Choosing the right heater

For convenience in a commercial setting electric radiant heating is likely to be the method of choice, as there will be no gas cylinders to order, store or change.

There are, however, significant disparities between the kinds of electric radiant heaters available; and major differences in their efficacy in an outdoor setting.

The principle of radiant heating is well-known, and there are important distinctions to be made between long wave and medium or short wave emitter quartz lamps. For example, the radiant efficiency of a short wave infrared heater is up to 96% and that of a medium wave heater around 40%.

Electric infrared energy travels outward in straight lines from the heat source, diffusing over distance, and is directed into specific patterns by optically designed reflectors. For successful comfort heating, there must be reasonably even levels of heat throughout the area to be heated. Proper mounting heights of the individual heaters, accurate heater spacing, reflector beam patterns, and heat wattage must all be specified to generate the proper heating levels.

Short wave high intensity quartz radiants work like sunshine and have a warming effect the instant the heaters are switched on. Short wave heaters warm people and objects within the beam rather than the air; resulting in a pleasantly fresh rather than stuffy environment, whereas long and medium wave heat has comparatively poor heating characteristics, especially when used outdoors, as it relies on heating the air and does not penetrate the skin to warm up the person.

In addition long and medium wave heat is susceptible to air movement and is not directional.

The wavelength is inversely proportional to temperature. As the temperature goes up, the wavelength goes down. In reality, a medium wave filament, which only heats up to around 900º Celsius, is more suitable for curing and drying processes rather than for outside heating applications, although cheap heaters with medium wave filaments can be purchased as exterior heaters. Long wave heaters are most suited to heating inside areas where a low level of heat is required and it is acceptable for the heaters to be in use for some time to pre-heat the area before it is occupied. Ceramic plaque heaters fall between medium and long wave, heating up to around 500º Celsius but, again, are of little use for alfresco heating as they warm the air rather than penetrating through it and warming the person.

Short Wave Lamps
Short wave halogen heat lamps consist of a tungsten filament heated by the passage of an electric current to a temperature of some 2200º Celsius. At this temperature most of the emission is in the short wave infrared band.

The moment they are switched on, a warming effect can be felt, so the heaters only need to be switched on when an area is occupied, and the ambient temperature dictates that heating is needed.

For heating applications a ruby sleeve or gold dichroic coating encloses the halogen heat lamp to filter out the intense white light and provide an aesthetically pleasing warm glow.

What to Look For
When selecting short wave electric quartz heaters, it is important to consider the place in which they will be mounted. As a rule, ordinary lamps should only be mounted horizontally, and will burn out in a vertical position. Always look for a quality branded lamp inside the heater, for example, Philips or GE, as they offer maximum reliability.

A quartz linear heater should always have a highly reflective, long-lasting aluminium reflector which directs a focused energy beam on an area as required. A special benefit of the adjustable beam direction is that high intensity radiant heating can be provided at low level even though the heater is mounted at a high level.

Always look for heaters with a dedicated reflector; not ones relying on the surface of their extrusion to reflect heat back. The method of extrusion production leaves draw marks on the surface and it is usually not of mirror quality so cannot act as a true reflector. It is merely a cost saving measure for the manufacturer, and one which will impact both on the heater’s performance and on its life span. High grade Miro 4 aluminium is always used for reflectors in Hartman’s heaters since its reflectance is 90-95% in the IR-A range, giving the high heat levels which are required when the heaters are mounted at a high level. Many imitation quartz patio heaters only have around 1/3 of the output of a Hartman heater as they use low grade lighting material which is just 0.2-0.4mm thick; it has insufficient reflective coating and absorbs the heat, eventually closing up around lamp.

It is essential that the parabola shape of the reflector is accurate and the lamp is placed in the correct focus within the reflector in order to obtain maximum heat output. The lamp should be mounted in such a way to dissipate heat away from the ceramic on the lamp towards the heater body, which in turn will act as a heat sink. Specify heaters with side reflectors as they keep the heat away from the critical part of the lamp, helping to prevent premature lamp failure and significantly improving the output of the heater.

Beware cheap Chinese copies of quartz patio heaters - the old adage “you get what you pay for” applies to most things in life including patio heaters. These heaters only use ordinary glass which does not allow heat to pass through and can shatter under the heat duress. The component parts give poor heat output and an inadequate lamp life of around 12 hours rather than 1,100 - 7,000 hours, depending on the heater model, from Hartman.

Consider Ways to Make Cost Savings
The running cost of a Hartman electric quartz radiant heater is from under 20c per kilowatt hour, and there are ways to ensure that costs are kept to a minimum without compromising on comfort for those using the outside space. As we have seen, the efficient nature of short wave heaters mean that they can be left switched off when the area is not in use; as they work instantly when heat is needed. A variable control can also be installed by an electrician, which enable heat output to be varied between 30 per cent and 100 per cent, as the ambient temperature varies and user preference dictates.

This type of system is highly flexible and allows a heater operating at 30 per cent of its capacity to make an energy saving of 70 per cent.

Increasingly creating an area for smokers is a pressing need for many businesses hoping to avoid a downturn in business as bans on smoking in enclosed public places make their impact felt. A little research into the available options for heating will ensure that the heated outdoor area can help to bolster profits, rather than becoming yet another drain upon them.

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