A google search for dryer temperatures typically brings up temperatures of 180f on hot, 160f on medium, and 140f on low. All of these temperatures are adequate as all stages of bed bugs die at 122f in one minute. But I have noted that in field use dryers often have very different temperatures. For example some laudromat dryers (on hot setting) never melt plastic garbage bags while others do melt the bags.
As such I made an experiment. I measured the exhaust temperature of my own home dryer (medium load of dry clothing on “delicate”) with a high quality thermometer (electro-therm model TRH670A). The exhaust temperature was 138.1f and rising quickly at 5 minutes. Shortly thereafter a maximum temperature of 146.2 was recorded and it then modulated between 146f and 124f as the thermostat maintained temperature. At ten minutes the temperature was 134 and falling due to the modulation. I then immediately turned off the dryer and placed the thermometer probe in the middle of the clothing and measured 135.9f – more than adequate to kill bed bugs.
I then checked the heat levels on the “regular” heat setting and found the exhaust temperatures modulated between 155f and 128f. Again more than adequate.
I then decided to check the dryer in my garage that I use to sterilize my work clothes. On the “hot” setting I noted that the modulations of temperature slowly increased. For example the first time the dryer started decreasing in temperature was at 112f – very concerning. But as time went on the upper limit hit 155f with a low limit of 124f. As such this dryer, though adequate, would take a few minutes longer to complete the task. I do not understand why this dryer slowly ramped up the temperature in a modulating fashion.
A further interesting piece of information about my garage dryer is that the temperature of the air coming off the heating coils was measured at 190f just before I purchased the dryer and, due to heat loss and heat being absorbed by the dryer and clothing, the exhaust temperature never exceeded 155f. I wonder if the 180f, 160f, and 140f temperatures commonly cited relate to the temperature of the air coming directly off the heating coils? If this is true a low setting (140f) would be have exhaust temperatures just barely over 100f. That would be inadequate.
One thing to be aware of with the dryer is they often have a “cool down” phase at the end of the cycle where no extra heat is added. Always operate the dryer with at least 10 minutes left on the timer to avoid that problem.
The most interesting thing I learned here was that 10 minutes was more than adequate to kill the bugs even on the “delicate” cycle of my dryer. But as always it is best to be cautious and use more than the minimum amount of time to kill the bugs. 20 minutes would allow plenty of room for error. Also ensure that the dryer is not overloaded.
If you are concerned about your dryer just measure the exhaust temperatures. If they exceed 140f on the hot end of the cycle it is more than adequate. Also you can measure the middle of a pile of clothes after 20 minutes to ensure you reached a minimum of 122f. Subsequent loads can be adjusted for time depending on what you learn with your thermometer.