An enclosed pool in your basement or sunroom used to mean a six-figure addition with a structural engineer on speed dial. That has changed. With prefabricated shells, stock-tank conversions, and modular swim-spa units, cheap indoor pool ideas now start around $8,000 installed and rarely cross the $30,000 mark when you handle the framing and finishes yourself. The trick is matching the pool type to the room you already own.
I have built three of these on tight budgets, and the cost killer is almost never the water — it is the humidity. Skip the dehumidifier and your drywall will crumble inside two winters. Plan for that one line item up front and the rest is surprisingly approachable.
Stock-Tank Plunge Pools for Under $1,500
An 8-foot galvanized stock tank from Tractor Supply runs $549 to $799 and holds about 700 gallons at 24 inches deep. Drop one into a sunroom with a tiled floor, plumb a small 1.5 HP pump and sand filter ($380), and you have a plunge pool that handles two adults. Total build sits near $1,400 if you tile a 12-inch surround. Heat it with a 1,500-watt immersion heater and you can swim year-round in zones 6 and warmer.
Seal the seam where the tank meets the floor with marine-grade silicone — Sikaflex 1A holds up better than the standard tubes from Home Depot. Backfill the exterior with pea gravel if you want a more finished look, then cap it with reclaimed barn wood.
Converted Shipping Container Pools
A 20-foot shipping container costs $1,800 to $3,500 used, and the steel walls already pass structural inspection for water loads up to 4 feet deep. Cut a viewing window, line the interior with EPDM pond liner (around $1.40 per square foot), and you have a 17-foot lap pool. Set it on a poured slab inside a pole barn or attached garage. The whole conversion lands between $9,000 and $14,000 including a sand filter, ladder, and basic LED lights.
Endless Pools and Swim Spas
If you want resistance swimming in a small footprint, a refurbished Endless Pool Original system runs $6,000 to $9,000 on the secondary market. New SwimEx models start at $19,000 but include the shell. Pair either with a 14-foot by 10-foot room and you can swim laps in a space smaller than most master bedrooms. Pull-behind delivery and crane placement add $800 to $1,500 — factor that in before you assume the unit drops in for free.
Repurposing a Garage or Basement
A two-car garage with a 4-inch slab will support a 12-foot by 24-foot fiberglass shell holding 9,000 gallons of water if the soil underneath drains well. Sub-slab insulation matters here: 2 inches of XPS rated R-10 keeps the floor from sweating in summer. Frame the walls with pressure-treated 2x4s, sheathe with cement board (HardieBacker 1/4 inch at $13 per 3×5 sheet), and finish with porcelain tile. A basement install adds $2,000 to $4,000 for waterproofing the foundation walls with a product like Drylok Extreme.
The Humidity Problem Nobody Mentions
Indoor pools evaporate 1 to 2 gallons per square foot of surface area each week. That moisture has to go somewhere. A dedicated swimming pool dehumidifier like the Aprilaire E100 ($1,200) removes 100 pints per day and ducts into existing HVAC. Cheaper portable units from hOmeLabs ($249) work for plunge pools under 60 square feet but burn out within 18 months at pool-room duty cycles.
Install a vapor barrier behind every wall — 6-mil polyethylene minimum, taped seams with Tyvek tape. Skip this step and the framing will rot from inside out. Use mold-resistant drywall (Purple Board from Gold Bond, around $18 per 4×8 sheet) on any wall facing the pool.
Heating on a Budget
A 5.5 kW electric pool heater from Hayward costs $700 and raises a 5,000-gallon pool from 60°F to 82°F in roughly 14 hours. Heat pumps are more efficient at 4.5 COP but cost $2,200 and only work above 50°F ambient. For year-round use in cold climates, a propane heater like the Raypak 156,000 BTU ($1,800) heats a 12,000-gallon pool in 6 hours but burns through a 100-gallon propane tank every three weeks at heavy use.
Solar covers cut evaporation by 70 percent and heat loss by 50 percent. A 12-foot by 24-foot bubble cover runs $90 and pays for itself in one heating season.
Lighting and Finish Touches
Recessed LED pool lights from Pentair Globrite cost $180 each and run on 12 volts — safe to wire yourself if local code permits. String warm-white festoon lights (Brightech Ambience Pro, $65 per 48-foot strand) above the waterline for a cabana feel. A cedar plank ceiling over the pool absorbs sound and resists moisture better than painted drywall.
Finish the deck surround with anti-slip porcelain rated DCOF 0.42 or higher — Daltile Florentine or MSI Tundra Gray both meet the standard at $3.50 to $5 per square foot. Avoid natural stone unless you seal it twice a year; chlorine etches travertine within six months.
Permits, Insurance, and Resale
Most jurisdictions require a building permit for any pool over 24 inches deep, even indoors. Permits run $150 to $600 and trigger an electrical inspection of the GFCI circuit feeding the pump. Call your insurance agent before you start — indoor pools raise homeowner premiums by $200 to $500 a year, and undisclosed pools can void liability coverage entirely.
Resale-wise, indoor pools are polarizing. A well-built plunge pool in a sunroom adds value in luxury markets. A garage conversion in a starter-home neighborhood often subtracts value because buyers see the conversion cost to undo it. Build with reversibility in mind: bolted framing, surface-mount plumbing, and a shell that can be drained and removed.
Where to Spend and Where to Save
Spend money on the dehumidifier, the vapor barrier, and the GFCI electrical work. These are the items that protect the structure and keep you safe. Save on the shell (used fiberglass, stock tank, or container conversion), the decking (porcelain over stone), and the lighting (12V LED instead of line-voltage fixtures). With smart trade-offs, a finished indoor pool under $15,000 is genuinely achievable — and far more enjoyable than the backyard version you can only use four months a year.
