Placement of infrared heaters is influenced by many factors. Aside from safety factors, considerations such as the number of vents or heater elbows that are allowed, maximum vent lengths, ducting of combustion air, and combining exhaust vents are a few examples. All installation manuals, along with national, state, provincial, and local codes, address these issues. It is critical that you read, understand, and follow all guidelines and instructions.
Heater Size and Quantity
After conducting the building survey and heater placement, now the size and quantity of the heater(s) need to be determined. The options for the heater size have already been established based on the available mounting height and clearance to combustibles. For this example we will use a tube heater with a heater input of 100,000 BTU/h. To determine the quantity of heaters you will need to divide the total building heat loss (calculated on Heat Loss Form) by the heater size you have chosen. If the total heat loss is 300,000 BTU/h, three 100,000 BTU/h units (i.e. 300,000 ÷ 100,000 = 3) are needed to match the load.
A well designed heating system will result in even heat distribution throughout the space. Concerns regarding uneven heat distribution should be addressed by looking at alternative heaters. Recommended mounting heights for heaters do overlap and distribution concerns can sometimes be solved by using more heaters of a slightly smaller input (e.g.: using four 75,000 BTU/h units in place of three 100,000 BTU/h units to match the load of 300,000 BTU/h heat loss).Heat distribution can also be controlled with the use of reflectors, side shields, guards, and ‘U’ or ‘L’ shape. Reflectors and reflector accessories direct infrared energy to the floor level. The reflector assembly depends on the heater configuration, proximity to combustibles, and space surrounding the heater.
In a total heating design for a building, the concern is to replace heat losses with heat input and to create the most uniform radiant pattern as possible. The arrangement of heaters influences the effectiveness of the heating system, but because of limitations imposed by building construction as well as other factors, it is not always possible to use the most efficient arrangement. There are two basic heater layouts: perimeter mounting and ridge mounting. Under certain conditions combinations may be required.
In this arrangement, the infrared heaters required to satisfy the total heat loss are located along the outside walls of the building. Experience has proven this to be the most effective layout for gas-fired infrared heaters. This arrangement should be used whenever possible as it permits a 15% perimeter heat loss reduction.
NOTE: The following criteria must be met to allow the reduction.
The number of infrared heaters placed along each wall depends upon the amount of heat loss through the wall in proportion to the total conduction heat loss through all the walls. In most cases, this is also roughly proportional to the length of the particular wall.
Heaters Along Wall = Heat Loss of Wall / Total Wall Heat Loss x Total Number of Heaters
Areas where very high heat losses occur may require supplementary spot heating. Areas of very low heat loss, such as walls adjoining other heated areas, may be best heated by smaller units than are used throughout the rest of the building. Rotating the reflectors of units placed on outside walls allows the infrared to be directed into the surrounding work area. Observance of minimum mounting heights is critical to a proper installation.
Due to heat variations, the burner control box and first sections of radiant tube should be placed in the area(s) of highest heat loss (e.g.: overhead doors). Cooler sections of the tube should be located in areas that do not require as much heat. When placing the heater system along an exterior wall, pairs of heaters are usually installed opposing each other and then common vented together.
In this arrangement, infrared heaters are mounted along the ridge line of the building, usually with adjacent heaters inclined in opposite directions for maximum coverage, although horizontal mounting may be used. This arrangement is the least desirable for infrared heaters. The heat input is concentrated at the farthest distance from walls where the conduction losses occur. A ridge mounting layout can provide the inside design temperature required, but increased fuel consumption should be anticipated.
Combinations of perimeter and ridge mounting arrangements are usually employed in large buildings where the closest opposite walls are more than 100 feet apart.
The basic perimeter layout is followed for greatest system efficiency. To counterbalance large heat losses through the roof in the center of the building, some of the infrared heaters are installed nearer the center instead of placing them all on the perimeter.
Locating a heat input of 10% to 20% of the total heat loss near the center area is usually sufficient. The 15% perimeter heat loss reduction may be taken if the heating in the center does not exceed 20% of the total input.
Low intensity infrared heaters can be placed in a straight, ‘L’, ‘U’, or extended ‘U’ configuration to allow maximum flexibility in the placement of the heater and control of heat distribution.
Specific localized needs have slight influence on the overall selection of heaters, but can dictate local deviations. Reflector extensions are often used to provide higher radiant intensity in these areas, although a total heating system ordinarily does not require the use of such extensions.
A maximum of two 90 degree elbows or one 180 degree ‘U’ fitting can be installed on a low intensity series heater. Placement of these accessories is determined by the high fire input of the specific model. Chart 4.1 shows the minimum distance from the burner control box that elbows or ‘U’ fittings must be placed for different model low intensity heaters.