Energy Use

Most existing buildings use energy very inefficiently: this section identifies the causes in the building's design and construction, and how to fix them. Occupant behavior also effects total energy use, and in a very efficient building, behavior can be a major factor--and also not within the scope of this document.

Energy use can be broken down into four major categories, roughly order by size: heating/cooling, hot water, lighting, and plug loads, which are covered in the following four sections.


In most climates, heating and cooling is the largest energy use in a residential buildings, so in those climates its the one you most want to reduce.  The best way to save heating and cooling energy is to not use it, which means keeping the cold (or hot) outside: mostly via insulation, but also thru better windows & doors and sealing air leaks.  The next best thing after that is to use whatever heating and cooling your local weather provides, or at least to not let the sun & wind cause you to use more energy than you need to.  Finally, choose efficient equipment.

The heating and cooling system is designed by creating an energy model for the building; in the model we can see how much energy is lost thru walls, ceilings, windows, doors, and air leakage, trade them off against each other, then all of them against the size of the HVAC unit.  We can also use the model to compare choices  for insulation windows and doors, and to estimate yearly energy usage.

The final topics are using solar energy and designing to take advantage of whatever sun and wind is available, including avoiding excess solar gain. 

Here are in-depth discussions on each topic:


Hot Water

After heating and cooling this is often the second biggest energy use, although how much gets used tends to depend on occupant behavior as much as anything else.  Families that are careful about how much hot water they use will have less concern with the efficiency of hot water.  Solar hot water collectors can reduce hot water energy use--in sunny climates to near zero.  The detailed discussion is in the Hot Water section.


Lighting energy is typically the third biggest use of electric, although as insulation values go up and hot water gets more efficient, the energy used by lighting goes up proportionally unless its efficiency is also improved.  Much effort has gone into getting people to use more efficient bulbs, mostly because its an easy, low-cost change, and the federal government has made older incandescents illegal, although slightly more efficient versions are still legal.  The details are all in the lighting section.

Plug Loads

Plug loads consist of every electrical device you plug into a socket.  The biggest users like refrigerators are rated by energy-star so there is a way to guarantee at least that the device is reasonably efficient, but many are not, and manufacturers don't make the information available. Most appliances aren't on for very much time, so even though a blow-dryer or toaster consumes over 1000 watts, they're usually on for less than 5 minutes a day, which adds little to your overall consumption (1000 watts for 5 minutes is .083kwh).   More info about major appliances is in the appliances section.

Many devices are effectively on all the time even when they're theoretically off, because when they're off, they're really in standby mode.  Details are in the phantom load section.

Energy Use in the Big Picture

This section is not about building at all, but about issue of global energy use and the various initiatives that have been started to deal with the problems.  Needless to say, if you're not that concerned about the environment, there really is no point in reading this section.