All electric heaters are 100% efficient at converting electrical energy to heat. However, as for how warm they make a room occupant feel, this varies from a lot one type of heater to another. Some heaters are also more efficient at heating an area or minimising heat loss out the ceiling.
Heat pumps and dehumidifiers are a few electric appliances that deliver more heat energy than the electrical energy they consume. Heat pumps work by transferring heat from one area to another and dehumidifiers release latent heat by condensing water vapour.
In this article, I will compare various portable heaters I am familiar with or have used over the years. I also suggest which heater works for what type of environment and cover a few gas and liquid fuel portable heaters.
This article is broken down into the following sections:
- Electric heaters
- Convector heater – Cheap to buy, silent, heats ceiling down.
- Oil filled radiator – Maintains a stable temperature.
- Fan heater – Cheap to buy and rapid room heating.
- Ceramic heater – Safer, some oscillate for even heating.
- Halogen/quartz heater – Cheap to buy, instant radiant heat.
- Radiant bar heater – For difficult to heat / draughty rooms.
- Carbon heater – Energy efficient alternative to halogen.
- Panel heater – Energy efficient supplemental radiant heat.
- Other portable heat sources
- Air conditioner – Portable models that pump heat inside.
- Dehumidifier – Reverse of an evaporative air cooler.
- Gas heater – Cordless “pay as you use” operation.
- Radiant Paraffin heater – Cordless heater, using paraffin.
- Workshop torpedo heater – Rapid large area heating.
- Laser/Inverter heater – Paraffin/kerosene fan heater.
- Bioethanol Fireplace – Flames without a flue or chimney.
- Heater safety – A few safety tips on various portable heaters.
This section covers heaters that fully operate on electricity only.
These heaters work by heating the air, which in turn raises out the top vents by convection. There generally completely silent apart from the occasional click of its thermostat. Higher capacity 3kW heaters are quite large.
As the warm air heads straight for the ceiling, some of that heat will escape the ceiling and upper wall area by the time it reaches the occupants. As a result, these heaters tend to be the most expensive to run. With no moving parts, these heaters are generally very cheap to purchase and have a long lifespan.
Oil filled radiator
Like a convection heater, these heat the air and rely on convection to lift and distribute the heat. They take around 10 minutes to fully warm up, but provide the benefit of a steady flow of heat. This makes them very effective at keeping a stable room temperature.
With no exposed heating elements, they are safer than convector heaters. For example, smaller heaters can safely operate under a desk. These heaters also radiate some heat, making the room feel warmer than with a convector heater. This is particularly true of panel oil-filled radiators that resemble a central heating radiator.
The oil-free variant heats up quicker, however, the thermostat cycles more frequently due to their lower heat retention. Apart from the periodic thermostat click, both heater types are generally completely silent in operation.
Instead of relying on convection, a fan heater blows out warm air. By blowing warm air, these heaters are better at distributing heat than convection heaters. These heaters can be quite noisy, particularly with smaller fan heaters. Larger electric workshop heaters blow a larger quantity of air to gradually warm the room. This further reduces the amount of warm air that raises towards the ceiling.
With less heat reaching the ceiling, these heaters are generally cheaper to run than convection heaters. Although they distribute the heat better, many fan heaters struggle with temperature regulation. For example, most fan heaters will continue blowing after the thermostat clicks off. This blowing air can make the make the room feel cooler like a desk fan running until its thermostat turns the heating element back on.
These operate like fan heaters, but use a PTC heating element instead of a resistive wire. They cannot go red hot if something obstructs air flow through the heater. This makes them less of a fire hazard should the fan fail or if something blocks its vents. These heaters tend to be larger and heavier than standard fan heaters.
Oscillating models are better at evenly distributing heating throughout the room. By oscillating, this prevents a stream of heat hitting a wall or raising to the ceiling. This further reduces room heat loss and makes them very efficient at heating the air at seating level. Most oscillating models stand up like a column fan, such as shown on the right.
Halogen / quartz heater
Like a halogen lamp, these are effectively halogen lightbulbs designed to emit less light. By radiating most of the heat as infrared light, they warm objects directly in view of the heater. This makes them useful for immediate heat, such as in a workshop without waiting for the air to heat up.
As halogen heaters do no not directly heat the air, they must run continuously for heat. Most of the infrared heat will escape the room as it strikes the walls, out the window and so on. This makes them expensive to run for long run times. As the halogen elements are like filament lightbulbs, they tend to have a short lifespan.
Some higher end quartz heaters provide a combination of infrared light and a fan heater in one unit. These provide the benefit of instant heat, while at the same time warming the air. Despite what some claim, they are no more efficient at warming the air than a ceramic heater. However, they can make the room feel warmer due to their additional infrared heat. A cheaper alternative would be to purchase a separate halogen heater and ceramic heater and operate them simultaneously.
Radiant bar heater
Although superseded by cheaper halogen heaters, radiant bar heaters are still available. Like halogen heaters, they radiate most of their energy as infrared light and do little to warm the air. These heaters were quite a popular alternative to running an open fire place, particularly in older draughty homes. As such, they are known as electric fires. As they use resistive wire elements instead of halogen lamps, they have a much longer lifespan.
Despite a high running cost in continuous use, they are an economical alternative to a lighting an open fire place. For example, assuming an electric tariff of 20c/kWh, a 2 bar heater running 5 hours each evening will cost €2 per day or €14 a week. Most people with an open fire will burn through more than €14 of fuel a week.
A carbon heater uses a lamp very similar to a halogen heater, but with a carbon filament. They emit more medium and far infrared heat than halogen heaters, which is more effective at heating human skin.
In addition to a vertical orientation and a focused reflector, a 500-watt carbon heater provides similar warmth to a 1kW halogen heater. This makes them a very economical form of infrared heating, particularly in continuous use. A 1kW carbon heater provides a similar warmth feeling to a blazing open coal fire. However, as with other infrared heaters, a carbon heater does little to raise the air temperature.
Most carbon heaters can concentrate the heat to a specific area across the room, such as to a single sofa. Some models can oscillate to distribute the heat across a wider angle, like an oscillating fan heater.
Despite their high price (Argos an exception), they typically have a very long lifespan, much like the obsolete carbon filament light bulbs.
These typically resemble a central heating radiator, but generally heat up on one side only. They emit most of their heat as infrared heat, like a radiant bar heater but with a lower intensity. This makes them economical to run for making a room feel warm at a lower air temperature. As with other infrared heaters, the person must be in view of the heater.
As panel heaters do not have exposed heating elements, they are safer than other radiant heaters. They have a much lower fire risk if, such as if someone accidentally place something flammable near the heater.
Other portable heat sources
In this section, I will compare a few other types of portable heaters and heat sources.
Most split type air conditioners can operate in reverse to heat a room. In heating mode, they are known as a heat pump as they transfer heat into the building. By pumping heat from the outdoors into a room, they provide more heat energy than what they consume in electricity. A typical air conditioner in heating mode will provide 2kWh and 4kWh of heat for every 1kWh of electricity.
Some portable vented air conditioners can also provide heat by venting the cold air outdoors via the duct. As this will draw in outdoor air to replace the vented air, these are ineffective below about 5C outside. Split air conditioners on the other hand are a lot more effective below freezing. Portable split air conditioners still require an outdoor unit, such as through an open window for the refrigerant pipes and power cable.
When a dehumidifier condenses water vapour, it releases latent heat as a by-product. This process is much like an evaporative air cooler operating in reverse. This is particularly noticeable with a desiccant dehumidifier, which uses a heater to regenerate its desiccant. A typical 7 litre desiccant dehumidifier that consumes 630 watts will produce about 820 watts of heat output. Compressor dehumidifiers typically emit between 1.2 and 2 times the heat energy as what they consume in electricity.
This also makes them very effective at drying clothes, which in turn evaporate moisture from the dry heat. This cycle of reusing heat to evaporate and condense moisture is a very energy efficient means of drying clothes. For comparison, a vented tumble dryer disposes of all its heat energy outdoors. Although a condenser tumble dryer condenses moisture, it releases this heat into the room and continuously relies on a heater to provide fresh heat inside the drum. A heat pump tumble dryer reuses heat by releasing the latent heat from the condensed water back into the drum.
These use a butane gas bottle and have the advantage of being cordless and operate during power cuts. Most radiant gas heaters emit 1.4kW to 4.2kW of heat depending on the number of panels operating. They emit a combination of radiant and convection heat. At full power, they can quickly heat a large room with similar warmth to a large blazing coal fire.
Gas heaters provide a substantial amount of water vapour and carbon dioxide, requiring room ventilation to safely operate. They also emit Nitrogen Dioxide, which can mildly irritate the nose and throat, falsely giving the impression of dry air. Without adequate ventilation, the oxygen depletion sensor (resembles a pilot light) will cut out. Its thermocouple will in turn disconnect the gas supply and turn off the heater.
Another type of gas heater uses a catalytic converter instead of an open flame. This type of heater provides convection heat much like an electric convection heater. By operating at a lower temperature, they pose a much lower fire risk. These heaters typically emit up to 3 kW of heat.
Divide the price of a 11.34kg butane gas bottle by 155 to get the cost per kWh. For example, a €31 bottle works out at 20c/kWh. For a typical radiant gas heater, a 11.34kg bottle will last 110 hours on 1 bar, 55 hours on 2 bars and 36 hours on 3 bars. With a catalytic converter heater, the same bottle will last 86 hours on low, 67 hours on medium and 51 hours on high.
Radiant Paraffin heater
Like a radiant gas heater, these do not require electricity to run and are fully portable. They are considerably smaller than a gas heater. Radiant paraffin heaters typically emit up to about 3kWh of heat. Most wick heaters require Class C1 Kerosene (ROLF Paraffin) to operate correctly.
Due to the special fuel requirement, these heaters can be expensive to run. To calculate the cost per kWh, divide the price per litre by 10.2. For example, if a 20 litre drum costs €40, this works out at €2 per litre or 19.6c/kWh. Use of other fuels can lead to a short wick life, soot or excess fumes and odours.
Workshop torpedo heater
These are available to run either on Kerosene, Gas Oil or LPG. As the name suggests, these are intended for heating a large area such as a workshop and require plenty of ventilation. Whereas an electric heater is typically limited to 3kW for a standard wall socket, torpedo heaters typically exceed 10kW. Divide the BTU figure by 3400 for the rating in kW.
LPG heaters are expensive to run, with a similar kWh cost to electricity in Ireland. Kersoene heaters are designed to run on domestic kerosene heating oil, unlike smaller radiant paraffin heaters. They have a third to half the running cost of an electric or LPG heater for the same heat energy. On the other hand, they produce a noticeable kerosene or oily odour during operation.
For running on Kerosene, divide the cost per litre by 10.2 to get the cost per kWh. For running on Diesel (marked gas oil), divide the cost per litre by 10.6 to get the cost per kWh.
Laser/Inverter paraffin heater
These operate much like a workshop torpedo heater, but are designed for use within the home. With the use of Class C1 Kerosene (ROLF Paraffin), they are odourless in operation and only produce a faint odour during lighting and shutdown. Although not recommended by most manufacturers, many will also run on domestic kerosene heating oil (28 second oil.) With this fuel, the heater will produce a faint Kerosene smell during operation, although not to the extent of a workshop torpedo heater.
As with radiant paraffin heaters, these cost about the same as electricity to run with the proper fuel. As they also require electricity to operate, the only benefit they offer with such fuel would be for off-grid use to conserve battery power. Otherwise it would be cheaper to purchase and operate a fan heater, which does not require filling up or servicing.
While these heaters can run on domestic kerosene heating oil, residual moisture can corrode the burner. This means this fuel requires a suitable filter to remove moisture. Use of such fuel may also void the warranty and negate any savings if the heater has a short lifespan. See this website, which has extensive content on using standard kerosene as well as servicing such heaters.
To calculate the cost per kWh, divide the price per litre by 10.2. For example, if a 20 litre drum costs €40, this works out at €2 per litre or 19.6c/kWh. For Kerosene at 70c/litre, this works out at 6.9c/kWh.
A bioethanol heater is a portable decorative flame effect fireplace that does not require a flue or chimney. Like a gas heater, it is odourless in operation and does not produce any soot or ash. Despite its impressive fire effect, these heaters are very expensive to run for heat energy alone.
According to Wikipedia, Ethanol has an energy range of between 18.4 and 21.2MJ. Assuming Bioethanol uses the middle point of 19.8MJ, this works out at 5.5kWh per litre. To work out the cost per kWh, divide 5.5 into the price per litre. For example, if a litre costs €4, this works out at 73c/kWh. Consider using an electric heater for additional heat rather than with a bioethanol fireplace alone.
All electric heaters can pose a fire hazard, particularly when run in an unoccupied room or with a timer. Oil filled radiators, panel heaters and ceramic (PTC) fan heaters are generally safe to run on a timer. Halogen, bar, carbon and regular fan heaters should never operate on a timer. This is due to the risk of someone obstructing a heater or badly positioning it, without realising it is on a timer. Do not overload the power socket, particularly when using a power strip.
Radiant heaters require supervision when elderly or children are present. These heaters can scorch or burn items in close proximity. These heaters generally lack thermostats and can overheat a small room. This is especially the case with most gas and radiant paraffin heaters.
For heaters that operate on gas or liquid fuel, these require adequate ventilation. Most modern heaters have safety features to switch off the heater if there is insufficient ventilation. Even with adequate ventilation, these heaters will humidify the air as a by-product of combustion. For additional safety, place a carbon monoxide alarm in the same room as the heater.
Be sure to read the product instruction manual for additional safety instructions specific to the heater. For example, the minimum clearances from surfaces such as walls varies from one heater model to another. Gas and liquid fuel heaters also have minimum room size and ventilation requirements.