Heat detectors are often used in conjunction with smoke detectors, however, they only sense heat produced by combustion. Heat detectors are generally mounted on the ceiling, so height requirements reflect local zoning codes for ceiling height. While height requirements depend on local jurisdictions, spacing requirements fall under federal guidelines.Heat Detectors
The heat detector's alarm sounds whenever there is a quick rise in temperature. reached. These detectors must conform to the standards of the National Protection Association. Heat detectors contain a thermal sensor set at a fixed temperature, or a combination of fixed temperature or rate rise sensor. In most heat detectors, the temperature must rise to either 135 degrees or 194 degrees F to trigger the alarm. The rate rise detectors trigger an alarm at an increase of 15 degrees F per minute.
Spacing
On smooth ceilings, heat detectors should be placed between 50 square feet or 2,500 square feet apart, according to the National Fire Alarm Code. The difference in spacing depends on air movements and the ceiling height. As ceiling height increases, the spacing between heat detectors is reduced. The manufacturer also lists the area the product can protect on its specifications and instructions.
Other Ceilings
Not all ceilings are smooth. Different types of ceilings have different requirements for heat detector spacing. For joisted ceilings, reduce the heat detector's spacings by 50 percent perpendicular to the joists. For beamed ceilings, reduce the spacing by one-third perpendicular to the beams. The heat detector may be mounted on either the ceiling or the beam. For smooth peaked ceilings, install the device within 3 inches of the peak. For peaked joisted ceilings, also install the detector within 3 inches of the joist but reduce spacing by 50 percent perpendicular to the joists.
Testing
Heat detector spacing is based upon performance results during testing. The test ceiling height for heat detectors is 15 foot and 9 inches in a room with very low air movement. The National Fire Alarm Code provides information for spacing for various ceiling heights as well as a formula for making calculations. If installing heat detectors on new construction, refer to local zoning codes for height requirements or consult with the local construction official.
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