2014 February Newsletter

Online Spring Courses Available in Energy Resource Management

Davis, Calif.— Explore UC Davis Extension’s online spring courses in Energy Resource Management. Visit our website for a full listing of courses and to learn about the online certificate program in Energy Resource Management.

ONLINE: Energy Resource Management: Supply
•     Enroll now through April 7 and complete by June 16. Passwords will be issued on March 31.
•     $1,495 ($1,645 if postmarked after 03/24/2014). Enroll in section 134ERM102.

ONLINE: Energy Resource Management: Leadership
•     Enroll now through May 19 and complete by June 20. Passwords will be issued on May 6.
•     $1,495 ($1,645 if postmarked after 03/16/2014). Enroll in section 134ERM105.

For more information or to enroll, call (800) 752-0881, email extension@ucdavis.edu or visit our website.

www.extension.ucdavis.edu/erm

UC Davis Extension, the continuing and professional education division of UC Davis, has been an internationally recognized leader in educational outreach for individuals, organizations and communities for more than 50 years. With more than 50,000 annual enrollments in classroom and online university-level courses, UC Davis Extension serves lifelong learners in the growing Sacramento region, all 50 states and more than 100 countries.

• Duct leaks are very common; in many homes, duct leaks are responsible for significant energy losses.
• For ducts located in an unconditioned attic, any leaks in the supply system tend to depressurize a house, while return-system leaks tend       pressurize a house.  Either condition can cause problems.
• Duct leaks outside of a home’s thermal envelope waste more energy than duct leaks inside a home’s thermal envelope.
• Even if ducts are located inside of a home’s thermal envelope, duct leaks can still connect to the outdoors.  For example, supply system leaks in a ceiling between the first and second floors of a two-story home can pressurize the joist bay, forcing conditioned air outdoors through cracks in the rim joist area.
• It’s much easier to seal duct seams during new construction than in an existing house.

Characteristics of a good duct system
A good duct system:

• Has been designed to meet ACCA Manual D requirements, with each duct carefully sized to provide the airflow needed to meet room-by-room heat loss and heat gain calculations;
• Has been designed so that duct runs are as short and straight as possible;
• Does not use building cavities (for example, panned joists or stud bays) as ducts;
• Locates all ducts within the home’s thermal envelope;
• Includes ducts or air paths that allow return air to flow back to the air handler from every room with a supply register;
• Has all seams sealed with duct mastic; and
• Has been tested for duct leakage.

Code requirements for duct sealing
Although model codes have included duct-sealing requirements for years, enforcement has been spotty or nonexistent.  For example, a 2001 study of 80 new homes in Fort Collins, Colorado, found that the number of homes that complied with code duct-tightness requirements was zero.  Astonishingly, the average duct leakage in the studied homes was 75% of total system airflow.

Another 2001 study found that Massachusetts Energy Code requirements for duct sealing were widely ignored.  Researchers who inspected 186 new Massachusetts homes reported that “serious problems were found in the quality of duct sealing in about 80% of these houses.”

The 2006 International Residential Code (IRC) requires (in section N1103.2.2) that “Ducts, air handlers, filter boxes and building cavities used as ducts shall be sealed.” Elsewhere, in section M1601.3.1, the IRC requires that “Joints of duct systems shall be made substantially airtight by means of tapes, mastics, gasketing or other approved closure systems.” Hardware-store duct tape is not an approved tape.

Mandatory testing
Builders will soon need to get up to speed on duct testing, since recent code changes will require that all residential duct systems except those that are located entirely within a home’s thermal envelope will need to be tested for leakage.

If some ducts are outside of the thermal envelope, the 2009 IRC will require duct tightness to be verified by either a “rough-in test” or a “post-construction test.” Either test requires all register boots to be taped or otherwise sealed during the test.

The threshold for the rough-in test is total duct system leakage of 6 cfm per 100 square feet of conditioned floor area (when tested at 25 Pascals).  If the air handler is not installed, the total leakage must be less than or equal to 4 cfm per 100 square feet of conditioned floor area.

The threshold for the post-construction test is duct system leakage to outdoors of 8 cubic feet per minute (cfm) per 100 square feet of conditioned floor area when tested at 25 Pascals.  Alternatively, total duct system leakage must be less than or equal to 12 cfm per 100 square feet of conditioned floor area.

Testing for duct leakage
Energy auditors have developed several methods for testing duct tightness.  These methods vary from fast and dirty to time-consuming and accurate.  Builders interested in tight duct systems should familiarize themselves with the range of available duct testing options:

• Using only a blower door;
• Using a blower door and a pressure pan;
• Using a Duct Blaster;
• Using a Duct Blaster and a blower door; and
• Using a theatrical fog machine.

A fast, rough test
In Residential Energy, authors John Krigger and Chris Dorsi describe a quick (but not particularly accurate) method for estimating duct leakage: “The simplest way to estimate duct leakage in cfm50 is to perform two blower-door tests: one with the home’s registers sealed with paper and tape, and one without.  Subtracting the two readings provides a very rough estimate of total duct leakage.”

Because of the inherent inaccuracies of this method, it is rarely used.

The pressure-pan method
A pressure pan is a diagnostic tool consisting of a metal pan (similar to a cake pan) connected by a tube to a manometer (that is, a pressure gauge).  The device is used to temporarily cover a forced-air register to measure the pressure exerted on the pan by a blower door.

To conduct a pressure-pan test, you need a pressure pan and a blower door.  Here are the basic steps:

• A blower door is used to depressurize the home to 50 Pascals.
• The air handler fan is turned off.
• The tester then blocks each register (one at a time) with the pressure pan and records the reading of the pressure-pan manometer.  (The                manometer shows the pressure created by air leaking into the duct system.) Typical readings of the duct system pressure (with                respect to the house pressure) range from 1 Pascal to 45 Pascals.
• The higher the reading, the leakier the duct run.

In a Home Energy magazine article, “Pressure Pans: New Uses and Old Fundamentals” (January/February 1998), Jeffrey Siegel and Bruce Manclark explain, “A duct system at 0 Pa is entirely within the pressure envelope of the house and has no leaks to the outdoors.  A system approaching 50 Pa is essentially outside the pressure envelope, meaning that it has catastrophic leakage to the outdoors.”

It’s important to note that the pressure pan readings don’t really provide measurements of duct leakage; rather, they provide a method for comparing the relative leakiness of several duct runs in the same home.
That hasn’t prevented some energy experts from recommending thresholds for pressure-pan measurements.  According to Krigger and Dorsi, “Registers of newly installed ducts should read less than 0.5 Pascals and existing duct registers should read less than 1 Pascal after being sealed.”

In “Duct Improvement in the Northwest,” (Home Energy magazine, January/February 1996), author Ted Haskell provides this advice for existing homes: “Houses with fewer than three pressure-pan readings above 2 Pa are unlikely to be cost-effective to seal.”

The pressure-pan test has several virtues.  First, it is fast — especially when an auditor is already conducting a blower-door test.  Second, it identifies which of a home’s duct runs are the leakiest, so that a contractor knows where to focus duct-sealing efforts.

However, many experts warn contractors not to jump to conclusions based only on the pressure readings recorded during a pressure-pan test.

As with many other diagnostic tests — infrared scanners come to mind — it takes an experienced auditor to interpret the results of a pressure-pan test.  “Pressure-pan readings are difficult to interpret, and the same number can reflect quite different leakage rates in different houses,” wrote Siegel and Manclark.  “The disadvantage of the pressure-pan test is that it is more art than science.  The one exception is when homes have very similar duct geometry and installation, as is the case with manufactured homes or identical homes in a subdivision.”

The Duct Blaster test
The most common method for testing the tightness of a duct system is the duct-blower test (also known as the Duct Blaster test).  A duct blower resembles a miniature blower door; the most common brand is the Duct Blaster, manufactured by the Energy Conservatory in Minneapolis.

Here are the steps:

• All supply registers and return grilles are sealed with polyethylene and tape.
• The air handler fan is turned off.
• The Duct Blaster is set up and attached to the duct system (near the furnace or at a large return-air grille).
• The manometer’s reference probe is inserted into the air handler plenum.
• The Duct Blaster is turned on to pressurize the duct system to 25 Pascals (a pressure which represents typical operating pressures for forced-air systems).  The airflow through the Duct Blaster fan (which is displayed in cfm on the Duct Blaster’s manometer) equals the flow escaping through leaks in the duct system.  The results are reported as “cfm @ 25 Pascals” or “cfm25.”

Although this test reveals the leakiness of the duct system, it doesn’t tell the tester where the leaks are located; nor does it quantify what percentage of the leakage is leakage to the outdoors.  Moreover, it doesn’t tell us how much a duct system leaks under normal operating conditions — conditions which may differ from Duct Blaster pressurization to 25 Pascals.

According to Krigger and Dorsi, “Leakage ranges from less than 50 cfm25 for a fairly tight duct system to more than 500 cfm25 for a very leaky duct system.”

Builders hoping to comply with the 2009 IRC duct-testing requirements will need Duct Blaster test results showing total duct leakage equal to or less than either 6 or 12 cfm (depending on whether it is a rough-in test or a post-construction test) per 100 square feet of conditioned floor area.

Using a Duct Blaster to test duct leakage to the outdoors
Energy auditors often want to know how much of a duct system’s leakage is leakage to the outdoors.  Leakage to the outdoors can occur when air escapes through a leak in a duct installed in an unconditioned attic.  It is also possible for a portion of the leakage through a duct that seems to be within a home’s thermal envelope to turn out to be leakage to the outdoors, since such leaks can pressurize joist bays, forcing conditioned air through rim-joist cracks.

One quick-and-dirty indication that a duct system has sizable leaks to the outdoors occurs when an auditor notices obvious air flow from forced-air registers during a blower-door test.  Since the house is strongly depressurized, the airflow represents exterior air; and since it’s coming from the duct system, the airflow is a sign that the duct system has leaks that connect with the outdoors.

To determine how much duct leakage is leakage to the outdoors, a tester needs a blower door and a Duct Blaster.  Here are the steps:

• A blower door is set up in an entry door.
• All supply registers and return grilles are sealed with polyethylene and tape.
• The air handler fan is turned off.
• A pressure tap is temporarily installed in the duct system to measure the pressure of the duct system with respect to the house.
• Another manometer or tube is set up to measure the outside pressure with respect to the ducts.
• The Duct Blaster is set up and attached to the duct system (usually near the furnace).
• The blower door is turned on and the house is pressurized to 25 Pascals.
• The Duct Blaster is turned on to pressurize the duct system; the Duct Blaster fan is adjusted until there is no pressure difference between the ducts and the house.  At that point, all of the air going through the Duct Blaster is going outdoors through duct leaks.  The airflow indicated on the Duct Blaster’s manometer (in cfm) quantifies that duct leakage to the outdoors.

Obviously, duct leaks to the outdoors represent heating or cooling energy that is lost.

Testing ducts with a fog machine
To find the location of duct leaks, nothing beats a theatrical fog machine.

Gary Nelson, the founder of the Energy Conservatory, describes the method: “You tape up all the registers and you pressurize the ducts.  Then you introduce fog into the Duct Blaster — you aim the fog nozzle at the fan blades, without letting the fog get drawn into the vent holes in the motor, and you watch where the fog pours out.  Sometimes you may be working with an HVAC contractor who says, ‘This is a good duct system.  This is the way we have always done it.  This is normal.’ Well, when you show them the fog coming out of the leaks, they shut up really fast.”

For more information on this technique, see “Pinpointing Leaks With a Fog Machine.”

Sealing the leaks that matter most
The mechanics of duct sealing are beyond the scope of this article, but it’s worth noting:

• Duct seams need to be mechanically fastened (using sheet-metal screws for galvanized ducts and compression straps for flex duct) before being sealed.
• For sealing most duct leaks, mastic works better than any tape.  (Bruce Manclark calls tape “the band-aid of the HVAC industry.”)
• Mastic is messy, so wear old clothes when you apply it.
• Install mastic “as thick as a nickel.”
• Cracks or seams wider than 1/8 inch need to be repaired with fiberglass mesh as well as mastic.

It’s important to prioritize duct-sealing efforts so that the most important leaks are addressed first.  As Philip Fairey, the deputy director of the Florida Solar Energy Center, likes to say, “Duct leakage is like real estate — it’s all about location, location, location.”

• In existing homes, it’s surprisingly common to find disconnected duct components — takeoffs that are coming loose from ducts or ducts disconnected from register boots — in attics or basements.  Such disconnected ducts can waste tremendous amounts of energy.
• Leaks connected to the outdoors are more important than leaks inside the home’s thermal envelope.
• Holes that see high pressures — in other words, holes near the air handler — are more important than distant holes that see relatively low pressures.  Bruce Manclark’s mantra is, “Follow the pressure: boots for show, plenums for dough.”
• Most furnaces have many bad leaks close to the blower fan, including leaks in the furnace jacket seams, leaks between the furnace and the plenums, and leaks between the duct takeoffs and the plenums.
• Supply system leaks waste more energy than return system leaks.

For more information on sealing duct leaks, see Duct Tape and Mastic.

Measuring air flow
Anyone who commissions a duct system needs to learn how to measure airflow at registers and grilles.  Manufacturers offer an array of accurate (and expensive) instruments to measure airflow.   However, builders who need to troubleshoot problems may be interested in several low-cost methods of measuring airflow:

• The August 2002 issue of Energy Design Update describes how to build a homemade flow hood using a cardboard box and a $90 digital anemometer.
• Two Lawrence Berkeley National Laboratory engineers, Iain Walker and Craig Wray, have written a paper describing a method of measuring airflow with a “calibrated” laundry basket and a manometer.
• Terry Brennan promotes a method of measuring bath exhaust fan airflow with a cardboard box and a credit card.
• The easiest way to measure airflow at a supply register is the garbage bag technique developed by Don Fugler of the Canada Mortgage and Housing Corporation.

Duct testing is coming to your job site — soon
For decades, plumbers have routinely tested newly installed supply and drain pipes.  Meanwhile, most HVAC contractors have gotten away with leaky, untested duct systems.  However, the tide is now turning.   In the future, testing residential duct systems for leaks will become a routine part of residential construction.

• The 2006 IRC section                N1103.2.2 requires that “Ducts, air handlers, filter boxes and                building cavities used as ducts shall be sealed,” while IRC                section M1601.3.1 requires that “Joints of duct systems shall be                made substantially airtight by means of tapes, mastics,                gasketing or other approved closure systems.” Hardware-store                duct tape is not an approved tape.
• Section 403.2.2 of                the 2004 International Energy Conservation Code (IECC) requires                that “All ducts, air handlers, filter boxes, and building                cavities used as ducts shall be sealed.”

To learn how to test residential duct systems for           leaks, see Duct           Leakage Testing.

All about           mastic
Most energy-conscious builders seal duct joints with mastic. Mastic           is a gooey, non-hardening material with a consistency between           mayonnaise and smooth peanut butter. Duct joints should always be           secured with #8 sheet-metal screws before seams are sealed with           mastic.

Sealing duct seams is messy work, so wear old clothes. The mastic is           spread over duct seams with a disposable paintbrush, putty knife, or           your fingers. (If you spread mastic with your fingers, wear rubber           gloves.)

Gaps in ductwork or plenums that are over 1/16 or 1/8 inch wide can           be sealed with mastic as long as the gap is first reinforced with           fiberglass mesh tape. If you’re using mastic to seal seams in           fiberglass board ductwork, use fiberglass mesh tape for all joints.

Sources of           mastic
Manufacturers of mastic include: Hardcast           (Versi-Grip 181 mastic), McGill           AirSeal (Uni-Mastic 181), Polymer           Adhesives (AirSeal #22), RCD Corporation (#6 Mastic), and ITW/TACC           (Glenkote mastic).
Among the distributors of AirSeal #22 mastic is AM           Conservation Group.

All about           duct tape
Since common hardware-store duct tape — technically known as           cloth-backed rubber-adhesive duct tape — fails quickly when used on           ducts, most energy-conscious builders seal duct joints with mastic.           Although mastic works well on galvanized steel ductwork, it has its           disadvantages: it is messy to apply and awkward to use on clamped           flex duct joints.

According to section 503.3.3.4.3 of the International Energy           Conservation Code (IECC), any tape used on duct board or flex duct           must be labeled in accordance with UL 181A or 181B. In most regions           of the U.S., however, local inspectors have little or no interest in           the leakiness of residential ducts, and duct tape labels are rarely           checked for UL compliance.

“I’ve been to wholesale distributors in Ohio, and I don’t see them           displaying anything with UL markings,” says Mark Pulawski,           former cloth tape market manager for Intertape Polymer Group, a duct           tape manufacturer in West Bradenton, Florida. “When I ask them, ‘Where           are your UL products?’ they say, ‘We don’t sell any of those.’ They           hold up a roll of [cloth] duct tape, and they say, ‘This is what the           guys use.’”

Does UL           181 duct tape perform any better?
In some areas, however, building inspectors insist that duct tapes           sport a UL 181 label. Yet the UL 181B standard alone is no guarantee           of long-term tape performance. “The UL 181 listing is more of a           smoke-and-flame listing,” says Bob Davis, an energy consultant for           Ecotope in Seattle. “The testing doesn’t have much to do with whether           it will work as a duct sealant.”

At least four different types of tape have met the UL 181B standard,           including some cloth-backed rubber-adhesive duct tapes, foil-backed           tapes with acrylic adhesive, oriented polypropylene (OPP) tapes, and foil-backed           butyl tapes. Unfortunately, according to tests           performed at Lawrence Berkeley National Laboratory by Max           Sherman and Iain Walker, a UL 181 listing is no guarantee that a tape           will last any longer than unlisted cloth duct tape.

“In California, the duct-tape industry wanted the code to approve the           use of UL 181-listed products,” says Walker. “But in our lab tests we           have found that the UL 181 products fail. Just because it is UL 181           listed does not mean that it performs any better than non-UL 181           listed products. The listed tapes may be of a higher quality — the           mechanical properties of the tape are better — but they are not any           better in terms of longevity at high temperature. Under those           conditions the UL 181 tapes failed as well as the non-UL 181 tapes.”

More important than a tape’s UL 181 label is the material category           into which it falls. At least two new types of duct tape — butyl duct           tape and oriented polypropylene (or OPP) duct tape — may offer better           performance than cloth duct tape, without the messiness of mastic.

Oriented           polypropylene tape
For sealing the inner core of flex duct to metal collars, as well as           to repair the outer jacket of flex duct, many contractors have begun           using oriented polypropylene (OPP) tape. OPP tape is a film-backed           (as opposed to cloth-backed) tape resembling packing tape. (Housewrap           tape is a type of OPP tape.) The tape has a smooth backing and an           acrylic adhesive, said to be more tenacious than rubber adhesive. The           backing can be manufactured in a variety of colors, including a shiny           “metallized” plastic finish. “In new construction in California,           we’re seeing more and more contractors using OPP tape and a clamp to           seal the core of the flex duct to a metal collar,” says Walker.

At least three manufacturers make UL 181B-FX listed polypropylene           duct tape: Intertape           Polymer Group (manufacturer of AC698 tape), Shurtape Technologies (manufacturer           of DC-181 tape), and Berry           Plastics (manufacturer of FlexFix tape).

Manufacturers of OPP tape take pains to distinguish their product           from the gray stuff. Although their DC-181 is a tape designed for use           on ducts, Mark Hooks, a product manager at Shurtape Technologies,           insists that “it’s not a duct tape.”

As long as joints sealed with OPP tape are clamped, it will probably           perform better than cloth duct tape.

Butyl duct           tape
Foil-backed butyl tape performs much better than cloth duct tape,           although it isn’t cheap.
Hardcast, the manufacturer of           Versi-Grip 181 duct mastic, sells several types of butyl duct tape;           one of them, Foil-Grip           1402, has a UL 181B listing.

Foil-Grip 1402 consists of 12 mils of butyl adhesive (similar to the           adhesive used in some flexible window flashings) with a 2-mil           aluminum-foil top layer. Hardcast recommends Foil-Grip butyl tape for           use with galvanized steel duct, duct board, or flex duct. The           manufacturer claims that Foil-Grip 1402 is rugged enough to use           outdoors or below grade.

Berry Plastics sells a butyl-adhesive duct tape under two different           brands (Nashua and Polyken). Nashua           558CA is basically the same product as Polyken           558CA. The tape consists of a butyl adhesive on a           polyethylene-coated cloth backing; it has a UL 181 BFX listing for           use with flex duct.

Like OPP tape manufacturers, butyl tape manufacturers want to           differentiate their product from duct tape. “We don’t like to use the           word ‘tape,’” says David Barnes, a technical service representative           at Hardcast. “We’re trying to overcome all of the perceptions           associated with duct tape.”

Butyl tapes have fared well in the Lawrence Berkeley tests. “The           butyl tapes come with a metal foil backing as opposed to the cloth           backing,” says Walker. “The cloth-backed tapes are the ones we see           shrinking and failing. The butyl tapes have much more adhesive on           them, so they will take longer to dry out and will stay flexible           longer. In our testing we’ve done several different orientations over           the years, and we haven’t found any failures in the butyl tape.”

Choosing           between tape and mastic
Since all duct-sealing products, including mastic and all types of           duct tape, have disadvantages, deciding on the best duct-sealing           strategy is tricky. Chuck Murray, an Energy Specialist with the           Washington State University Energy Program, sees no reason to abandon           mastic. “I haven’t seen a tape yet that I like for use in a crawl           space,” says Murray. “But we continue to monitor the situation.”

One of mastic’s chief advantages is that, unlike some tapes, it           performs well without clamping. Yet mastic will not prevent a joint           from opening up. “Mastic is not a mechanical fastener — you still           need sheet-metal screws, and scrap metal or fiberglass drywall mesh           for big holes,” notes Davis. “You need to be sure that everything           will hold together on its own merits. But, unlike with tapes, you           don’t have to worry about whether the surfaces are clean.”

Most installers don’t bother to clean their joints before applying a           sealant, and Davis feels that mastic holds up better under the           circumstances. Yet mastic manufacturers, like duct tape           manufacturers, generally require joints to be clean. “You need to           clean the joint with soap and water and a rag,” says David Barnes from           Hardcast. “The same surface prep is required no matter which sealing           system is used.”

High quality duct tape — not mastic — should be used to seal holes in           a furnace or air handler. As energy expert Bruce Harley notes,           “Mastic would render the cabinet unserviceable.”

Making           good duct joints
Here are some tips for creating durable, airtight duct seams:

• Duct seams need to be                mechanically fastened (using sheet-metal screws for galvanized                ducts and compression straps for flex duct) before being sealed.
• To secure seams in                round galvanized ducts up to 12 inches in diameter, use at least                three #8 screws per joint. To secure ducts over 12 inches in                diameter, use five screws per joint.
• For securing joints                in rectangular galvanized duct, use at least one screw per side.
• In most locations,                mastic is preferable to tape.
• Mastic is messy, so                wear old clothes when you apply it.
• Install mastic “as                thick as a nickel.”
• Cracks or seams wider                than 1/16 or 1/8 inch need to be repaired with fiberglass mesh                as well as mastic.
• Don’t forget to seal                collar connections between plenums and duct take-offs.

Sealing joints in flex duct
Flex duct sections are usually connected with a beaded metal sleeve           or coupling. Here’s the procedure for sealing flex-duct connections:

• The duct boot or                coupling should be inserted at least 2 inches into the end of                the duct. The fitting should be attached to the inner sleeve of                the flex duct with a drawband (clamp) or #8 screws.
• Seal the joint                between the inner section of duct and the fitting with high-quality                duct tape or mastic.
• Seal the exterior                vapor-barrier sleeve with a drawband and tape.

Nonresidential building activity is expected to increase by 5.8           percent in 2014, according to the American Institute of Architects’           (AIA) semi-annual Consensus Construction Forecast. A stabilizing           economy signals a significant improvement in the construction           industry, which has been recovering slowly yet steadily over the last           two years, AIA Chief Economist Kermit Baker, Hon. AIA, said in a           statement. “At a more granular level,” he added, “the surging housing           market, growing commercial property values, and declining office and           retail vacancies are all contributing to what is expected to amount           to a much greater spending on nonresidential building projects.”

Looming concerns for 2014 include rising interest rates, an uncertain           economy causing owners and developers to delay projects, shortage of           skilled labor, project financing difficulties, and rising costs           (Obamacare, liability insurance, rents and new technology investments).           “Factors such as the standoffs in Washington, uncertainty in the           European economy, and still-tight lending have muted construction           growth coming out of the recession, said Bernard Markstein, chief           economist for Reed Construction Data, during the “2014 Outlook:           Emerging Opportunities for Construction” webinar. “Until these are           resolved, there will be uncertainty,” he said. “The growth in           construction is barely acceptable.”

New Kitchen           Exhaust Reference Guide Available

The new Kitchen Exhaust Reference Guide is now           available; click here           for more information.

Homes shall meet this Item. Alternatively, the prescriptive duct           sizing requirements in Table 5.3 of ASHRAE 62.2-2010 are permitted to           be used for kitchen exhaust fans based upon the rated airflow of the           fan at 0.25 IWC. If the rated airflow is unknown, ≥ 6 in. smooth duct           shall be used, with a rectangular to round duct transition as needed.           Guidance to assist partners with these alternatives is available at www.energystar.gov/newhomesresources.           As an alternative to Item 8.1, homes that are PHIUS+ certified are           permitted to use a continuous kitchen exhaust rate of 25 CFM per 2009           IRC Table M1507.3.