Updated: Sep 5, 2019
Author: Wei-Tai Kwok, Past President, Sustainable Lafayette
One of the first steps in converting our home from gas to electric was to understand how much energy our house consumes today, in order to properly size the future heating and cooling systems we planned to install, and to prioritize what work was going to give us the most value for our dollars. This meant that we needed to get an “energy audit” (or “energy assessment”) of our house.
The energy audit involved a technician coming to our house and inspecting it and photographing issues from top to bottom (literally crawling every bit of the attic, and then in the crawlspace under the house). Our home in Lafayette, CA was built in 2004, so it was already built to fairly stringent energy efficiency targets, but there was still room for improvement as building science has advanced greatly since that time.
Some of the key findings of the energy audit included:
1. Energy Loss Analysis
Where is energy being lost in our home? For example, in the summer when our AC is on, is some of that cool air “leaking” out through cracks and crevices in the wall? Or in my case is the cool air generated from the AC being lost as it moves through ducts in our super-hot attic and getting heated up prior to coming through the vents into our living space? In the winter, is our heat rising up to the ceiling and leaking out through our light cans? Yes, yes and yes. Here’s the breakdown of energy loss discovered in my house:
As you can see, the biggest culprit is Air Leakage via cracks and crevices, accounting for 23% of the total energy loss. Duct Leakage (14%) and (lack of proper) Duct Insulation (11%) accounted for 25% of losses. Energy is lost via our exterior walls (17%) and double-pane windows (16%). Upstairs ceiling (13%) and downstairs floor (6%) round out the remaining areas of loss. I’ll show you pictures to best illustrate my losses, as well as best practices for addressing them.
I didn’t know this when we built our home in 2002-2004, but building a home that meets high levels of airtightness is often the single most effective step you can take towards a more efficient, healthy and comfortable home. Minimizing air leakage can reduce heating and cooling costs by keeping conditioned air inside the building envelope, while preventing unconditioned air from entering the building. Much of the air entering a leaky house travels through the attic or crawlspace, bringing dirty contaminated air into the living space.
During my energy audit, our technician Kyle from Eco Performance Builders sealed all windows and doors to our house, then installed a “blower door” to suck air out and determine how much air leakage we had. All our leaks here and there amounted to the equivalent of a gaping 19” diameter hole in our house (not too bad, but clearly not airtight!).
Kyle used an infrared thermal imaging camera to “see” the temperature variance in my home’s building structure. On a cool March 26 at 9:45am, the temperature of our library ceiling (left) varied from 67F (purple, where cold air was leaking in from the attic due to poor insulation) to 77F (bright orange). By sealing air cracks in the above attic and then laying on more insulation, this energy waste could be mitigated.
Our attic air conditioning ducts were improperly installed hanging *above* rather than buried under the pink blown-in fiberglass insulation. In summer afternoons when outside temperatures reach 97F, attic temperatures can get to 150-160F. No wonder for 16 years my upstairs AC never blew cool air from its vents! I could have buried these in insulation, but we chose the better solution of removing the ducts and vents ENTIRELY and installing high efficiency heat-pump minisplits to heat and cool every zone.
2. HVAC Sizing
The energy audit’s findings concluded that if we performed some energy efficiency improvements first (e.g. seal our air leaks, get rid of our leaky ducts, improve our attic insulation) our home would need less energy to heat and cool it, and we could save money by sizing smaller HVAC equipment.
Specifically, the vendor recommended a “Good” approach which would achieve 30% Load Reduction, and a “Best” approach which would achieve 44%. We chose to implement the 44% option. What does “Load Reduction” mean? Think of it as taking 44% of the weight out of a car, by reducing the “load” we could have a smaller engine, which uses less gas/energy. So by reducing our home “load” we could procure and install smaller, more economical heating and cooling equipment, and not do the typical route of oversizing and overpaying.
This chart shows a model of my home before and after recommended energy efficiency improvements (aka load reduction work). My existing HVAC heating system was sized for 129,000Btu/Hr Heating (80% oversized for the 72,285 Load). My existing HVAC cooling system was sized for 78,000Btu/Hr Cooling (33% oversized for the 59,501 Load). I’ve learned that oversizing is quite common in the traditional HVAC industry.
3. Water Heating
We have a 75-gallon natural gas hot water heater that at 15 years old is likely reaching its end of life and will likely rust-out and start leaking before long. It’s a perfect time to look for a more energy efficient, heat-pump electric model. I’ll get into much more detail of what I learned in a future blog article, but suffice it to say at this point that my old-school hot water heater has an Energy Factor rating of 0.58 (only 58% of the energy from burning natural gas is used to heat the water, while the 42% is lost in the combustion process), while the new heat-pump models are rated 3.3 – 3.7, which is nearly 6x more efficient. So it definitely looked promising, although I wasn't ready for the price tag! Read my future blog article to see what I learned.
The energy audit performed by Eco Performance Builders covered more ground than I expected. I thought I was just going to swap out my gas appliances for more efficient electric heat pump technology, but instead learned (not surprisingly) the value and need for some energy efficiency improvements first, to take down my load, and then size my heating and cooling systems accordingly.
Stay tuned for my next few blog entries, where I will go into more detail on the choices and decisions I faced related to:
INDUCTION ELECTRIC COOKTOP