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If you don’t know what type of mobile heater to use for your site, factory or warehouse, here are some helpful tips to help you decide on the best option for you.

Heating air increases its capacity to hold water and therefore reduces its relative humidity.

Air can be heated in two ways:

1. Directly (the air comes into contact with the heat source) or

2. Indirectly (the air bypasses the heat source through a heat-exchanger).

Direct heating gives a heating efficiency of almost 100% as most of the energy from the heating element is absorbed into the air stream. (Only a small amount of heat is absorbed within the body of the heater).

The most clean and dry form of direct heating is electric, as nothing is absorbed by the air passed over the heating element apart from thermal energy.

The use of heating fuels is also an effective form of direct heating. The most economical fuel is gas oil (diesel) or paraffin. Burning these fuels produces moisture, combustion gases and smell, along with other hazards such as soot and combustion particles. This can cause health complications if used in an enclosed area without adequate ventilation. In addition to this, the soot settles on surfaces, meaning that absorbent goods, materials and clothing can become tainted. Operatives can experience breathing difficulties unless the correct precautions are taken and, ultimately, carcinogenic emissions can have a serious affect on health.

An alternative heating fuel is LPG which can be cleaner and easier to handle but its combustion produces moisture and gases which carry a smell, causing similar problems as burning gas oil or paraffin if the correct procedures are not followed and precautions not taken.

Indirect heating has traditionally produced efficiencies as low as 70% but developments in heater design mean that we are now achieving results in excess of 90%. This represents an enormous cost-saving, considering the reduction in heating energy exhausted through the flue along with the residues of combustion, moisture, gases, soot etc.

Indirect heaters are usually powered by gas oil, paraffin, or LPG and circulate clean, dry air through the heat-exchanger. They can be used safely in enclosed areas, providing the flue is correctly ducted away from any enclosed areas. In many installations of this nature, the flue itself will radiate an amount of thermal energy into the enclosed areas, thus increasing the overall efficiency of the system. Alternatively, indirect heaters can be placed outside the enclosed area and the warm air ducted in. This is especially useful where a supply of fresh air is required or where an area (such as a marquee) is to be kept under slight positive internal pressure.

Mobile heaters are usually fan-assisted for effective air movement. Where it is important to minimise airflow or noise, radiant heaters can be used which rely on natural convection currents to circulate the warmed air.

They should not be used where flammable fumes or dust can be drawn into the air stream. In contaminated and flammable areas, indirect-fired heaters sited externally may be suitable if used correctly.

Electric quartz radiant heaters conduct thermal energy by light, heating whatever material the light falls on. As these materials warm up, they will themselves radiate some thermal energy which is absorbed by the air, although the air is not heated directly by the heater itself. This form of heating is especially effective in draughty or open areas.

Where heat is being applied for purposes of drying – e.g., building materials, crops, water damaged buildings – it would be most effective to use electric heat although this is not often practical due to the amount of power required to achieve the heat output. Especially taking into consideration that a 3KW electric heater on a 110V supply draws the best part of 32A, it’s not surprising that alternative forms of heating are looked for on site.

In most drying situations, the optimal solution is the use of indirect-fired heaters but, if the fumes and soot aren’t going to be an issue, direct-fired heaters can still be effective because the water-holding capacity of warming air exceeds the volume of water produced by the combustion process.

If you are looking for expert advice on the best kind of mobile heater for your circumstance, look no further than Airflo – the temporary air quality rental specialists since 1972. We can assist with whatever requirement you may have. Send us a message now at or give us a call on 0800 289 191.

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