🧖 Harvia Hidden Heater 9kW Steel – Concealed Commercial Sauna Heater for 10-14m³ Rooms

Invisible Power for the Modern Sauna – Professional-Grade Heating with Minimalist Design

♨️ Product Overview

The Harvia Hidden Heater 9kW Steel represents the pinnacle of concealed sauna heating technology from Finnish manufacturer Harvia. Designed to disappear behind your sauna benches, this innovative heater delivers powerful 9kW performance whilst maintaining a completely unobstructed sauna environment.

Engineered specifically for medium to large community and commercial saunas, the Hidden Heater installs into a purpose-built recess, creating clean sightlines throughout your sauna room. The streamlined stainless steel construction ensures durability in demanding environments, whilst the generous 15kg stone capacity provides excellent steam production for authentic löyly experiences.

This professional-grade heater requires an external control unit (sold separately), giving you flexibility in control placement and advanced functionality. Whether you’re designing a contemporary home spa, boutique wellness centre, or commercial fitness facility, the Hidden Heater 9kW delivers discreet performance that matches your design vision.

✨ Key Features

✅ Concealed Installation Design – Mounts behind sauna benches for a completely unobstructed sauna interior and clean minimalist aesthetics

✅ 9kW Power Output – Efficiently heats sauna rooms from 10 to 14 cubic metres to optimal bathing temperature

✅ Premium Stainless Steel Construction – High-grade stainless steel body ensures long-lasting performance in humid conditions

✅ 15kg Stone Capacity – Generous stone load provides excellent heat retention and authentic steam production

✅ 400V Three-Phase Supply – Commercial-grade electrical system ensures reliable, powerful heating

✅ Flexible Control Options – Requires external control unit (sold separately) allowing customised control placement and advanced features

✅ Integrated Safety Systems – Built-in thermal protection with separate temperature sensor and overheat limiter

✅ Finnish Engineering – Designed and manufactured by Harvia, world leaders in sauna technology since 1950

✅ CE Certified – Fully compliant with European safety and performance standards

🔧 Technical Specifications

Specification	Value
Power Rating	9 kW
Voltage	400V 3N~ (3-phase with neutral)
Fuse Size	3 × 16A
Room Capacity	10 – 14 m³
Dimensions (H × W × D)	830 × 1175 × 255 mm
Weight (Net)	33 kg
Weight (Gross)	34.3 kg
Stone Capacity	15 kg (max)
Recommended Stone Size	5 – 10 cm diameter
Heating Elements	6 × 1500W (240V)
Mounting Type	Wall (concealed recess)
Material	Stainless Steel
Control System	External (sold separately)
Minimum Room Height	1900 mm
Certifications	CE Marked
GTIN	6417659008310
Warranty	2 years (domestic), 1 year (shared residential), 3 months (commercial)

📏 Room Sizing Guide

Basic Calculation Principle: Approximately 1 kW of heater power is required for every 1 to 1.5 m³ of well-insulated sauna room volume.

Adjustment Factors to Consider:

Condition	Adjustment
Glass door or windows	Add 1.2 m³ per m² of glass area
Uninsulated log walls	Multiply room volume by 1.5
Exposed brick, tile, or concrete	Add 1.2 m³ per m² of exposed surface
Barrel sauna or outdoor installation	Add 25-30% to calculated volume
Ceiling height above 2.3m	Calculate additional air volume

Worked Example:

📍 Example Sauna Room: 2.5m × 2m × 2.2m (length × width × height)

• Base volume: 2.5 × 2 × 2.2 = 11 m³
• Glass door (0.8m × 2m = 1.6 m²): Add 1.92 m³
• Total calculated volume: 12.92 m³

✅ This 9kW Hidden Heater is ideal – perfectly suited for rooms between 10-14 m³

💷 Running Costs

Energy Rate Used: £0.28/kWh (UK average electricity rate, January 2026 – based on Ofgem price cap of 27.69p/kWh)

Estimated Annual Running Costs:

Usage Level	Sessions/Week	Hours/Year	Annual Cost
🏠 Light Use	2	150	£378
🧖 Regular Use	4	300	£756
🏢 Heavy Use	6+	450	£1,134

Calculation Formula:

Annual Cost = Power (kW) × Hours/Year × Electricity Rate (£/kWh)

Example (Regular Use):
9 kW × 300 hours × £0.28 = £756 per year

Per Session Cost (1.5 hour session):
9 kW × 1.5 hours × £0.28 = £3.78 per session

⚠️ Actual costs depend on your electricity tariff, usage patterns, session duration, and sauna insulation quality. Costs calculated at typical consumption – actual heater draw varies during operation.

⚡ Installation Requirements

Electrical Specifications:

Requirement	Specification
Supply Voltage	400V 3N~ (three-phase with neutral)
Fuse Rating	3 × 16A
Power Supply Cable	5 × 2.5 mm² (HO7RN-F or equivalent)
Control Unit Cable	5 × 2.5 mm²
Sensor Cable	4 × 0.25 mm²
Dedicated Circuit	Required
RCD Protection	Not recommended (see manual)

Installation Opening Dimensions:

Dimension	Measurement
Opening Height	1900 mm
Opening Width	1255 mm
Opening Depth	345 mm

Minimum Safety Clearances:

Position	Distance
Front (combustible materials)	90 mm
Front (non-combustible materials)	90 mm
Side walls (combustible)	80 mm
Side walls (non-combustible)	80 mm
Ceiling	1070 mm
Minimum room height	1900 mm

Ventilation Requirements:

• Fresh air inlet: Position minimum 50cm above heater level, 5-10cm diameter pipe
• Exhaust outlet: Lower section of opposite wall, cross-section twice that of inlet
• Air exchange rate: Minimum 6 air changes per hour recommended
• Ventilation gap: 80mm gap required under partition wall in front of heater

⚠️ 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 are NOT permitted as heater connection cables due to 
thermal degradation risk. Junction boxes must be splash-proof and positioned 
no higher than 50cm from floor level.

🔒 Safety Features & Certifications

Built-in Safety Systems:

• ✅ Thermal overheat protection with automatic shut-off
• ✅ Separate temperature sensor and overheat limiter in sensor box
• ✅ Temperature sensor positioning 100mm from ceiling for accurate monitoring
• ✅ Grid protection over partition wall to prevent contact with heating elements
• ✅ Professional-grade terminal connections

Certifications:

• ✅ CE Marked – European conformity certification
• ✅ Compliant with EN 60335-2-53 (Sauna heating appliances)
• ✅ Designed for commercial and residential applications

Safety Warnings:

• Keep combustible materials away from the heater at all times
• Do not exceed recommended stone capacity
• Children under 8 years must be supervised in the sauna
• Do not use the sauna under the influence of alcohol or sedatives
• Consult your doctor regarding health-related bathing limitations

🎯 Ideal Applications

Application	Room Size	Suitability	Notes
🏢 Commercial Saunas	10-14 m³	✅ Excellent	Purpose-designed for community use
🧖 Boutique Spa Facilities	10-14 m³	✅ Excellent	Premium aesthetics for wellness centres
🏋️ Gym & Fitness Centres	10-14 m³	✅ Excellent	Built for high-frequency commercial use
🏨 Hotel Wellness Suites	10-14 m³	✅ Excellent	Discreet installation for guest areas
🏠 Large Home Saunas	10-14 m³	✅ Suitable	Premium option for design-conscious homeowners
🛖 Garden Room Saunas	10-14 m³	✅ Suitable	Allow 25% additional capacity calculation

🪨 Sauna Stones

Stone Specifications:

Specification	Details
Maximum Capacity	15 kg
Recommended Size	5-10 cm diameter
Stones Included	No – sold separately

Recommended Stone Types:

• ✅ Peridotite – excellent heat retention
• ✅ Olivine diabase – traditional Finnish choice
• ✅ Olivine – high durability
• ✅ Vulcanite – superior thermal properties

Stone Care Guidelines:

• Wash stones to remove dust before first use
• Arrange stones loosely to permit airflow through heater
• Do not pack stones too tightly – air circulation is essential
• Inspect and rearrange stones at least annually
• Replace crumbled or degraded stones promptly
• With heavy commercial use, check stones more frequently

💡 High-quality sauna stones are available separately from Parts4Tubs – ask our team for recommendations.

🎛️ Control Options & Accessories

Control System:

The Hidden Heater 9kW requires a separate external control unit (not included). This design allows flexible placement of controls outside the sauna room and enables compatibility with various Harvia control systems.

Compatible Control Units:

• Harvia C-Series Controllers
• Harvia Griffin Control Systems
• Harvia Xenio Digital Controllers
• Harvia WiFi-enabled control systems

Control Features (depending on unit selected):

• Adjustable temperature range (typically 40-110°C)
• Timer function with delay start capability
• Temperature sensor included with heater
• Optional WiFi connectivity for smartphone control

Optional Accessories:

• Water bowl and flexible hose for löyly (steam) – recommended accessory
• Safety rail/guard for partition wall
• Temperature and humidity gauge
• Sauna lighting systems

❓ Frequently Asked Questions

Q: What size room will this heater work for? A: The Hidden Heater 9kW is designed for well-insulated sauna rooms between 10 and 14 cubic metres. For rooms with glass doors, uninsulated walls, or exposed masonry, add 1.2m³ per square metre of these surfaces when calculating your room size.

Q: How long does it take to heat up? A: A well-insulated sauna room will typically reach bathing temperature (65-80°C) within approximately 45-60 minutes. Actual heat-up time depends on room size, insulation quality, and starting temperature.

Q: What electrical supply do I need? A: This heater requires a 400V three-phase supply with neutral (3N~) and three 16A fuses on a dedicated circuit. Professional installation by a qualified electrician is mandatory.

Q: Is a control panel included? A: No, the Hidden Heater requires a separate external control unit (sold separately). This allows you to choose the control system that best suits your needs and enables optimal placement outside the sauna room.

Q: Are sauna stones included? A: No, sauna stones are sold separately. This heater requires up to 15kg of high-quality sauna stones with 5-10cm diameter. We recommend peridotite, olivine diabase, or vulcanite stones.

Q: What is the warranty? A: Warranty coverage depends on usage: 2 years for family/domestic use, 1 year for shared residential buildings, and 3 months for commercial/institutional installations.

Q: Can I install this myself? A: No. Due to the high-voltage three-phase electrical requirements and safety regulations, installation must be completed by a qualified electrician in compliance with BS 7671 and relevant building codes.

Q: Is this heater suitable for outdoor saunas? A: Yes, but outdoor and barrel sauna installations require increased room capacity calculations (add 25-30% to base volume) to account for additional heat loss. Ensure proper weatherproofing of all electrical connections.

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📥 Downloads & Resources

📄 Installation & User Manual – Complete installation guide with wiring diagrams, safety clearances, and operating instructions

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

🏆 Why Choose the Harvia Hidden Heater 9kW

• ✅ Concealed Design – Creates uninterrupted sauna aesthetics with behind-bench installation
• ✅ Commercial-Grade Durability – Stainless steel construction built for demanding environments
• ✅ Finnish Heritage – Engineered by Harvia, the world’s leading sauna manufacturer since 1950
• ✅ Powerful Performance – 9kW output efficiently heats rooms up to 14m³
• ✅ Flexible Control Options – Compatible with a range of Harvia control systems including WiFi
• ✅ Proven Reliability – Backed by comprehensive warranty and global service network

🤝 Why Buy from Parts4Tubs

• ✅ UK-Based Company – Local support from our Northamptonshire headquarters
• ✅ Expert Advice – Specialist knowledge from Andi and the team on sauna heating solutions
• ✅ Fast UK Delivery – Quick dispatch on in-stock items
• ✅ Competitive Pricing – Great value on genuine Harvia products
• ✅ Full Warranty Support – We handle any warranty claims on your behalf
• ✅ Easy Returns – 30-day returns policy for peace of mind
• ✅ Comprehensive Stock – Access to the full Harvia range and compatible accessories

🔥 Summary

The Harvia Hidden Heater 9kW Steel delivers exceptional concealed heating for medium to large saunas between 10 and 14 cubic metres. With its premium stainless steel construction, 15kg stone capacity, and behind-bench installation design, it creates the clean, minimalist sauna environment demanded by modern spas and wellness facilities. Finnish-engineered to commercial standards and backed by Harvia’s industry-leading reputation, this heater combines invisible installation with powerful, reliable performance. Order today from Parts4Tubs for fast UK delivery and expert support.