Bill of Materials for a Hot Tub – What Goes into a Hot Tub?

So what materials go into building a quality hot tub? In this article we will examine the manufacturing bill of materials (MBOM) as well as some other indirect costs.

Here is a breakdown of the materials required to build an average hot tub (90”x90”) with 2 pumps/motors and 50 jets;

1. Cast Acrylic Sheet – this is thin sheet of acrylic that comes most commonly in seven and eight foot sheets used as the top, cosmetic layer of a hot tub shell. The acrylic is available in variety of colors and textures to suite any taste.

Cast acrylic sheet for hot tub
Cast acrylic sheet

2. Resin – bonding layer of material that goes between the acrylic and the fiberglass

Hot Tub Resin
Hot Tub Resin

3. Fiberglass – structural layer that is chopped, sprayed, and rolled onto the acrylic and resin.

Hot Tub Fiberglass
Hot Tub Fiberglass

4. Motors (2 x 4hp) – also referred to as jet pumps. These components move the water throughout the plumbing, manifolds, and ultimately the jets of the hot tub. Most of your mid or high end hot tub models have at least two motors (aka jet pumps). The motor/pump typically has a 2” intake and 2” discharge.

Hot Tub Pumps
Hot Tub Pumps and Motors

5. Pump Unions – heavy duty plastic rings that attach the pump head (intake and discharge) to the 2” plumbing (referenced in item #10 below).

6. Spa Pack with Topside Controller – this is the main control box of the hot tub that holds the mother board and heater. The pack is directly hard wired with the 220v electrical service (4 wires). The pack also connects to a topside controller that mounts flush to the surface of the hot tub shell toprail.

hot tub spa pack
Spa Pack
Topside Controller
Topside Controller

7. Jet Bodies (50 total) – once holes are drilled in the hot tub shell then the individual jet bodies, made of heavy duty plastic get attached on each side of the shell and sealed with silicone for a leak proof fit. Jet bodies are different sizes to accommodate different size jets which get inserted into them. The back of the jet body (the portion behind the shell of the hot tub) has two ports coming out of it. One is for designated for air source and one is designated for water source. Below are four sizes of jet bodies and quantities for a 50 jet hot tub.
a. Cluster Body x 15
b. Mini Spinner Body x 15
c. Poly Storm Body x 10
d. Power Storm Body x 10

Hot Tub Jet Bodies
Hot Tub Jet Bodies

8. Jet Inserts (50 total)– nozzles or inserts as they are referred to in the industry snap into the jets bodies referred to in #7 above. The inserts are what you see when you look into the hot tub. The pumps move the water through these jet inserts to massage the bathers. There are different sizes and styles of jets available. Some are proprietary designs and some are industry standard designs. You should have an equal number of jets bodies and jet inserts. Below are the corresponding jet inserts that go with the jet bodies referenced in #8 above.
a. Cluster Inserts x 15
b. Mini Spinner Inserts x 15
c. Poly Storm Inserts x 10
d. Power Storm Inserts x 10

hot tub jets inserts
Various Sizes of Jet Inserts
hot tub jet insert
Jet Insert

9. Suctions – or intakes as they are referred to are typically mounted in the bottom of the footwell and they draw water into the pump as part of the circulation system. These are typically 2” fittings with a screen around them so nothing gets sucks into the pumps/motors. The general rule of them is to have two intakes or suctions per pump/motor.

Hot tub suction fittings
Hot Tub Suction Fittings

10. 2” Plumbing – 2” flex PVC plumbing is used to run the water from the pumps/motors located in the equipment panel to the individual seats where the 2” plumbing connects to a water manifold that feeds the jets in one or more seats in the hot tubs.

11. 3/4” Vinyl Plumbing – the ¾” vinyl tubing is used between the water manifold (connect to the 2” PVC plumbing) and the water ports on each jet body.

12. 3/8” Vinyl Plumbing – the 3/8” vinyl tubing is used between the air manifold and the air ports on each jet body

13. Water Manifolds – typically 2” diameter hard PVC fitting with multiple ports. Used to connect a 2” plumbing line to multiple smaller (3/4”) water lines

14. Air Manifolds – typically 1” diameter hard PVC fitting with multiple ports used to connect an air venturi to multiple smaller (3/8”) air lines.

15. Filter Housing with Filter – large plastic housing that holds the filter cartridge.

16. Roto Clamps – small metal clamps used to secure tubing or plumbing

17. Gate Valves – also referred to as slide valves, these are typically 2” in diameter and made from hard PVC plastic. Gate valves are typically installed near the pumps/motors or heater and used to shut off waterflow through the plumbing so that a component such as a pump or heater can be removed without having to drain the hot tub.

Hot Tub Gate Valve
Hot Tub Gate Valve

18. Motor Mounts – typically made from thick rubber or plastic and used to dampen noise or vibration from the pumps/motors.

19. Frame (wood or steel) – extensive wood frame work used to support the hot tub shell. Better quality hot tubs use treated wood frames. Steel frames are also used to support the hot tub shell in lieu of wood, however, it is not common practice in the industry.

Steel Frame Hot Tub
Steel Frame Hot Tub

20. ABS Plastic Bottom – thick sheet of ABS plastic that is typically stapled or nailed to the bottom framework of the hot tub to prevent rodents or critters from entering the hot tub.

ABS Plastic Bottom on Hot TUb
ABS Plastic Bottom for Hot Tub

21. Exterior Wrapping – packaging for transportation and shipment

Hot Tub Packaging for Shipping
Hot Tub Packaging

22. Labels – labels and decals

23. Bag for Plumbing

24. Insulation – this is typically a spray in foam that covers the shell and all of the plumbing inside the cabinet of the hot tub except for the equipment panel side which remains uninsulated so that the equipment can be easily worked on.

Hot Tub Foam Insulation
Hot Tub Foam Insulation

25. Cabinetry/Skirting – cabinets or skirts are made from wood or synthetic materials although synthetics have the predominant share of the market as they are low maintenance and more durable

Hot tub cabinets and siding
Hot Tub Cabinets

26. Drain – fitting and hose that runs from the base of the spa (footwell) to the exterior of the hot tub for convenient and easy draining

hot tub floor drain
Hot Tub Floor Drain

27. Drain Valve – valve fitting that has a shut off and hose attachment for easy draining. Drain valves are typically located on the exterior of the hot tub for convenience.

hot tub drain
External Hot Tub Drain

28. Vents – plastic vents placed in the cabinet panels to allow the heat from the equipment to dissipate.

29. Ozone Jet – Small jet placed in the footwell of the hot tub that is connected to the ozone generator and supplies ozone gas bubbles to the tub to oxidize and kill bacteria.

30. Diverter Valve Control – large valve mounted on the toprail of the hot tub that directs water from the pump to one seat or another seat or both.

31. Air Valve Controls – smaller valves mounted on the toprail of the hot tub that allow air to mix in with the jets as well as water.

hot tub air valves
Hot Tub Air Valves

32. 6” Waterfall – water feature that can typically be shut on or off with a valve. Designed for mostly aesthetic purposes.

33. Waterfall Valve Control – small water valve mounted on the toprail of the hot tub that shuts the waterfall on or off.

water valve control
Water Valve Control

34. Hard Cover – tapered cover that is crowned in the middle (4”) and tapers to the edges (2”) made of high density styrene foam and covered in marine grade vinyl. The covers are locking for safety meeting ASTM standards.

The items referenced above do not cover labor, engineering and design, or mold production. Labor is a variable cost based on the specifications, features, and complexity of the hot tub but we can use $500 per unit as an average. Engineering and design is difficult to burden on one model because it is a broad expense category that is also tied to research and development. Many manufacturers set annual budgets for this expense category and amortize that expense over the entire factories unit volume to come up with a per unit cost. For our purposes we will leave not assign an arbitrary number as it can vary drastically form one manufacturer to the next. The last piece is mold production and tooling. It has been said that a mold can cost between $20,000-$40,000. The most common molds are made of a tooling resin, high temperature fillers, and fiberglass. A finished mold is good for production of 1000 or more spas before it needs to be reconditioned or replaced. That tooling cost also needs to be burdened on a per unit basis.

Hopefully this article provides some level of appreciation for what actually goes into a hot tub and why an acrylic and fiberglass hot tub retails for around $4000 and up. For more information please visit our buyer’s guide pages or our brands directory.

Leave a Reply