Preparation for a Hot Tub

There are a number of things to deliberate before putting a hot tub in your home or backyard. First and foremost is finding a suitable location with sufficient space. When choosing the hot tub location make sure to give careful thought to privacy from neighbors and onlookers, proximity to the home for ease of access for bathers, maximizing views and vantage point from inside of the hot tub, access for delivery, placement and installation of accessories (steps, cover lifter, etc.), and service access for a hot tub repairman. A great way to help visualize the hot tub is to outline it with chalk, duct tape, or rope in several potential locations in the yard until you find the one that you feel is the most suitable.

Also, when choosing location it is important to consider the hot tub size since those two things go hand in hand and one thing may limit or preclude the other. Hot tubs are available in footprints that can be as small as a 4’ x 6’ (2 person) and as large as 8’ x 22’ (swim spa). Hot tub height is another consideration which is usually 36” although they can be found as short as 30” and as tall as 40”. Another consideration for a hot tub shopper is shape or profile. Hot tubs today can be found in triangular (corner), hexagonal, octagonal, square, rectangular, oval, and various others. The most popular shape by far is square. At the end of the day, shape and size has lot do to with personal preference and restrictions as referenced above.

The second consideration is site preparation and foundation. Once you’ve chosen the designated location for your hot tub then the next decision is how to support the hot tub with a suitable foundation. When choosing a foundation it is important to consider this formula for calculating pounds per square foot which can vary depending on the spa’s size and shape. This load calculation is what you would present to a structural engineer or contractor that is preparing your foundation. This calculation becomes more important when a spa is elevated such as a second story deck on a home or a rooftop deck.

Water = 8.36 pounds per gallon
Hot tub Water Capacity (gallons) = can be obtained thru dealer or manufacturer sales material
Hot Tub Dry Weight = can be obtained thru dealer or manufacturer sales material
Hot tub Footprint (square footage) = take the length and width measurements and multiply them to get the overall square footage of the base
Calculation: (8.36 x Number of Gallons) + Dry Weight = “Answer” / Surface Area = Pounds Per Square Foot
Example: Let’s take a 7’ x 7’ hot tub that is 325 gallons and weighs 750 lbs dry.
Example Calculation: 8.36 x 325 gallons + 750 lbs = 3467 lbs / 49 sq. ft. = 71 lbs per square foot

Listed below are the different types of foundations that would be suitable for a hot tub. It is important to note that the foundation should be level before placing the hot tub. A foundation that is not level can void a manufacturer’s warranty and cause damage to the hot tub.

  1. Concrete – A concrete pad is the most common type of foundation for a hot tub. An existing patio would also be a sufficient base to place your hot tub. If pouring a new pad or slab then the recommended thickness is 4” with rebar reinforcement to prevent the slab from cracking over time. Once your pad is poured it is important to allow time for it to cure before placing the hot tub. Consult your contractor or supplier for proper cure times as they can vary based on the type of concrete, weather, and thickness of the pad.
  2. Crushed Rock or Gravel – Crushed rock can also be a cost effective and fast way to create a hot tub foundation. The recommend thickness of the crushed gravel bed is at least 4”. It is also important to use a compactor on the gravel so as to avoid settling after the spa is placed. Use crushed rock rather than pea gravel. Crushed rock compacts well verses pea gravel which is round (and smooth) and does not compact well. Two additional considerations for a gravel bed might be to put down a weed barrier between the gravel and dirt and also to frame in the gravel area with treated wood beams which helps support the gravel and prevents settling over time.
  3. Patio Pavers– A paver foundation is another cost effective and easy option when creating a foundation. Pavers can be very decorative as there are lots of different concrete or stone paver types to utilize. It is also important to prep the area with crushed gravel before setting the pavers to level the area out and avoid settling. The recommended paver thickness is 2-4 inches.
  4. Synthetic Hot tub Pad – These premade pads have gained increasing popularity over the years as a quick and simple way of creating a hot tub foundation. The pads are made of synthetic materials and are usually available in small, interlocking tiles and can be assembled in whatever size foundation you need. They are made of a high density plastic so they are lightweight and very portable. The best part about them are that they are light and portable which makes them easy to transport if you move from one home to another or decide to relocate the hot tub in a different part of your yard.
  5. Decks – Decking is also a very popular foundation for a hot tub. Decks can be designed in a variety of ways to accent a hot tub. Note that when placing a hot tub on an elevated deck it is important to consult a structural engineer or licensed contractor due to the dead weight.
    Another important consideration when doing a deck application is serviceability. The majorities of hot tubs and swim spas on the market today are portable units and have at least one access panel. The access panel on a hot tub is one of the four sides where the equipment such as pumps, heaters, control boxes, etc. are located. Some models of hot tub even require access on all four sides because the equipment is placed along more sides than just the access panel. In either case it can be difficult if one decides to recess the hot tub in a deck part way or even with the surface of the deck to achieve a more custom appearance. The best way to address access for servicing the hot tub properly is by creating access hatches (removable sections) in the deck surface all the way around the spa so that a service technician can easily remove that particular section of decking and climb down to access the equipment. The recommend size for an access hatch is at least 24” or large enough for a person to access.
  6. In-ground or Semi-in-ground– Fully-in-ground or semi-in-ground concrete vaults are another tasteful and unobtrusive way of installing a hot tub. Vaults have a very custom appearance and are nice way to blend a hot tub into a landscape design. Lowering the hot tub into the ground also makes getting in and out of the hot tub very easy for bathers and also reduces the need for external steps. The concerns with lowering a hot tub in-ground are similar to that of a deck application because access is required on at least one side of the hot tub in order to service the equipment. When vaulting the hot tub it is important to build the vault at least 18” or more of clearance on all sides of the hot tub so that a technician can climb down in the gap between the vault and hot tub to service the equipment. The space between the hot tub and walls of the vault are typically filled with removable sections of decking or some other removable surface such as stone or tile. It is also important that the floor of the vault has some sort of drain to eliminate pooling water. Please note that many hot tub service and repair companies will not service a hot tub with poor access or they will charge a heavy premium to raise the hot tub on blocks to get the access they need.
  7. Indoors – Indoor hot tub applications are easily the most accessible and convenient to use. However, there are some important considerations and precautions one must take to make sure it is done properly. These considerations include having proper structural support, proper ventilation, and good accessibility for service. Consult a structural engineer or licensed contractor to make sure that all of the necessary calculations for support have been done and that the proper materials are used for building the support structure. Ventilation is important because hot tubs produce a lot of steam and moisture which can cause mold and mildew if not ventilated properly. Many contractors use windows, doors, exhaust fans (venting fans), or dehumidifiers to address moisture concerns from a hot tub. The final consideration is accessibility which has two definitions in this particular application. The first is serviceability for hot tub repairs which would require at least 18” on all sides of the hot tub. The second definition of accessibility has to do with delivery of the hot tub or potential removal of the hot tub 10-20 years down the road when it needs to be replaced. Hot tubs like any appliance have a shelf life and need to be replaced from time to time and it is wise to plan the installation of the hot tub in a location in the home where it is close to an exterior wall with an oversized door, sliding patio doors, or french doors which can make it easier for the initial delivery or replacement down the line.
  8. Gazebos and Enclosures – Gazebos or Enclosures are a beautiful addition to anyone’s backyard or landscape. They can be custom built by a contractor or purchased as pre-manufactured kits which come in various sizes and styles to fit every taste and budget. The term gazebo typically refers to an open air structure with a roof and in some cases a floor.
    Traditional gazebos are octagonal or round although there are many other styles on the market. They can also have handrails, bar & stools for dining, or be partially enclosed with windows or walls on one or two sides.
    Another popular hot tub structure is an Enclosure. An enclosure is a gazebo but with walls so it is completely enclosed on all four sides and features sliding doors or French doors to get in and out. Many enclosures feature options like sliding windows, skylights, bay windows with bench seating, screen kits for windows, and interior lighting to just name a few.
    Gazebos and enclosures provide privacy and shelter which attribute to increased hot tub usage all year long especially on cold or rainy days.
    Foundation requirements for a gazebo are either large decks or concrete slabs. If pouring a slab then make sure the thickness is 4” or greater with rebar reinforcement. Also ensure the deck or slab is level to avoid issues with installation of the gazebo. Assembling a gazebo on a foundation that is not level can create gaps in the joints which can result in a leaky roof or weakened support.
    It is important to note that when choosing a gazebo that you should plan for proper service access and clearance to get in and out of the hot tub. For example, if you purchase an 8’x8’ spa with a cover lifter and place it in a 9’x9’ enclosure then you will have little to no room to get in and out. We recommend at least 24” of clearance on all sides of the hot tub for proper servicing and bather access.

The third consideration is to make sure your home meets the electrical requirements. For this step it is advisable to have a licensed electrician come to your home and examine your electrical panel to make sure you have the room to add the circuit and amperage required for a hot tub. Similar to an oven, a hot tub typically runs on 220v electricity and requires a 50 AMP GFCI breaker, however, there are some models that run on 110v and require only a 15 AMP breaker. In either instance there must be a separate, dedicated line and circuit which means the location for the hot tub can be predicated on how far it is from your home’s main electrical panel. Basically, the further the hot tub is away from the house the more wires, materials, and obstacles would be involved to do the job which can make the installation more time consuming and costly. For more detailed information we have a separate section on the subject of “Electrical Requirements”.

The final consideration before installing a hot tub is to evaluate the need for any permits or approvals. In most places around the country, hot tubs are considered nonpermanent, portable structures and don’t usually require a permit or approval, however, we would recommend checking with your local building and planning departments to be sure. Additionally, they don’t require a fence around the hot tub if it has a locking safety cover that complies with ASTM F 1346. If you live in a housing development or condominium that has a homeowners association (HOA) or strict covenants then you may be required to get formal permission before installing a hot tub.