often don’t need planning permission because they fall under permitted development. The limits are the same as for outbuildings. For example, no more than half the land around the original house can be covered by additions and other buildings, and it can’t go in front of the house. Listed buildings, conservation areas, national parks and other designated land need a check with the council. Scotland, Wales and Northern Ireland have their own rules.

The electrics are a different matter. They fall under BS 7671 Section 702 (swimming pools), which is stricter than a normal garden circuit. More on that below.

USA

Expect to need a building permit for an in-ground pool, and expect an inspection of the electrical bonding (NEC 680). Most areas also require a safety barrier. The International Swimming Pool and Spa Code, which many areas adopt, sets the top of the barrier at not less than 48in (1,219mm) above grade. Some inspectors treat a swim spa with a locking safety cover differently from a pool, so ask yours early. I’ve covered this in Do I need a permit for my hot tub?

Suction safety (everywhere)

Fit two bottom drains, and not just in case one gets blocked. The real reason is more serious: suction entrapment. A single blocked drain on a powerful pump can hold a swimmer under. The US Pool Safely rules for public pools require certified anti-entrapment drain covers, and multiple drains need their cover centres at least 3ft (0.9m) apart so one person can’t block both. That law is aimed at public pools, but I’d follow it on any DIY pool: two drains at least 3ft apart, teed together, with certified covers. See Installing a main drain.

Materials and construction

Gunite and shotcrete (concrete sprayed at high pressure over a rebar cage) look impressive in videos, but they need specialist kit and crews. I wouldn’t try it as a DIYer. Friendlier options:

• Concrete block (CMU): cheap and familiar. This is what I used. Hollow blocks with vertical rebar tied into the slab, then core-filled with concrete.
• ICF (insulated concrete form): what I’d use today. It’s Lego for adults: light, easy to cut, simple to run pipes through, and once it’s filled you get a strong, insulated wall in one go. Insulation matters much more on a pool you’re heating. See the best ICF blocks for building a hot tub.
• Poured concrete: strong, but on a long pool the formwork gets expensive.

There’s a full comparison in Hot tub wall construction: what are the options?

Breaking ground

This is the exciting bit, and in my case it was as hard as it was exciting. There was no way to get a digger round to my back garden, so I dug the whole thing by hand. It took nearly two weeks of evenings and full weekends. Once the ground got hard, I bought an electric breaker. I still think it’s one of the best investments I’ve ever made.

An exercise pool is a much bigger hole than my hot tub. A 14ft x 8ft pool with 1.2m of water, dug to around 1.7m deep with room for the walls and to work, is roughly 25m³ of soil in the ground, and it bulks up by about a third once it’s dug. Don’t try that by hand. If a micro or mini digger can get in, hire one, and book the muck-away before day one.

Before you dig, check for buried services: LinesearchbeforeUdig in the UK, and 811 in the USA. Plan the depth so it allows for every layer under the water. If you dig to the water depth, you’ll end up with a pool that’s too shallow.

The base

The electrics and plumbing didn’t worry me much. I knew the basics of both. What gave me sleepless nights was whether I could build a hole that wouldn’t leak and wouldn’t give way under the weight. My tub holds about 2.8 tonnes of water. A 12,000-litre exercise pool holds 12 tonnes, so the base matters even more.

Here’s what I did, and what I’d do now:

• Sub-base: I put down about 6–7cm (2in) of Type 1 and compacted it with a sledgehammer. If I did it again, I’d lay 100–150mm (4–6in) and hire a plate compactor (“wacker plate”). The sub-base spreads the load so the slab doesn’t crack, and cracks mean leaks.
• Membrane: I laid a thick PVC pond liner over the gravel as extra protection. Today I’d use sand blinding and a proper 1200-gauge polythene DPM, plus rigid insulation under the slab.
• Rebar: I tied a steel rebar grid together with wire. Some builders might call that overkill for a hot tub. For a pool it’s essential. Leave starter bars sticking up to tie the walls in.
• Concrete: I mixed about 4 parts sand to 1 part cement by hand, with plenty of waterproofing additive, working up from the bottom. It’s held, but that’s really a mortar or screed mix, not structural concrete. For a pool, order ready-mix (C25/C30) and pour the slab in one go, with the main drains, a hydrostatic relief valve and any pipe sleeves already in place.

I’ve written the whole groundwork stage up step by step, with a cross-section, in How to build a DIY in-ground hot tub: digging, base and blockwork.

Blockwork

I’d never laid a block before, and I was slow. It isn’t a race. What mattered:

• Start from a level base. The deepest part of mine wasn’t 100% level when I started the first course, and I spent ages compensating. By the second course I had guide lines in and it got much easier. By the end, the top courses were perfectly square.
• Check the diagonals. If both diagonals match, the shell is square. On a long pool, a small error at one end is a big one at the other.
• Mortar: I mixed about 4–5 parts sand to 1 part cement, slightly wetter than normal because I was slow. Too wet, though, and heavy blocks won’t sit properly.
• Block strength: I used 7N blocks, as I was only going up a few courses and the main load is the water pushing sideways. On a deeper pool with core-filled blocks and rebar, follow your plans or engineer.
• Cuts: pick dimensions that use full blocks where you can, and order a few spares for the ones that split. A block hand saw cost me about £15 and did every cut I needed.

Backfilling

As a first-time block layer, I worried the walls would move under the weight of the water. So I dug the hole bigger than needed and backfilled behind the walls with concrete, in stages, once the pipes and jet bodies were in. With no space to move, the walls weren’t going anywhere. It was also a handy place to get rid of block offcuts. On a pool, I’d do exactly the same.

Waterproofing

Back then I added waterproofing agent to every mix of mortar, render and concrete, and sealed the render with PVA. That helps, but on its own it isn’t a waterproofing system, and PVA isn’t something I’d put under pool tiles today. The modern approach is:

1. Waterproof render on block walls to give a flat, sound surface.
2. A pool-rated waterproofing membrane in two coats, such as Ardex S 7 Plus in the UK or Laticrete Hydro Ban in the USA, following the data sheet.
3. A flood test before you tile. Fill it, mark the level and leave it.

The swim jet

This is the part that makes it an exercise pool. There are two main types:

• Pump-driven (electric) jets. A pump draws water in through the sides of the jet unit and pushes it back out through the nozzle. It’s simpler and much cheaper, and good enough for fitness swimmers.
• Hydraulic systems. A hydraulic power pack drives a propeller. The current is stronger and smoother, but they cost several times more. They’re for serious swimmers and triathletes.

For most DIY builds, a pump-driven jet is the right choice. I sell four versions of the counter current / endless pool swim jet:

Option	What you get	Best for
Swim jet (faceplate, body and tubes only)	Jet body, faceplate, LED light, hoses and fixings	You’re sourcing your own pump and plumbing
Swim jet (no pump)	Jet plus air switches, 75mm couplers, 2in reducers, ball valves and bends	You have a suitable pump already
Swim jet with pump	As above, plus a 4HP single-speed pump (230V)	Most DIY exercise pools
Swim jet with dual pump	Two 4HP pumps for more flow	Stronger swimmers and longer pools

A few things to design around:

• Nozzle depth: the jet nozzle sits about 250mm (10in) below the water surface.
• Pump position: the jet pump must be installed below the waterline. That drives how deep your control room is.
• Hole size: the jet body is 260mm in diameter, so allow an 11in hole through the wall. Set it before the concrete goes in.
• Plumbing: the jet uses 75mm fittings reducing to 2in. Keep the runs short with sweeping bends, and fit valves and unions so you can service the pump.
• Keep it separate: the swim jet runs on its own pump and plumbing, not through your filter and heater.

There’s a full walk-through in How to install a counter current swim machine, and more on choosing one in Swim jet considerations. If you want to see one going in, follow this infinity hot tub with a swim jet in Virginia and Darren’s swim spa build in Arizona.

Plumbing and filtration

The concept is simple: water leaves through the skimmer and drains, goes through the pump, filter and heater, and comes back through the returns. Doing it without leaks is the work.

Pipe

You’ll use pressure-rated PVC pipe, both rigid and “flexible” (which bends a little, but you can’t tie knots in it).

My mistake: I bent flexible pipe out of the bottom drains to keep joints to a minimum, thinking fewer joints meant fewer leaks. I was wrong. Pipe and fittings are made so well that a properly solvent-welded joint is rock solid. I knew exactly where my first leak would be, a complicated joint at a terrible angle, and sure enough, that’s where it leaked. Use proper 90s and 45s, keep runs neat and parallel, and make every joint properly. See How to make the perfect PVC solvent weld joint.

I used Waterway pipe and fittings and rated them highly. One trap for UK builders: imperial 2in pipe and metric 50mm pipe look almost identical but aren’t the same size. Pick one system and stick to it. On my hot tub, suction lines are 2in and the returns 1.5in. On a pool, your plans will size the pipework to the pump and flow rate.

The skimmer

The skimmer sets your water level. The water should come about halfway up the skimmer mouth so debris flows in freely. I got mine wrong twice: I forgot to allow for the 90° bend underneath it, and I misjudged the height so the lid didn’t sit flush with the deck I built later. I made a cover to fit, but it should have been flush. Measure everything, including your finished deck height. I used a Certikin skimmer, and they’re still widely available.

Pump and filter

On a pool, the circulation pump’s job is to turn the water over through the filter, not to power jets. It’s sized by your plans to the volume and pipe runs. A variable speed pump makes a lot of sense here, as it can tick over quietly and cheaply most of the day.

For the filter, my top tip still stands: go bigger than you think. An oversized filter means less restriction, less strain on the pump and longer between cleans. If you’re not sure, go up a size. On my hot tub I used a 50 sq ft Waterway cartridge filter. On a pool, a sand filter is a common choice, as it’s cheap to run and easy to backwash.

Heating an exercise pool

This is the biggest difference from a hot tub, and it’s where people get caught out.

On my hot tub I have a 3kW heater in a Balboa BP601 spa pack. From cold (about 8°C in December), it took around 40 hours to reach 39°C. The heater gained about a degree an hour at first, then slowed down as the water got warmer and the nights got colder. It’s a bit like watching paint dry, but it got there.

Now scale that up. Here’s the maths: it takes about 1.16kWh of heat to warm 1,000 litres of water by 1°C. For a 14ft x 8ft pool with 1.2m of water (about 12,400 litres), that’s roughly 14.4kWh per degree. Heating it from 10°C to 28°C needs about 260kWh, before any heat is lost.

Heat output	12,400L pool, 10°C to 28°C	Degrees per hour (no losses)
3kW spa heater	~87 hours	~0.2°C
6kW heater	~43 hours	~0.4°C
12kW heat pump output	~22 hours	~0.8°C
18kW heat pump output	~14 hours	~1.2°C

Real times are longer because the pool loses heat while it warms, especially overnight and in wind. The takeaways:

• A spa pack heater on its own isn’t enough for an outdoor exercise pool. At best it tops up heat.
• An air source heat pump is the go-to. It’s what I use on my own tub, and it cut my running costs dramatically (see How I reduced the running costs of my hot tub by 66%). The US Department of Energy puts pool heat pump COPs at 3–7, meaning 3–7 units of heat for every unit of electricity, although efficiency drops as the air gets colder. For choosing and sizing one, see How to choose the right air source heat pump for your hot tub or pool.
• Gas heats fastest and suits occasional use or very cold climates. That’s why Darren went gas on his swim spa.
• Cover it. Evaporation is by far the biggest heat loss from a pool, and the US Department of Energy says covering a pool when it’s not in use can save 50–70% of heating costs. Insulating the shell (another point for ICF) helps too.

What temperature?

Swim cooler than you soak. U.S. Masters Swimming recommends 77–82°F (25–28°C) for competition pools, with multi-purpose pools at 83–86°F (28–30°C). It also warns that hard aerobic exercise in hot water can be dangerous. So run an exercise pool at 26–30°C, not the 38–40°C of a hot tub. If you want both, build a separate hot tub alongside, with its own heating.

Controls and Wi-Fi

Wi-Fi control was a must for me, so I could heat up remotely and keep an eye on the temperature. I used a Balboa BP601 with Wi-Fi. For Balboa BP packs, I now sell the ControlMySpa module, and many pool heat pumps have their own Wi-Fi control too.

Electrics

This is one of the few jobs where you must use a professional. It’s dangerous, it’s regulated, and DIY electrics can void your insurance.

UK

• Section 702 applies. BS 7671 treats swimming pools as a special location with zones. Zone 0 is the water itself, zone 1 extends 2m from the rim, and zone 2 goes a further 1.5m. In zone 0, only SELV equipment at no more than 12V AC is allowed, which is why pool lights are 12V. Mains circuits need 30mA RCD protection, and supplementary bonding is required.
• A dedicated circuit from the consumer unit, so if the pool trips, the house doesn’t go dark.
• An outdoor isolator, a simple rotary on/off switch for emergencies, placed where someone in the water can’t reach it. Under Section 702 it needs to sit outside zone 1 as a minimum, so ask your electrician where it should go.
• Armoured (SWA) cable for the outdoor run, so a stray spade doesn’t become a disaster. I clipped mine along the garden wall, partly so my kids couldn’t drive their toy cars into it.
• Cable size. There’s no one-size rule for this. Cable size depends on the total load (a swim jet pump, circulation pump and heat pump add up), the length of run and how it’s installed. Your electrician calculates it, and a registered electrician should notify the work under Part P and certify it.

USA

• You’ll need a 240V supply. Most US homes have split-phase 120/240V already, so it’s usually available at the panel. 120V equipment is too small for this job, as a 120V spa heater gives you well under 2kW.
• NEC Article 680 requires GFCI protection and, for permanently installed pools, an equipotential bonding grid. The rebar, metal parts and pump motors are bonded with solid copper no smaller than 8 AWG, and the grid extends at least 3ft under the deck. Plan this before you pour concrete.

Voltage and frequency

Equipment is built for a specific supply: 230V/50Hz in the UK and Europe, 120/240V/60Hz in the USA. Frequency matters too: a motor on 50Hz turns about 17% slower than on 60Hz (or 60Hz is 20% faster). Either way, buy equipment made for your country’s supply. There’s more in A guide to hot tub electrics.

Lights and audio visual

Lights

I can’t stress this enough: put a light in. It transforms the pool at night and means you can use it at any time of day. I expected the light to be the easiest part of my build. It was straightforward, but my big multi-coloured LED pool light caused me some early headaches. To make things easier for DIY builders, I’ve since launched my own Super Slim DIY hot tub and swimming pool light. Whatever you use, in the UK a light in the water must be 12V SELV.

TV and sound

AV is something I’m fussy about. Plan it at the start rather than bolting it on, and scale it to your budget. What I did:

• The TV: IP-rated outdoor TVs cost a couple of grand, which wasn’t in my budget. So I bought the cheapest 32in TV I could find and built a splash-proof cabinet from leftover decking, with house wrap under the lid, a Perspex front and a few 12V PC fans to stop the screen misting up. A shop-bought outdoor TV cover drops over the lot, and it’s held up well.
• Source and network: an Apple TV in the cabinet, fed by HDMI under the deck and a hard-wired network cable. Use outdoor-rated Ethernet. My first run failed within a year, and next time I’d use two shorter runs with a join halfway so a fault is easier to find.
• Sound: a marine-grade amplifier and two marine-grade speakers. I’d fit four next time, with two behind where I sit.
• Power: a separate supply for the AV and lighting, installed by your electrician outside the pool zones.
• Control: the one thing I’d improve. I have to get out to change what’s on, so plan a waterproof remote or phone control from the start.

Tiles, adhesive and grout

Tiles

Don’t rule out porcelain. Of porcelain and ceramic, porcelain is the less porous. By definition it has water absorption of 0.5% or less. For a pool, use tiles the manufacturer rates for submerged use. Small glass or porcelain pool mosaics are the best choice. They aren’t the cheapest, but they cope with curves, look the part and grip better underfoot. I used large wall and floor tiles on my build, and having seen so many customer builds since, I’d go mosaic next time.

Adhesive and grout

Don’t just buy “waterproof” shower grout. You need a pool-grade flexible adhesive and grout designed to be underwater all the time. Ardex recommends epoxy grouts for moving water, outdoor and salt water pools, and a swim jet definitely counts as moving water.

Let it cure

This is the one my wife was right about. I was racing to finish for Christmas, and waiting three weeks after grouting would have wrecked my self-imposed deadline. Don’t cut it short. Follow the data sheet. For example, Laticrete specifies 10–14 days at 21°C depending on the grout, and longer when it’s cold. After all the time and money you’ve spent, it would be a nightmare to watch the grout wash out in the first few months.

Edging and cutting

I used plastic bathroom-style edging trim from the DIY shop. It’s hidden once the water’s in, so it’s an easy place to save money, although metal trim or proper bullnose pool edge tiles look better. For cutting, a cheap wet diamond tile cutter is money well spent. Wear eye protection, because the chips fly.

Filling, testing and fixing leaks

Filling mine was the most stressful and most exciting moment of the whole build. Would it hold? Would the pump prime? Would the heater work?

I filled it with the garden hose (roughly 1,000 litres an hour), watching every inch. No leaks over the seats, none when the water reached the jets. At the skimmer, I ran the pump on low for 5 minutes and checked every joint in the control room. One had a drip, the joint that wasn’t quite square because I hadn’t left enough room, and on full speed the pump unions needed a turn. Then I turned on the blower and, voilà. The water was about 8°C, so on went the heater for the long wait.

Here’s what I learned about leaks:

• Weekly top-ups aren’t normal. I assumed at first that evaporation explained it. It didn’t. If the level drops noticeably every week, you have a leak.
• My first leak was a constant tiny drip from the bottom of a tee joining the skimmer line into the pump feed. I couldn’t get it dry enough to re-glue, so I used a plumber’s putty that cures wet, and it worked.
• My second leak was on the ozonator pipework. I’d already disconnected the ozonator because it wasn’t working properly, but the joints held with jubilee clips leaked badly under pressure. I isolated it, drained that section, cut it out and replaced it with pipe and a couple of 90° elbows. Anything held with a jubilee clip under pump pressure will leak eventually.
• Nine times out of ten, leaks are in the plumbing, not the shell. That’s why the flood test before tiling, and a pressure test of the pipework before you backfill, pay off.

After those fixes, I only top up every few months, mostly for evaporation and people getting in and out. For tracking down a leak, see How to detect and fix a hot tub leak.

Water care

You need a sanitiser to kill bacteria, and you need to keep the pH in range so the sanitiser works and the water is comfortable. The CDC recommends at least 1ppm free chlorine in pools (2ppm with stabiliser) and 3ppm in hot tubs, with pH between 7.0 and 7.8. An exercise pool run at pool temperatures sits with pools. Your basic kit:

• Sanitiser: chlorine or bromine. Chlorine is cheap, widely available and effective. Bromine is gentler on sensitive skin and more stable in warm water. A salt chlorinator is also a popular choice on a pool this size.
• pH increaser and decreaser.
• Total alkalinity increaser, to stop the pH bouncing around.
• Test strips or a test kit, and use them.
• Optional: clarifier and anti-foam.

At the right levels, chlorine is safe and effective.

Finishing touches

I finished mine with a deck and a new fence, and it looks the part. But when I costed my build I left all of this out, so budget for it. Choose surfaces that cope with years of wet feet: grass gets muddy and doesn’t love chlorinated splashes, decking can get slippery (anti-slip coatings exist, though I didn’t use one), and cheap artificial grass looks rubbish in my opinion. Slip-rated paving or porcelain slabs are the practical choice right around a pool.

What does it cost?

It varies hugely with size, finish and how much you do yourself. Here are some real numbers:

• Swim jets from my shop run from $997 for the jet only up to $2,699 for the dual-pump version. Hydraulic systems cost several times more.
• In What does a swim spa cost? I put shop-bought swim spas at $10,000 to $40,000+, before delivery and installation, and a DIY build at under $20,000.
• Don’t forget the digger, muck-away, the heat pump, a cover, the electrician and the landscaping.

Common mistakes to avoid

• Too short for the jet. Under 4m (14ft) and you’re swimming in your own wash.
• A control room that’s too small, or too high for the jet pump to sit below the waterline.
• Under-heating. A 3kW spa heater on 12,000 litres will disappoint you. Plan a heat pump and a cover.
• A single main drain. Fit two, at least 3ft apart, with certified covers.
• Relying on additives to waterproof it. Use a proper membrane and flood test.
• Bending pipe to avoid joints. Use proper fittings. It’s the awkward joints that leak.
• Filling before the grout has cured.
• Forgetting the finishing touches in the budget.

Planning your own exercise pool?

My swim spa plans come in sizes from 14ft x 8ft to 20ft x 10ft, and include CAD drawings, plumbing diagrams, a parts list, the build guide and the video course. They’re designed around a counter current swim jet, so pair them with one of the counter current / endless pool swim jets.

If your space is an odd shape, or you want a pool, hot tub and swim jet combination, start with the free Tub & Pool Designer Pro software. I can then turn your design into architectural CAD and a 3D plumbing design that you can hand to a builder or use for permits.

FAQs

How big does an exercise pool need to be?

For a counter current swim jet, at least 4m (about 14ft) long. Most are 14–20ft long and 8–10ft wide, with about 1.1–1.3m (42–51in) of water.

How do you heat an exercise pool?

Usually with an air source heat pump, or gas if you want fast heat-ups or live somewhere very cold, plus a good cover. A spa pack’s 3kW heater is too small to heat 10,000+ litres from cold.

What temperature should an exercise pool be?

Around 26–30°C (79–86°F). Competition pools run at 25–28°C. Hard exercise in 38–40°C hot tub water isn’t safe.

Do I need planning permission for a swim spa or exercise pool in the UK?

Often not. In England, outdoor pools usually fall under permitted development, within the same limits as outbuildings. Check with your council if you’re in a conservation area or a listed building, or on other designated land. The electrics must meet BS 7671 Section 702 and Part P.

Can I add a swim jet to an existing pool?

Often, yes, if the pool is at least 4m long and you can fit the jet body and a pump below the waterline. See How to install a counter current swim machine.

Planning an exercise pool, or already halfway through one? Drop your questions in the comments below. I read them all.

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Andi

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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