Can you add a spa to a fiberglass pool?

There are three, and they suit different yards and budgets.

• A pool with the spa built in. Liberty Composites, whose shells we install, makes Deluxe versions of several models with a spa molded into the same shell. The Hero Deluxe, Relaxation Deluxe and Unity Deluxe all include a built-in spa, and the Heavenly 14 Deluxe pairs a spa with a tanning ledge and swim-up seating. The Unity Deluxe is a 16 by 35 foot freeform with a spa about 3 feet deep.
• A separate fiberglass spa beside the pool. Liberty makes two spa shells, the Blessing and the Refinement, each in a standard and a spillover version. They are set next to the pool and plumbed into the same equipment.
• A custom spa. Where a mold will not fit the design, a spa can be built to a custom shape and size alongside the pool, which pairs naturally with an ICF concrete pool, since those can be built to any shape.

From Liberty's published specs:

Liberty describes the Blessing as having ample seating for family and friends and the Refinement as the more intimate of the two. As a rough guide, the Blessing suits households that expect a crowd in the spa, and the Refinement suits a couple or a small family and fits better in a tight layout. Both come in the same Crystite Classic colors as the pools, so the spa and pool can match.

A spillover spa sits slightly higher than the pool and shares its equipment. When the system runs in pool mode, water is pumped up into the spa and spills over a lip back into the pool, which looks and sounds good and keeps the spa water filtered and treated with the pool. When you switch to spa mode, valves isolate the spa so the heater only has to warm the small volume of spa water.

The spillover is also part of the pool's look from the house. Water falling over the edge is a quiet, steady sound in the evening, and with the LED lights on it becomes the focal point of the yard. For many owners it replaces the need for a separate water feature.

Spillover spas also change how the equipment is set up. The system needs valves, often motorized and tied to automation, to move between pool mode and spa mode, and the heater has to be sized to bring the spa up quickly. We plan those pieces in the design so switching modes is a button press rather than a trip to the equipment pad.

A built-in spa is simpler. It is one shell, one set in the ground and one piece of coping. The layout is fixed, though, so you get the spa where Liberty put it, and it takes part of the pool's footprint.

A separate spa gives you more control. You can put it at the end of the pool nearest the house, at a corner facing the view, or raised so the spillover is more dramatic. You keep the full swimming area of the pool you picked. The trade-off is a larger overall footprint and more plumbing, deck and structural work around the joint between the two shells.

If you already know you want a spa, choose now, during the design, even if you install it later. Planning the plumbing and deck for a future spa is far cheaper than cutting into a finished patio.

Closer to the house than you might think. In spring and fall you will be walking to the spa in the dark, in a robe, on a cold deck, so a short path from the back door makes a real difference in how often it gets used. Placing the spa at the house end of the pool also puts the spillover in view from inside, which is where you will see it most.

Wind matters more for a spa than for a pool, because hot water loses heat fast in moving air. The Department of Energy's heater guidance lists wind exposure and cool nights among the factors that raise heating load. A corner sheltered by the house, a fence or a row of evergreens will hold heat better than an open spot facing the prevailing wind. Just avoid heavy tree cover directly overhead, since leaves in a small spa clog the filter quickly.

Finally, think about the equipment. A spa adds valves and sometimes a separate blower or jet pump, and those need to sit on the equipment pad within reach of the heater and power. A shorter run between the spa and the pad also means less heat lost in the pipes.

Our unheated swim season runs roughly Memorial Day to Labor Day. A spa holds a small fraction of the water in a pool, so it can be brought up to temperature in a fraction of the time. That makes it usable on cool evenings in April, May, September and October, when the pool itself feels cold. It also changes how the whole backyard gets used: people who would never swim in 70 degree water will happily sit in a spa and look at a lit pool.

Heating is the main decision. The U.S. Department of Energy notes that gas pool heaters heat water quickly and, unlike heat pumps and solar heaters, can hold a set temperature regardless of the weather. For a spa you want to use on short notice in cool weather, that fast heat is usually the deciding factor. A heat pump can still suit a pool without a spa, but spa owners in Ohio usually want gas.

It is possible, but it is a different project from a summer spa. An attached spa shares plumbing and equipment with the pool. To run it through January, the pump, heater and lines must keep circulating in freezing weather, which means the pool cannot be winterized in the usual way and the whole system is exposed to freeze damage if the power goes out or a heater faults during a cold snap.

Most attached spas in Northeast Ohio are opened and closed with the pool. If a year-round hot tub is the goal, a standalone hot tub with its own insulated cabinet and equipment is usually the simpler and safer route, and it can sit on the same patio.

• Temperature. The Consumer Product Safety Commission recommends keeping spa water at 104 degrees Fahrenheit or below, and it recommends a locked safety cover whenever the spa is not in use.
• Suction. Federal law, the Virginia Graeme Baker Pool and Spa Safety Act, requires pool and spa drain covers to meet an anti-entrapment standard, currently ANSI/APSP/ICC-16. The CPSC also notes that safety standards call for two suction outlets per pump in a spa, which reduces suction at any one outlet.
• Barrier. An attached spa sits inside the pool's barrier fence, so the fence has to enclose both. Check your town's rules for any spa-specific requirements.
• Kids. Hot water is no place for toddlers, and a spa's deep seats and heat are hard on small children. Supervise as you would at the pool.

Latham's Liberty warranty covers the pool shell. It excludes damage caused by installing or using attached structures such as decks, waterfalls, fountains or spas, and it treats spa spillways and the top of any wall between a pool and a built-in spa as part of the pool's beam, where cosmetic marks are not a warranty item. In practice, the joint between a pool and a separate spa depends on the builder's base, backfill and deck work, so ask how it is supported.

We price spas from the design, because the cost depends on which option you choose and what surrounds it. A Deluxe model with the spa built in changes the shell and equipment. A separate spillover spa adds a second shell, plumbing, valves, often automation to switch modes, and structural and deck work where the two meet. A heater is close to essential for a spa in Ohio.

For reference, our fiberglass pool packages start at $68,400 installed, with the Pentair pump, filter, heater and lights, a 4 foot concrete wrap deck and startup included. We design every pool and spa in 3D on your lot, so you can see the spa's position, the spillover and the deck before you decide, and we work with lenders if you want to finance the project.