How to build a hot tub Tuesday, 21 January 2020  |  Jon Pennington

Using Concrete, Wood, Tiled or Fibreglass

There are many ways to build a hot tub, which could consist of infinite component possibilities, sizes and scenarios, however they all seem to be built out off 1 of 4 main components, Concrete, Wood, Tile and Fibreglass. It’s also possible to build out of other materials for example metal, however this is less common and but probably easier due to thinner walls for jets to be mounted through.

Each style of material comes with restrictions and advantages, for example:

Fibreglass - An unrestricted method of making a hot tub would be to use a fibreglass mould, which means you could use virtually any jet on the market, have built in skimmers and suctions.

Wooden staves - The thickness restricts the usage of jets designed for thinner walls and needs a jet that can be fitted to walls up to 30mm thick. Putting a skimmer in is possible but not easy due to rounded walls and suctions are again restricted due the thickness of the wooden staves.

Note both hot tub styles can use any control system, and pump combination, it’s just the plumbing components that are restricted.

Designing a Hot Tub

When it comes to designing the content of a hot tub there are rules that govern the control system, quantity of jets and the pump required. If you think of air ducting and use that as a comparison the largest pipe always splits into 2 or 4 and then splits down maybe a couple more times until the pressure in the air vents is correct, this is the same for water pipes and jets. Which means that when designing you need a complete picture to acquire the cost of the total components like the pumps that are required.

Drawings

The correct method is to define the finished size preferably scaled on something like 'green graph paper' (or the software equivalent) and then add the jets to the drawing, once you are happy with the quantities you can then define the amount of pumps required to make it into a spa (hot tub is actually just a tub of hot water without jets), this in turn will define the rest of the plumbing for example the suctions and finally the control system that is needed to manage the pumps. Link to Control System

Jets and pumps

Only experience can define how many jets you can connect to a single pump, however every pump must always have 2 suctions.

Note: Diverters - if you are thinking of adding a diverter into the pump plumbing you can alter the power to different jets by moving a handle on the top of the spa, or having normal power when in the middle (water to both sets of jets), or have the system so it can be twice as powerful on one side or the other when the diverter handle is rotated to the left or the right.

Air Blowers

An air blower is a great edition to a hot tub and does exactly what it says blows air into the water, the dynamic of air jets Vs jets water jets gives a greater massage experience, but again comes with rules when being fitted, the power of the blower needs to match the amount of jets other wise it can be to powerful and burn out or under powered and not reach all the air jets.

Note: water jets are normally used for horizontal massage and air jets vertical.

Air jets are easier to install on fibreglass however when putting air in to a wooden hot tub you wouldn't put them into the floor, instead you would fit a ring under the seats and have the air coming up the front and rear of the seat.

In a tiled spa it would depend on the structure behind, for example a concrete and tile built hot tub would have 1" pipe structure where the jets need to be with a Gunite air jet fitted after on top and a tile and wood hot tub would be fitted with a normal screw together air jet in the edges of the seats.

Concrete

A little on concrete spas / hot tubs.

Building a concrete hot tub is done slightly differently because you would build a frame of pipework where you need the jets to be using Gunite fittings or similar. This would then be concreted, tiled or similar finish and then the front of the jets added afterwards. There are some great videos on how to build concrete spas on YouTube, and we would advise speaking to an experienced engineer about component requirement before anything is started because the location of the components needs to be considered beforehand and can define the total cost.

Hot Tub DIY is happy to help people with components to build any of the above hot tubs and spas, so please get in touch if you require more detail.

We have a range of pre-designed component bundles for people that who are considering making or converting a wooden stave based hot tub which you can see here: Wooden hot tub bundles