Quick Answer: The best steam shower generator for most home remodels is the SteamSpa Oasis package ($1,559-$2,499 on SteamSpa’s store, October 31, 2026), because it includes the touch control and steam head that other brands sell separately, and its generator carries a lifetime warranty if you register it and keep an inline filter. For the strongest warranty, pick the ThermaSol PRO Series III (generator alone from $4,435, with 2 years of in-home parts and labor). Size the unit by cubic feet and wall material, using that maker’s own chart: for a 3 x 5 x 8 ft tiled shower (120 cubic feet), Amerec’s guide says 6 kW, MrSteam 7.5 kW, ThermaSol 8 kW and SteamSpa 9-10.5 kW.
We’ve covered steam as one of three products in our best steam sauna decoder and given MrSteam its own brand review. This guide is about the generator itself: the box in your vanity or closet that boils water and pipes steam into a tiled shower. We read each maker’s own spec sheets, sizing guides, manuals and warranty documents, and took prices from the brands’ own stores on October 31, 2026. The biggest finding: for the same shower, the four sizing charts we could check disagree by up to 75%, and that changes the breaker you need too.
Steam shower generators at a glance
| Brand / line | Sizes | How it's sold | Price (maker, Oct 31 2026) | Generator warranty |
|---|---|---|---|---|
| SteamSpa Oasis | 4.5-12 kW | Package: generator + touch control + steam head | $1,559-$2,199 (no AutoDrain), $1,895-$2,499 (with AutoDrain) | Lifetime, conditions apply; controls 1 yr |
| SteamSpa Royal | 4.5-12 kW | Package with dual inside/outside controls | $2,149-$3,149 | Lifetime, conditions apply |
| SteamSpa Black Series | 4.5-24 kW | Package with touchscreen, WiFi app, Bluetooth speakers | $2,338.99-$3,598.99 (list $2,599-$3,999) | Lifetime, conditions apply |
| ThermaSol PRO Series III | 6-24 kW (84-1,200 cu ft) | Generator only | $4,435-$8,270, plus control from $910 and steam head $310 | 2 yr in-home, then lifetime factory |
| MrSteam MS90-MS400 | 5-9 kW (71-257 cu ft) | Generator only, dealers | Not published (see our MrSteam review) | Limited lifetime |
| Amerec AK | 4.5-14 kW single unit, gangable | Generator only, dealers | Not published | Limited lifetime; parts 5 yr, in-home labor 2 yr |
| Kohler Fast-Response | 5 kW and up | Generator only; control kit separate | K-1708 7 kW $1,543.01 (kohler.com, Oct 2025 capture) | Not checked |
SteamSpa and ThermaSol prices come from each brand’s own online store. Kohler blocks automated access to kohler.com, so its figure is the price on Kohler’s product page as archived by the Wayback Machine on October 6, 2025, labelled as such.
Same shower, four different answers: how the makers size a generator
Every maker starts with the same math: length x width x height = cubic feet. What they do with that number is where they split. Here is a standard 3 x 5 ft shower with an 8 ft ceiling, which is 120 cubic feet, run through each maker’s published chart:
| Maker | Model for 120 cu ft (tile) | kW | Draw at 240V | Source |
|---|---|---|---|---|
| Amerec | AK 6.0 (rated 80-150 cu ft) | 6 | 25 A, 40 A breaker | AK sizing and rough-in guide |
| MrSteam | MS225 (up to 161 cu ft) | 7.5 | 32 A | MS90-MS400 spec sheet |
| ThermaSol | PRO III-140 (up to 140 cu ft) | 8 | 37 A max, NEMA 6-50P plug | PRO III manual and spec sheet |
| SteamSpa | 9 kW or 10.5 kW | 9-10.5 | 38-44 A | Oasis/Royal manual sizing chart |
| Kohler | K-1708 7 kW tops out at 112 cu ft, so the next size up | above 7 | n/a | kohler.com product page (2025) |
That’s 6 kW at the low end and 10.5 kW at the high end, a 75% spread for one room. Neither end is “wrong”: a generator that’s too small takes longer to fill the room and may never reach the top of its temperature range, while a bigger one gets there faster but needs a heavier circuit. SteamSpa’s chart even adds a note that it is “safe and even recommended” to go one size above what it shows. The practical rule is simple: pick your brand first, then size with that brand’s chart, not with a generic calculator or another maker’s table.
Three things push every chart up a size:
- Stone and porcelain. Amerec’s guide says to multiply the volume by 1.75 for natural stone, and it names porcelain tile in that group alongside marble, granite, travertine and slate. A 120 cu ft porcelain shower becomes 210 cu ft, which moves Amerec’s pick from 6 kW to 9 kW and the breaker from 40 to 50 amps. MrSteam’s online calculator also asks for the material, but it groups porcelain with ceramic tile on cement board instead.
- Ceiling height. ThermaSol’s manual tells you to go up one generator size for every foot over 8 feet, to a maximum of 10 feet, and Amerec recommends an 8 ft maximum. SteamSpa’s chart is built on 7 ft cabins. If you’re planning a 9 or 10 ft ceiling, a sloped or lowered steam ceiling usually beats a bigger generator.
- Cold surfaces. Exterior walls, glass block and large glass panels soak up heat. Size up one step if your shower has them.
Electrical: amps and breakers by generator size
The generator is the biggest load most bathrooms will ever have. Each maker requires a dedicated 240V circuit and a licensed electrician. Amerec is the only one of the four that prints the breaker size next to the amps, so its column is the most useful starting point:
| Generator | Amerec AK (240V) | SteamSpa (240V) | MrSteam (240V, 1-phase) | ThermaSol PRO III (max amps) |
|---|---|---|---|---|
| 4.5-5 kW | 19 A / 30 A breaker | 19 A | 21 A (5 kW) | n/a |
| 6 kW | 25 A / 40 A breaker | 25 A | 25 A | 28 A, NEMA 6-30P plug |
| 7.5-8 kW | 31 A / 40 A breaker | 32 A | 32 A | 37 A (8 kW), NEMA 6-50P plug |
| 9-10 kW | 38 A / 50 A breaker | 38 A (9 kW) | 38 A (9 kW) | 46 A (10 kW), NEMA 6-50P plug |
| 10.5-11 kW | 46 A / 60 A breaker | 44 A (10.5 kW) | n/a | 55 A (11 kW), hardwired |
ThermaSol’s figures are labelled “maximum amperage” for its 208-240V units, which is why they run higher per kW. ThermaSol ships its PRO III-84, -140 and -240 with a 5 ft cord and plug (NEMA 6-30P or 6-50P), so the electrician installs a matching receptacle instead of hardwiring; the 11 kW PRO III-395 and up are hardwired. If your panel lacks room for a 40-60 amp double-pole breaker, that’s the cost to price first. Our sauna installation cost guide breaks down what a new 240V circuit typically costs.
The best steam shower generators
SteamSpa Oasis Series Package
- The lowest price for a full system in this guide: generator, touch control with memory settings, and a solid steel steam head with an aroma reservoir in one box. The 9 kW size for a typical 120 cu ft shower is $1,959, or $2,299 with SteamSpa's AutoDrain, which flushes the tank after each session.
- SteamSpa's manual says the unit fills and heats in 1-2 minutes, with a 50-130°F range and a 1-60 minute timer.
- The lifetime generator warranty has strings attached: register within 90 days, use a licensed installer, fit an inline water filter and change its cartridge at least every 6 months. Damage "by reason of local water conditions" is excluded, and the control and steam head get 1 year.
- Step up to the Royal ($2,149-$3,149) for a second control panel outside the shower, or the Black Series ($2,338.99-$3,598.99 on sale) for WiFi app control, Bluetooth speakers and sizes up to 24 kW.
ThermaSol PRO Series III
- The model number is the maximum room size: PRO III-84 (6 kW, $4,435), PRO III-140 (8 kW, $4,790), PRO III-240 (10 kW, $5,475) and PRO III-395 (11 kW, $5,890) cover almost every home shower, per ThermaSol's spec sheets and store.
- Warranty is the reason to pay more: 2 years of in-home parts and labor, then lifetime parts and labor at ThermaSol's factory. After year two you pay to remove the unit and ship it to Round Rock, Texas.
- Stainless split tank, automatic PowerFlush tank cleaning (ThermaSol recommends flushing every 1,000 minutes of use) and up to 50 ft between generator and shower.
- A full system costs much more than the sticker: PRO III-140 + MicroTouch control ($910) + SteamVection steam head ($310) = $6,010, about 2.6x a SteamSpa Oasis 9 kW package with AutoDrain.
MrSteam MS225 (MS90-MS400 range)
- MrSteam's spec sheet rates the MS90 at 71 cu ft (5 kW), MS150 at 107 (6 kW), MS225 at 161 (7.5 kW) and MS400 at 257 (9 kW). The MS225 draws 32 amps at 240V.
- MrSteam says its generators use less than two gallons of water per session, versus 40 gallons for an ordinary bath, and allows the generator up to 60 ft from the steam room with zero clearance to combustible surfaces.
- 60-minute automatic shutdown with a 75-minute safety back-up. Read the warranty tiers in our MrSteam review before you buy, because the budget Steam@Home line is covered differently.
Amerec AK Series
- The most conservative chart on room size per kW (6 kW for 80-150 cu ft of ceramic tile) but the strictest stone rule (x1.75). Rooms over 550 cu ft can run several AK units on one control, each on its own circuit.
- Prints amps and breaker sizes for 208V and 240V, single and three phase, in one table, which makes the electrician's quote easier.
- Limited lifetime warranty if you register within 60 days of installation; component parts are covered for 5 years and in-home labor for 2 years. The steam line can't run longer than 20 ft, much shorter than ThermaSol's 50 ft or MrSteam's 60 ft.
- Amerec is a Sauna360 brand. Sauna360's September 2026 recall covered infrared heater panels in Finnleo and Helo saunas, not Amerec steam generators.
Kohler Fast-Response Steam Generator
- Kohler rates the 7 kW K-1708 at 112 cu ft and the 5 kW K-1695 at 56 cu ft for custom showers, smaller rooms per kW than MrSteam or Amerec.
- The control kit is sold separately. The archived kohler.com prices were $1,543.01 for the K-1708 (October 2025) and $1,415.51 for the K-1695 (December 2025). Check a Kohler dealer for current pricing.
- Mainly worth choosing if the rest of the shower (valves, rain head, controls) is Kohler and you want one brand on the trim.
What a complete system costs for a 120 cu ft shower
The generator is only part of the bill. Here’s what each brand’s own store charges for the hardware you actually need (generator, control and steam head) for the 3 x 5 x 8 ft example, before installation:
| System | Generator | Control | Steam head | Hardware total |
|---|---|---|---|---|
| SteamSpa Oasis 9 kW, no AutoDrain | Package | $1,959 | ||
| SteamSpa Oasis 9 kW with AutoDrain | Package | $2,299 | ||
| SteamSpa Royal 9 kW with AutoDrain | Package, dual controls | $2,899 | ||
| ThermaSol PRO III-140 + MicroTouch + SteamVection | $4,790 | $910 | $310 | $6,010 |
| ThermaSol PRO III-140 + SignaTouch 5 | $4,790 | $1,705 | $310 | $6,805 |
On top of the hardware, budget for a licensed electrician (dedicated 240V circuit), a plumber (3/8 in. water supply, 1/2 or 3/4 in. steam line, drain and pressure-relief line per the maker’s rough-in guide), and an enclosure that is vapor-sealed, sloped on the ceiling and closed with a floor-to-ceiling door. Our sauna vs steam room guide covers the build cost, and the sauna ventilation guide explains why SteamSpa’s manual “strongly” recommends an exhaust fan outside the steam room.
What a steam shower costs to run
Running cost is the easy part. A 7.5 kW generator running flat out for 20 minutes uses at most 2.5 kWh. At the 18.16 cents per kWh U.S. average residential price the EIA reported for August 2026, that’s about 45 cents per session, and less in practice, because the generator cycles once the room is at temperature. Water use is small too: MrSteam says a session uses less than two gallons. The real ongoing cost is maintenance: SteamSpa’s warranty requires a new filter cartridge at least every 6 months, and hard water will scale any tank faster. If your water is hard, plan for the filter or a flush routine from day one.
Warranty fine print, side by side
| Brand | Generator coverage | Labor | Conditions worth knowing |
|---|---|---|---|
| ThermaSol | Lifetime factory parts | 2 yr in-home, then at the factory | Owner pays removal and shipping to Round Rock, TX after year 2; residential only; original purchaser from an authorized dealer |
| SteamSpa | Lifetime (generator) | Not stated as in-home | Register within 90 days; licensed install; inline filter, cartridge every 6 months; excludes local water conditions; controls and steam heads 1 yr |
| Amerec | Limited lifetime; component parts 5 yr | 2 yr in-home | Register within 60 days of installation |
| MrSteam | Limited lifetime (MS generators) | See our review | Steam@Home line has a separate, shorter warranty |
ThermaSol and SteamSpa both exclude non-residential use from their warranties, so a generator in a gym, short-term rental or hotel needs a commercial-rated unit.
Recalls and safety
The CPSC’s recall database (checked October 31, 2026) lists no recall of a residential steam shower generator from SteamSpa, ThermaSol, MrSteam, Amerec or Kohler. Two steam-adjacent recalls are worth knowing about. In January 2024, Steamist recalled about 3,900 wall-mounted Tilt-Up Bath & Shower Seats (sold 2009-2015 for $490-$660) after 62 reports of seats breaking and 4 injuries. If you’re inheriting an older Steamist shower, check that seat. And CPSC recall 26-506 (May 2026) covered Giantex and Costway portable steam saunas, a tent-style product, not a shower generator.
On the safety side, SteamSpa’s manual says children under 16 shouldn’t use a steam bath. ThermaSol and MrSteam both say the generator must never sit inside the steam room or outdoors, and every maker’s guide says to keep it away from freezing temperatures.
How to choose a steam shower generator
- Measure first. Length x width x height in feet. Round up, and write down the wall material and ceiling height.
- Choose the brand, then use its chart. The charts differ by up to 75% for the same room. Don’t mix one maker’s chart with another maker’s generator.
- Stone or porcelain? Apply the maker’s material rule. Amerec’s 1.75x factor can move you up two sizes.
- Check your panel before you shop. A 9-11 kW unit needs a 50-60 amp double-pole breaker. If the panel can’t take it, a smaller generator plus a lower ceiling may be the cheaper fix.
- Compare complete systems, not generators. ThermaSol and MrSteam sell the generator alone; SteamSpa bundles control and steam head.
- Read the warranty conditions. Lifetime coverage means very different things at ThermaSol and SteamSpa.
- Plan the location. The generator can sit up to 50 ft (ThermaSol) or 60 ft (MrSteam) from the shower, but only 20 ft with Amerec.
If you’re still deciding between steam and a dry sauna, our sauna shower combo guide explains what “combo” units really include, and the best sauna heater guide covers the dry-heat side.
Bottom line
For most home steam showers, the SteamSpa Oasis package is the best value: a complete generator, control and steam head system for $1,959-$2,299 at 9 kW, with a lifetime generator warranty as long as you register it and keep the inline filter changed. If you’d rather pay more for the strongest warranty and a dealer network, the ThermaSol PRO Series III (from $4,435 for the generator) gives you 2 years of in-home service and lifetime factory repairs. MrSteam and Amerec are strong dealer-installed choices, and Amerec’s published amp-and-breaker chart is the easiest to hand to an electrician. Whichever you pick, size it with that maker’s own chart, after accounting for stone, porcelain and ceiling height, because the same 120 cu ft shower gets anything from 6 to 10.5 kW depending on whose chart you read.
Prices checked October 31, 2026 on steamspa.com and thermasol.com; Kohler prices are from archived kohler.com product pages (October and December 2025). Specs from SteamSpa’s Oasis/Royal installation manual, ThermaSol’s PRO Series III spec sheets and manual, MrSteam’s MS90-MS400 technical specifications, Amerec’s AK sizing and rough-in guide, and each brand’s warranty document. Electricity price: U.S. EIA Electric Power Monthly, Table 5.6.A.