Ceiling Heating - Installation

1. Introduction

Safe-t-FLEX is an efficient method of radiant ceiling heating

Safe-t-FLEX radiant ceiling heating efficiently heats to a comfortable temperature

The principle of Safe-t-FLEX heating elements is based on a continuous resistive sheet providing heat evenly over the black surface areas.

Safe-t-FLEX consists of specially formulated conductive dispersions on either an impregnated glass cloth or coated polyester film substrate. Copper electrodes are fixed parallel to each length edge. Transparent high electrical insulating film, which is wider than the black area to allow subsequent stapling of the element to the ceiling joists, completes the robust laminated product construction characteristics of Safe-t-FLEX heating elements.

For ceiling heating installations elements are normally supplied at an output of 200 W/m2 over the heated area of element and supplied in standard overall widths of 400 mm, 450 mm and 600 mm (16", 18" and 24") to accommodate standard joist centres. Other widths and outputs are available on request.

Low temperature Safe-t-FLEX ceiling heating elements produce a gentle heat that evenly warms the whole room. Once the surfaces have been warmed, the heat is reflected resulting in comfortable, natural warmth with minimum floor to ceiling temperature variation.

For a more detailed installation guide in pdf format, or an installation guide for the Safe-t-CASSETTE Heating Cassettes, see our Downloads section.

2. Installation Procedure

Safe-t-FLEX radiant ceiling heating carbon film is easy to install

Safe-t-FLEX radiant ceiling heating carbon film: easy to install

Before commencing work on site, check:

  1. The building is weatherproof, with glazing and doors in place.
  2. Any floor screeds, asphalt etc. above heated ceilings have been laid and allowed to dry out.
  3. All electrical-insitu mechanical services through ceilings are completed, including lagging to any pipe work.
  4. Joists and battens have been positioned at accurate and agreed centres. In certain instances cross noggins may have been fitted to allow additional cross fixing of ceiling boards. Where this has occurred the Safe-t-FLEX element should be cut and reconnected as illustrated by referring to Instruction 7.

Element layout drawings are not normally required for Safe-t-FLEX Installations, thus enabling elements to be cut and fixed on site to accommodate last minute alterations to joist and service layouts.

  1. Firstly, check that the element identification labels and information printed on the selvedge complies with the grade required for the installation and the quantities shown on the installation Test Certificate.
  2. Fixing Wiring harness from the room thermostat to heating elements.

1.5 mm2 - 2.5 mm2 standard single double insulated t.p.s. cables are used for making up the wiring harness. The cable size used depends on circuit load and de-rating factors. Olex, Pirelli, C.M.A, Burton, etc or approved equal cables may be used and are available from CBS Radiant Heating Systems or your local supplier.

Safe-t-FLEX heating elements are designed to accommodate a current carrying capacity of 10 amps. Consideration must be given by the Electrical Contractor in respect of the individual ceiling heating circuit ratings relative to thermostat rating, circuit breakers and the need for switching contactors where time clock control is incorporated.

Text Box: Easy to install and wire Safe-t-FLEX element simply staples to ceiling joists.

Normal good wiring practice must be observed and the wiring must comply with local electrical authority requirements. Holes for carrying the cables must be drilled at least 50 mm below the top of the ceiling joists where the cables cross over joists which would support floorboards, the cables must be positioned so that they cannot come into contact with any heated part of the element. Note that all main distribution boards incorporate an E.L.C.B. device or combination R.C.D. for each circuit.

3. Install Thermal Insulation

This will normally be glass fibre, mineral wool quilt and be 75 mm - 150 mm thick. Other insulation types may be used. Do not use insulation containing cellulose or other combustible type material. In all instances, only non-combustible, non-metallic thermal insulation must be used and have the equivalent R-value to glass fibre or mineral wool insulation. Foil faced material should not be used next to the heating element, be it in the form of a vapour check or as part of the insulation. Ensure that no insulation is trapped between the element and ceiling, particularly when using loose fill type insulation. Where vapour checks, are specified by the Architect, these are best provided in the form of a polythene membrane positioned between the Safe-t-FLEX ceiling heating elements and ceiling board depending upon the house type and construction. If in doubt further advice should be sought from your specifying authority.

Fitting the vapour check, following the installation of the Safe-t-FLEX ceiling heating elements, helps prevent damage to the membrane during looping of elements and final connection to the elements. The installing engineer must ensure that the vapour check covers the entire room with joints overlapped and taped.

The insulation quilt should be positioned to lie firmly onto the Safe-t-FLEX element so as to minimise the air space between the element and the insulation.

Safe-t-FLEX: radiant ceiling heating: fibre glass installation cross-section

Safe-t-FLEX radiant ceiling heating carbon film: cross section of installation

In some instances, insulation can be installed after the Safe-t-FLEX elements have been fixed, for example in the roof void of bungalow type construction or pitched roof two storey dwellings.

When positioning insulation in the roof space, care must be taken not to block the eaves opening, thereby restricting ventilation into the roof void.

4. Element Preparation

Safe-t-Flex: radiant ceiling heating: check element

Safe-t-FLEX radiant ceiling heating carbon film: heating element check

  1. Referring to the Installation Test Certificate Information, check that the total specified length required is easily installable against the joist layout. Allowance must be made for cutting back to accommodate coving, noggins or dwangs and surface or recessed light fittings. Elements must not be allowed to pass over partitions, full height wardrobes, cupboards, false beams or any other objects in contact with the heated portion of the ceiling.
  2. Unroll the element on a clean working surface and mark off the required length. The polyester external surface of the heating element can be marked with any proprietary felt tipped industrial marker. Using a straight edge cut the element to length using scissors or a sharp knife.
  3. Seal ends of the element using only the correct polyester insulating tape (supplied by CBS Radiant Heating Systems). Ensure that the tape is folded over to form a neat seal.
  4. Using only the flat headed crimping pliers supplied by CBS Radiant Heating Systems attach metal crimp connectors to both copper conductors at one end of the element. Locate the crimp centrally on the end of the copper strip, then fold it shut between thumb and forefinger. Fitting the crimp with the barrel to the same side as the copper electrode will assist locating the wiring harness. The crimping pliers are now utilised with 2 diagonal applications (firstly from the hinge side of the crimp, and then from the open side) to ensure that the whole area of the crimp in contact with the element is pressed flat. The ratchet mechanism on these pliers prevents the jaws being opened until the correct pressure has been applied. Normal pliers must not be used for this operation as crimps fitted in this way may overheat due to high contact resistance.
Safe-t-Flex: radiant ceiling heating: stapling elements to joist

Safe-t-FLEX radiant ceiling heating carbon film: attaching to the joists

5. Stapling Elements to Joists

Position the elements, close to the wiring harness to allow the fixing of cold tails. Staple element to joist on one side through the clear fixing edge and unroll approximately 1 metre in order to align direction. Unroll element, stapling both sides at a spacing of approximately 40cm (16") keeping the element taught and smooth to prevent any creasing. Elements must be fitted with the copper conductor strip face downwards and care must be taken to ensure that only the clear selvedge covers any timber grounds. Wood framing must be dry with the maximum of 15% moisture content.

For steel joists or furring channel use double sided tape or flat head screws, to attach elements. If elements do not span joist centres attach one side as above, and extend using ducting tape or rubber bands.

Safe-t-Flex: radiant Floor heating: Using the crimp

Safe-t-FLEX radiant ceiling heating carbon film: attaching the cold tails

6. Installing Cold Tails

Bare connecting leads and insert singly or in pairs into the cylindrical ferrule of the crimp connector.

Using the Safe-t-FLEX crimping tool to complete the crimp connection with the tool so that the "W" form of the tool is to the seamed side of the cylindrical female of the crimp. If crimped in reverse the crimp will "neck" and the crimp cover may not fit. Pliers should have calibration gap checked regularly.

7. Fitting Crimp Covers

When connection has been made to each individual element, Safe-t-FLEX plastic crimp covers must be fitted to insulate each crimp connection. Supplied in two halves connected by a flexible hinge, the open end allows access for the conductor wire to the crimp and the two small pegs locate in mating holes when closed with finger pressure. When the cover is fitted a cable tie must be strapped around the cover for additional security.

Where cross noggins or dwangs are fitted the element must be bridged as shown, below. This extra work can be assisted by factory made cables. Panels must be wired to bridge ceiling lights or any cross bracing in heated areas.

8. Installation from above

In certain cases where access to the ceiling is available, Safe-t-FLEX elements can be installed from above. If not already supplied at the pre-defined width, the stapling border can be trimmed back along either side. Do not cut the border closer than 12 mm from the copper electrode. Be certain that the area in which the elements are to be laid is free from debris and any sharp objects that may puncture the element. Tape or staple the element in place and connect up as detailed previously.

9. Testing Procedure

To protect the Safe-t-FLEX element, ceiling boards should be installed immediately after the Safe-t-FLEX elements are installed. Before this and referring to the data sheet appended, a cold resistance and megger test should be carried out at each thermostat position using accurate meters. The actual recorded reading must be entered on the Installation Test Certificate. After ceiling erection and when power is available, a further live current test may be performed. It may however, be more practical for this to be carried out by the electrical contractor at the time of fitting the room thermostats.

Safe-t-Flex: radiant ceiling heating

Safe-t-FLEX radiant ceiling heating carbon film: testing tools

Measure the resistance of each room circuit with an accurate Ohm-meter before connecting the thermostat. The resistance should fall within +10% and -5% of the specified values in the appended installation table (see below). If the resistance It should then be recorded in the Installation Test Certificate.

Before leaving the site.

  1. Fix mandatory label for positioning adjacent to the distribution board and any access trap doors to roof spaces.
  2. Complete Installation Test Certificate and remove all surplus materials from site. Safe-t-FLEX ceiling heating element is a specialised product and should not be allowed to fall into the hands of people who are not qualified to use it. Equally, it is important to maintain a high standard of security at the installer's site stores.
  3. Ensure that the ceiling heating installation complies with the relevant authorities installation rules and regulations. Submit installation notices as required to the relevant authorities.


Output Power Element Width (m) for specified Joist Spacing Cold Resistance Live Current
kW 300 mm 400 mm 600 mm Ohm Amps
0.05 1.07 0.61 0.43 1152 0.21
0.1 2.15 1.23 0.86 576 0.416
0.15 3.22 1.84 1.29 384 0.625
0.2 4.3 2.45 1.72 288 0.833
0.25 5.36 3 2.15 230.4 1.041
0.3 6.44 3.68 2.58 192 1.25
0.35 7.5 4.3 3 165.57 1.458
0.4 8.58 4.9 3.43 144 1.666
0.45 9.66 5.5 3.86 128 1.875
0.5 10.73 6.13 4.3 115.2 2.083
0.6 12.9 7.36 5.15 96 2.5
0.7 15 8.6 6 82.28 2.916
0.8 17.17 9.8 6.87 72 3.333
0.9 19.3 11 7.7 64 3.75
1 21.46 12.26 8.6 57.6 4.166
1.1 23.6 13.5 9.44 52.36 4.583
1.2 25.75 14.7 10.3 48 5
1.3 27.9 16 11.6 44.3 5.416
1.4 30 17.2 12 41.14 5.833
1.5 32.2 18.4 12.9 38.4 6.25
1.6 34.33 19.6 13.73 36 6.666
1.7 36.5 20.8 14.6 33.88 7.083
1.8 38.6 22 15.5 32 7.5
1.9 40.8 23.3 16.3 30.31 7.916
2 42.9 24.5 17.2 28.8 8.333
2.1 45 25.8 18 27.43 8.75
2.2 47.2 27 18.9 26.18 9.166
2.3 49.4 28.2 19.75 25.04 9.583
2.4 51.5 29.4 20.6 24 10
2.5 53.65 30.66 21.5 23.04 10.416
2.6 55.8 31.9 22.3 22.15 10.833
2.7 57.9 33.1 23.2 21.33 11.25
2.8 60.1 34.34 24 20.57 11.666
2.9 62.2 35.6 24.9 19.86 12.083
3 64.4 36.8 25.8 19.2 12.5
3.1 66.5 38 26.6 18.58 12.916
3.2 68.7 39.24 27.5 18 13.333
3.3 70.8 40.5 28.3 17.45 13.75
3.4 73 41.7 29.2 16.94 14.166
3.5 75.1 42.9 30 16.45 14.583
3.6 77.25 44.15 30.9 16 15


Individual circuit loads must not exceed 3.60 kW. Loads exceeding the thermostat rating must be switched through a suitable contactor. The installation can be taken as correct if the resistance and current recorded is within +10% to -5% of the specification.

Any shortfalls are to be reported to the site agent and CBS Radiant Heating Systems immediately. For other outputs and voltages refer to the identification label for element rating per metre and apply the following formulas (all are for 240 V).

Element Rating Wattage / linear metre for specified centres
W/m2 300 mm 400 mm 450 mm 600 mm
200 40 60 70 100
233 46.6 69.9 81.55 116.5
250 50 75 87.5 125