AskPablo: Electric Hand Dryer or Paper Towel?

cnt00125.jpg So you’re standing in a public bathroom, having just washed your hands. You look to the paper towels, you look to the electric hand dryer on the wall, which one do you choose?

Electric hand dryers use a lot of energy; the one I looked at today uses 2,300 watts! But you typically only use it for about 30 seconds. 2,300 watts ( 2.3 kW) times 30 seconds (0.0083 hours) is 0.019 kWh, or about 1/4 of a cent worth.
A typical paper towel (depending on the type) may be around 2g and probably doesn’t contain any recycled content. Most people probably use two sheets. Let’s assume that one roll can take care of 42 people, and weighs 168g. To make it a fair comparison between the two I’ll scale it up a bit, so let’s look at 100 rolls worth, or 4200 people’s hands dried.
The electric hand dryer uses 0.019 kWh per person, so that would be 80.5 kWh for 4200 sets of hands. The California grid CO2 emissions factor is 0.51 mT/MWh, so 0.0805 MWh x 0.51 mT/MWh is equal to 0.04106, or 41.1 kg.
To compare, let’s look at the CO2 emissions from the paper towel production. According to the Wuppertal Institute’s MIPS data tables, paper pulp has a greenhouse gas intensity of 1.275 kg CO2 per kg of paper (or 0.05 for 100% recycled). One hundred 168g rolls weigh 16.8 kg, so they are responsible for 21.42 kg of GHG emissions (16.8 kg x 1.275 kg/kg).
According to these results it it better to use the paper towels than the electric hand dryer, from a GHG perspective. There might be other factors to consider though. Consider that a tree has to be cut down to make the paper towels and that that tree will no longer sequester CO2. I researched for a good half hour and wasn’t able to find a great deal of hard data on sequestration so the following is based on what little data I could find (if you have better data please share it with us by commenting below). It takes 2.56 kg of tree to make 1 kg of paper so we need 43 kg of tree to make our 100 rolls. Assuming that the trees used weigh around 900 kg we need about 0.05 trees. One tree sequesters 172 kg of CO2 per year and would probably live for at least 60 more years. So 493.16 kg of CO2 are not sequestered as a result of our 100 rolls.
I would take that last result with a grain of organic sea salt, unless you have some better assumptions to plug in. Personally I would advocate my favorite, and highly sustainable, hand drying method; your pant leg.
Pablo Päster, MBA
Sustainability Engineer
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