How to Build a DIY Infinity or Overflow Hot Tub (Balance Tanks, Pumps and Plumbing)

Last updated: September 2026

Can you build your own infinity (or overflow) hot tub? Yes, and I get asked about it several times a week. Sitting in hot water with the edge falling away in front of you, so the tub seems to run on into the view, is about as good as a backyard gets.

I’ll be straight with you, though. An infinity hot tub is a lot harder than a normal skimmer-based hot tub. There’s more plumbing, more to go wrong, and the edge has to be built dead level. It’s a project for the adventurous, but the result can be spectacular.

What is an infinity hot tub?

An infinity or overflow hot tub is designed so the water flows over an edge rather than into a skimmer. You can overflow on every side (a “perimeter overflow”), but most DIY builds use one edge to form a waterfall facing the view. With the water falling away on that side, it looks as if the tub carries on forever, hence the name.

What’s different about an infinity hot tub?

Fundamentally, not a huge amount. It still needs a heater, pumps, a filter, a spa pack and jets, just like a normal hot tub. The difference is how the water gets back to the equipment.

In a regular hot tub, the skimmer and main drains feed the pump. The water goes through the filter and heater and back out of the jets. It’s a closed loop, and the water level barely changes.

In an infinity tub, there’s no skimmer. The water flows over the edge into a trough, and from there into a balance tank. The circulation pump draws from the balance tank, not from a skimmer, and pushes the water back into the tub. Because it’s constantly adding water, the tub overflows, and the edge also does the skimmer’s job of taking floating debris away.

What is a balance tank, and how big should it be?

Think of it like this. If your hot tub is full to the brim, it won’t overflow until more water is added. Each adult who gets in displaces around 70 litres (about 18 US gallons) of water, and that water goes over the edge. When they get out, the level drops by the same amount. Without somewhere to store that water and give it back, the edge stops flowing and the pump runs short.

That’s the balance tank’s job. It needs space for three things:

1. Bather displacement. This is about 70 litres (15 gallons) per adult. For 8 people, that’s about 560 litres (124 gallons).
2. Water in transit. When the pump’s running, there’s a layer of water above the weir, water pouring over the edge and water sitting in the trough and pipes. When the pump stops, all of it drains back into the balance tank.
3. An operating reserve. The circulation pump must always have water above its suction. Running a pump dry, or letting it suck air, will ruin it in no time.

My rule of thumb is to work out the displacement for the maximum number of people, then roughly double it. For an 8-person tub, that means a balance tank of around 1,000 litres (about 260 US gallons). It won’t normally be full. The spare space is what soaks up the surge when everyone climbs in, and the water that drains back when the pump stops.

If you’re a pool builder reading this, you might think that’s oversized. But a person displaces the same amount of water in a hot tub as in a pool, and a hot tub holds far less water. So the balance tank is much bigger relative to the size of the tub than it would be for a pool. For comparison, the pool method popularised by Skip Phillips sizes the surge for 2 inches of displacement across the whole water surface, plus the water in transit and an operating reserve. On a small hot tub, the per-person figure is the one that matters.

How the plumbing works: why I use two pumps

You could, in theory, run everything through the balance tank with one big pump. But hot tub jets need a lot of water. The jets I use need around 10 GPM each, so 16 jets need about 160 GPM. If all of that has to come from the balance tank, all of it has to go over the edge. That’s a torrent rather than a sheet, it’s loud, and it means a lot more water in transit for the balance tank to hold.

So a dual-pump layout (which is what my infinity hot tub plans use) splits the two jobs:

• Pump 1, the jet pump, draws from two split main drains in the floor and pushes water straight back out through the jets. It’s a closed loop, so it doesn’t change the level or drive the edge. The two drains are teed together, so if one is blocked the pump can’t pull hard on it. In the USA, drain covers must meet ANSI/APSP/ICC-16 under the Virginia Graeme Baker Act. There’s more in Installing a main drain.
• Pump 2, the circulation/edge pump, draws from the balance tank. It pushes the water through the filter and the heater (spa pack), then back into the tub through the returns, which sets the edge flowing. Turn it down (a variable-speed pump is ideal) for a gentle sheet, or off if you want a quiet tub at night.

See How many pumps do you need for your DIY hot tub? for more on pump layouts.

How much water should go over the edge?

Less than most people think, as long as the edge is level. Skip Phillips recommends about five gallons per minute per linear foot of vanishing edge. For a thin 6mm (¼in) sheet, Pool & Spa Marketing suggests 7–10 gpm per foot, with more flow needed if the edge isn’t perfectly level or has a rounded top. So a 6ft (1.8m) edge needs roughly 30–60 gpm (115–230 litres a minute), which is the kind of flow a circulation pump provides, not a 160 GPM jet pump.

The edge itself

• Dead level. Any low spot takes all the flow, and you get a dry patch elsewhere. Build the weir with a sharp, flat top and check it with a laser or water level.
• Waterproof both sides. The outside face of the edge wall and the trough are wet all the time. AQUA Magazine recommends waterproofing both sides and the top of the edge wall.
• A catch trough wide enough for the wind, so water doesn’t blow past it. If you prefer, you can use a stainless water blade as a spillway feature.

Other plumbing you’ll need

Top-up and overflow

The balance tank needs an overflow to a drain, so that when the pump stops and the water in transit drains back, the excess has somewhere to go. It also needs a top-up to replace evaporation and splash-out. A hot tub doesn’t lose water to evaporation or splashing the way a pool does, but it still loses some.

A simple ball float valve is tempting, but set its level carefully. With the pump running, the balance tank level drops, and a float will keep topping up. Then, when the pump stops, it all runs out of the overflow. AQUA Magazine warns against cheap float valves for exactly this reason and recommends putting the auto-fill on the lower basin, not the tub. An electronic level controller with high and low points is the better option. There’s more in my pool auto top-up guide. Whatever you use, the mains feed needs an air gap or backflow protection to keep your water supply safe, so check your local water or plumbing regulations.

Stop the pipes draining back

Fit check valves so the pipework doesn’t drain back into the balance tank every time the circulation pump stops. That’s exactly what happened on Brian’s build in the Bahamas. It gave him air locks and water draining back, and you can read how he sorted it in his infinity hot tub case study.

Filter the balance tank

The edge is your skimmer, so leaves and debris end up in the trough and balance tank. Put a basket or strainer on the suction, and make sure you can get into the tank to clean it.

Disadvantages of a DIY infinity hot tub

• Cost. You’re building a trough and balance tank as well as the tub, and you need a second pump. You may need a bigger heater too.
• Plumbing difficulty. It’s harder than a skimmer tub, but my plumbing diagrams take a lot of the guesswork out.
• More water to heat. The water in the balance tank has to be heated as well, so it costs more to run.
• More heat loss. Water tumbling over an edge loses heat and evaporates faster, and the balance tank needs insulating too. See DIY hot tub insulation.
• Noise. A waterfall is lovely, until it isn’t at 11pm. Plan to be able to turn it down or off.

A real build: Chris’s infinity hot tub in Utah

Chris from Utah got in touch knowing exactly what he wanted. He’d even modelled it in 3D, but he didn’t know how to plumb it. That’s where I came in. Not all my consultancy work is a full design. Sometimes I’m brought in just for the plumbing, or for the structure.

Chris started, like all great projects, with a big hole in the ground. He spread a base of crushed aggregate for stability and drainage, laid a rebar frame, and poured the concrete base.

Next came the through-wall plumbing. Getting this right matters, because everything ends up set in concrete. After that, he formed the walls with concrete forms.

Then the exterior plumbing went in, connecting the tub to the control room. After that came the decking, a layer of waterproofing on the concrete and, finally, black tiles.

Wait for it, and then all that hard work comes together. This is definitely one of the best-looking hot tubs any of my customers have built. I love the infinity edge and the landscaping. Chris, it’s spectacular, and thanks for letting me share your photos.

For more infinity builds, see Etienne’s infinity hot tub project and the infinity hot tub with a swim jet in Virginia. If you’re building a pool rather than a tub, read Infinity and zero edge pool design.

Common mistakes

• A balance tank that’s too small, so the pump sucks air when everyone gets in, or it floods when the pump stops.
• Running the jets through the balance tank, so there’s far too much water going over the edge.
• An edge that isn’t level.
• No overflow on the balance tank, or a float valve that fights the overflow.
• No check valves, so the pipes drain back and air-lock.
• No access to the balance tank for cleaning.
• Forgetting to insulate the trough and balance tank.

Planning your own infinity hot tub?

My infinity hot tub CAD plans are a dual-pump infinity edge design, with the overflow trough doubling as the balance tank. You get architectural CAD drawings, the plumbing diagrams, a shopping list, the assembly guide and the video course. They come in imperial sizes from 6ft to 12ft square and metric sizes from 183cm to 365cm.

If you’ve got something more unusual in mind, like Chris did, I can draw up architectural CAD and a 3D plumbing design, or help with just the plumbing through my plumbing consultancy. Pop your details in below if you’d like to talk it through.

FAQs

Can you build an infinity hot tub yourself?

Yes, if you’re a confident DIYer. The structure is much like any concrete or ICF hot tub. The extra work is a dead-level edge, a catch trough, a balance tank and a second pump.

How big should a balance tank be for a hot tub?

Allow about 70 litres (about 18 US gallons) per adult for displacement, then roughly double it to cover the water in transit and a reserve for the pump. For 8 people, that’s around 1,000 litres (about 260 gallons).

Do you need two pumps for an infinity hot tub?

It’s the best way to do it. The jet pump runs a closed loop from the main drains, and a separate circulation pump draws from the balance tank to drive the edge through the filter and heater.

How much flow does an infinity edge need?

About 5 gpm per foot of edge (roughly 60 litres a minute per metre) for a thin sheet over a level, sharp edge. Uneven or rounded edges need more.

Can I turn the infinity edge off?

Yes. With a dual-pump layout, turning down or stopping the circulation pump calms or stops the overflow. The jets still work.

Does an infinity hot tub cost more to run?

Yes. There’s more water to heat, including the balance tank, and more heat and evaporation lost over the edge. Insulate the balance tank and use a good cover.

Got a question about your own infinity 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