What is a trench heater? How it works, types and applications

June 20, 2026

A trench heater is a heating appliance recessed into the floor that works as part of a water-based (hydronic) heating system. It is installed along panoramic windows, glazed façades and curtain walls, where a conventional radiator would be visible and intrusive. The unit stays hidden in the floor — only a decorative grille is visible at floor level.

In this article we explain what a trench heater is, how it works, the difference between fan-assisted and natural-convection models, where they are used and how to choose one.

What is a trench heater in simple terms

A trench heater consists of a casing set into the floor screed, containing a heat exchanger filled with warm water. Cold air falling from the window passes through the heat exchanger, is warmed and rises, forming a thermal curtain along the glazing that prevents cold draughts and condensation on the glass.

Note that this is a water (hydronic) appliance — the heat-transfer medium is water from a boiler or heat pump — not an electric convector heater.

How a trench heater works

The principle is convection:

  1. Warm water enters the heat exchanger of the floor-recessed unit.
  2. Cold air from the window descends and passes through the warm heat exchanger.
  3. The heated air rises, creating a thermal curtain along the glazing.
  4. Cold zones and glass condensation are prevented.

Trench heaters come in natural-convection (no fan) and fan-assisted versions — see below.

Trench heaters with and without fans

  • Natural convection (no fan) — air moves naturally; the unit is silent. Ideal for residential spaces where quiet matters. Example: trench heater FC.
  • Fan-assisted (forced convection) — built-in EC fans greatly increase heat output for the same length. Suited to large glazed areas, low-temperature systems and heat pumps. Examples: FH4-H and FH4-M.

If you also need cooling, use trench fan coils FCH, which both heat and cool.

Where trench heaters are used

Trench heaters are essential wherever there are large glazed areas:

  • panoramic windows and curtain walls in homes and apartments;
  • office and administrative buildings;
  • hotels, retail and public spaces;
  • airports, museums and exhibition halls.

Konveka supplies trench heaters to projects in more than 30 countries — from office buildings to airports.

Benefits of trench heaters

  • Invisible — hidden in the floor, only the grille is seen;
  • Thermal curtain — protects against cold and condensation on large windows;
  • Design freedom — walls and sills stay clear;
  • Efficiency — a water heat-transfer medium and EC fans use less energy than electric units;
  • Durability — a stainless-steel casing resists corrosion.

Trench heater vs radiator

A radiator takes up wall space and is visible; along panoramic glazing it is hard to place. A trench heater solves this: hidden in the floor, it forms a thermal curtain exactly where it is needed — at the glass. It connects to the same heating system as radiators.

How to choose a trench heater

Consider the heat output (depends on glazing and heat loss), the unit’s length, width and depth (to suit the floor build-up), with or without a fan (output vs silence), the grille type (material and colour), and the system temperature (important for heat pumps). Need help? Contact the Konveka export team.

Konveka trench heaters

Konveka is a European manufacturer of hydronic convectors and fan coils since 2005. Konveka trench heaters have a stainless-steel casing, EC fans (on forced-convection models) and are tested to EN 442 and EN 16430. The range includes FH4-H, FH4-M (fan-assisted) and FC (natural convection). See the full range.

Frequently asked questions

What is a trench heater in simple terms? A floor-recessed heating unit that warms the air at the window using warm water and forms a thermal curtain along the glazing.

Is a trench heater water or electric? Konveka makes water (hydronic) trench heaters — they connect to the heating system (boiler, heat pump) and are more economical than electric units.

Do I need a fan? Not necessarily. Without a fan the unit is silent; with EC fans it delivers more heat for the same length — the choice depends on the glazed area and required output.Can a trench heater cool? Trench heaters are for heating. For heating and cooling, use trench fan coils FCH/FCHV.