An internationally recognized bed bug expert recently questioned our standard treatment protocol which calls for extending a treatment for three hours after reaching 120 degrees. She felt that running for three hours didn’t automatically guarantee that internal temperatures in mattresses, pillows, and upholstered furniture had reached fatal temperatures.
Although we had tested this earlier while developing the protocol, we repeated our tests using a food thermometer with a 1/8” steel spike and accuracy of +/- 1 degree C. The thermometer allowed us to check temperatures 4-5” below the surface of mattresses, foam couch cushions, armrests, etc. What we found was that the internal temperatures were 8-10⁰ F cooler than the surrounding air, and that the internal temperatures basically paralleled the external temperatures, meaning they went up at the same rate, but stayed 8-10 degrees cooler.
What this means is that by the time your air temperatures reach 130 degrees, which is typically 30-60 minutes after you get to 120⁰, the internal temperature of insulated items is at or above 120⁰. So if you continue heating for three hours after reaching 120⁰ in the room, the internal temperature of insulated items is without question above the required 120⁰. You can test this yourself using a quality thermometer such as Grainger models 3KTW1 or 5WG21, or other similar devices you can find online.