Energy Star for Homes: What is it and Do I Want It?
How it works: A builder works with an Energy Star “Rater” (who is basically an efficiency inspector). The rater evaluates the plans and calculates projected energy use. He may make recommendations for better efficiency and cost effectiveness. The builder then builds the house, the rater inspects, and if it is up to par, the house gets an Energy Star label.
OK great, now what exactly does that mean…? I’ll break it down some. The main things the rater is looking for are as follows: insulation values of the building, efficiency of the heating and AC systems, air leakage, electrical usage, and air quality.
The rater uses modeling software which will compare the house you are building with an identical house that was build exactly to the current building codes. The energy usage of both the replica house and your house is calculated. Whatever percentage of energy your house uses compared to the replica house is the “Energy Star index”. For instance, a house that uses half as much energy as a house build just to code will have an index of 50. 75% is a 75 and so on.
Be careful that you are seeing the “INDEX”, not the energy star “rating”. Some states use a formula that is based on the index but gives you a different number which doesn’t reflect percentages. (In New York they start with 80 and add 1 point for every 5% savings. A 70 index (70%) is an 86 rating).
The rater checks that the builder follows what is known as the “Thermal Bypass Checklist”. This lists all the details which must be followed in order to get an energy star label. These details make the house safe, efficient and durable.
Now, about Insulation values … The rater measures all the walls, ceilings, floors, windows and doors (every surface that is between the inside air and outside, called the shell or envelope). He then determines their insulation value and calculates heat loss for the structure. This is compared to the replica house with just enough insulation to pass code.
He will then count up lighting and appliances and their electrical uses. These are also input into the software (things like fluorescent fixtures really help here).
Next, the rater inspects the heating, hot water and AC systems. He checks for combustion safety and for efficiency. The efficiencies are input into the modeling software.
A leakage test known as a “blower door test” is done. The house is closed up, windows and doors sealed, and a blower is installed in a door opening. The house is then de-pressurized a little bit and the amount of air blowing out is recorded using precise instruments. From these measurements, the rater can determine how much air leaks through the outside walls and from that… how much heat is wasted. The same is done for the AC system.
Just a note … super sealing a house could cause problems if not addressed. People need fresh air to be healthy (you’ve probably heard the term “sick house syndrome”, this is where it comes from). This is solved through the use of mechanical ventilation. Instead of just having an unknown amount of air leakage, the amount is calculated and fresh air is blown in to make up the difference. This way, you can pull the air out from the bathrooms and kitchen where is needs it most.
Some of the fancier systems have a heat recovery unit which uses the air being exhausted to condition the air coming in to replace it. You get plenty of fresh air without much heat loss.
All these details are inputed into the modeling software, along with info on any alternative energy sources the house may have. Solar PV, solar HW, wind generators, even solar heat gain through windows is factored in.
If the house meets all the standards, It gets an Energy Star label. The builder may get a nice incentive check. You as the homeowner can feel secure that you are getting a house that will cost significantly less to operate.
And … you’ll be helping to save the environment too. Almost as nice as saving money.
