Since its introduction to the United States in the late 70s, use of blower doors has been confined largely to building science researchers, utility-sponsored weatherization programs, and a few enlightened insulators. While only a fraction of United States heating and cooling contractors actively use blower doors in the field, they're a common tool among many of our European trades counterparts.
If you've read the occasional trade article espousing the benefits of blower door testing, and have always thought that the blower door just wasn't for you, maybe it's time to give it a second look. The benefits of blower door testing are multifold, and the contractors that have adopted its use are employing it in a variety of creative, valuable ways to strengthen the bottom line and improve quality of service to their customers.
Some HVAC outfits now offer energy audits, or comprehensive whole-house assessments as an additional stream of income. For typical homes, energy audits that include blower door testing usually take 30 minutes to three hours, with many contractors charging prices as low as free (as part of an estimate), or has high as $1,000, depending on the market, additional procedures performed, the depth of analysis, or whether specialized software modeling and/or detailed reporting is involved.
Pointing out the sources of drafts and leaks, and the ability to quantify them in terms of actual dollars lost, is a powerful tool in any sales situation. With blower door testing, you're no longer going to claim energy savings, you're going to measure it. Additionally, the blower door helps uncover hidden problems that normally go unnoticed by other contractors, which provides more opportunities to offer solutions and increase sales.
Knowing a home's leakage rate improves the accuracy of heating-load calculations, ensuring properly sized equipment and optimum long-term performance. And instead of selling bigger appliances, sell smaller ones. By identifying problems with insulation or air leakage, and facilitating their repair and improvement, heating loads can be reduced. This gives homeowners an opportunity to downsize equipment and lower the cost of replacement.
And if a customer should complain of being too cold or too hot - and you know you've sized the appliance right - a blower door test can show the homeowner that they've been a victim of air leaks or shoddy insulation, not an undersized HVAC system.
A small rubber hose connects the pressure/flow sensors in the blower to a handheld manometer (Figure 3). A second hose connects the manometer to the outside.
To get a whole-house air leakage reading, first a base pressure reading is taken, measuring the pressure difference between the inside of the house (at the blower door location) and the outside. All windows and doors should be closed, as well as the fireplace damper to prevent soot from being sucked into the room. All combustion appliances should be turned off to avoid back drafting.
Noting the base pressure readout in the manometer, the blower is then turned on (fan should be pointed to the outside) to create a negative pressure 50 pascals (Pa) below the base pressure.
Once the house is fully depressurized to -50 Pa, make-up air equivalent to the force of a 20 mph wind will force its way in through the leaks, cracks, and gaps of the home.
With the blower door running, a walk around the home will help reveal sources and locations of major air leaks. A smoke puffer (Figure 4) can be used to reveal and trace air movement.
The manometer is then switched from the pressure reading display to the flow reading setting. The flow reading setting will provide the home's overall air leakage rate (Figure 5), expressed in cubic feet per minute (cfm). If the home's volume is known, this reading can then be quickly converted from cfm - of natural ventilation - to air changes per hour (ACH), which is used to determine the home's mechanical ventilation requirements.
Some state energy agencies and gas and electric utilities offer a variety of energy-efficiency programs aimed at trade contractors. In addition to providing technical training, some programs offer generous equipment purchasing and leasing programs.
In New York, for example, the Home Performance with Energy Star program (www.getenergysmart.org), the state's utility ratepayer-funded energy-efficiency program, offers an equipment "forgiveness" clause to contractors' participation agreements. Contractors that conduct a specified number of "comprehensive home assessments," or energy audits, through the program are relieved of a significant portion of their loan obligations on purchased equipment.
A directory of training programs is available from the Residential Energy Services Network (RESNET) Website (www.natresnet.org).
Training courses and equipment are also available through blower door manufacturers directly, as well as trade organizations, such as the National Comfort Institute (www.nationalcomfortinstitute.com).
2. Manual-J software: Rule-of-thumb heat-load methods often lead to equipment oversizing that robs the effectiveness of your installations. From appliance sizing to designing distribution systems, Manual-J software is critical to getting your install right - the first time. Several software makers offer robust, bundled packages that include useful tools and features that can take your entire HVAC project from point-of-sale to final commissioning.
3. Laptop computer: Heat-load calculations, radiant design software, duct calculators, in-home sales presentations, data logging - laptops are as invaluable in the field as in the office.
4. Blower door device: Use of blower doors among Americans has been largely confined to the weatherization/energy auditing crowd. By measuring a building's actual leakage rate (air changes per hour), contractors can calculate loads more accurately, determine proper mechanical ventilation needs, and point out thermal weaknesses in the building envelope. Have you ever been called back because a shoddy insulation job left your customer cold? Blower doors end finger pointing.
5. Combustion gas analyzer: You simply can't tune appliances without them. If you're not testing, you're only guessing. In the realm of combustion safety, one bad guess can lead to unthinkable catastrophe. If there's only one of these tools you can have, this is the one.
Raised in the contracting environment since birth, John Bishop is vice president of Enhanced Living Inc. (www.enhancedliving.net), his family's HVAC contracting and building science consultancy based in Troy, N.Y. With extensive experience in building science, public policy, and marketing, he was formerly the state marketing coordinator for New York's Home Performance with Energy Star and Energy Star Labeled Homes programs. He also served as press secretary to U.S. Rep. John E. Sweeney (R-N.Y.). Bishop can be contacted at email@example.com.
Publication date: 01/23/2006