Why are radiant heaters more energy-efficient than central heating?

Key operating differences:

The different modes of operation between radiant and convection systems are key to their relative efficiencies:

Radiant heaters heat surfaces in a room increasing the mean radiant temperature (MRT) to which the occupants are exposed without warming the air.

Convective heat sources like central heating panels produce an environment in which air temperature is greater than MRT. Why does this difference result in different energy consumption?

Key areas of saving:

Infrared Versus Convection
Infrared Versus Convection

1) The energy requirement to heat the volume of a room’s air versus the surfaces of the same room requires a higher heat load and higher peak load in the convection-based heater. (Zmeureanu et al., 1988; Howell and Suryanarayana, 1990; Imanari et al., 1999; Petras and Kalus, 2000; Miriel et al., 2002; Feng et al., 2006). The Laboratory of heat transfer and environmental and mechanical engineering, Aristotle University of Thessaloniki state up to 32% higher capacity may be required for the convection-based heater (“Infrared Heating Comparison with Conventional Heating” 2010 p5) depending on building-related factors. (See tab at bottom of page for full list of sources).

2) Infiltration losses (cold air mixing with warm air – i.e. draughts) are one of the most significant factors affecting energy use and comfort in a building (DeWerth & Loria 1989). Because convection heating systems produce an environment where air temperature is higher than MRT, infiltration losses are higher with convective-based heating systems than in radiant heating systems (Hart 1981; Zmeureanu et al., 1988).The Laboratory of heat transfer and environmental and mechanical engineering, Aristotle University of Thessaloniki state the difference in capacity required to cover infiltration losses can require up to 35% greater capacity in convection-based systems depending on building-related factors (not necessarily additional to above 32%) (opp. cit p5).

3) Radiant heaters can be operated at lower air temperatures than convection heaters when the MRT falling on the human and other objects is within comfort levels of about 21C (Hart, 1981; Zmeureanu et al., 1988; Howell and Suryanarayana, 1990; Kalisperis et al., 1990; Ling and Deffenbaugh, 1990). So it is possible to be comfortable in up to 2C lower air temperatures under radiant heat compared to classical methods that heat the air to the comfort level of 21C (Dudkiewicz and Jezowiecki, 2009). The Laboratory of heat transfer, University of Thessaloniki state some further difference in capacity is possible through proper control (again depending on building-related factors and not necessarily additional to the above savings).

4) Objects in an environment heat up, building up “thermal mass” and are in turn able to “radiate”. Conventional systems that use air as the transport medium have lower potential for delivering sufficient heating since they are limited to the thermal capacity of the air and its ability to transfer thermal energy to or from a surface (Ardehali et al., 2004).

5) Convection-based systems respond slowly to step-changes in temperature, requiring up to 6% increase in energy consumption to alter temperature by 1C (Roth et al., 2007).

Aren’t central heaters radiant heaters?

No: a 1 kW central heating “radiator” will radiate only 1/3 – 1/4 of its energy and convect the remainder. A 1kW radiant heater operating at 100°C will radiate 93-97% of its energy and only convect the remainder.

The paradox of the last 50 years is that oil & gas central heating – whilst making for less efficient radiators – has just been a lot cheaper to run than any alternative for of radiant heater and consequently it has made more economic sense to use them (because you can overlook their inefficiency and just run them longer). Infrared now reverses this situation, being cheaper to run than oil or gas as well as being a more efficient radiator.

Why has Far Infrared now emerged as the most cost-effective solution?

What is “new” about Far Infrared panels is that the technology has finally emerged to enable a form of electrical heater to become more cost-effective than any other form of heating. This is achieved through the right combination of temperature (100°C), panel surface area and a watt density of 0.1w/cm2 throughout the panel surface.

Low watt density

Older Far Infrared panels have a thinly stretched nickel or FeCrAl wire woven over the entire surface area of the panel. More modern ones use carbon fibre or carbon crystal and are slightly more energy-efficient.

The principle is that a 1m square panel at 100°C only requires a wattage of 0.1w/cm2 to radiate one kilowatt of heat. Depending on panel manufacturer, this implies only a kilowatt of input energy to create, so long as energy and temperature are evenly dispersed over the panel surface.

A 1m2 panel at 100°C makes for a very efficient radiator, projecting effective heat energy adequately into the room to warm up objects in the room which then radiate back themselves.

Panel Quality

Panel manufacture does differ. We have noticed the more recent carbon fibre and carbon crystal panels have a slight “edge” over the earlier panels with woven wire surfaces – both in terms of temperature accuracy, better distribution of heat over the panel surface area and a nearly perfect ratio of input energy to output (radiated) energy.

There are other architecure differences that manufactuers will claim make a difference. Some manufactuers also include a semi-storage core, claiming this allows the panel to cut power and continue to radiate during its operating cycle. Herschel doesn’t espouse this philosphy, as remember the panel temperature drops off quickly too when the power goes and radiative effectiveness also drops away quickly. Plus you sacrifice a small energy overhead in warming up the core and maintaining the core instead of emitting that into the room. Herschel’s philosophy is to “get rid” of the IR from the panel – i.e. emit it and only control the panel via a thermostat, not some internal mechanism.

Low “TCO” – the way traditional heating manufacturers DON’T want you to think!

If you compare the cost of replacing a boiler, or purchasing any other form of heating with the cost of installing infrared for a whole house – there’s almost no comparison. A boiler replacement will cost around £3,200 and an equivalent whole-house Infrared installation would cost about £4,500. A new electric radiator would cost around £130 and a new equivalent Infrared panel would cost about £330. No case to make then?

This is the way traditional heater manufacturers want you to think.

Because what you are not told is that by year 3, the COST of your infrared purchase, plus all the intervening running costs, will have been saved when compared with the ongoing running costs of any other form of heating.

This is what we call low “total cost of ownership” or “TCO”.

Infrared's lower Total Cost of Ownership compared with other heater types

The only close cost-competitor to Infrared Heating is to be found in the higher-rated modern Gas boilers (A-rated). And while that is true comparing per-hour running costs (Gas works-out marginally cheaper), what they do not tell you is that you have to run your gas 3x longer per day to get the equivalent of the 24×7 heat you’d be getting from Infrared. This is because Infrared heats the room, not the air and therefore only ever “tops-up” once everything is warmed through. With gas (oil, heat pumps, underfloor heating etc) once the thermostat reaches its set point, everything cools down, the warm air disappears and you have to start again.

Energy-savings studies

We performed experiments to determine heat-efficiency over time, by using infra red heat to maintain a constant indoor temperature and level of comfort despite changes in outdoor temperature. The point being that with standard convection-based heating, large changes in outside temperature typically require large changes in energy required to heat the house (house insulation remaining the same before and during the experiment). The tests demonstrate that whilst heating was required as the outside air temperature dropped (i.e. house insulation was not perfect), the heat energy required to maintain comfort was far lower than standard convection-based heating. Consequently heating bills over the winter period were a fraction of what they would be using convection heating.

Single Family House – Swiss Midlands – ROOM 1


Single Family House - Swiss Midlands - ROOM 1

Energy Saving Construction

RoomdataRoom 1 – Playroom
outer wallsu/value 0,23 W/m2K
windowsu/value 1,55 W/m2K
heated net area12,70 m2
heated net volume30,50 m3
heat output needed451 W

Statistics period from 1.10.2007 – 31.3.2008

Max. outside temp.23,2 CMax. wind speed65,25 Mph
Min. outside temp.– 8,10 CMin. wind speed0,00 Mph
Average outside temp.4,10 CAverage wind speed5,78 Mph

Statistics for the winter period showing that regardless of outside temperature, internal temperature remained consistent for very little input of infrared

Energy costs: 208 kWh x 0,10 £ = 20,80 £ (here)
(room – total heating period)


Single Family House – Swiss Midlands – ROOM 2

Single Family House - Swiss Midlands - ROOM 2

Energy Saving Construction

RoomdataRoom 2 – Playroom
outer wallsu/value 0,23 W/m2K
windowsu/value 1,55 W/m2K
heated net area17,00 m2
heated net volume40,80 m3
heat output needed612 W

Statistics period from 1.10.2007 – 31.3.2008

Max. outside temp.23,2 CMax. wind speed65,25 Mph
Min. outside temp.– 8,10 CMin. wind speed0,00 Mph
Average outside temp.4,10 CAverage wind speed5,78 Mph


Room 2 statistics for the winter period

Energy costs: 325 kWh x 0,10 £ = 32,50 £ (here)
(room – total heating period)

Other ways Infrared Heating is more energy-efficient

There are other advantage Infrared heating has over other types of heater and these include:

There is no “system loss” in having to heat an interim “medium” (such as water in central heating or oil in electric radiators) or in having to pipe that medium around the house (very wasteful).

Oil and Gas boilers also consume electricity (as well as oil and gas) in order to actually run and this figure is often left out of comparisons.

Infraredheaters convert all their energy into heat. Only the top A-Rated condensing boilers can claim levels of efficiency approaching 97%, but in order to permit the temperature drop required to allow a condensing boiler to work, you have to fit larger radiator panels, which can end-up being a considerable expense.

Oil and Gas boiler efficiency deteriorates rapidly after the first 3 years and after 7 – 10 years you should be looking to replace them. Again, modern boilers will provide better performance than this for at least 10 years so long as you maintain and service them regularly (and you will still ultimately have to replace). With Infrared there are no maintenance costs and you should never have to replace a reliable make.


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DeWerth, D.W. and Loria, R.L. 1989. In-space heater energy use for supplemental and whole house heating. T ASHRAE 95 (1) : 239-250.

Dudkiewicz, E. and Jezowiecki, J. 2009. Measured radiant thermal fields in industrial spaces served by high intensity IR. Energy and Buildings 41 (2009): 27-35.

Feng, G., Cao, G., and Gang, L. 2006. Practical analysis of a new type of radiant heating technology in a large space building. 6th International Conference for Enhanced Building Operations, Shenzhen, China, Nov 6-9, 2006.

Hart, G.H. 1981. Heating the perimeter zone of an office building. T ASHRAE 87(2): 529-537.

Howell, R.H. and Suryanarayana, S. 1990. Sizing of radiant heating systems: Part I-Ceiling Panels. T ASHRAE 96(1): 652-665.

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Kilkis, B.I., Eltez, M., and Sager, S.S. 1995. A simplified model for the design of radiant in-slab heating panels. T ASHRAE 101(1): 210-216.

Laboratory of heat transfer and environmental and mechanical engineering, Aristotle University of Thessaloniki “Infrared Heating Comparison with Conventional Heating” 2010 p5).

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Miriel, J., Serres, L., and Trombe, A. 2002. Radiant ceiling panel heating-cooling systems: experimental and simulated study of the performances, thermal comfort and energy consumptions. Applied Thermal Engineering 22 (2002): 1861–1873.

Petras, D. and Kalus, D. 2000. Effect of thermal comfort/ discomfort due to IR heaters installed at workplaces in industrial buildings. Indoor Built Environment 2000 (9): 148-156.

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Simmonds, P. 1996. Practical applications of radiant heating & cooling to maintain comfort conditions. T ASHRAE 102 (1): 659-666.

Zmeureanu, R., Fazio, P.P., and Haghighat, F. 1988. Thermal Performance of Radiant Heating Panels. T ASHRAE 94(2): 13-27.


Publisher: Herschel Far Infrared