• Posts
  • RSS
  • ◂◂RSS
  • Contact

  • Rough Marginal Costs

    April 6th, 2014
    money  [html]
    We pay for most things directly as we use them: to park at a meter you put in quarters; to rent an apartment you send a check each month. For some things, however, our usage is metered and we pay after the fact: electricity, gas, water. In these cases we're often not well calibrated for marginal cost, which means we're not in a good position to make tradeoffs. Can I leave the fan on all night? Should I worry about letting this frozen food thaw in the fridge before I put it in the oven? How much should I be trying to take shorter showers? Colder ones?

    I thought it would be useful to compile some rough costs of these pay-later activities:

    Gas Oven one hour $0.16 [1]
    Gas Dryer one load $0.35 [2]
    Front Loading Washer, Warm one load $0.39 [3]
    Cold Shower ten minutes $0.57 [4]
    Hot Shower ten minutes $0.76 [5]
    Dishwasher one load $0.31 [6]
    Microwave two minutes $0.01 [7]
    Box Fan overnight $0.17 [8]

    This is based on a marginal cost of electricity of $0.21/kWh, natural gas of $1.40/therm, and water of $0.017/gallon which includes the sewer charge. [9] These come from our current bills in Medford MA; it's probably cheaper in lower cost of living states.

    While these are approximately in line with what I'd thought, I do see two changes I should make:

    • Be willing to use the dryer when line drying is inconvenient. (Previously I never used the dryer, for cost reasons.)
    • A long cold shower (in summer) is actually more expensive than a short hot one.


    [1] Gas Oven, 0.112 therms per hour.

    [2] Gas Dryer, 0.21kWh to spin the drum and 0.22 therms to heat the clothes.

    [3] Front Loader, 0.26kWH to run the machine, 0.064 therms for the water heater to heat the incoming water, 14.7 gallons of water.

    [4] Cold Shower, 3 gallons per minute, 30 gallons total, $0.57 for the water.

    [5] Hot Shower, 0.00014 therms per gallon per degree F. Ground water at around 55F, shower water at around 100F, so a 45F rise. Shower flow of about 3 gallons per minute. So over ten minutes that's thirty gallons each heated 45F. So $0.57 for the water [4] and $0.19 to heat it.

    [6] Dishwasher, 4 gallons of hot water and 1kWh to run the machine. That's $0.10 for the water and heating [5] and $0.21 for the electricity.

    [7] Microwave, 0.024 kWh per minute.

    [8] Box Fan,100W.

    [9] This is much higher than I'd thought, 10x the cost of desalination.

    Comment via: google plus, facebook

    Recent posts on blogs I like:

    Best Practices Civil Service

    I propose that transportation agencies hire people whose job is to keep abreast of global developments in the field and report on best practices. Which agencies should do it? Ideally, all urban ones. Very small ones should piggyback on large ones, or part…

    via Pedestrian Observations June 14, 2021

    Collections: The Queen’s Latin or Who Were the Romans? Part I: Beginnings and Legends

    Who were the Romans? How did they understand themselves as a people and ‘Roman’ as an identity? And what were the implications of that understanding – and perhaps more importantly the underlying reality – for Roman society and the success of the Roman Emp…

    via A Collection of Unmitigated Pedantry June 11, 2021

    It's ok to feed stray cats

    Before we had kids, Jeff and I fostered a couple of cats. One had feline AIDS and was very skinny. Despite our frugal grocery budget of the time, I put olive oil on her food, determined to get her healthier. I knew that stray cats were not a top global pr…

    via Giving Gladly May 15, 2021

    more     (via openring)


  • Posts
  • RSS
  • ◂◂RSS
  • Contact