Throwin’ high heat

Mittens and truck mechanics just don’t mix. So if you want your shop staff thinking warm thoughts about you next winter, turn up the heat in the work area. For many garages, a furnace fuelled by used motor oil is a sensible choice: you’re doing away with an environmental liability and a shop-heating fuel bill at the same time. High-quality furnaces are efficient and let you run ductwork to direct heat right where you need it.

But not all shops generate enough waste oil to justify having a furnace (although the better furnaces on the market can burn No. 2 fuel oil), or are ideal in terms of the space involved. Planting small space heaters around individual work areas is inefficient, energy-wise–and a hazard. And as much as you might like the efficiency of hydronic heat, the thought of ripping up the floor of a working shop to lay down the necessary plumbing could leave you cold.

A common alternative is infrared heat, a system that works well not only in large shops but any area with high ceilings, like a warehouse or crossdock facility. Suspended from the rafters, infrared heaters mimic the sun–heat energy radiates in the form of electro-magnetic energy. This excites molecules in an object, thus producing heat.

Infrared heaters aren’t new–many large industrial building use them. What makes them effective (or not) is how the overall heating scheme is designed. “Everybody touts fuel savings associated with infrared heating equipment,” notes Kevin Mahoney, vice-president of sales and marketing for Roberts-Gordon, a heater manufacturer in Buffalo, N.Y. “But that fuel savings is difficult to attain unless you design (the system) properly.” The first step, he says, is to use a professional heating contractor who can do an accurate heat-loss calculation for your space.

There are two common types of infrared heaters. High-intensity or “luminous” equipment involve an open flame and are often used for spot heating defined areas: in hockey arenas, for example, where they can warm the seating area without affecting the ice. They require wall-mounted exhaust systems, each serving a number of high-intensity heaters.

Low-intensity or “tube-type” infrared heaters form the bulk of the infrared market. They operate at lower temperatures than high-intensity heaters, have a sealed combustion area, and can be either direct-vented or draw air from inside the building. Tube-type heaters put out a “softer” heat (for lack of a better word) and may provide better comfort at lower ceiling heights. And sealed combustion makes them a good choice where volatile chemicals are present. Keep in mind, however, that the surface of the heating tube is hot and must be separated from any volatile chemical by at least 10 feet.

Building height is a key factor in determining the size of heater you need. Below 20 feet, you can’t use heaters of 150,000 Btu/h or greater (some manufacturers offer special models for low-ceiling applications). However, unlike a space heater which can “throw” its heat only so far, the electro-magnetic energy of an infrared heater travels through space with little apparent loss. As a result, the rule of thumb is to place the heaters as high in the building as possible to maximize the “radiant footprint” on the floor.

Heating systems are a trade-off between efficiency and installed cost. The number and placement of infrared burners are critical factors, says Mahoney. Installations that give infrared a bad name are generally those where burners are few in number or poorly placed, leaving occupants too hot or too cold. In a 20,000-square-foot shop or warehouse, for example, depending on the climate, the heating load would range up to 75 Btu/h per square foot, or up to about 1.5-million Btu/h. You would need about 10 150,000-Btu/h heaters to do the job. Overlapping the radiation of the heaters assures even coverage.

“The floor is a heat sink and it’s important to get a good radiant charge in that floor,” adds Mahoney. You don’t want to dump radiation on areas that don’t require heating: walls for example. Redirect the heat with a reflector (rather than tilting the heater, which results in substantial convection losses).

In practical terms, you’ll want heaters placed over aisles, open areas, and around dock doors–but out of the way of shelving, overhead cranes, etc. Tube-type heaters should have their burners over the greatest source of heat loss, like along an outside wall.

Infrared heaters are not all created equal. Design, materials, and control strategies can make big differences. Industry standards require that 35 per cent of a luminous infrared heater’s output is infrared heat energy; most do better and some are 80 per cent plus infrared efficient. In tube-type low intensity heaters, new designs that modify airflow through the burner and use different materials along the emitter tube have reduced temperature variation. A deeper reflector and end caps can reduce convection losses.

Two-stage variable heaters have been available for a number of years. And at least one manufacturer offers full burner modulation that varies vacuum, gas and combustion air to match system input to building heat loss through outdoor temperature. And while this article has pointed to typical applications for high-intensity versus tube-type heaters, manufacturers continue to push those boundaries. A heating contractor with experience designing systems for shops, warehouses, and other industrial locations can help you spec a system for your space and budget.

Most infrared systems are controlled with a conventional thermostat. Objects heated by infrared transfer heat to the air, so this works to some extent. However, comfort with an infrared system is a combination of ambient (air) temperature and radiant heat. You can achieve more precise control with a thermostat that measures both and hence the temperature setting is a true sensible heat indicator. Things like zoning, burner modulation, and more control though precision electronics can bring major gains in efficiency and comfort, as well as productivity: just imagine–a mechanic who doesn’t have to work in mittens.