♨️ Harvia Hidden Heater 12kW Steel Sauna Heater – 12-17 m³ Capacity

Seamless power meets invisible design – commercial-grade heating concealed behind your sauna benches

🧖 Product Overview

The Harvia Hidden Heater 12kW Steel is a revolutionary concealed sauna heater engineered for those who demand powerful performance without compromising their sauna’s aesthetic purity. Manufactured by Harvia, Finland’s leading sauna specialist with over 70 years of expertise, this innovative heater mounts discreetly behind your sauna benches, delivering robust 12kW heating capacity whilst maintaining clean, uncluttered interior lines.

Constructed from premium stainless steel for exceptional durability and corrosion resistance, the Hidden Heater transforms larger saunas into authentic Finnish bathing experiences. Its unique concealed installation design makes it the ideal choice for contemporary wellness facilities, luxury residential saunas, and commercial spa environments where visual sophistication is paramount. With optimised air circulation ensuring even heat distribution throughout the sauna room, this heater represents the perfect marriage of form and function.

✨ Key Features

• ✅ 12kW Power Output – Delivers substantial heating capacity for sauna rooms between 12-17 m³, ensuring rapid heat-up and consistent temperature maintenance
• ✅ Concealed Installation Design – Mounts behind benches for a minimalist, uncluttered sauna interior with no visible heating equipment
• ✅ Premium Stainless Steel Construction – High-grade steel body provides exceptional durability, corrosion resistance, and long service life
• ✅ 15kg Stone Capacity – Generous stone compartment produces abundant, soft steam (löyly) for an authentic Finnish sauna experience
• ✅ Optimised Air Circulation – Engineered airflow design ensures even heat distribution throughout the entire sauna room
• ✅ 6 × 2000W Heating Elements – Industrial-grade resistors (240V) deliver reliable, efficient heating with replaceable components
• ✅ 400V Three-Phase Power – Professional electrical specification suitable for commercial and high-end residential installations
• ✅ Thermal Cut-Out Protection – Integrated safety systems prevent overheating and protect against electrical faults
• ✅ External Control Unit Compatible – Works with Harvia’s range of digital control panels including WiFi-enabled options
• ✅ CE Certified – Meets all European safety and quality standards for electrical sauna equipment

🔧 Technical Specifications

Specification	Value
Power Rating	12 kW
Voltage	400V 3-Phase (3N~)
Fuse Size	3 × 20 A
Cable Size	5 × 4.0 mm²
Room Capacity	12 – 17 m³
Dimensions (H × W × D)	830 × 1175 × 255 mm
Net Weight	29.8 kg
Gross Weight	34.5 kg
Stone Capacity	15 kg
Stone Size	Ø 5 – 10 cm
Heating Elements	6 × 2000W (240V)
Installation Type	Wall-mounted, concealed behind benches
Minimum Room Height	1900 mm
Installation Opening (H × W × D)	1900 × 1375 × 375 mm
Material	Stainless Steel
Certifications	CE Marked
Product Code	HH120400
GTIN	6417659008327

📐 Room Sizing Guide

Basic Formula:

1 kW ≈ 1 - 1.5 m³ sauna room volume

Adjustment Factors:

Condition	Adjustment
Glass door/windows	+1.5 m³ per m² of glass
Uninsulated/log walls	+25-50% to volume
Outdoor/barrel sauna	+25-30% to volume
High ceiling (>2.3m)	Add extra volume

Worked Example:

📍 Example Room: 2.5m × 2.5m × 2.2m
- Base volume: 13.75 m³
- Glass door (0.8m × 2m = 1.6 m²): +2.4 m³
- Total calculated: 16.15 m³
- This 12 kW heater: ✅ Suitable for 12-17 m³ - Perfect match

💡 Tip: For log-walled saunas, multiply the room volume by 1.5 when selecting heater power. For rooms with extensive glazing or poor insulation, always size up to ensure adequate heating performance.

💷 Running Costs

Energy Rate Used: £0.2635/kWh (Ofgem Price Cap, October-December 2025)

Cost Calculation:

Usage Level	Sessions/Week	Hours/Year	Annual Cost
🏠 Light Use	2	150	£474
🏠 Regular Use	4	300	£949
🧖 Heavy Use	6	450	£1,423

Calculation Formula:

Annual Cost = kW × Hours/Year × £0.2635

Example (12 kW heater, Regular Use):
12 kW × 300 hours × £0.2635 = £948.60

Per session cost: Approximately £4.74 per 1.5-hour session

⚠️ Actual costs depend on usage patterns, session length, room insulation, and current energy rates. Rates shown are based on Ofgem Q4 2025 price cap and are subject to quarterly review.

⚡ Installation Requirements

Electrical Requirements:

Requirement	Specification
Voltage	400V 3-Phase (3N~)
Fuse Size	3 × 20 A
Cable Size	5 × 4.0 mm²
Control Cable	4 × 0.25 mm² SSJ
Connection Type	Semi-stationary to junction box
Cable Type	H07RN-F rubber cable or equivalent
Dedicated Circuit	Required

Minimum Safety Clearances:

Position	Distance
Front (non-combustible)	120 mm
Front (combustible)	120 mm
Side walls (non-combustible)	100 mm
Side walls (combustible)	100 mm
Ceiling	1070 mm
Minimum room height	1900 mm
Gap under partition wall	80 mm (for air circulation)

Installation Opening Requirements:

Dimension	Size
Height	1900 mm
Width	1375 mm
Depth	375 mm

Ventilation:

• Fresh air intake: Located above the heater at minimum 500 mm height, diameter 50-100 mm
• Exhaust vent: Lower part of sauna, away from heater, cross-section twice the supply air pipe
• 80 mm gap required under partition wall for air circulation
• Grid installation above partition wall with 10-20 mm ceiling clearance

⚠️ IMPORTANT: Installation must be carried out by a qualified electrician in accordance with BS 7671 (IET Wiring Regulations) and local building codes. PVC-insulated cables must NOT be used due to thermal degradation. Junction box must be splash-proof and positioned maximum 500 mm from floor level.

🛡️ Safety Features & Certifications

Built-in Safety:

• ✅ Thermal cut-out protection with automatic reset
• ✅ Overheat protection system
• ✅ Temperature sensor with overheating limiter in sensor box
• ✅ Professional-grade wiring connections
• ✅ Heat-resistant construction materials
• ✅ Grid protection over partition wall to prevent contact with heating elements

Certifications:

• ✅ CE Marked – Full European conformity
• ✅ Designed for professional/commercial use
• ✅ Complies with electrical sauna heater safety standards

Safety Notes:

• Control unit and sensor must be installed according to manufacturer specifications
• Sensor box must be positioned 100 mm below ceiling, centred above heater
• Never place objects or devices that could obstruct airflow near the heater
• Children under 8 years should not use without supervision

🎯 Ideal Applications

Application	Room Size	Capacity	Notes
🏠 Large Home Sauna	12-14 m³	4-6 people	Premium residential installation
🛖 Garden Sauna Building	12-15 m³	4-6 people	Modern outdoor wellness space
🧖 Boutique Spa	14-17 m³	6-8 people	Commercial wellness facility
🏋️ Gym/Fitness Centre	12-17 m³	4-8 people	High-traffic commercial use
🏨 Hotel/Resort Spa	12-17 m³	4-8 people	Luxury hospitality installation
🏢 Corporate Wellness	12-15 m³	4-6 people	Office building amenity

Especially Suited For:

• Contemporary sauna designs where visual purity is essential
• Renovations where traditional heaters would disrupt the aesthetic
• Commercial installations requiring discreet, powerful heating
• Minimalist wellness environments
• High-end residential projects

🪨 Sauna Stones

• Stone Capacity: 15 kg
• Recommended Stone Size: Ø 5-10 cm (jagged edges, designed for sauna use)
• Stones Included: No – sold separately
• Recommended Types: Peridotite, olivine diabase, olivine, or vulcanite
• Important: Decorative stones are NOT suitable and void warranty
• Maintenance: Rearrange stones annually; replace damaged/disintegrated stones
• Preparation: Wash stones to remove dust before first use

💡 Stone Care Tip: Stones disintegrate with use due to thermal cycling. Check annually and remove stone fragments from the heater base. Using stones smaller than recommended or allowing debris to accumulate can block airflow and cause overheating.

🎛️ Control Options & Accessories

Control System:

• Type: External control unit required (not included)
• Location: Outside sauna room in dry area, approximately 170 cm height
• Sensor: Temperature sensor and overheating limiter in sensor box above heater
• Sensor Position: 100 mm from ceiling, centred above heater

Compatible Control Units:

Model	Features	WiFi
Harvia C170VKK	Weekly timer, 3-17 kW heaters	No
Harvia Xenio CX170	Digital display, programmable	No
Harvia Xenio CX170XW	Digital display, WiFi app control	Yes

Optional Accessories:

• Water bowl and flexible hose for löyly (steam) – recommended for HH models
• Compatible sauna stones (15 kg required)

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❓ Frequently Asked Questions

Q: What size room will this heater work for? A: The Harvia Hidden Heater 12kW is designed for sauna rooms between 12 and 17 m³. For rooms with glass doors, windows, or uninsulated log walls, add 25-50% to your room volume calculation before selecting your heater.

Q: How long does it take to heat up? A: A well-insulated sauna room of appropriate size will typically reach bathing temperature (65-80°C) in approximately 60 minutes. Heat-up time varies based on room size, insulation quality, and starting temperature.

Q: What electrical supply do I need? A: This heater requires a 400V three-phase (3N~) supply with a dedicated circuit protected by 3 × 20A fuses. Professional installation by a qualified electrician is mandatory. The connection must use H07RN-F rubber cable (5 × 4.0 mm²) – PVC cables are not permitted.

Q: Are sauna stones included? A: No, sauna stones are sold separately. You will need 15 kg of suitable sauna stones with diameters between 5-10 cm. We recommend peridotite, olivine diabase, olivine, or vulcanite stones designed for sauna use.

Q: What is the warranty? A: Harvia provides the following warranty periods: Family/domestic use – 2 years; Shared residential use (e.g., apartment building) – 1 year; Commercial/institutional use – 3 months. Warranty does not cover damage from improper installation, unsuitable stones, or poor water quality.

Q: Can I use this heater in an outdoor sauna? A: The Hidden Heater can be installed in properly constructed outdoor sauna buildings. However, additional volume compensation (25-30%) should be factored into room sizing, and the installation must be protected from direct weather exposure.

Q: Why is a concealed installation beneficial? A: The hidden installation creates a clean, contemporary aesthetic with no visible heater disrupting your sauna’s design. It’s particularly popular in modern wellness facilities and luxury residential saunas where visual refinement is prioritised.

Q: Do I need a separate control panel? A: Yes, all HH-series heaters require a separate external control unit (sold separately). The control panel mounts outside the sauna room and connects to a temperature sensor positioned above the heater.

📥 Downloads & Resources

📄 Installation Manual (PDF) – Complete installation guide with wiring diagrams, safety distances, and ventilation requirements

📄 Technical Datasheet (PDF) – Full specifications, dimensions, and spare parts information

🏆 Why Choose the Harvia Hidden Heater 12kW

• ✅ Finnish Engineering Excellence – Harvia’s 70+ years of sauna expertise in every component
• ✅ Invisible Power – Full 12kW commercial-grade output from a completely concealed position
• ✅ Premium Construction – Stainless steel body built for years of reliable service
• ✅ Authentic Steam – 15kg stone capacity delivers traditional Finnish löyly experience
• ✅ Future-Ready – Compatible with WiFi control systems for smart home integration
• ✅ Proven Reliability – Industrial-grade heating elements with readily available spare parts
• ✅ Safety Assured – CE certified with comprehensive thermal protection systems

🤝 Why Buy From Parts4Tubs

• ✅ UK-based company with expert local support
• ✅ Fast UK delivery
• ✅ Specialist advice from dedicated sauna professionals
• ✅ Competitive pricing on genuine Harvia products
• ✅ Full manufacturer warranty support
• ✅ Easy returns within 30 days
• ✅ Comprehensive range of compatible accessories and spare parts

✨ Summary

The Harvia Hidden Heater 12kW Steel delivers exceptional performance for sauna rooms up to 17 m³, combining powerful 12kW output with innovative concealed installation. With premium stainless steel construction, 15kg stone capacity for authentic Finnish steam, and compatibility with Harvia’s advanced digital controls including WiFi options, it’s the definitive choice for contemporary wellness spaces where aesthetics matter as much as performance. Backed by Harvia’s renowned Finnish engineering, CE certification, and Parts4Tubs expert UK support, this heater transforms any suitable space into a sophisticated sanctuary. Order today for fast UK delivery.