HERS Ratings and what a good HERS rating is…
The Home Energy Rating System is a procedure that compares the energy efficiency of a new home with a code built home and based on the results assigns the new home an index number or rating.
The lower the index, the more efficient the home is. An index of 0 would mean the home is off the grid, not needing any power or energy other than what it produced itself. A zero also means the home doesn’t have a surplus of energy, if the home had a surplus, the index would be in the negative.
An index of 100 would mean that the home is built exactly to the 2006 International Residential Energy Code
As NYS has adopted the 2015 International Residential Energy Code, AKA the 2016 NYS Energy Conservation Construction Code many towns require a HERS rating to show compliance.
Some Towns have stricter than NYS code laws and require an index of 54 or less.
All Energy Star labeled homes must be HERS Rated, Passive House requires Energy Star compliance and there is the HERS ERI path now in State Code.
A bit of information is needed to provide a HERS rating;
- A complete set of construction plans with pages for the foundation, 1st floor, 2nd floor and all 4 elevations.
- A schedule with window and door sizes.
- Window U and SHGC values. (or at least Low-E, Ultra Low-E etc.)
- Insulation type and R-values are helpful for a starting point.
- How the home will be heated. (Oil, Gas, Boiler or furnace, Heat pump, etc.)
- How the home will be cooled. (Traditional ducted system, mini split, etc.)
- If present, the location of ductwork (Conditioned space/Basement/Attic/Both).
- Location of HVAC equipment.
- How Domestic Hot Water (DHW) will be heated and location of equipment.
- Percent of high-efficiency lighting (CFL’s or LEDS).
- Optionally, if Energy Star appliances will be used.
- The efficiency ratings for all of the mechanicals.
To have a better understanding of what follows, one term should be understood. the building “Shell”.
The building shell is what separates the inside of a home from the outside. Inside the shell, it is heated and cooled. The shell separates the inside or conditioned space from a multitude of outdoor areas. A wall might separate a conditioned space from the outside or an attic, a basement, even a garage.
With the information above, the actual rating can begin. While an entire rating is beyond the scope of this primer a general scope of work is as follows.
Measure from plans to accurately determine the area of the home’s building shell, and separating every area based on assembly type, R-value and what that part of the shell is exposed to.
Measure the habitable square footage of the home. Measure the volume of the home. Determine building occupancy, measure linear footage of all foundation walls, If there are slabs on grade, measure the square footage and how many linear feet the slabs are exposed to outdoors. Measure how many square feet of insulated first floor there is, measure any cantilevers, Measure roof areas over the 1st floor, Measure the square footage of exterior walls, measure area of garage walls, basement walls, attic knee walls. Measure the areas of windows based on the direction they face, include overhangs and eaves, enter in all the mechanicals, ducts locations and duct insulation values, appliances, lighting and evaluate the ventilation strategy.
Many of the homes I Rate for the 2016 NYS code (2015 IECC) are also drawn in 3-d modeling software so that all of the volume in a home is accurately included in the model. Simply stated, the more volume a home has the easier it is to meet the blower door requirement.
The architectural plans for every home I Rate are imported into specialized take off software. Discounting waste, I can easily tell anyone how many Sq. Ft. of roof and wall sheathing is needed, how many sheets of subflooring is needed, how many linear feet of exterior wall there is. At this point, it’s quite simple. All my customer has to do is ask, and I can provide.
All of the information above and more is entered in specialized energy modeling software. At that point, the software can now give the HERS Index as well as many other metrics.
Most plans by professionals new to the HERS index and NYS Code don’t pass as drawn. Failures are typically due to the fact that some architects are a little behind the building science curve or don’t know the requirements of the threshold chosen. Other’s leave all of the values out purposely as they know that the rating process will determine what is needed.
If the plan fails to meet whatever threshold was chosen and I need to upgrade the home, I know I am spending your money, so I do so wisely. I typically add incremental upgrades to the model and continually check for compliance.
After deciding and agreeing to the final details the required HERS paperwork is printed and only now can work begin on the heating and cooling loads, or Manual J 8th Ed.
Many of my customers ask me to also provide the Duct Design and Equipment verification (Manual D and S).
The time needed to get to this point varies with each home. An accurate rating, Manual J, D and S could take anywhere from 4 to 16 hours.
After the home is framed and sheathed it’s always smart to have a site meeting with the owner and GC. It’s important to include the HVAC, Insulation and framing contractor at this time, and have the meeting scheduled before any contractors begin working in the home.
This is also the time I try to get the builder up to speed on any last-minute air sealing details and what’s needed for the thermal bypass checklist.
Fast forward, we are nearing the end of planning, and much work has gone into the project, the insulation is installed. It’s very important to have it inspected it before the sheetrock is installed. Not only is it a RATERS responsibility to I check the R-values of installed insulation, but I also have to grade the quality of install, verify that the home is being built as per plans and to inspect that the items on the thermal bypass checklist have been done and done well.
The next time I see the home, it is generally 100% done.
At that time I perform the final test which includes blower door testing, duct testing, combustion safety testing, measuring the ventilation air flow, and a host of other verification’s that will be the subject of another article.
This is also the stage where all of the planning and hard work is generally rewarded. We get a confirmation of the HERS index and know that a durable, healthy safe and efficient home has been built by design.
That is a summation, of the procedures any generic HERS rating should follow.
If you belong to my favorite group of customers, you will be among those who want a home that is built to be durable, built to be safe and built to be efficient. To have that goal met, you will recognize the true value of my services and trust my recommendations.
Those who value my services, also begin to understand first hand what efficiency means. Efficiency can raise the cost in some areas, but true efficiency should also decrease costs in others. At a minimum, the net effect should be to balance construction costs. When my customers are willing to trust my recommendations over other industry “professionals” not only are the costs for my recommended improvements usually paid for, but all of the fees for my services as well.
Lastly, it’s the customers who care the most who are able to use my services to the fullest.
If you are building a new home and are interested in letting me act as a set of eyes for you, and always act in your best interests. please contact me.