How Do You Earn a Strong HERS Score?
Many variables affect a home's energy efficiency. The best way to think about it is to break it down into three components:
1. Design Considerations
Consider all the early design decisions that affect your home's energy usage. The home's size, the orientation to the sun, the number of windows and their U-factor, the tightness/leakiness of the house envelope, and the type and level of insulation greatly impact your energy usage, especially if you live in more extreme climates. Rise has written extensively about all of these components.
The most important thing is communicating your goals to your design and construction team if you are building new. Do you want a net-zero energy home (meaning it produces as much energy as it uses)? That might require more upfront costs, but it will decrease your operating costs year after year. Whether you are building new or remodeling, these upfront design decisions will significantly impact your HERS score.
2. Energy Use
Next, consider the things in your home that use energy. According to the US Energy Information Administration, on average, 51% of a home's energy usage comes from space heating and cooling. Ground-source heat pumps and air-to-air heat pumps can be very efficient choices for both cooling and heating.
After space heating and cooling, hot water heating is the biggest energy consumer. Research water heaters before you buy, as there are many different options in terms of cost and efficiency (see Rise's Home Water Heater Buyer's Guide). Additional ways to reduce your hot water usage include installing low-flow showerheads, pipe insulation, and an ENERGY STAR washer and dishwasher.
On the topic of appliances, refrigerators are one of the biggest energy hogs in a home—so make that ENERGY STAR rated as well. And don't forget lighting. LEDs (light-emitting diode) dramatically reduce the electricity needed to light up your home, and prices have been declining every year. Be sure to check out Rise's LED Lighting Guide even further to reduce your home's energy usage. While many more energy-consuming devices are in the house, the HERS Index only looks at these larger components.
3. Energy Production
Once you've addressed #1 and #2, then you can think about whether and how much your home produces energy with renewable resources. Solar panels can help collect much of your required electricity. Once you pay for them upfront, any electricity they produce is free. You might also consider solar thermal panels to heat your water directly from the sun.
An energy rater will take all of these variables and input them into an energy model. The result is a HERS rating that will tell you how much more efficient your home is than that same home built to the 2006 code.
For a new home (as opposed to a major renovation), a HERS Index relates to LEED points as follows:
- HERS Indes of 70 will meet the prerequisite but not earn any points
- HERS Index of 69 achieves one point
- A HERS Index of 50 gets you 26 points
- If your home is net-zero, you earn all 36 points.
For a significant renovation, you get a little more leeway: your home only needs a HERS rating of 84 to start earning points.
In this case, home size matters. The larger the home, the more energy it uses, on average. So, LEED requires that you deduct your "home size adjustment factor" from the HERS score. It is a complicated formula; know that your energy rater will need to include that as a factor.
Suppose you have a single-family home with a significant energy user such as a pool, hot tub, heated garage, or heated driveway. In that case, those components are not included in the HERS Index. A different, more complicated "LEED Energy Budget" must be followed to earn any points.