HERS stands for Home Energy Rating System. Home Energy Rating System is a uniform rating scale of the efficiency of a building compared to the energy usage of a standard reference home. HERS came from the mortgage industry as a way to score a homes energy usage to give buyers better information about the total cost of ownership. In 1992 FHA began a pilot program called Energy Efficient Mortgages (EEM) which allowed a purchaser to borrow more money than their credit would allow. It was allowed because the added money would go into cost effective upgrades which would reduce energy costs offsetting the increased monthly mortgage cost. To prevent the additional funds from being spent frivolously the program required a third party auditor to diagnostically test the home and prioritize upgrades based on cost effectiveness. Only cost effective upgrades can be financed with an EEM. This auditing system to “score” the homes energy usage is called Home Energy Rating System and the audits were performed by HERS raters. The program was so successful that in 1995 the FHA expanded the program nationwide. Most homes can be financed with an EEM. Older homes, especially in Southern California, have at least one major appliance or feature which can be improved and financed through an EEM. New construction homes can also qualify for an EEM because the third party HERS rater will have confirmed the home was built correctly therefore using less energy making more of the purchasers income available to pay the mortgage.
So how does this apply to California? The north east black out of 1965 was the impetus to national energy efficiency standards for buildings and was spearheaded by ASHRAE. The oil embargo of 1973 put further pressure on planners to address skyrocketing energy costs and the damage to the national economy. California responded with the Warren-Alquist act which directed the creation of the State Energy Resources Conservation and Development Commission, currently know as the California Energy Commission. This Commissions was given statutory authority to create and issue cost effective building energy efficiency standards. In 1978 the first California energy code was published. The energy code is periodically updated to reflect market conditions.
The energy code requires permit applicants to document then demonstrate how the building they wish to construct will comply the energy code. Every project has an energy budget based on where the building is located and the budget allows the designer some flexibility in how they comply with the energy code. Some assumptions based on historical evidence are built into the energy budgets. For example, most buildings are not properly air sealed or insulated causing them to use about 20% more energy. The energy budgets assume a building which complies with the energy code will not be insulated properly and use 20% more energy than a properly insulated home. If you have a third party inspection to verify the home was air sealed and properly insulated then you get that 20% back in your energy budget as a credit! Not only do you get a better performing home, but you also can use that credit to address design questions like maybe you want more south facing windows to watch the sun set or maybe you want to reduce the amount of solar your home will need. HERS as a compliance option was first added to the California Energy Code in 1999. Ten years later whole home energy ratings were added and duct leakage verification by a HERS rater became a requirement in some areas. So HERS in California is a little different from the rest of the country in we are not scoring a home to give it a HERS rating to compare energy usage against all other homes, we are measuring the quality of the installation against the California energy code.
The code has been on a three year update cycle and each update since 2009 has included additional HERS measures. Some HERS ratings are mandatory and cannot be traded off such as duct leakage verification or indoor air quality verification. Some are prescriptive which means they are only required in certain climate zones. A prescriptive example would be refrigerant charge verification in air conditioning systems, it is not required along the coast where the weather is mild, but it is required inland where the weather conditions are much more severe between summer and winter. Prescriptive HERS measures can be included in projects in climate zones where it is not required as addition credit in the performance method.
Which HERS tests need to be performed?
When a mechanical system such as a furnace or air conditioning system is replaced, California Energy Code requires third party testing to ensure the system meets minimum requirements. Which HERS tests are required is currently based on the climate zone your project is located in. California is divided into 16 different climate zones based on the weather conditions. AAE always recommends you enter your job information into one of the HERS providers registry to determine the list of required forms once you have been awarded a job. To understand which HERS tests are required, start with your climate zone.
CEC EZ building CZ tool link
There are a few ways to determine your climate zone. First would be to create your project on one of the HERS providers registry, once you enter the zip code the climate zone and requirements will automatically populate on your forms. The next is to query the California Energy Commission web site and find their pdf of climate zones by zip code. Download the most current copy of this pdf, search the document for your zip code and your climate zone will be listed. The last is to use the CEC EZ Climate Zone tool by clicking here. Type in the project address, hit enter, and you will have the climate zone information listed on the left side of the map overlay showing the climate zone.
For a list of all HERS tests and what they involve click here.
