Which material should be avoided for insulation around a furnace due to clearance restrictions?

Foam board insulation is typically rigid and can have a low flame spread rating, which is important to consider when placed near a furnace. The clearance restrictions around furnaces are usually established to prevent fire hazards and ensure that heat can dissipate safely. Using materials like foam board may not comply with local building codes and safety regulations, as it can potentially trap heat and create a fire risk if placed too close to the furnace.

In contrast, fiberglass insulation is designed for thermal resistance and is non-combustible in the context of furnace installation, making it a safer choice. Paper-backed insulation is generally used for other types of insulation applications and its placement is often determined based on moisture control rather than direct exposure to heat sources. Plastic sheeting, while not particularly suited for insulation around a furnace, is usually employed for vapor barriers rather than for providing thermal insulation. Therefore, foam board is the material that should be avoided due to its potential fire risk when installed near heating equipment with specific clearance requirements.