Test Procedures and Tools

This page describes some of the most common tests we perform while conducting an energy inspection and analysis.  During the “house call” to your home we decide which tests are appropriate given the construction, types of equipment and potential problems we find in your house.  For example, a home with hot water heating radiant floors does not need a duct test, because there are no ducts.  A home that has an odor of combustion gas must be tested for carbon monoxide for safety reasons, even if the combustion appliances are in the garage. A home with a new sealed combustion furnace and water heater does not need a backdraft test.

 Blower Door Test 

Except for some recently built homes, most homes in California are quite leaky.  Air that you have paid to heat or cool escapes from narrow cracks and larger holes in attics, joints between walls and floors or ceilings, electrical outlets, recessed lighting and heating ductwork and many other hidden areas. That air is replaced by unconditioned air from outside. In a leaky house, it’s like you are continuously throwing dollar bills into a burning fireplace.  Furthermore, depending on where leakage air is drawn in from, it can contain dust, odors, insulation fibers, radon, pesticide residues, mold or other undesirable substances from under the house. 

A certain amount of fresh air ventilation is needed for health and safety. However, most houses leak several times the needed amount.  It is true that there are indoor pollutants that need to be flushed out, but only a certain flow of air is needed for this purpose. As in many health matters, more is not necessarily better. The most efficient approach is to test for and eliminate pollutants and then seal the house tighter. We usually conduct a blower door test in which we depressurize the whole house and measure the amount of air that escapes through the leaks in the house in cubic feet per minute at a pressure of -50 pascals.  Our test is conducted using the Minneapolis Blower Door, shown to the right.  When we find high leakage, we usually recommend that the leaks be sealed.  This is often a very cost effective project.

After knowing the leakage rate of your house, we calculate and report the minimum natural ventilation, required under the California Energy Code, so that you know when your sealing project has reached a good stopping point.  The current standard for minimum ventilation rate is .35 changes of all the air in house per hour, (about one complete air change every three hours) or 15 CFM per person, whichever is greater. We calculate the volume of air in your house using the conditioned floor area and average ceiling height and use this in calculating your required ventilation rate.  A conversion factor converts leakage at our artificially high test pressure, to leakage ventilation occurring under typical natural conditions. In 2010, a new California energy code will require that most new houses have fan-assisted ventilation.

The chart below shows guidelines for sealing. You can find your measured leakage rate reported above on this chart. 


Approximate Guideslines for Air Sealing


Estimated Leakage Area

Converting our estimated leakage value, we calculate the area of a single large leak that would have the same leakage rate as all the little hidden leaks in your home combined. [ELAsqft = .055 * CFM50H / 144 ].  We often find leaks equivalent to leaving a window open all the time.

Blocked Return Paths

Your central heating system is designed to recirculate air.  Heated air that is distributed by ductwork to the registers in rooms, heats those rooms. Then the air must find its way back to one or more return registers, usually centrally located, so it can be reheated.  If the way back is blocked by closed doors or other obstacles and no other return path exists then the air will escape around windows, recessed lighting fixtures, electrical wall sockets and other hidden cracks, wasting its heat.  This forces the furnace to draw new cold air through other cracks that must be heated to replace the lost air.  The same process operates when a central air conditioner is running.  The problem often happens when people close their bedroom doors at night.  Alternatively if the room is tightly sealed and also blocked by a door, then pressure builds up and supply air cannot get into the room – the room may remain too cold or hot, even with its register wide open and the furnace running continuously. We test for these conditions using the manometer shown to the right.

Rooms that have supply registers but no return registers can use a return path under the door to the rest of the house, if the door is cut short enough at the bottom to provide an inch or two above the floor or carpet as a return path.
  Alternatively, you can install a special return register that connects the two spaces, or run a return duct to the room or install a “jump duct” with registers on either side of the wall.

Duct Leakage

PG&E studies have shown the average California home’s ductwork leaks 30%, representing an enormous waste of energy and money, as shown in the diagram below.  When energy prices were lower and there was no awareness of global warming, homeowners and builders did not pay to have ducts well sealed.  Venerable old fabric duct tape that may have been used for sealing may have dried out, peeled off and cracked.  Codes now forbid the use of fabric duct tape and require the use of a special mastic, and/or aluminum tape for sealing.

We conduct a test to determine leakage of your ducts by attaching an Energy Conservatory Duct Blaster device to your ducts, shown to the right, after sealing off all the registers but one, where the tester is attached.  When necessary, we measure only the leakage of ducts to the outside, since leaks to the inside of the house still contribute to warming or cooling the house and do not drive envelope leaks.

The guidelines below help you determine how much effort and money to put into duct sealing, depending on our measured leakage rate, which you can find above. Bigger or smaller duct systems can be expected to show higher or lower readings.

Approximate Guideslines for Duct Sealing

Electrical Load Measurements

DENT ElitePro DataloggerTo find out which of your electrical equipment is drawing excessive amounts of electricity we use various electrical meters and loggers.  With equipment that turns on and off automatically, like refrigerators, forced air heating blowers, pool pumps and well pumps, we are interested in the average consumption over a period of time, so we program dataloggers with a laptop computer and connect them to your electrical panels. We leave them for a period of days or weeks.  Then we return to collect and analyze the data.  We can thus accurately measure just how much money and energy each piece of equipment is using.  Then we can work with you to reduce loads by specifying needed repairs, modifying timer schedules, or recommending more efficient equipment. We own several loggers and PG&E loans us all the other datalogging equipment we need, even for large jobs, such as the DENT ElitePro equipment shown to the left.

Insulation Measurement

We determine the type, condition and insulation value of insulation in your walls, ceiling and floor by looking in your attic and crawl space and probing behind electrical outlet covers in walls.  When an area is inaccessible, we can take inside and outside temperature measurements that allow us to estimate the effective insulation value of a wall, using an infrared temperature gun like the one to the right.  We also look at how difficult it would be for a contractor to improve your insulation.

Carbon Monoxide Testing

We measure parts per million of carbon monoxide (CO) near furnaces, water heaters, boilers and other combustion appliances that burn fossil fuels, using the Bacharach Monoxor III instrument, shown to the left. CO is a combustion product, resulting from escaping flue gasses and/or incomplete combustion of appliances that burn fuel.  It is odorless, colorless and toxic.  However, when it is the product of incomplete combustion, it is often present in combination with other gasses than can be smelled.  In low concentrations it leads to drowsiness, headaches and sometimes nausea.  In high concentrations it leads to brain damage and death.  The Environmental Protection Agency recommends a level of 9 ppm as the maximum for safe exposure over an 8 hour period.  As a rule of thumb, if you can smell anything when a gas-fired appliance is working, you should call a professional, leave windows open for ventilation until the problem is fixed.  We may also measure the CO content of undiluted flue gas within the flue itself.  If we measure more than 100 ppm, it is an indicator of incomplete combustion which is inefficient, polluting and dangerous.  Incomplete combustion has many possible causes, so when we find it we recommend that the appliance be immediately serviced by a professional.

Furnace and Water Heater Inspection

We usually open up your furnace and examine the air filter, the blower and the contractors' workmanship, particularly where sheet metal parts are taped and screwed together.  This is often a large source of air leaks.  The photo to the right shows a buckled plenum where it joint the furnace and the joints were not sealed in any way making a big leak.   Dirty filters and blowers are a common source of inefficiency.  We check your water heater for leaks and signs of backdrafting and incomplete combustion. We confirm that both appliances have a sufficient source of combustion air and look for ways to make sure that the combustion air can be drawn from outside the house. We note down the model numbers so we can look up the efficiencies and determine your possible benefits from upgrading to a high efficiency appliance.  If you appliances have "gravity" flues that are open to the indoor air, we conduct a backdraft test using the manometer shown above to make sure flue gasses cannot be drawn indoors. sickening you and potentially causing a fire.

Relative Humidity Indoors

We often test the air inside and outside your house for moisture content (humidity) using a psychrometer, after making sure that no indoor activities such as boiling water or taking a showers temporarily raise.  People are generally healthiest, unless they have specific medical conditions, in a limited range of humidity as shown in the chart below. Excessive moisture encourages the growth of mold, mildew and wet rot in and around the home, as well as bacteria, viruses, fungi and mites that infect humans.  It can also cause condensation of water on windows and other cool surfaces.  Excessive dryness can cause respiratory problems and the formation of ozone, which is toxic in high concentrations. One tool we might use to measure humidity is the General DLAF8000, shown on the right, a combination tool that includes a psychrometer, anemometer, light meter, and thermometer.


Our humidity measurements, taken only at one time of day in one season, do not tell the complete story.  Humidity problems are often seasonal and vary with time of day, so that if you have a stubborn problem, it may be necessary to make measurements during different seasons to arrive at an optimal solution.  There are logging humidity analyzers for professional use that can record changing humidity levels over a period of time.  There are also consumer “weather stations” that contain a measurement of relative humidity that you can use yourself.

Some photos and diagrams courtesy of The Energy Conservatory, Inc. – used with permission. Copyright (c) 2010 by Home Energy Saving Analysts. All rights reserved.