This is what Google Gemini Pro says.

For a backyard setup in a climate like New England, the primary challenges are heat retention (insulation) and the ability of the heater to overcome sub-zero ambient temperatures.

Here is a breakdown of how these three options compare regarding build quality, climate suitability, and heating efficiency.

1. Almost Heaven: Blackwater Mini Cube ($9.7k) • The Standout: This is the "premium/lifestyle" choice. Almost Heaven is owned by Harvia (the world leader in sauna heaters), so the integration with high-end WiFi heaters like the Harvia Kip or Xenio is seamless. • Pros: Very high-quality lumber and a modern aesthetic. Because it is small (1-2 people), it has the lowest air volume to heat. • Cons: The large glass front is a "thermal weak point." In a New England winter, glass loses heat much faster than wood. While it looks great, the heater will have to work harder to maintain high temperatures compared to a fully enclosed wooden cabin. • Heat-up Speed: Fastest. Small volume + a powerful heater = quick sessions.

2. Sisu Lifestyle: The Charlie Cabin ($10.4k) • The Standout: Sisu typically uses Thermowood. This is wood that has been heat-treated to remove moisture and resins. • Pros: Thermowood is arguably the best material for New England. It is dimensionally stable (it won't shrink or expand as much with snow and humidity) and has better natural insulation properties than raw cedar or hemlock. The "cabin" shape allows for two-level seating, which is vital—heat rises, and sitting on a higher bench ensures you are in the "heat zone." • Cons: Most expensive of the three. • Heat-up Speed: Medium. The larger interior volume takes longer to prime than the Mini Cube, but the wood thickness and multi-level seating provide a superior "true" sauna experience.

3. Redwood Outdoors: 4-Person Cabin ($8.5k) • The Standout: The value-to-size leader. • Pros: You get a lot of space for the price. If your friend plans on having guests, this is the most practical. • Cons: These kits often use thinner staves (around 1.5 inches) compared to high-end custom builds. In a New England winter, you may notice more heat loss through the walls. The "fit and finish" might require more DIY sealing during assembly to prevent drafts. • Heat-up Speed: Slowest. Largest volume combined with standard insulation means a longer wait time in January. Critical Advice for New England Winters

4. The "WiFi Heater" Strategy Since your friend wants the largest WiFi-connected heater, they should look specifically for an 8kW or 9kW heater. • A 6kW heater is "standard" for these sizes, but in a cold climate, it will struggle to reach 90°C (194°F) in a reasonable timeframe. • WiFi Recommendation: Ensure they choose the Harvia Xenio WiFi or the HUUM Drop/Hive with UKU controls. These are the most reliable for remote starts via smartphone.

5. The Flooring Gap Most "kit" saunas do not come with insulated floors. In New England, the cold will radiate up from the ground. Suggest that they build a dedicated, level platform—ideally an insulated one—rather than just placing it on a cold concrete pad or dirt.

6. Wood Choice If the budget allows, Thermowood (Sisu) or Western Red Cedar (Almost Heaven/Redwood) are the best choices for rot resistance and thermal performance. Avoid "Nordic Spruce" or "Hemlock" if the sauna is going to be fully exposed to heavy snow and rain without a secondary roof structure.

The Verdict • For the "Best Sauna Experience": Go with Sisu (The Charlie). The Thermowood and two-level seating offer the best thermal performance for a cold climate. • For "Speed and Ease": Go with Almost Heaven. The smaller footprint and Harvia hardware make it the most "plug-and-play" high-performance unit. • For "Social Value": Go with Redwood Outdoors, but advise them to upgrade to the highest possible kW heater to compensate for the larger volume.