What is the Home Energy Rating System (HERS) Index?
The Home Energy Rating System (HERS) Index is the home building industry standard by which a home’s energy efficiency is measured. It’s a nationally recognized system for inspecting and calculating a home’s projected energy use.
What is a good energy rating for a house?
When it comes to HERS ratings the lower the number the better. To give some perspective a typical home built to 2006 energy efficiency standards scores 100. This is the standard by which new homes are compared. For example, if your new home has a HERS rating score of 60 this tells you that it is 40% more efficient than the standard code built home.
New homes are required to have a HERS rating number of 55 or less in most cities and towns in Massachusetts. Because it is mandatory, the expense of hiring a certified HERS rater is the responsibility of the person building the home. In Rhode Island however, there is no such requirement. Although in Rhode Island Blower Door and Duct Leakage testing with passing grades have been mandatory and continue to remain so.
Rhode Island Residential New Construction Program
Did you know? In Rhode Island, National Grid has established the Residential New Construction program (RNC). The RNC was created to encourage more energy efficiency in new home construction and major remodels. In order to comply with program rules, a HERS rater must be brought on board. The HERS rater you choose will provide all the necessary paperwork to facilitate the enrolment process.
It’s best that these steps are taken early while still in the planning stages of the project. This allows for input from the HERS rater at the beginning while changes are still easy to make. Afterward, as long as the builder follows program requirements the entire cost of the HERS rating including the mandatory Blower Door and Duct Leakage testing is paid for through the RNC program at no cost to the builder. As an added bonus, if the home reaches certain energy-saving milestones additional monetary incentives may be available.
New Home Energy Ratings
What needs to go into a home to assure a good HERS number? The construction of a new home can be a complicated process as there are many components and trades involved. Not every component affects the HERS rating but the items that do must be carefully planned for and installed. Some examples of items that will affect the HERS rating are as follows: insulation, air sealing, mechanical equipment, windows, appliances, lighting.
In this column, we discuss the selection of the mechanical equipment (i.e. furnace, air conditioning, and water heater) and how these choices can affect the HERS rating score.
The scope of this column only covers basic mechanical systems. More sophisticated mechanical systems of which there are many including Hybrids will be topics for future columns.
Note: A basic heating system may include either a furnace that heats air that is distributed through ductwork or a boiler that heats water that is pumped through pipes such as those found in radiators.
Furnace / Boilers
Here in the Northeast heating makes up a large portion of the energy used in a typical home. It is important from a HERS rating perspective to keep this in mind when choosing the efficiency of your heating system. Every new furnace and boiler sold in the United States receives an annual fuel utilization efficiency rating (AFUE). This number is usually found on a sticker adhered to the outside of the unit (see picture below).
This efficiency, typically listed as a percentage, relates to how much of the fuel goes to actually heating the home during the combustion process. As an example a heating unit with an AFUE of 80% converts this much of the fuel to energy while the remaining 20% is wasted and escapes up the flue. Heating systems running between 80 & 85% are considered medium efficient while units running between 90 & 98 are considered highly efficient. These high efficient units have sealed combustion which requires combustion air to be drawn directly from outside rather than from the space where the unit is located.
The takeaway, in order to improve your HERS score consider installing heating equipment with an AFUE of 95% or better. Worth mentioning, these units may be eligible for a federal tax credit.
A typical energy guide on the outside of a furnace
An air conditioner’s cooling efficiency is measured by a metric called Seasonal Energy Efficiency Ratio (SEER). This efficiency is calculated by taking the cooling output for an entire cooling season and dividing by the total electrical input used during the same period. Generally the higher the SEER number the higher the efficiency. The minimum SEER rating is 13 to 14 depending on where you live. Modern air conditioning units have SEER ratings ranging between 13 and 21. Higher SEER numbers mean more cooling power and lead to more comfortable spaces.
Take away: In order to improve your HERS score consider more efficient cooling equipment that has a SEER rating of 14 or higher. Some units may be eligible for federal tax credits.
A water heater’s energy efficiency is determined by the Uniform Energy Factor or UEF. The UEF is based on the amount of hot water produced per unit of fuel consumed throughout a typical day. The higher the energy factor, the more efficient the water heater.
Water heaters with high UEF ratings will yield a higher return on every dollar of energy you put in. In general, ENERGY STAR certified conventional gas and electric water heaters have UEF ratings between 0.65 and 0.95 — or 65 to 95 cents on the dollar — while hybrid electric heat pump water heaters have much higher UEF ratings of 2.75 to 3.5.
The takeaway: The higher the UEF the greater the positive effect on the overall HERS score.
Use a HERS Rater at the Beginning of Your Home Construction Project
As stated earlier, for best results it is smart to bring a HERS rater in at the beginning while still in the planning stage. A good HERS rater using the right software will model your project and test the model using different scenarios in search of the most economic path to achieving the required HERS rating score. But that’s not all, a good Rater will advise and assist as necessary throughout the entire duration of the project.