Can I Use My Hot Tub as a Swimming Pool in Summer?

Updated September 2026. I’ve expanded this post with clearer summer settings, updated chlorine and pH advice based on current CDC guidance (including one thing I’d now do differently), more on safety, and what to think about if you’re designing a tub to double as a small pool.

When the mercury tops the 80s here in the UK (that’s around 27°C and up), we have to make the most of it. Those of you in warmer climates get this weather all the time. We don’t! In my house, it means “converting” the hot tub into a small swimming pool, or a spool as they’re affectionately called.

With the inflatable crocodile and flamingo ready to go, here’s what you need to do to run your hot tub as a cool summer pool, and how to do it safely.

Turn down the temperature

The first thing to do is obvious: turn the temperature down. If you usually keep your hot tub at 102°F (39°C), drop it to the late 80s (around 31°C) to make it refreshing. If it’s particularly hot, you can go lower. This is personal preference.

For us, around 91°F (33°C) works well. The kids can stay in for as long as they want without getting cold.

A few tips:

• Your spa pack may not go that low. Many controllers have a minimum set point. On Balboa systems, the heat modes also change how often the tub checks and heats. See Balboa heat modes explained.
• In a heatwave the water can creep above your set point from sun, pump heat and a closed cover. Leave the cover off (or open) during the day when you’re around, and run the circulation in the cooler hours.
• Want it colder? Some pool heat pumps can chill as well as heat. Jandy’s VersaTemp, for example, heats and chills. If you’re choosing a heat pump anyway, a heat/cool model can be worth it in hot climates. See my guide to air source heat pumps for hot tubs.

Safety first

Please remember that your hot tub is nowhere near the size of a swimming pool, and nowhere near as deep. Jumping in, bombing and diving are all HUGE no-nos. If you have children, please, please, please remind them it’s a hot tub and not really a swimming pool. The last thing you want is a trip to A&E (the ER) instead of a relaxing afternoon.

• Supervise, always. The CDC points out that more children aged 1–4 die from drowning than from any other cause, and that drowning happens quickly and quietly. A designated adult should be watching, not on their phone.
• Drain covers. With more small people in the water, make sure every suction cover is in place and undamaged. Body and hair entrapment at drains is a known hazard.
• Lock the cover as soon as you’re done. A hot tub in “pool mode” is still open water in your garden or backyard.
• Keep drinks in plastic, not glass.

Filter and purge cycles

When your hot tub is heating, the pump runs on low speed (or the circulation pump runs) and the filter is doing its job. But on many systems, if the tub isn’t calling for heat, it isn’t filtering either, apart from its programmed filter cycles.

So check your filter cycles and lengthen them if you’re not heating. A summer tub full of kids, sun cream and grass needs more filtration than a winter one, not less. Nobody wants a green or cloudy tub! Clean the filter more often too, and see my spa pack survival guide for how to set cycles.

Chemical levels

Hot tub chemistry is usually run at higher sanitiser levels than a swimming pool. That’s because hot tubs are small, warm and have lots of people per litre of water.

Chlorine: what I’d do differently

When I first wrote this, I said that if you use your tub as a pool for a while, you can drop the chlorine to 2–4ppm. I’d be more careful today. The CDC recommends at least 1ppm free chlorine in pools (2ppm with stabiliser) and at least 3ppm in hot tubs. A spool at 31–33°C with kids splashing about still behaves far more like a hot tub than a pool. Add strong sun, which burns chlorine off quickly, and I’d now keep free chlorine at 3ppm or above and test more often.

The CDC also recommends not using cyanuric acid (stabilised chlorine) in hot tubs. If you’re tempted to add stabiliser for the sunny months, read Cyanuric acid: a hot topic in hot tub care first.

pH

Aim for 7.2–7.6. The CDC’s acceptable range is 7.0–7.8.

If pH is too high	If pH is too low
Chlorine works much less effectively	Aggressive water that damages pumps, heaters and fittings
Skin irritation	Stinging eyes and irritated skin
Scale (lime) forming	Damage to liners, if you have one
Cloudy water
Lower it with sodium bisulphate (pH minus)	Raise it with sodium carbonate (pH plus)

There’s much more in The ultimate guide to balancing chemicals in your hot tub, and if things do go wrong, Cloudy water in a hot tub will help.

Summer “pool mode” checklist

Setting	Hot tub mode	Summer pool mode
Temperature	37–39°C (99–102°F), max 40°C (104°F)	~31–33°C (late 80s–91°F) or lower
Free chlorine	3ppm or above	3ppm or above, and test more often
pH	7.2–7.6	7.2–7.6
Filtration	Normal filter cycles	Longer cycles, cleaner filter
Jets and blower	On for a massage	Optional, and they add heat and bubbles
Cover	On when not in use	Off while supervised, locked on when not

Designing a hot tub to double as a pool

When I first wrote this, I said there weren’t really any design considerations, because the filter, heater and pump are much the same and you simply don’t use the jets. That’s still broadly true if you just want to cool off in summer. But having designed a lot of spools and plunge pools since, there are a few things I’d now think about:

• Size and depth. A standard hot tub is great for a dip. If you want to actually swim, or float about properly, you’re looking at a spool or plunge pool. See What is a spool? and Hot tub vs plunge pool: which should you build in 2026?
• A swim jet. A counter-current swim jet turns a small pool into something you can genuinely swim in. See How to install a counter current swim machine.
• A skimmer. Summer means leaves, insects and grass. A skimmer makes a big difference. See How to install a skimmer on your DIY hot tub or plunge pool.
• Steps and a wide entry so kids can get in and out safely.
• Heating that can cope both ways: an air source heat pump sized for your volume, ideally with a cooling mode if you’re somewhere hot.
• If you’re adding a hot tub to a real pool, keep the plumbing separate. See Why pool and hot tub plumbing should remain separate.

It’s still much easier to use a hot tub as a pool than to convert a pool into a hot tub!

Want help with your hot tub, spool or cocktail pool design?

Watch the video below to see how I can help you design a hot tub, cocktail pool or spool.

If you want a tub that works as both, my plunge pool and cocktail pool plans come in several sizes with metric and imperial dimensions. There are also swim spa plans, and a counter-current swim jet with pump if you want to swim against the current. For a classic hot tub, start with my DIY hot tub plans.

FAQs

Can I use my hot tub as a pool in summer?

Yes. Turn the temperature down, lengthen the filter cycles and keep your chemistry in check. It’s great for cooling off and for kids, but it’s too small for proper swimming.

What temperature should a hot tub be in summer?

For cooling off, around 31–33°C (the late 80s to low 90s °F) feels good. We use about 91°F (33°C). Go lower if your spa pack allows and it’s very hot.

Can I turn off the heater on my hot tub in summer?

You can lower the set point, but keep the filtration running. On many systems, the pump only filters during heating calls and programmed filter cycles, so lengthen the cycles.

Do I need less chlorine if I use my hot tub as a pool?

Not really. A small, warm tub with a lot of bathers still needs hot tub levels. Keep free chlorine at 3ppm or above and test more often in hot, sunny weather.

Can kids swim in a hot tub?

At a cooler temperature and with constant adult supervision, yes. No diving or jumping, because it’s only about a metre deep.

Do you use your hot tub as a pool in summer? Tell me your settings in the comments below.

Cheers,
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