Almost Heaven Blackwater 4 Person Cube Sauna

1. Heat & research 30% of the rating 4 of 5

   A 9 kW stone heater built for traditional dry heat and steam; the page gives 140 to 194 °F (60 to 90 °C) in a general comparison and the manual calls 160 to 185 °F typical, with no measured cabin temperatures.

2. Materials 25% of the rating 4 of 5

   Solid untreated cedar with stainless hardware and no glue or finish named; the Onyx stain option is unnamed, no emissions test was found, and cedar can trigger asthma in some people.

3. Safety & EMF 20% of the rating 4 of 5

   The Spirit heater’s part number (HSPE90U1M) fits Harvia’s ETL listing to UL 875, but the listing covers the heater, not the cabin, and the Virta option’s part number does not match.

4. Trust 10% of the rating 4 of 5

   No recall, Prop 65 notice or warning letter found, the maker discloses its Harvia ownership and names its wood in its FAQ; its FAQ lists detoxification and burned calories as sauna benefits.

5. Value 15% of the rating 3 of 5

   About $2,817 a seat at 4 people ($1,878 at 6) on sale, with the heater and stones included, plus an electrician for a hard-wired 240 V, 45 A circuit; the regular price is $14,085.

The rating, 3.9 of 5, is the weighted average of these scores. See how we rank saunas and our standard.

• Finnish Sauna Builders (retailer) (opens in a new tab) approx. $9,998 for the kit only, Rustic Red Cedar (Onyx approx. $11,498). A retailer, not the maker, and the only other seller we found. The kit has the cedar room, roof kit and glass door; its page says heaters, lights and stones are sold separately, while Almost Heaven’s price includes them. The same dealer’s 9 kW Spirit heater with control and stones is $3,630, which brings the total to about $13,600.

Prices as we saw them on October 23, 2026. They change often. These links carry no tracking code and earn us nothing.

1. Rustic Red Cedar, which the maker’s FAQ calls Rustic Western Red Cedar: 1 3/8 in ball-and-socket boards, untreated per the manual (no glue or finish named)
2. Stainless steel bands, hinges and fasteners
3. Tempered glass door and windows
4. 9 kW Harvia electric heater with sauna stones included (stone type not named on the page)
5. Interior LED light

• Paid certification Intertek (ETL directory, for Harvia Finland Oy heaters)

  Lists Harvia’s Spirit (HSPE) and Virta (HL) heater model patterns to UL 875, with a sister listing to CSA E60335-2-53. Almost Heaven’s part number for the 9 kW Spirit, HSPE90U1M, fits the Spirit pattern; the Virta’s, HL9U1, lacks a suffix the pattern shows. It covers heaters, not the cabin, the wood or the air. Open ↗ (opens in a new tab)

Does the cedar or its finish give off fumes?

The maker’s manual (opens in a new tab) says the outdoor sauna’s wood is untreated and to never treat the interior unless the product is approved for saunas. No glue or finish is named for the cedar version, and we found no emissions or odor test. The Onyx option is stained inside and out with an unnamed stain (the FAQ calls it stained hem-fir, a retailer calls it cedar), so choose Rustic Red Cedar.

Is cedar a problem for people with asthma or wood allergies?

Western red cedar causes occupational asthma in some workers, as a follow-up of 125 patients shows (PubMed 7058838 (opens in a new tab)). We found no study of home sauna users, so this is a precaution: if you have asthma or a wood allergy, ask your doctor before choosing cedar.

Does sauna lower sperm count?

In one small study, 10 men who used a Finnish sauna at 80 to 90 °C for 15 minutes twice a week for 3 months had lower sperm counts and motility, which recovered within 6 months of stopping (PubMed 23411620 (opens in a new tab)). If you are trying to conceive, ask your doctor.

Is the detox talk true?

The product page makes no detox or calorie claims, but Almost Heaven’s FAQ (opens in a new tab) lists detoxification and burned calories among sauna benefits. Our detox page says metals show up in sweat, but no trial shows a lower body burden.

• Traditional heat. The product page gives dry and wet heat at 140 to 194 °F (60 to 90 °C) in a general comparison, and the manual calls 160 to 185 °F or more typical. The Finnish cohort studies on our heat therapy page used saunas at about 80 °C.
• One heater option has an independent safety listing. Intertek’s ETL directory lists Harvia’s sauna heaters to UL 875, and Almost Heaven’s part number for the Spirit option, HSPE90U1M, fits a listed model pattern. The Virta’s part number (HL9U1) lacks a suffix the listing shows, so choose the Spirit. The quick-ship kit comes only with the Virta.
• Unfinished cedar. The maker’s FAQ names Rustic Western Red Cedar for the cedar option. The manual says the outdoor sauna’s wood is untreated and warns never to treat the interior unless the product is approved for saunas.
• Plain build. The page lists 1 3/8 in ball-and-socket boards, stainless steel bands, hinges and fasteners, tempered glass and stones included. It names no glue or finish for the cedar version.
• Support is spelled out: a limited lifetime warranty against manufacturing defects, and a Harvia heater warranty of 1 year on the elements and 5 years on other parts.

• It costs about $11,300 with the heater, stones and LED light on a 20% sale (regular price $14,085), plus an electrician to hard-wire a 240 V, 45 A circuit. Almost Heaven quotes installation from $1,400. Standard orders ship in 8 to 12 weeks; the maker’s quick-ship kit ships in 3 to 5 days at the same price but comes only with the Virta heater.
• Choose Rustic Red Cedar if you want bare wood inside. The Onyx version is stained inside and out with a stain the maker does not name. Its FAQ calls Onyx stained hem-fir, while the retailer calls it cedar. It costs about $1,051 more.
• The product page says only “premium North American cedar”. The species comes from the maker’s FAQ, and we found no emissions or odor test on the wood.
• The warranty covers manufacturing defects only. It does not transfer to a second owner and applies in the contiguous US.
• Ask a doctor first if you have heart disease, or are pregnant, and skip alcohol before and during a session (see our hot baths page and the manual’s own warnings).

Third-party tested

Yes

Tested by

Intertek (ETL listing of the Harvia heater)

1. Almost Heaven Blackwater 4 Person Cube Sauna: maker’s product page. Maker’s page. Price, specifications, heater options and the 140 to 194 °F range, seen 2026-10-23. Open ↗ (opens in a new tab)
2. Almost Heaven FAQ: lumber choices and treatment. Maker’s page. Names Rustic Western Red Cedar and calls Onyx stained hem-fir. Lists detoxification among benefits. Open ↗ (opens in a new tab)
3. Blackwater installation and owner’s manual (PDF). Maker’s page. Untreated wood, typical 160 to 185 °F, safety warnings. Hosted by the retailer. Open ↗ (opens in a new tab)
4. Intertek ETL directory: Harvia Finland Oy, Electric Dry Bath Heater (UL 875). Certifier or regulator listing. Lists Spirit (HSPE) and Virta (HL) model patterns, which end in a suffix for the Virta. A sister listing covers CSA E60335-2-53. Open ↗ (opens in a new tab)
5. Intertek ETL directory: Harvia Finland Oy, Electric Sauna Heating Appliances (CSA E60335-2-53). Certifier or regulator listing. The cETL listing for the same heater families, under the trade names Harvia and Sentiotec. Open ↗ (opens in a new tab)
6. Almost Heaven warranty. Maker’s page. Limited lifetime on the sauna; Harvia heater 1 year on elements and 5 years on other parts. Open ↗ (opens in a new tab)
7. Almost Heaven about page: joined the Harvia family in 2019. Maker’s page. The sauna maker and the heater maker are now the same group. Open ↗ (opens in a new tab)
8. Finnish Sauna Builders: Blackwater kit page. Independent source. Retailer page with the kit-only price, read 2026-10-23. Open ↗ (opens in a new tab)
9. Finnish Sauna Builders: Harvia Spirit 9 kW heater. Independent source. The same dealer’s price for the 9 kW Spirit with control and stones ($3,630), used for the total. Open ↗ (opens in a new tab)
10. US Consumer Product Safety Commission: recalls with “sauna” in the title. Certifier or regulator listing. No Almost Heaven or Harvia recall on 2026-10-23. Open ↗ (opens in a new tab)
11. California Attorney General: Prop 65 60-day notice search. Certifier or regulator listing. No notice names Almost Heaven Saunas or Harvia. Open ↗ (opens in a new tab)
12. Occupational asthma due to western red cedar (Chan-Yeung 1982, PubMed 7058838). Independent source. Follow-up of 125 workers with red cedar asthma. Open ↗ (opens in a new tab)
13. Sauna exposure and human spermatogenesis (Garolla 2013, PubMed 23411620). Independent source. 10 men, sauna at 80 to 90 °C twice a week for 3 months; sperm count and motility fell and recovered. Open ↗ (opens in a new tab)

• Almost Heaven Salem 2 Person Barrel Sauna Same maker, wood and warranty in a smaller barrel. About $6,700 with a 6 kW Harvia Spirit heater.
• Dundalk LeisureCraft barrel and cabin saunas (opens in a new tab) Made in Ontario. The Canadian Timber line uses eastern white cedar and the Dundalk line uses Western red cedar, with a 5-year warranty. Sold through dealers, so ask what the price includes.

• Heat Therapy Basics Article How regular sauna use and heat exposure affect cardiovascular health, brain function, inflammation, and longevity
• Infrared vs Traditional Article How Finnish sauna, infrared sauna, and steam rooms compare in temperature, mechanisms, and health outcomes
• Hot Baths and Passive Heat Therapy Article What research says about hot baths: better sleep when timed before bed, promising but early heart and mood findings, and who should be careful.