Last fall we asked BMC to audit my home and invited our readers to observe the process. We would like to share with you how the process was that day and our results!
Basic Energy Audits are required for home sales in the City of Austin to help buyers of an existing home to know more about that home’s efficiency. They are also a good idea for homeowners wishing to remodel their home and improve the home’s performance while they’re already paying an insulation contractor, dry-waller, electrician, and other trades to work on the addition. The idea is that while the trades people are working on the addition they can come into the existing portion of the home which may not otherwise be modified during the project and to make improvements that will increase the level of insulation and air sealing, and reduce the amount of electricity and/or water being used by major appliances, lighting, and plumbing fixtures.
To assist with prioritization on my own home and to get some personal experience with the process I’ve been recommending to my clients I had an energy audit performed on my own home. Built in 1981, my house had reasonable amounts of insulation in the walls and cathedral ceilings, but was not well insulated on the attic floors (flat ceilings) and not air sealed very well – so I figured it would test out to be very leaky even though I had shot 16 cans of air sealing foam into various openings around the perimeter in the past year.
The process started with a call to an energy auditor. I used BMC’s Energy Auditing division, and after scheduling a visit, which had to be rescheduled due to poor weather, Josh Peterson and Alex McIntyre came to my home with a few pieces of equipment about the size of large suitcases, a ladder and a clipboard. The audit started with an inventory of the appliances and light fixtures in my home. The windows were measured, the walls and doors were classified and measured, and exterior conditions such as shading, solar orientation and roof reflectivity were noted. They were gathering information about the shape and makeup of the house to input the information into an energy usage calculator too.
Next came about 20 minutes of questions about how we use the home and it’s appliances. The answers to these questions were for the same energy usage calculator, and would help the calculator program understand how much a particular appliance would typically use due to our family’s behavior. For example, our oven uses 2500 watts and our TV uses 175 watts. It’s easy to see which one uses more power at a given moment when they’re on, but since the TV is on 8 hours a week in our house and the oven is only on for about 30 minutes on average (once it’s up to temperature the heating coil switches off and on) we see that the TV is the larger user of power over the course of a month. If you have your previous year’s electric and gas bills handy, they are helpful to compare the modeled energy usage with the actual energy usage in your home.
Although the actual modeling is done back at BMC’s office, when we received the report we noticed a large difference between what the computer program said my family uses and what our actual use is. Since I am a geek and needed an excuse to put my electrical engineering degree to work, I set out to find out why with Josh and Alex’s help. Part of the difference was our PV array that powers most of our home’s small appliances and lights, but we also noticed that some large wattage appliances like the oven, toaster oven, microwave oven and hairdryers are easy to overestimate due to the fact that their wattage draw varies during usage. If we estimated 4 hours of oven usage the actual time the heating element was on would make a big difference in the actual wattage used. I was able to use an energy monitoring computer I have installed in my home to determine the average wattage our oven uses is 1000 watts per hour if cooking something for at least an hour, even though the coils use 2500 watts. The heating coils were cycling on and off once the set temperature was reached.
For items like the water heater, which may be rated at 4500 watts but mostly only runs when hot water has been used, the modeling software uses averages as determined by the Department of Energy. I found that our actual usage is lower than the averages, which could be because our water pressure is set low to save water and help our well pump, which doesn’t have to work as hard, plus our showers are short because of tight schedules in the morning, and we don’t run the water long to warm up the shower since our most used bathroom is right above the water heater. The DoE averages were fine for the purpose of the audit, however. I just wanted to see why our numbers were different.
The next part of the audit was the most fun. Thermal imaging cameras are like an X-ray machine for a home – they can detect and display temperature differences in materials – so for instance, if you look at a door you can see that the door is cooler than the surrounding walls (because it’s thinner and less insulated) and you may see air streaming around the edges of the door – leakage – that you can’t normally see and might not even feel. Josh went through the whole house, including the attic, viewing the walls, ceilings and floors to determine where there was temperature difference, and therefore, energy transfer (loss) Part of the reason we had to reschedule is that this particular part of the Audit requires a decent temperature difference between inside and out, and a calm day is helpful. A rainy, windy day with the outside temperature the same as the inside temperature is not the ideal condition for testing. The camera stores images just like a digital camera – so the worst places with energy loss were photographed and placed into the final report. We also took the time to look at some places where loss was particularly bad while the blower door was running to see the path that some leaking air was taking to get in the house – this allowed the option of sealing both ends of the leakage path rather than just the part we could feel inside the house.
The next test performed was to measure the duct leakage, which is critical in Central Texas due to the fact that most homes have their air handling equipment and ductwork located in the attic. Duct leakage can pull 120-140 degree attic air into the house, or create negative pressure which pulls that air or hot, humid outside air into the house through gaps and cracks in other parts of the home. A newly built home should have less than 10% duct leakage, but most older homes have much greater leakages – as much as 30-40% of the air could be wasted due to torn ducts or connections that have come loose. The duct leakage test was performed by Josh and Alex covering all of the registers and the return air grill in the house, then attaching a fan that pulls the air out from the duct system. A computer calculates the total airflow being "sucked" from the ducts, and based on the size of the AC system, the auditor can then calculate the leakage rate during normal system operation. My home has a very worn and leaky duct system that I’ve had to repair numerous times in the two years I’ve lived here. The ducts are in need of replacement due to the insulation material (fiberglass) falling off of the ducts due to the decay of the outer jacket. My main repair technique has been to wrap the broken ducts in new insulation and to seal them with aluminum foil tape to seal them up until we replace the whole system. We were rather shocked to find that the house was only leaking about 11-12% of it’s air. Apparently I did a pretty good job sealing up the leaks, but we could still see some major leaks with the thermal imaging camera. We re-tested the duct leakage by "blowing" air into the duct system just to double check our figures, and the results were the same.
Finally – the big test. The blower door test is similar to the duct leakage test, but on a larger scale. It measures the total leakage into the house from all sources other than the ductwork. This includes gaps around building materials like the exposed wood beam in my master bedroom, the cracks around windows and doors, and unknown sources – such as the vent duct under our kitchen floor for a downdraft range that was never installed. For the blower door test, the house is completely closed up and all interior doors are opened. One door of the home is then opened, and a tent-like apparatus with a metal frame and fabric panel with a large fan in it is installed in the opening. Pressure sensors then determine the airflow into the house just like the duct leakage test. The results are compared with the size of the house, and a figure is arrived at that shows the total air changes per hour. I was expecting my house to leak quite a bit due to errors in it’s construction, and the test did not disappoint. Every 8 minutes, my home can completely exchange it’s air with the outside air while pressurized. The test takes place with the house pressurized as if there is a 20 mph wind acting on all sides of the house, so it’s easy to understand why in the winter, with 30+mph winter winds coming up the hill toward my house, that the house can be so difficult to keep warm!
Once all of the testing was complete, Alex and Josh went back to their office and compiled the results into a comprehensive report. The report was in several sections, including energy consumption patterns, energy efficiency upgrades, (suggestions for improvements) results from the duct leakage and blower door tests, and the IR (thermal imaging) camera photos. Along with each section was information from the DoE with suggestions for improvements, with explanations written for the "normal" consumer who may not be an electrical engineer energy geek like myself. The report was personalized with suggestions based on the usage patterns of my family, and not just the national averages.
So what did I learn from the report? The biggest lesson was that most of the leakage in my house was through the interior, not the exterior walls and windows and doors where the builder had focused all his energy and effort in ’81. We found that the interior walls were letting in most of the leakage through interior electrical outlets (the ones in the outside walls were sealed) and through door casings and baseboard trim. The IR camera confirmed that this air was coming from the attic and between the first and second floor, which was not sealed from the outside when the house was built and which effectively made worthless the extra money originally spent on "upgraded" windows.. Because of these air leaks, any insulation present in these areas is worthless, because the air just goes around it and it might as well not be there. The solution is to partially disassemble the house and seal up the perimeter framing with spray foam, which will unfortunately mean the removal of part of the ceiling in nearly all of the rooms in my home. The Audit has told me however, that the payback in utility bill savings will be very long since we’re already using less than average amounts of energy to run our home. The decision to spend the money to make these upgrades will need to be justified by our comfort – reducing drafts and cold floors in the winter, and better temperature control in the summer.
The comprehensive energy audit allows us to decide how to spend our upgrade money and plan repairs in the future. We would like to remodel the interior in the next few years, and we now know that we should plan to remove some of the perimeter ceilings to fix the leakage in the floors and ceilings. We also know that we can continue to use our current forced air heating and cooling system until the end of it’s useful life, because replacement of the current system will not save us much energy due to reasonably low leakage and our minimal pattern of usage. Our plan is to schedule additional blower door and thermal imaging camera tests in the future after we make upgrades, to keep track of our progress and to make sure we’ve done all we can to tighten up our home and reduce energy usage with that project.
Thank you to BMC, Josh Peterson and Alex McIntyre for indulging my need to explore the inner workings of the audit process while conducting the audit on our home. In addition, I had invited others to observe the process, and Josh and Alex generously shared their knowledge and showed everyone how the equipment works and what they were looking for during the tests.
To obtain a copy of the test results and the audit report, please email me at email@example.com and put "Energy Audit" in the subject line. Three PDF documents from the audit. (about 2.5mb total) will be sent to you. Thank you for your interest!