Thermal curtains: how much energy do they really save in a hotel or office?

Glazed areas are the number-one heat-loss point of a hotel or office building. Before committing to a six-figure window replacement, there is a textile lever that is fast to deploy, reversible and immediately felt by occupants: a properly made and properly installed thermal curtain. Here is how it works — and what it can and cannot save you.

What makes a curtain "thermal"?

Three parameters drive thermal performance, far more than fabric marketing:

• Composition: a dense, lined fabric — ideally with an interlining — traps a still layer of air between glazing and room; that air layer does the insulating.
• Make-up: generous fullness, weighted hems, side returns that close the air layer.
• Installation: from ceiling (or a closed pelmet) down to the floor, overlapping the window generously. A curtain stopping at the sill lets convection bypass it and loses most of its benefit.

What the studies say — and what to remember

Research on window coverings converges: on old or poorly performing glazing, a well-fitted lined curtain significantly reduces night-time heat loss through the window, and summer solar gain. The magnitude depends heavily on the existing glazing, the climate and usage discipline (curtains actually drawn). Remember the reasoning rather than a single figure: the older your glazing, the bigger the gain — precisely where window replacement is most expensive.

For an operator, three benefits that stack

1. The energy bill

Heating at night in winter, cooling in summer: in a hotel, rooms with curtains drawn during unoccupied days and winter nights represent thousands of window-hours a year during which the textile works for you.

2. Perceived comfort — and guest scores

The cold-wall feeling near a window triggers complaints and thermostat overrides. A thermal curtain removes it, and its blackout improves sleep: two major guest irritants addressed by a single fitting.

3. Energy regulations and certifications

For buildings subject to energy-reduction obligations, textile window treatment is one of the lowest-capex actions that can be documented in your action plan, and it is compatible with HQE/BREEAM renovation schemes.

The mistakes that ruin performance

• Unlined "thick-looking" fabric: visual thickness does not insulate — the air layer does.
• Narrow face-fit without overlap: convection goes around the sides.
• Open top: warm air dives behind the curtain and feeds the convection loop — a pelmet or ceiling fixing closes the circuit.
• Forgetting the fire rating: in a public building your thermal curtain must also be M1. The two requirements combine perfectly — if specified from the start.

How we size a thermal project

Window survey and glazing diagnosis, fabric/lining pairing by orientation and room use, make-up with returns and weighting, full-height installation. On hotel projects we validate in a model room before rollout — the full method is described on our thermal and acoustic technical curtains page.

See also our dedicated page: Thermal & acoustic technical curtains →