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What are the characteristics of an ideal heater? Technical principles and performance comparison

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  1. The main principles of residential heating: convection or radiant heating convection ou par rayonnement
  2. The expected characteristics of an ideal heater
  3. Comparison of different heating methods
  4. Summary table of different radiator technologies: pros and cons

The main principles of residential heating: convection or radiation?

No matter which heat emission technology is used (electric or hot water heating), there are 3 heat emission modes for heating:

  • the conduction heating (eg: low temperature floor heating. Feet are in contact with the floor)
  • the convection heating (hence the name convectors)
  • the radiant heating (hence the name radiators = radiant / radiation wrongly used to any existing heater)
Chauffage idéal basse consommation

Thermal comfort and low consumption

A convection heating heats the air directly. The cold air heats up on contact with the heat emitter (grid, plate, resistance), and then rises to the ceiling while getting warm. Then it gradually cools down because of the heat loss of the room. This creates an air flow (stirring dust burned in contact of the emitter) and a cycle of cooling and heating.

The radiant heating do not heat the air directly, it heats the mass surfaces (floor, walls, ceiling, objects) that absorb and return the heat to the ambient air of the room. Unlike the convectors with which the hot air is stratified (floor at 15°C, mid-height at 19°C, ceiling at 25°C), with radiant radiators the air temperature is almost homogeneous from floor to ceiling. This distinction is critical since the air is not stirred (with allergens and dust) and the experienced thermal comfort is significantly higher (comparable to the sun), therefore you avoid increasing the temperature of the thermostat (and the consumption).

>> The choice of radiant heating is not being discussed anymore these days: it is the heating technology that we should be looking for!

What are the expected characteristics of an ideal heater?

This article takes interest in the efficiency of different heat emitters and not in the comparison of various heating technologies (heat pumps, wood/pellet stove, etc.).

Do not lose sight that the radiator is not everything! The 3 golden rules to optimise the bill and comfort are:

  1. An effective insulation of the walls, floor, ceiling and windows. A good airtightness.
  2. A good orientation of the rooms to benefit from the external energy inputs.
  3. An efficient radiator which means:
    • one that emits as much radiation as possible (and therefore the less convection possible). Today no legislation imposes a minimum radiation rate to be able to “use” the name of a radiant heater/radiator. A radiator emitting at least 50% of radiation is the minimum you should be looking for. Note, radiant heaters for less than 500€ do not exceed 40% of radiation rate. Among the best brands of radiant radiators on the market: DEGXEL, CAMPA, CINIER, HEAT4ALL, etc.
    • one with a large heat-emitting surface according to its power.
    • one with little inertia (by its design) and associated with a high performance thermal regulation.The radiator with little inertia (thin, no cast heat emitter) associated with a high performance thermostat will deliver heat rapidly to the room avoiding heat waves. Indeed, the more inertia the heater has, the longer it will take to load the energy and thus to restore it. Besides, when the outside temperature rises during the day due to solar heat, the heater keeps providing the stored energy even if it exceeds the set desired temperature and thus creates heat waves and unnecessary consumption. To respond with flexibility to any changes of settings (comfort, eco, absence, anti-freeze), theheater must be responsive.
    • one with the right power. Ask the manufacturer or installer for a power balance. An electrician uses mostly 100W per m2 for electric heating (1000W for a room of 10 m2). For the most efficient electric radiant radiators (infrared), 60W per m2 are sufficient. There is no need to oversize when we know the thermal parameters of the room (surface, height, insulation, orientation, desired temperature) and can deduce the heat losses and the required power of the heater.
    • one that is well placed in the room. Radiant radiators are especially effective when well placed so that the radiation can reach all areas of the room (floor, wall, ceiling). Do not place the heater behind any furniture that would block the radiation. Only high performance radiators can radiate up to 3-4 meters of distance in order to reach all the areas of the room.

Comparison of different heating modes, advantages and disadvantages…

Can not decide between different technologies of radiators? This article is made for you.

Convectors are the basic version that has popularised the electric heating in the 80s. Technologically, it has changed little. Expect a power need (therefore consumption) which ranges from 100 to 150 Watts per m2! They only work on the principle of convection by heating the ambient air that stratifies in the room (15°C at the floor level, 27°C under the ceiling). Most often it dries the air and creates heat waves (hot air current) sometimes experienced as unpleasant. This outdated technology is to be removed.

convecteur électrique

Electric convector

chauffage caniveau

Trench Heaters

Electric baseboard heaters operate on the principle of convectors. Their length helps mitigate the convection effect with a good heat distribution in the room. They heat cold air immediately at ground level. It costs around €300 € per meter. Trench heater (or floor fan coil) is a variation of an electric baseboard heating for even more space saving.

Le radiateur à inertie est composé d’un corps de chauffe en céramique, en fonte, en stéatite, en verre, en brique, ou en pierre. Ce dernier a des propriétés d’accumulation thermique importantes via une résistance électrique située en son cœur (radiateur à inertie sèche) ou grâce à un fluide caloporteur qui le parcoure (radiateur dit à inertie fluide). L’énergie est ensuite transmise à la carcasse du radiateur (à forte émissivité – aluminium) qui émet lentement par rayonnement basse température et par convection, même lorsque le radiateur n’est plus alimenté électriquement. Le concept est séduisant.

radiateur inertie

Dry or fluid inertia heater – Photo credit Thermor

The inertia heater is composed of a ceramic, cast iron, soapstone, glass, brick, or stone heating body. The latter has important thermal storage characteristics via an electric resistor located in its core (dry inertia heater) or through a coolant which passes through the heater (fluid inertia heater). Th energy is then transmitted to the heater’s shell (high emissivity – aluminium) which slowly emits heat by radiation at low temperature and by convection, even when the heater is no longer electrically powered. The concept is attractive.

We speak of “gentle heat” (often wrongly) only if the heater has the ability to radiate the heat accumulated in the form of infrared (like the sun). Fluid inertia heaters give us a better feeling of gentle heat (than dry inertia heaters) due to a more uniform surface temperature and a better thermal efficiency. The main problem is the lack of responsiveness of the heater (due to its inertia) to stick strictly to the selected temperatures in order to avoid overconsumption and heat waves. The integrated regulation of the heater must be very efficient to “master” the inertia.

Hot water heaters connected to the central heating (gas boiler, wood, fuel oil, etc.) typically offer a good thermal comfort if they are low temperature.

radiateur à chauffage central eau chaude

Water loop heater central heating

plancher chauffant

Radiant floor heating (hydraulic or electric)

The floor heating (hydraulic low temperature or radiant electric) is an investment that must be carefully considered. Indeed, except fully renovating the floor, it is not replaceable as a heater. It has the advantage of good heat distribution (no cold area) throughout the room and a great comfort. However, its inertia can cause overconsumption and discomfort on midrange models. The radiant hydraulic floor has the advantage to help cooling in summer (cold water circulation).

The radiant heaters with a frontal perforated grid emit the heat by radiation (between 10% and 30%) and by convection. The range of the radiation is 1 meter. Only close surfaces will be heated by the radiation, the remaining volume will be heated as a convector. There are radiant panels of first generation (so-called opened) of which the heat emitter is visible through the perforated grid and enclosed panels (so-called heating panels). Enclosed panels are more efficient from a comfort and energy point of view. Most of the time these are infrared radiators (see below).

radiateur rayonnant radiant

Simple radiant heater with frontal grid

radiateur électrique infrarouge

High performance electric far infrared radiators – Picture Credit HeatGood.com

High performance infrared heaters are radiant radiators which radiation performance is > 50% (thus 50% of convection only). These are the heaters which are the closest to the notion of ideal radiators because they meet all required characteristics (see above) to optimise comfort and low consumption: enclosed panel, uniform surface temperature over the whole panel, low inertia, electronic control of your choice as they are not onboard (hence the possibility to choose a performant control system), high radiant component (so gentle heat), large panel surface.

Warning! The lack of regulation on the infrared radiators should lead buyers to be especially vigilant. Indeed, we can find in this category extremely performant radiators as well as simple radiators operating mainly as convectors. The prices vary from 100€ to over 1500€ for the same power. To know more about the infrared radiator.

Summary table of different radiator technologies

The thermal efficiency of a radiator corresponds to the capacity of the heat emitter to producehomogeneous heat in the space (from floor to ceiling), constant over time and comfortable (no heat waves and no drying air). Therefore its electronic control must efficiently take into account the outside temperature variations (and solar gain) and the variable presence of the occupiers (setpoint changes (eco, comfort)). It is therefore the couple radiator – regulation that defines the aptitude of a radiator to its function (its aptitude coefficient).

Advantages Disadvantages
Electric Convector
THE – :

  • Air stratification (cold at floor level, hot at ceiling level). Sensation of hot and cold air streams. Very difficult to achieve comfort. Many tend to increase the temperature of the room to compensate the absence of warming the walls. Drying the air.
  • Very high consumption related to the principle of convection. It is often necessary to heat at 2-3°C higher than with other technologies.

Electric Baseboard Heaters

THE + :

  • Good coverage thanks to great lengths, can be placed in complex area
THE – :

  • High consumption.

Trench Heaters

THE + :

  • Good coverage thanks to great lengths, can be placed in complex area, significant space saving. Heat curtain effect for the glazing.
THE – :

  • High consumption, depending on the technology.

+++ Inertia Heaters (dry or fluid)

THE + for the best models:

  • Gentle heat under condition of an important radiation portion (best models)
  • Low consumption, best models: approximately 30-40% of radiation.
  • The air quality remains unchanged
THE – :

  • Slow initial temperature rise (about 45 mn) except with double core heaters which in addition incorporate a radiant foil of infrared radiator type. Overall not suitable for rooms to be heated quickly over short periods. Fluid inertia is slower than dry inertia.
  • As the heater diffuses the heat on both sides of the latter, the wall of fixation should be well insulated.
  • The larger the heater’s surface is the better the radiation.
  • Count 100 Watts per m2 for a moderately insulated room. 80 Watts per m2 for a well insulated room.

+++ Hot Water Heaters (central heating)

THE + for the best models:

  • Gentle heat at low temperature.
  • Temperature rise fast enough.
  • Compatible multi source of energy (gas, solar, geothermal, wood, etc.).
  • Low temperature heat emission.
THE – :

  • As the heater diffuses the heat on both sides of the latter, the wall of fixation should be well insulated.
  • Heat losses at the distribution circuit level.
  • The larger the heater’s surface is the better the radiation.
  • Need a thermostat (thermostatic valve) to avoid heat waves.
  • Maintenance (boiler and heater).

Underfloor Heating

THE + :

  • Great comfort of use: good heat distribution over the entire surface, possibility of moving barefoot.
  • Space saving (no heaters at all).
  • Compatible multi source of energy (gas, solar, geothermal, wood, etc.).
  • Prefer hydraulic underfloor heating rather than electric one.
THE – :

  • Be aware of the inertia management which is minimally reactive: initial temperature rise or temperature descent is slow. A good regulation is essential for the floor heating to constantly adapt to variable needs of users and to outside weather conditions (including solar gains).
  • As the radiation is both sided, the supporting slab should be well insulated to avoid the losses.
  • High initial investment. Maintenance. Complicated when under renovation.
  • Some layout constraints (limit the carpets, some floor tiling and furniture without feet to be avoided).

Electric Radiant Radiator

THE + :

  • Gentle heat under the condition of important radiant power (just few models)
  • Quick heat diffusion
  • Best models: Radiation heat of at least 40% for poorly insulating housing.
THE – :

  • Imperative to choose high-end models, because the performances drop very quickly (intermittent radiation and less powerful).
  • As the radiator diffuses the heat on both sides of the latter, the wall of fixation should be well insulated.
  • The larger the heater’s surface is the better the radiation.
  • The air is in contact with the heat emitter which is very hot, causing convection and degrading the air.

+++ Far Infrared Radiator

THE + for the best models:

  • Gentle heat under the condition of important radiant power. Apparent temperature Apparent temperature superior to other technologies = able to heat at a lower temperature.
  • Quick heat diffusion.
  • The air is never in contact with the heating element which is embedded in the completely enclosed structure of the radiator. Thus there is no air degradation and only little convection.
  • Especially suitable for high ceilings.
  • Low consumption. In the absence of data regarding the aptitude coefficient you should ask the manufacturer for documents proving the radiation rate of their radiators (min > 50%, 70% is the maximum known in Europe).
  • Wall and ceiling mounted.
  • Zero maintenance. Failure rate close to 0% for high-end models.
THE – :

  • As the radiator diffuses the heat on both sides of the latter, the wall of fixation should be well insulated. Except for high-end models with a high performance insulation on the back of the radiator. The slimliness of this technology allows the addition of the latter.
  • The high surface temperature if you want to obtain very low consumption (50W per m2).
  • The space in front of the radiator must be clear in order to allow the radiation to spread out well in all directions.
  • The price of high-end models.

Sources: Foxof Consultancy – Appellations according to European standard CEI 675

Conclusion: to date, we believe the best heaters (high-end models) are the fluid inertia heaters and the electric far infrared radiators. Note that from a thermal (comfort and consumption) point of view it is always more efficient to increase the number of hot spots (radiators) in the room. For instance, when in need of 2100W you should prefer 3 rheaters of 700W rather than 2 of 1000W. This is a constant whatever the technology of the radiator is.

Discover the latest innovations of leading companies in terms of efficient electric radiators:

radiateur rayonnant

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What are the characteristics of an ideal heater? Technical principles and performance comparison. The main principles of residential heating: convection or radiant heating convection ou par rayonnement The expected characteristics of an ideal heater Comparison of different heating methods Summary table of different radiator technologies: pros and cons
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