Choosing infrared heating film by wattage alone is an easy way to oversize one room and underheat another. An 80 W/m² film is not automatically “too weak”, and a 220 W/m² film is not automatically “better”. The right infrared heating film output is the one that can replace the room’s heat loss through the floor area that is genuinely available for heating—without exceeding the finished-floor temperature limit or the electrical design limits.
Termofol’s standard 230 V heating-film range includes 80, 140, 180 and 220 W/m² options. All four convert electrical energy into heat at the point of use; the wattage tells you the maximum connected output per square metre of installed film. It does not tell you how much heat a particular room needs, how warm the floor may safely become or how long the thermostat will call for heat.
This guide explains how to make that choice properly for an Irish home and gives worked examples you can use at the planning stage.
The short answer
As an initial planning guide:
| Film output | Typical planning role | Output from 10 m² of film | Approx. current at 230 V* |
|---|---|---|---|
| 80 W/m² | Low-demand rooms, gentle supplementary floor warming or projects with generous usable coverage | 0.80 kW | 3.48 A |
| 140 W/m² | A balanced option for many insulated rooms and compatible floating floors | 1.40 kW | 6.09 A |
| 180 W/m² | Higher room demand or less available heated floor area; often considered for primary heating | 1.80 kW | 7.83 A |
| 220 W/m² | High output from a restricted usable area or a higher-loss project that has been properly calculated | 2.20 kW | 9.57 A |
*Current figures are simple planning calculations: watts ÷ 230 V. They are not a circuit design.
Termofol generally positions 80 and 140 W/m² films for lower-demand or supplementary applications and 180 and 220 W/m² films for higher-demand or primary-heating applications. Treat that as a useful starting point, not a substitute for a room-by-room heat-loss calculation. The Termofol heating-film range also includes different widths, allowing the layout—not only the wattage—to be adapted to the room.
What W/m² actually means
The rating describes the film’s power density. If 12 m² of 140 W/m² film is energised, its maximum connected output is:
12 m² × 140 W/m² = 1,680 W, or 1.68 kW
Change the same 12 m² to 220 W/m² film and the connected output becomes:
12 m² × 220 W/m² = 2,640 W, or 2.64 kW
This is the maximum rate at which the installed film can deliver heat while the thermostat is calling. It is not a prediction that the system will run continuously, and it is not the same as annual energy use. Once the room reaches its set temperature, the thermostat cycles the heating to replace the heat leaving the building.
That distinction matters. A higher-output film may warm a floor more quickly and run for shorter periods. A lower-output film may run for longer. If both systems maintain the same indoor temperature in the same building, the building’s heat loss remains the main driver of seasonal space-heating energy. Output selection changes available capacity, response and instantaneous electrical load; it does not repeal the physics of the room.
For a fuller explanation of energy use, see Infrared Heating Film Running Costs in Ireland.
The four checks that should decide film output
The correct selection comes from four connected checks:
- the room’s design heat loss in watts;
- the floor area that can actually contain heating film;
- the temperature and construction limits of the complete floor build-up;
- the connected load, controls and electrical circuit design.
If one of these is missing, choosing between 80, 140, 180 and 220 W/m² is still guesswork.
1. Start with room heat loss—not floor area alone
A 20 m² room in a well-insulated apartment can need far less heat than a 20 m² room with two external walls, older glazing, a suspended floor and high air leakage. The dimensions match; the heat losses do not.
A proper heat-loss assessment considers the room’s external walls, windows, doors, floor, ceiling or roof, insulation, air leakage, design indoor temperature and local outdoor design conditions. It should produce a design heat requirement in watts for each room. That number is the useful starting point for heating-system sizing.
An Irish Building Energy Rating is useful context, but it is not a room-by-room heat-loss calculation. SEAI describes BER as an asset rating based on the building fabric and installed systems under standard assumptions. Since 24 May 2026, the simplified domestic scale runs from A0 to G. A lower-insulation property will generally lose more heat, but two rooms in homes with the same headline BER can still need different outputs. Read more in SEAI’s guide to understanding a BER.
If the calculation shows very high heat loss, improving insulation and airtightness may be a better first step than simply selecting the strongest film. Reducing the load improves comfort and lowers the energy required by any heating system.
2. Measure the usable heated area
Heating film is designed around the permanent room layout. The whole room area is rarely the same as the usable film area.
Exclude locations where the approved system design does not permit film, including beneath fixed floor-to-ceiling units, kitchen islands and low flat-bottomed furniture that traps heat. Allow for perimeter clearances, transitions, sanitary fittings and other obstructions. A dining table or sofa on sufficiently open legs is a different thermal condition from a fitted cabinet sitting directly on the floor, but the final layout must follow the Termofol installation design.
The film can be cut at its designated cut intervals and is available in multiple widths, which helps cover irregular rooms efficiently. Termofol lists standard 25, 50 and 100 cm formats in its technical range and a 250 mm cutting interval. Never cut, overlap or modify the film outside the manufacturer’s instructions.
The usable-area calculation is crucial because the film must deliver the room’s requirement through that smaller area.
For example, a 20 m² living room may provide only 14 m² of usable heated area after the kitchen island, fitted storage and low furniture zones are excluded. That is 70% coverage. The required film power density must therefore be calculated using 14 m², not 20 m².
3. Check the complete floor build-up and temperature limit
The highest wattage that meets the heat-loss figure is not automatically suitable for the selected floor.
Laminate, engineered wood, click vinyl and carpet systems can each have different limits for maximum surface temperature, thermal resistance, underlay and installation method. A commonly seen limit is around 27°C for some wood, laminate and resilient flooring products, but this is not universal. The technical sheet and warranty conditions for the exact floor product take priority.
The complete construction must also be approved: subfloor, insulation layer, heating film, protective layer or membrane, underlay where applicable and final floor finish. Do not judge compatibility from the decorative material name alone. Our guide to flooring compatible with infrared heating film explains the differences in more detail.
A floor-temperature sensor connected to a suitable thermostat is essential for controlling the floor limit. It should be installed in the specified conduit and sensing position so it measures a representative heated area and can be replaced if necessary. Room-air control provides comfort; the floor sensor protects the floor build-up.
Termofol’s film data also lists maximum film temperatures for individual products. Do not confuse a film’s technical maximum with the permitted temperature at the finished floor surface. The lowest applicable limit in the complete design controls the system.
4. Convert the room requirement into required film output
Once the heat-loss requirement and usable film area are known, the first sizing calculation is simple:
Required film output (W/m²) = room design heat loss (W) ÷ usable film area (m²)
Worked example A: insulated 20 m² room
- Room design heat loss: 1,800 W
- Usable film area: 14 m²
- Required density: 1,800 ÷ 14 = 128.6 W/m²
On capacity alone, 140 W/m² film provides:
14 × 140 = 1,960 W
That exceeds the calculated 1,800 W requirement on paper. The designer must still confirm the floor temperature, chosen floor covering, control method, design margin and electrical arrangement.
Worked example B: the same room with greater heat loss
- Room design heat loss: 2,500 W
- Usable film area: 14 m²
- Required density: 2,500 ÷ 14 = 178.6 W/m²
The nearest standard Termofol output at or above that result is 180 W/m²:
14 × 180 = 2,520 W
This is only 20 W above the stated requirement, so a competent designer should consider calculation uncertainty and the required design margin. Moving immediately to 220 W/m² may provide more capacity, but it also raises the connected load and the importance of surface-temperature control. Improving the room fabric or increasing the usable heated area may be the better solution.
Worked example C: output cannot compensate for an unsuitable floor
Suppose a small room needs 1,600 W but offers only 7 m² of usable floor:
1,600 ÷ 7 = 228.6 W/m²
Even 220 W/m² provides only 1,540 W. This is not a signal to ignore the calculation or the floor limit. The project needs a design change: reduce heat loss, increase valid coverage, add an approved supplementary heat source or reconsider the heating method.
When 80 W/m² film makes sense
The 80 W/m² option provides the gentlest power density in the standard range. It may suit a low-heat-loss room, a supplementary comfort-heating zone or a project with a high proportion of usable floor coverage. It can also be useful where the complete floor specification calls for conservative heat input.
Its limitation is capacity. Ten square metres provides only 800 W. In a higher-loss room, 80 W/m² film may remain energised for long periods without reaching the room setpoint. A low wattage is efficient only when it is capable of meeting the actual load.
Choose 80 W/m² because the calculation supports it—not merely because the room is small.
When 140 W/m² film makes sense
The 140 W/m² option is a balanced planning choice for many insulated living spaces with compatible floating floors. It provides 1.4 kW from 10 m² of film while keeping connected load below the higher-output alternatives.
Depending on heat loss and coverage, it may serve supplementary heating or the calculated primary load. That role cannot be decided from the film rating alone. A well-insulated room with generous coverage may be fully served by 140 W/m²; a draughty room with restricted coverage may not be.
Termofol offers 140 W/m² film in multiple widths, which can make it easier to create an efficient layout around room features.
When 180 W/m² film makes sense
The 180 W/m² option provides more capacity where the room demand is higher or the available installation area is smaller. Ten square metres delivers 1.8 kW, so it is often evaluated for primary-heating designs after the heat-loss calculation.
The increase from 140 to 180 W/m² is about 29% in connected power for the same film area. That can make the difference between meeting and missing the design load, but it also changes circuit current and the speed at which the floor can approach its temperature limit.
Use it when the calculation, floor specification and controller design all agree—not as an automatic default for a colder-feeling room.
When 220 W/m² film makes sense
At 220 W/m², 10 m² of film provides 2.2 kW. This can be valuable when the design requires high output from a constrained usable area, or in an appropriately specified higher-loss application.
It deserves the most careful checks. The same 10 m² draws about 9.57 A at 230 V before any design allowances. Higher power density also makes correct floor sensing, thermostat settings, insulation and heat dissipation especially important. Fixed low furniture and unapproved floor coverings must not create local heat accumulation.
The 220 W/m² product is the highest-output standard option in this comparison; it is not the universal premium choice. If the heat-loss calculation indicates that even 220 W/m² cannot cover the room through the valid area, the solution is not to compromise the floor design.
You can compare currently listed sizes in the Termofol underfloor heating-film product category.
Check thermostat and electrical load before ordering
Total connected load is:
Film area × film output = total watts
Approximate current for a resistive load at 230 V is:
Total watts ÷ 230 = amperes
Termofol’s installation guidance describes a 16 A thermostat and recommends limiting continuous load to 80%, stated as 13 A. Using 13 A as a planning ceiling gives approximately 2,990 W. The corresponding theoretical film areas are:
| Film output | Approx. area at 2,990 W planning load |
|---|---|
| 80 W/m² | 37.3 m² |
| 140 W/m² | 21.3 m² |
| 180 W/m² | 16.6 m² |
| 220 W/m² | 13.5 m² |
These figures are not permission to connect that area to an existing circuit. Cable size, protective devices, thermostat rating, supply arrangement, installation method, grouping, circuit length and the applicable Irish electrical rules must be checked for the real project. Larger loads may require zoning or an appropriately specified contactor or relay arrangement.
Each controlled zone also needs sensible sensor placement. One thermostat should not be expected to represent rooms with different orientations, heat losses or usage patterns.
Final connections and electrical testing should be completed by a Safe Electric registered electrical contractor. Termofol’s installation process calls for resistance checks before and after the floor is laid, helping identify damage before the system is commissioned.
Does higher wattage cost more to run?
It increases the maximum instantaneous power draw. It does not by itself prove higher seasonal consumption.
Consider two correctly designed systems in the same room. A higher-output system can replace heat faster, reaches the setpoint sooner and then cycles off. A lower-output system runs longer. Over time, the energy required to maintain the same temperature is governed mainly by the building’s heat loss, weather, setpoint and schedule, plus system and control behaviour.
However, selection still affects cost in several ways:
- an undersized system can run continuously and fail to deliver comfort;
- excessive setpoints and long schedules increase heat loss and consumption;
- poor insulation beneath the system sends more heat in the wrong direction;
- an unsuitable floor build-up can slow response or impose a restrictive temperature limit;
- zoning and programmable controls can avoid heating rooms when they are not needed.
Use the Termofol running-cost calculator for an initial estimate, then confirm film output and layout with the technical team. A calculator estimate is only as good as the room area, energy condition, tariff and usage assumptions entered.
A practical selection workflow
Before asking “80, 140, 180 or 220?”, collect the information that makes the answer possible:
- Obtain a room-by-room design heat-loss figure in watts.
- Mark the permanent furniture and excluded zones on a scaled floor plan.
- Calculate the usable film area—not just the room area.
- Confirm the exact floor product is approved for the proposed heated build-up.
- Record its maximum permitted surface temperature and thermal-resistance conditions.
- Divide the room heat loss by the usable film area.
- Select a standard output that can meet the requirement, subject to design margin and floor limits.
- Calculate total connected watts and current for every thermostat zone.
- Have the electrical design, protective devices and final connection confirmed by a registered contractor.
- Keep the floor plan, resistance readings, product data and commissioning settings for future reference.
For the physical sequence, read Termofol’s heating film under laminate installation guide. Product-specific instructions and the approved project design always take priority over a general article.
Frequently asked questions
Is 220 W/m² heating film always better than 140 W/m²?
No. It provides more maximum output from the same area, but it also creates a higher connected electrical load and can bring the floor toward its temperature limit more quickly. The correct choice is the lowest suitable standard output that meets the calculated room load through the usable area while remaining within the complete floor and electrical design limits.
Can 80 W/m² film heat a whole room?
It can only do so if the installed area multiplied by 80 W/m² meets the room’s design heat loss and the system satisfies every other design condition. In a very low-loss room with generous coverage that may be possible. In many rooms it will be supplementary rather than primary heating.
Is 140 W/m² enough for an Irish home?
It may be enough for a particular room in an insulated home, but “Irish home” is too broad to size a system. Calculate each room’s heat loss, usable film coverage and floor limit. Orientation, glazing, insulation and air leakage can make two same-sized rooms behave very differently.
Should I choose output from the BER rating?
BER is useful evidence about overall energy performance, but it is not a room-by-room heating design. Use it as context and obtain a heat-loss assessment for sizing. Do not assign a film wattage from the BER letter alone.
What happens if the heating film is undersized?
The thermostat may call for heat for very long periods while the room struggles to reach its setpoint in cold conditions. That reduces comfort and leaves no useful capacity margin. It is better to find the shortfall at design stage than after the floor has been laid.
Can I install stronger film over a smaller area to save material?
Only if the resulting layout is approved, meets the room load, distributes heat acceptably and stays within the floor-temperature and electrical limits. A concentrated high-output patch is not automatically equivalent to balanced coverage across the usable floor.
Does a higher-output film make the floor hotter?
It can raise the floor temperature faster while energised, but the operating temperature should be limited by a correctly configured thermostat and floor sensor. The flooring manufacturer’s permitted surface temperature must not be exceeded, regardless of film rating.
Do I need an electrician to install heating film?
The floor preparation and film layout must follow the approved instructions, while final electrical connections, protection and testing should be completed by a Safe Electric registered electrical contractor. Arrange this before the floor is closed so the required tests and documentation are not missed.
Choose capacity as part of a complete design
The best infrared heating film output is not a product ranking. It is a design result.
Start with the room’s heat loss, divide it by the genuinely usable heated area, confirm the exact floor build-up and temperature limit, then check the thermostat zone and electrical load. That process may point to 80 W/m² in one room, 140 W/m² in another and 180 or 220 W/m² where demand or coverage requires it.
If you send Termofol a scaled floor plan, proposed floor finish, room-by-room heat-loss figures and permanent furniture layout, the technical team can help turn those inputs into a practical film layout and product selection. Contact Termofol Ireland before ordering if any part of the floor, output or control design is uncertain.