Energy Cost of Unit #5

by Eric Dolven

We’ve been living at the Commons for almost a year and I’ve been curious how energy efficient our house really is.  We spent extra money for a ductless mini-split heat pump, double paned Anderson-100 windows, a heat recovery ventilator, (all pictured here) blown in fiberglass insulation, energy star lighting and appliances, and I’m getting curious how much our energy bills are reduced by these measures.  Of course I can’t answer that question because this is a new house, but I can compare how much we are paying now versus how much we were paying at the same time last year in our old, leaky, drafty Seattle house. IMG_7865

Since we don’t have a gas line anymore, all of our energy comes in as electricity.  Heat, hot water, cooking, lights.  So it’s hard to single out heating costs.  But assuming the largest utility cost comes from heat and that we are lighting and using hot water in the same way, it’s probably fairly accurate to compare total energy cost of the old house with total energy cost of the new house.  So what


I’ve done is gone back and compared our utility bills from roughly June 1, 2012 (when we moved in) to the present, with the equivalent bills from the same time the previous year.

That said, here are the results:

Commons House

Old House


energy (KWh)


heat deg days

energy (KWh)


heat deg days




























I was missing some figures from the fall of 2011 and I don’t have the end of spring 2013, but I was able to capture the deep of winter 2011/12 and 2012/13.  Some things to note:

  • The heating degree days in the deep winter were about 6-7% higher in 2011/12 than 2012/13.  The heating degree day is a measure of how cold the month was.  The higher the number, the colder the month.  Thismeans the heating load was around 6-7% higher last winter than this past one.  With this correction, what we spent this year matches last year very well.
  • On the surface, this would be a bit surprising.  New house, expensive energy saving features, same energy cost.  There are two things to remember: The volume of our new house is about 2.2 times that of our old house.  We are heating windowtwice the volume for the same cost.
    • We had very different heating habits in our old house.  We tended to turn our gas furnace off as much as possible.  We would often let the house dip into the mid-50’s overnight.  When at home, we kept the thermostat quite a bit lower.  More like 62-63 degrees rather than the 67 degrees we currently heat to.   We closed heat vents in unused rooms.  While this saved us some money, it made for a rather uncomfortable house.  And because we let it get so cold, condensation would form on the walls in places with little circulation.  Not a good thing.  Now our practice is to set the heat pump to 67 degrees and leave it there.  Day and night, home and away.  A temperature that is very comfortable, keeps the whole house warm, and prevents the less efficient back-up Pick-a-Watt heaters from coming on.HRV

For the same cost, we are heating a house that is 2.2 times bigger than our old house and we are heating it to a much more comfortable temperature that keeps moisture away and promotes constant circulation.