Is “Infrared Wallpaper” any good?

Question

Is “Infrared Wallpaper” any good?

There have been a number of low voltage, very thin, carbon based heating products in the form of “Wallpaper”, in-wall, ceiling or underfloor mats that have recently appeared on the market promoting themselves as “Infrared”, “far infrared” and / or “Radiant” heating technologies. Typically these systems are low voltage (via transformers) heat mats which can be installed to cover a large area within walls, ceilings and floors.

These heating systems reach a maximum of 40°C surface temperature and are usually much cooler once covered with plaster, carpet, paint etc. For the reasons explained below, these systems usually demonstrate a relatively low percentage of radiant (infrared) heat as a proportion of their total power, with most of their heat energy being in the form of convection and conduction. It is therefore misleading to make claims of these systems as being “Infrared” or “Radiant” heating solutions and they cannot be classified as radiant (infrared) heating systems under UK and international electrical standards.

Radiant Heat Transfer

To have radiant (infrared) heat, you must have a distinct temperature difference between the heater and the things it is trying to heat. If two objects are at the same temperature, then no radiant heat (infrared) transfer occurs. If they are at nearly the same temperature, then very little radiant heat (infrared) transfer occurs. The greater the temperature difference between two objects, the more radiant heat (infrared) transfer occurs. The amount of radiant energy transfer as a proportion of the heater’s total power is known as the “Radiant Effectiveness” of a heater and it is a critical determinant of whether a heater can call itself “Infrared” or not.

The following diagram shows the difference in radiant heat (Infrared) transfer between 3 objects: one at 25°C (roughly surface temperature of human skin); 50°C (i.e. central heating radiator) and one at 100°C (i.e. Infrared Heating panel).

Planck Energy Distribution at 25, 50 and 100C You can see from the diagram that the infrared heat transfer between something at 50°C and another at 25°C is very small: around 0.2 watts per metre. This is barely discernible on the skin as radiant heat and you can easily test this yourself by moving your bare arm closer and closer to a central heating radiator until you can sense the heat. (You almost have to touch it). In other words the “Radiant Effectiveness” of a central heating radiator is going to be small as a proportion of its total power. Most of its energy will be producing convective, not radiant, heat.

Contrast this with an Infrared panel at 100°C and an object at 25°C where the heat transfer is about 1 watt per metre and easily discernible on the skin up to a couple of metres away from the panel. Radiant Effectivess of an IR panel is consequently high as a proportion of its power and is the reason why these heaters are classified as “Infrared”.

Heater Temperature, Surface Area and Power

The ratio between the surface area of a heater and its power is important in defining the heater temperature. More watts per area of surface = more temperature (= more infrared heat).

Infrared heating panels require between 900 – 1000 watts /m2 surface area to produce between 90 – 100°C panel temperatures (to be able to transmit infrared heat effectively per the above chart).

Infrared Wallpaper requires approximately 200 watts / m2 to produce a maximum of 40°C surface temperature. (Whilst lower energy per m2, the low resulting temperature does not produce effective infrared heat transfer per the above chart).

In our view, at this low power : surface area and low resulting temperature, there is little radiated heat transfer from the wallpaper and by being in direct contact with the walls and ceilings, all the wallpaper is doing is slowing down their rate of heat loss by conduction. (Indeed suppliers urge you not to place it on outside walls at all). Otherwise at 40°C, it is otherwise just warming the air in the room.

We don’t dismiss that this might be effective in some way if you cover enough of your walls and ceilings with it. However, at 40°C and 200W/m2 Electric Infrared Wallpaper cannot claim to be radiant (i.e Infrared) and claim the benefits that infrared heating panels have over convection heaters.

International Performance Standards

The international (IEC) standard for performance of household radiators classifies heated wallpapers (or any heater at or below 40°C) out of scope for radiant performance assessment. This is for the reasons described above and shown very clearly by the chart: there is too little transmissiveness of radiant heat as a proportion of the total power consumption to allow the heaters to claim they are radiant (as opposed to convective or conductive).

IG Infrared https://www.ig-infrared.com/en/home.html is the EU Infrared manufacturers trade association and defines infrared heaters as requiring a minimum surface temperature of 75°C and a minimum watts coverage over the panel surface of 900 watts/m2 to qualify as “Infrared Heaters”. (Wallpaper temperatures are a maximum 40°C and watts coverage is 200w/m2 and would not qualify on either requirement).

In the UK, the BEIS is also laying down the performance markers for Infrared panel performance along IEC lines, in two recently commissioned reports defining infrared panels as having 70% radiant efficiency and 80°C temperature. See:

Cost-Optimal Domestic Electrification (CODE) report from 2021
https://www.gov.uk/government/publications/cost-optimal-domestic-electrification-code which covers infrared-red radiant panels (page 41) and

Research paper no: 2019/021
https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/831079/Electric_heating_options_in_off-gas_grid_homes.pdf page 15.

We have had a number of customers who have installed this type of heating say it has not lived up to expectations and have switched to our infrared heating panels.