Attached spa cost in St. Louis

Adding a spa to a new St. Louis pool typically costs $15,000–$30,000. A survey of Missouri pool dealers averaged $14,775. The spa shares the pool's equipment, which keeps the cost down but means its heating and winter use are tied to how the pool is run.

Attached spa, new pool: $15,000–$30,000
Missouri dealer average: $14,775
Added to an existing pool: About $12,000–$25,000
Heat a 500-gal spa, 60→102°F: About $2.30 with gas
Standalone hot tub: About $4,000–$15,000 installed

Attached spa types and cost

Spa	How it is built	Cost position
Fiberglass combo or spa shell	A spa molded into the pool shell, or a separate fiberglass spa set beside it. Latham's spas hold about 470–600 gallons.	Low to middle. Manufacturers do not publish combo prices; get quotes with and without the spa.
Gunite spillover spa	Custom concrete spa, often raised, spilling into the pool.	Middle to top. A builder in Arizona priced a shotcrete spa at $15,000–$20,000 in 2022.
Spa with a vinyl pool	A fiberglass or concrete spa added beside the vinyl pool. Latham sells spas for its vinyl liner builders.	Similar to a fiberglass spa, plus the tie-in.
Raised vs. flush	A raised spa adds a wall, a spillway and more finish work.	Raised costs more; no reliable published premium.

Our $15,000–$30,000 range covers the spa, its plumbing, jets and controls on a new pool. River Pools notes that a separate fiberglass spa can cost up to $30,000, which is why many buyers choose a fiberglass model with the spa built in.

What else a spa needs

Valves and controls. A pool-and-spa system switches water between the two with valve actuators, usually run from an automation panel.
Jets and a blower. Jets may run off the pool pump or a dedicated spa pump; an air blower adds bubbles.
Heater. A spa is only worth having if it heats quickly, so most spas use a gas heater. See pool heater cost.
Electrical. HomeGuide says most spa panels need a dedicated 50-amp, 240-volt GFCI circuit, about $800–$1,600 if a new one is needed.

A spillover spa looks good but pulls cooler pool water back through, so River Pools warns you lose some heater efficiency.

Modern home and pool at dusk — Stock photography for illustration. A spa extends the evenings you can use the pool, as long as the heater can bring it up to temperature quickly.

What it costs to heat an attached spa

A spa is small, so each heat-up is cheap. Raising 500 gallons from 60°F to 102°F takes about 175,000 Btu. At the St. Louis rates on our heater page:

Heater	Cost, 60→102°F	Cost, 40→102°F	Time, 60→102°F
400,000 Btu natural gas	About $2.31	About $3.47	About 30 minutes
400,000 Btu propane	About $4.97	About $7.34	About 30 minutes
140,000 Btu heat pump	About $1.53	Will not run in cold air	About 1¼ hours; about 2 at 50°F

Our arithmetic, before heat lost while warming and soaking. Gas at Spire East's $1.149 per Ccf in summer and $1.168 in winter, 84% efficiency; propane at Missouri's $2.181 a gallon; heat pump at Ameren's October–May rate and a COP of 4.0. Hayward's heat-only heat pumps stop below 50°F.

That is why gas is the usual spa heater: Hayward calls it the quickest way to heat a pool or spa and ideal for occasional use. A 400,000 Btu heater burns about 386 cubic feet of gas an hour, so ask the installer whether your gas meter can supply it.

Using an attached spa in winter

An attached spa shares the pool's pump, filter, plumbing and heater. In a St. Louis winter, with January lows averaging in the 20s, that has consequences:

The whole system has to stay open. You cannot winterize the pool and keep the spa running, because they share pipes and equipment.
Freeze protection keeps water moving. Pentair's IntelliCenter turns on freeze protection at 36°F and alternates the pool and spa valves so both keep circulating.
The heater is not freeze protection. Hayward's heater manual says not to use the heater to hold water just above freezing, and freeze damage is not covered by its warranty. The pump must run continuously in freezing weather.

If year-round soaking matters most, a standalone hot tub is the simpler choice.

Attached spa vs. standalone hot tub

Compare	Attached spa	Standalone hot tub
Up-front cost	$15,000–$30,000	About $4,000–$15,000 installed
Heat	Pool heater, usually gas; heats in about half an hour	Built-in electric heater; stays hot all the time
Running cost	Pay per heat-up, plus the pool's pump	Hot Spring estimates about $21 a month for its 460-gallon Grandee in St. Louis
Winter	Only if the pool system stays open	Built for year-round use
Looks	Built in, can spill into the pool	Separate cabinet

Safety and code rules

Barrier. An attached spa sits inside the pool's fence. The model pool code lets a separate inground spa or hot tub with a lockable safety cover skip the barrier; Lake Saint Louis and O'Fallon, MO spell that out. See pool fence requirements.
Drains. Federal law (the Virginia Graham Baker Act) requires drain covers that meet the anti-entrapment standard. Local codes based on the ISPSC add rules such as two main drains at least 3 feet apart. Spas have strong suction, so this matters more than in the pool.
Temperature. The CPSC says hot tub water should never exceed 104°F. Hayward heaters are factory-limited to 104°F in spa mode.

Questions to ask a builder about a spa

What does the spa add to this quote, line by line?
How many gallons is it, and how many jets?
Does it share the pool pump, or have its own?
What heater size, and can my gas meter supply it?
How do the drains meet anti-entrapment rules?
Can the spa run in winter, and what freeze protection is included?

Pricing a pool with a spa?

The cheapest time to add a spa is when the pool is built. Get matched with a local builder who can price the pool with and without it.

Get matched with a local pool builder Estimate a pool with a spa

Common questions about attached spas

How much does an attached spa cost in St. Louis?

Adding a spa to a new St. Louis pool typically costs $15,000–$30,000. A survey of 10 Missouri pool dealers averaged $14,775. Fiberglass combos and simple spas sit at the low end; custom gunite spillover spas and raised spas at the top.

Is an attached spa or a hot tub cheaper?

A standalone hot tub usually costs less up front, often about $4,000–$15,000 installed, and runs on its own 240-volt circuit. An attached spa shares the pool's heater, pump and fence, looks built in, and costs more. A hot tub is also easier to use all winter.

How much does it cost to heat an attached spa?

Warming a 500-gallon spa from 60°F to 102°F takes about 175,000 Btu. At current St. Louis rates that is roughly $2.30 with natural gas, $1.50 with a heat pump and $5 with propane, before heat lost while it warms and while you soak.

How long does it take to heat an attached spa?

With a 400,000 Btu gas heater, a 500-gallon spa can go from 60°F to 102°F in about half an hour. A 140,000 Btu heat pump takes about 1¼ hours in warm air and about 2 hours at 50°F, and many heat pumps stop below 50°F.

Can I use an attached spa in a St. Louis winter?

Only if the whole pool system stays open and running. The spa shares the pool's pump, plumbing and heater, so freeze protection has to keep water moving through everything. Most St. Louis pools are closed for winter, which also closes the spa.

Can I add a spa to an existing pool?

Often, yes. HomeGuide puts it at about $12,000–$25,000, plus resurfacing if a concrete pool needs it to match. Latham sells spas that can be added to existing fiberglass or vinyl liner pools.

Does an attached spa need its own fence?

It sits inside the pool's barrier, so the pool fence covers it. The model code exempts a separate inground spa or hot tub with a lockable safety cover from the barrier rules, but that does not apply to the pool it is attached to.

Sources

Published October 27, 2026. Planning ranges, not quotes.