How to Build a DIY Infinity or Overflow Hot Tub?

What is an Infinity Hot Tub?

An infinity or overflow hot tub is designed in such a way that the water flows over the edge rather than through a skimmer. It could be all edges but for this example we are going to concentrate on one edge that is going to form a waterfall.

When you are sat in the Hot Tub, with the water just falling away on one side, it looks like the tub just extends into infinity – hence the name. Extremely visually pleasing, these kinds of tub look fantastic when you have that perfect view to frame with your hot tub.

What is Different about an Infinity Hot Tub?

Fundamentally, there is not a huge amount of difference in the construction of an Infinity Hot Tub to a normal one. The hot tub still requires heat, a pump a filter a Spa Pack plus of course Jets. The main difference is that a DIY Infinity Hot Tub is going to have an additional plumbing component called a “balance tank”.

If we look how a regular hot tub works, we can then see how an Infinity Hot Tub is slightly different. A regular hot tub has a skimmer and some bottom drains. This forms the inward flow of water that comes from the hot tub, sucked into the pump, then out through the filter, heater and back into the hot tub with the jets. This is very much a closed system and the water is circulated.

What is different about an Infinity Hot Tub is that instead of a skimmer, the water flows over an edge creating a waterfall, then is collected in a trough that then feeds into what is called a balance tank.

Instead of the water being sucked from the skimmer and the drains, it is in fact sucked from the balance tank instead and then returned to the hot tub, via the filter, the heater and ultimately the jets.

What is a Balance Tank?

The balance tank is essentially the part that collects the the water that is allowed to overflow. Think of it like this. If your hot tub is full to the brim, it will not overflow until more water is added.

Where is that water going to come from?

If we rely purely on displacement for example, an average sizes adult will displace 70 litres / 15 gallons of water when they get in the tub. Ok, great, but what happens when they get out? Where has that 70 litres / 15 gallons gone?

If we relied purely on this displacement to cause the overflow there would not be enough water flow to the jets. Remember, the average jet that I use in my builds needs 10 gpm of water flowing through it. With displacement alone, we are not going to have enough flow.

How Does an Infinity Hot Tub Work?

Enter the role of the balance tank. Instead of the water being sucked from a skimmer in a traditional hot tub setup, the water is being sucked from a balance tank. This means that the pump is actively adding water to the hot tub, causing the overflow when is then collected and stored in the balance tank. The balance tank will have enough space to house the extra water displaced when people are in the tub. It will then top it up again when they get out.

Think of it like this. The balance tank would need to be able to house for a 8 person hot tub, about 560 litres / 124 gallons of “extra displaced water” for when the hot tub was full of people. In addition to this, it would need to have enough water to constantly feed the jets and the pump as running a pump dry will burn it out in no time.

Therefore, if we know that our jet pump will be pumping around 200 GPM on full power. We also need to take into account the displacement of water that the number of people in our tub would cause. We’ve already calculated that 8 people would displace 124 gallons or 560 litres of water.

We need some water in there already for “flow” so we are really talking here about having a 1000 litre / 200 gallon balance tank. It would of course not be full, but it would allow for the extra space to house the overflowed water when the tub was full.

If there are any specialist pool building reading this, I am sure they will think that I am oversizing the balance tank. The displacement of a pool with people in it is going to be the same for a Hot Tub. Just because a person is in a pool rather than a hot tub doesn’t mean they are going to displace less water. They will of course displace the same amount of water. Therefore, a balance tank proportionally, against the size of a hot tub will be a lot larger than against the size of a pool.

Therefore. that said, this blog is or the DIYer who doesn’t want to pay 40K for an overflow Hot Tub so this method is going to allow them to create their own at a fraction of that cost.

What do I need in order to build a DIY Infinity Hot Tub?

The simplest way of answering this is you need all the parts you do for a regular hot tub, less the skimmer but plus the additional balance tank to store the water.

What Additional Plumbing Features do I need?

In terms of the plumbing, we’ve established that we need to have a balance tank. The balance tank is going to need to have an overflow drain. It is also going to need to have a “top up” or “fill” line plumbed into it. Many of the pools have an automatic mechanism for this DIY Infinity Hot Tub, I don’t think we need one.

The reason we don’t is that we are not going to be affected like a pool with evaporation to the same extent. We’ll also loose a lot less water to splashing etc. If you wanted to plumb one in, you could have it on something as simple as a ball valve like you have in a hot water header tank in your home.

Remember, this is a DIY Infinity Pool, going down the route of electrical solenoid valves and float controls is not worth it. Agin, this is in my humble opinion.

What are the disadvantages to a DIY Infinity Hot Tub?

Cost – It is going to cost you more because you need to have potentially an upgraded heater as well as and additional balance tank building.

Difficulty of Plumbing – The plumbing is more difficult but the plumbing diagrams that I provide will help you with this.

Additional water to heat – You do have additional water to heat so it is going to cost you more to run.

Additional Area to Insulate – You need to be mindful of the heat loss you will need to insulate the balance tank too