Rebecca Clarren of Salon.com asked TCC to help with some math on whether electric hand dryers or paper towels should be preferred by climate conscious consumers for a story published November 12, 2007: Public bathroom dilemma: Paper or air?
The Kyoto protocol recognizes six gases that contribute to global warming: carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), perfluorocarbons (PFCs), hydrofluorocarbon (HFCs) and sulfur hexafluoride (SF6). To avoid everyone having to re-take chemistry, each of these gases is referenced to CO2 by its global warming potential (GWP). For instance, methane has a GWP of 23 to carbon dioxide’s one. The summation of these values has become a standard and is known as CO2 equivalence or CO2e.
In order to determine the CO2e output of drying one’s hands with two paper towels or using one or two blasts from a hand dryer, we need to understand the respective life cycles of paper towel use and the amount of energy used to run a typical hand dryer.
The process flow of energy and materials related to use of a hand dryer is as follows:
That’s pretty much it. More about our definition of the system boundaries appears below.
The process flow of energy and materials related to paper towels is as follows:
Pulp processing/Paper milling
Refine oil to plastic for garbage bags
Manufacture garbage bags
Transport paper/garbage bags
Disposal of paper/garbage bags
The Footprint of a Hand Dryer:
We considered two hand dryers: one drawing 2300 watts and the other drawing 1725 watts, each running for 30 seconds. There are dryers on the market that claim to use either less power or dry hands in a shorter time (e.g. the Dyson Blade). We chose to look at the average hand dryer in the US today, even though these redesigned dryers may be a great way to conserve energy.
Based on an average distribution of fuels used to generate electricity in the U.S., a 2300 W dryer running for 30 seconds would account for 12.1 g CO2e emissions. If you hit the button twice, as I sometimes do, you’d double your value to 24.2 g CO2e. A 1725 W dryer calculated similarly would be 8.9 17.8 g CO2e. The calculations are as follows:
0.019 kWh * 636.3 g CO2e /kWh = 12.1g CO2e Hit the button twice: 24.2 g CO2e
Or by an EIO-LCA method:
2.3 kW * 0.0083 hours is 0.019 kWh * .1009 $/kWh = .0019 dollar/use = 19.95 g CO2e
Hit the button twice? = .0038 dollar/use = 39.90 g CO2e
For the lower wattage dryer:
0.014 kWh * 636.3 g CO2e /kWh = 8.9 g CO2e
Hit button twice? = 17.8 g CO2e
Or by the EIO-LCA method:
1.725 kW * 0.0083 hours is 0.014 kWh * .1009$/kWh/use = .0014 dollar/use = 14.7 g CO2e
Hit the button twice? = .0028 dollar/use = 29.4 g CO2e
So if you walk into an average bathroom and use an average hand dryer in an average way, you’ll be emitting anywhere from 9 40 g CO2e depending on the calculations and the type of dryer.
A Tale of Two Towels
Calculations for paper are a bit harder because of the greater number of inputs:
Paper Towel Production
According to the EIO-LCA model of the Green Design Institute at Carnegie-Mellon (which is in turn based the US Department of Commerce’s Input-Output tables), each dollar’s worth of paper produced results in 892 g CO2e .
Thus, $33/case divided by 12 rolls/case divided by 350 sheets/roll  * 2 sheets = .0157 dollar/use
892 g CO2e /dollar * .0157 dollar/use = 14.00 g CO2e
Garbage Bag Production
Again using the figures of the EIO-LCA model, a dollar’s worth of plastic garbage bags cause roughly 1030 g CO2e to be emitted.
1030 g CO2e /dollar * 0.00044 dollar/use = 0.45 g CO2e
(We assume 24" X 24" light weight commercial trash bags @ 22$ per carton of 1000 bags each = 0.022 dollars/bag divided by 50 uses/bag (of two towels each) = 0.00044 dollars/use).
Transportation of Paper Towels
The EIO-LCA method indicates the GHG intensity of shipping by truck is 2120 g CO2e /dollar.
2120 g CO2e /dollar * 0.0033 dollar/use = 7.00 g CO2e
(We assume 10 cases of 12 rolls of 350 towel sheets costs $69.97 to ship. Therefore, the shipping cost of two towels (one use) is $0.0033)
Transportation of Garbage Bags
Because one 4.1 kg carton of 1000 garbage bags would satisfy the needs of one commercial restroom for perhaps an entire year, we assume the transportation of the garbage bags to be negligible.
Disposal of Paper Towels
According the EIO-LCA model, 7310 g CO2e are emitted per dollar of waste management and remediation services. This large number is related to the production of methane through anaerobic decomposition of waste in landfills. Note that while some paper towels may use recycled material in their production, the used towels themselves are not recycled.
7310 g CO2e /dollar * 0.0045dollar/use = 32.90 g CO2e
(We assume landfill disposal rate of $0.88/kg, one case of towels is 10.77 kg, one roll of towels is 0.898 kg and one use (two towels) is 0.0051 kg. Therefore the disposal of one use costs $0.0045.)
Disposal of Garbage Bags
7310 g CO2e /dollar * 0.00004 dollar/use = 0.26 g CO2e
(We assume landfill disposal rate of $0.88/kg, one case of bags is 4.1 kg, one bag is 0.0041 kg and the fraction of a bag for one use (two towels) is 0.000041 kg. Therefore the disposal of one use costs $0.00004).
As stated above, if you walk into an average bathroom and use an average hand dryer in an average way, you’ll be causing somewhere between 9 40 g CO2e emissions. If you use two towels, data suggests you will be responsible for roughly 56 g CO2e emissions.
So, if you’re not willing to use your pant leg, your best bet is an efficient dryer and, if one is not available, go for one towel (28g CO2e) only.
 System boundaries are drawn so as not to take into account GHGs associated with employee travel, corporate travel, capital equipment, dispenser/dryer transportation costs, dispenser/dryer maintenance, dispenser/dryer disposal, dispenser/dryer installation, dispenser/dryer manufacture and mined or processed materials used in the fabrication of dispenser/dryer. GHG sequestration of the trees logged to produce the paper are also not included because we assume another tree is planted that has an even faster sequestration rate than an older tree.