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KORAFLEX Thin FKT is a trench heater with lowest unit height. It is particularly suited to interiors with low floor depth, and as a secondary heating unit for shielding cold from French windows.

ECONOMIC version – basic version, black lacquered galvanized steel casing, non-lacquered heat exchanger
EXCLUSIVE version – black lacquered galvanized steel casing, RAL 9005 black lacquered heat exchanger

FKT ikony

ECONOMIC version basic version, black lacquered galvanized steel casing, non-lacquered heat exchanger
EXCLUSIVE version black lacquered galvanized steel casing, RAL 9005 black lacquered heat exchanger
Depth [mm] 60 mm
Width [mm] 140, 200, 260, 320 mm
Length [mm] 800 to 3 000 mm (by 100 mm)
Heat output [W] from 43 to 644 W
Max. operating pressure [MPa] 1.2 MPa
Max. operating temperature [°C] 90 °C
Connecting thread inner G ½"

Cover grilles

Thin trench heaters may only be fitted with Thin grilles, and after casing
modifications Cross grilles. No other grilles are available for this range.

PM Thin   
picto info

Where a left-hand connection to the heating system is required, rotate the heat exchanger in the trench heater by 180°.
The design of trench heater casing does not allow substituting Thin and Cross grilles after ordering.

Note, please, that grilles must be ordered together with the trench heaters, as the casing must undergo alternation.

Thin grilles are not available in linear design.

Heat output [W] where t1/t2/ti / EN 16430. Measurements shown in mm including Thin-frame.

ΔT = 50 °C Length [mm] Temperature exponent
800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 2100 2200 2300 2400 2500 2600 2700 2800 2900 3000
60 140 43 53 63 73 83 93 104 114 124 134 144 154 164 175 185 195 205 215 225 235 246 256 266 1,3030
70 200 87 105 122 139 156 173 190 207 224 242 259 276 293 310 327 344 362 379 396 413 430 447 464 1,5168
70 260 100 120 139 159 179 198 218 238 257 277 296 316 336 355 375 395 414 434 454 473 493 512 532 1,7953
70 320 114 138 162 186 210 234 258 282 306 331 355 379 403 427 451 475 499 523 548 572 596 620 644 1,6785

Standard contents

  • RAL 9005 black laquered galvanized steel casing
  • Economic – non-lacquered Al/Cu heat exchanger with bleed valve
  • Exclusive – RAL 9005 black lacquered Al/Cu heat exchanger with bleed valve
  • aluminium T-frame for Thin grille, silver elox
  • metal cover plate
  • levelling set screws and 4 anchors
  • spacers for correct installation and concreting
  • hardboard cover to protect trench heater from contamination
  • durable packaging, installation instructions



Optional accessories

  • Thin or Cross grille
  • Cross grille – design solutions – necessary to order together with trench heater
  • silver, light/dark bronze and black elox or RAL colour chart lacquered aluminium frame for Thin grille
  • thermostatic head with incorporated control and immersion remote sensor
  • 24V DC power supply
  • 24V DC or 230V AC room thermostat for regulation
  • 24V DC or 230V AC thermoelectric actuator, cable length 2.5m or 5m
  • lockshield, thermostatic valve
  • ½" × ½" 90° brass elbow for connection facilitation
  • 10, 12 or 30 cm flexible stainless steel hose
  • strengthened OSB cover for installation purposes



Složení konvektoru FK_1

1black laquered galvanized steel casing

2choice of grille (please order separately)

3choice of aluminium frame

4Al/Cu heat exchanger

54 anchors

6levelling set screws

7metal cover plate


9spacers for correct installation and concretin


Standard Thin grille frame                               Optional Cross grille frame (upon request)
Thin rámečky

Suitable grilles

PM Thin EN

KORAFLEX  THIN FKT  -  PRODUCT RANGE                                                                                                                   DEPTH 60 mm

FKT - sirky


Typ 60/140 Typ 60/200
Thin typ 140 Thin typ 200
Typ 60/260 Typ 60/320
Thin typ 260 Thin typ 320

picto info  Measurements shown in mm. The given widths of trench heaters are identical for both models fitted with Thin or Cross grille frames.


Construction recommendations

To ensure correct operation, it is essential that the following principles are respected.

  • Trench heaters must be installed horizontally with the heat exchanger on the window side. For the grille to function correctly, the upper edge of the casing must be straight and level (not buckled or bent).
  • The maximum recommended distance of the trench heater from the wall/window is 100 mm.
  • The size of the trough in the floor for thrench heater installation should be at least 100 mm bigger (both in length and width) than the convector.
  • We recommend connecting the trench heater to the heating system using a lockshield and thermostatic valve. The heat exchanger connection is by an inner G½ thread. Following connection to the heating system, bleed and carry out a pressure test.
  • When concreting, the trench heater must be levelled using the set screws provided and fastened to the floor using the anchors provided. The anchors keep the trench heater in place while pouring concrete.
  • Using anchors will extend the bottom width of the trench heater by 42 mm from each side.
  • While pouring concrete, the trench heater may be weighed down.
  • While pouring concrete it is particularly important to brace the trench heater to prevent longitudinal buckling. Trench heaters are fitted with spacers for this purpose. (Please note: FKP models as standard are, however, not equipped with spacers.) Following concreting, these spacers are easily removed.
  • While pouring concrete or anhydrite it is essential to seal all connection openings to prevent leakage.
  • Where the trench heater is not concreted in, floor supports are recommended to use to incorporate the trench heater into a raised floor. Standard trench heater models are not self-supporting.
  • We recommend insulating the outer side of the trench heater casing along the length of the heat exchanger with polystyrene to prevent heat loss into the floor.
  • To avoid contaminating the trench heater, we recommend maintaining the protective hardboard cover in place during construction work. The board, which is included in the standard contents, is not suitable for walking on and serves solely to protect the trench heater from contamination during installation. Strengthened OSB covers for installation purposes are available as option extras.
  • Trench heaters fitted with stainless steel casings installed in humid environments – marked KORALEX Pool FKP – are equipped as standard with overflow drains. During installation the pipe at the bottom of the trench heater must be connected to piping with sufficient gradient to drain overflow water. We recommend installing a U-bend to prevent odour.

Raised floor installations

  • ​Structural supports for raised floor trench heater installations offer stable and effective solutions. Structural supports are manufactured from non-lacquered steel and are suitable for raised floors of a depth up to 500 mm. Structural supports are suitable for Optimal FKO and Basic FKB models.

Zdvojená podlaha

picto info

Supports must be ordered together with trench heaters due to structural alterations to convector casings! Components of several types of raised floor support are integral parts of the trench heater body.




FK - montaz konvektoru - 1-bez  FK - montaz konvektoru - 2-bez

1 - trench heater with natural convection, 2 - heat exchanger, 3 - grille, 4 - U-frame, 5 - F-frame,
6 - set screws, 7 - anchors, 8 - up to 300mm deep dividing partition, 9 - window,  10 - floor level, 
11 - grout, 12 - expansion joint, 13 - insulation, 14 - concrete filler, 15 - sub-floor


Alterations to technical specifications reserved


Recommended positioning of heat exchangers in trench heaters

  • Trench heaters should be positioned a maximum of 100 mm from windows. In order to achieve maximum performance, the recommended position for heat exchangers in the trench heater is always on the window side. This results in natural air flow, whereby warm air rises and cool air is drawn into the trench heater. In this way, cool air at the window is screened and the air in the room is heated.

Trench heaters are fitted as standard with right-hand connections to the heating system; a left-hand connection is achieved simply by rotating the heat exchanger 180°.

přirozená konvekce


Trench heater multiple installations

Casing types according to water connections and lowered sides for multiple installations

Lowered trench heater casing sides are used where invisible connections are desired between trench heaters (multiple trench heaters around a room, eg. in administrative buildings, restaurants, hotels, etc.). When ordering grilles, care must be taken to include information in the order code that the grilles required are to be used with trench heaters with lowered faces.

připojení FK


Example order code: FKT-100/06/20-V1T1P0

KORAFLEX trench heater with natural convection, Thin model, length 100 cm, depth 6 cm, width 20 cm, non-lacquered heat exchanger, T-frame for Thin grille, silver elox, right-hand connection to heating system, without lowered face.

KORAFLEX Convection Thin   Length/Depth/Width (cm)   Heat exchanger
Heat exchanger
Frame Frame colour Connection
F K T - 100/11/26 - V 1 T 1 P 0







V counter-flow
P* single-stream
0 without heat

1 non-lacquered
5 RAL 9005
9 other colour RAL
0 without heat

T for Thin grille
C for Cross grille
0 without frame

1 silver elox
2 dark bronze elox
3 light bronze elox

5 black elox
9 other RAL colour
0 without frame


0 without lowered face
1 lower face – input side
2 lower face – opposite input side
3 both sides lower

P* – single-stream heat exchangers are fitted as standard in trench heaters 140 mm wide.

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