Specification

Why Double-Glazed Aluminium Windows Make a Difference in an Outdoor Sauna

An expert guide to sauna window and door glazing — why double-glazed aluminium-framed windows and doors are the correct specification for a UK outdoor sauna, and why single-glazed windows are a false economy.

By Wellness One Lifestyle · Published 2026-08-02 · Updated 2026-08-02

The Glazing Problem in Outdoor Saunas

The majority of outdoor saunas — including most mid-range (mass market) models — use single-glazed windows and doors. This is a significant specification compromise that has a direct impact on performance, running costs, and longevity.

Single-Glazed vs Double-Glazed

Single-glazed glass has a U-value (thermal transmittance) of approximately 5.8 W/m²K. Double-glazed glass has a U-value of approximately 1.2–1.4 W/m²K. In practical terms, a double-glazed window loses approximately 75% less heat than a single-glazed equivalent.

In a sauna operating at 110°C with an external temperature of 5°C, the temperature differential across the glass is 105°C. Single-glazed windows under these conditions are a major source of heat loss.

Why Aluminium Frames?

Aluminium frames are the correct choice for outdoor sauna glazing. They are dimensionally stable in extreme temperature cycles, resistant to moisture and corrosion, and maintain a consistent seal over the product's lifespan. Timber-framed windows expand and contract with temperature and humidity changes, leading to seal failure over time.

Wellness One's Standard

Wellness One is the only major outdoor sauna brand using double-glazed, aluminium-framed windows and doors as standard across the entire range. This is not an optional upgrade — it is the baseline specification for every model from the Lifestyle 2 to the Connect 10.

The Impact on Running Costs

The combination of 100mm SIP insulation and double-glazed aluminium glazing means Wellness One saunas are significantly cheaper to run than competitors. The heater works less to maintain temperature, and the sauna reaches temperature faster.