20070419154457.pdfox EDo City of Edmonds
.aa PLAN REVIEW COMMENTS
BUILDING DIVISION
Fsr_ ig9° (425) 771-0220
DATE: April 19, 2007
TO: Dani Meyers
Hermanson, LLP
12212`1 Ave North
Kent, WA 98032
FROM: Ann Bullis, Assistant Building Official
RE: Plan Check #2007-0278
Project: Aegis -- Mechanical
Project Address: 21500 72n' Ave W
During re -review of the plans for the above noted project, it was found that the following information, clarifications or
changes are needed. Provide written responses to each comment and where changes can be found on the plans. Submit
revised plans/documents to Marie Harrison, Permit Coordinator.
1. Previous item 3: The dryer booster fans are not permitted. For clarification, enclosed you will find a copy from the
IMC Commentary (see page 5-25 highlighted area) regarding dryer booster fans. The dryers are not listed for use
with the booster fans. The City Building Official is not permitting the use of the dryer booster fans. Based on the
dryer duct lengths noted on the mechanical plans, it appears that they are within the limits of the maximum
permitted duct lengths shown on page 3 of the manufacturer's installation instructions for 4" rigid metal duct.
504.6.1
sufficient flow velocity to transport lint and fibers
through the duct to the discharge terminal.
Excessive friction losses will also result in reduced
flow velocities, which means that the exhaust ducts
would be much more likely to collect debris. An improp-
erly designed exhaust system will result in poor dryer
performance and poor energy efficiency and can cause
the appliance to cycle on its limit control which can be
hazardous.
Joints in the dryer exhaust system should be reason-
ably airtight, must have a smooth interior finish, and
must run in the direction of airflow. For example, the
male end of each section of duct must point away from
the dryer. This reduces turbulence and permits the
dryer exhaust system to function as intended so that
joints and connections do not serve as collection points
for lint or debris.
Proper support is required and necessary for main-
taining alignment of the dryer exhaust duct system and
to prevent excessive stress on ducts and duct joints. A
sagging duct will increase the internal resistance to air-
flow, reduce the efficiency of the system and cause the
accumulation of dryer exhaust products at low points.
Section 504.6 specifically addresses transition duct
connectors. Within the context of this section, a transition
duct is a flexible connector used as a transition between
the dryer outlet and the connection point to the exhaust
duct system. Transition duct connectors must be listed
and labeled as transition ducts for clothes dryer applica-
tion. Transition ducts are currently listed to comply with
UL 2158A. Such transition ducts are not considered as
flexible air ducts or flexible air connectors subject to the
material requirements of Section 603.6.
Transition ducts are flexible ducts constructed of a
metalized (foil) fabric supported on a spiral wire frame.
They are more fire resistant than the typical plastic spiral
duct. Transition duct connectors are limited to 8 feet
(1829 mm) in length and must be installed in accordance
with their listing and the manufacturer's instructions.
These duct connectors must not be concealed by any
portion of the structure's permanent finish materials,
such as drywall, plaster, paneling, built-in furniture or
cabinets, or any other similar permanently affixed build-
ing component; they must remain entirely within the
room in which the appliance is installed. Transition duct
connectors cannot be joined to extend beyond the 8 -foot
maximum length limit. Transition ducts are to be cut to
length as needed to avoid excess duct and unnecessary
bends.
Transition duct connectors are necessary for domes-
tic dryers because of appliance movement, vibration
and outlet location. In many cases, connecting a do-
mestic clothes dryer directly to rigid duct would be diffi-
cult. The question thatthis section has raised in the past
is whether the transition duct length is to be included in
the overall developed length limit of the exhaust duct
system, or whether it is in addition to the maximum de-
veloped length allowed by Section 504.6.1. This edition
of the code specifically states that the transition duct is
not to be included in the 25 -foot maximum length.
EXHAUST SYSTEMS
504.6.1 Maximum length. The maximum length of a clothes
dryer exhaust duct shall not exceed 25 ft (7620 mm) from the
dryer location to the outlet terminal. The maximum length of
duct shall be reduced 2'/z feet for each 45 -degree (0.79 rad) bend
and 5 feet (1524 mm) for each 90 -degree (1.6 rad) bend. The
maximum length of the exhaust duct does not include the transi-
tion duct.
Exception: Where the make and model of the clothes dryer to
be installed is known and the manufacturer's installation in-
structions for such dryer are provided to the code official, the
maximum length of the exhaust duct, including any transition
duct, shall be permitted to be in accordance with the dryer
manufacturer's installation instructions.
4- The maximum exhaust duct length of 25 feet (7620 mm)
is the normal installation requirement for domestic
clothes dryers. The 25 -foot (7620 mm) limit is based on
the worst case scenario where the dryer is rated for a
maximum duct length of 25 feet (7620 mm). The excep-
tion to this section allows longer exhaust duct lengths
when the manufacturer's instructions specify the addi-
tional length. The make and model of the dryer must be
provided to the code official, along with the installation in-
structions, to permit the code official to inspect the duct
installation based on the manufacturer's instructions.
If the exception to this section is used, the code offi-
cial must verify that the specific make and model dryer
is installed before final approval is given.
A point to consider is the situation that will exist when
the original occupant moves out and the new occupant
does not install a similar dryer that allows the longer
duct length. If the duct is not marked conspicuously, the
new resident will be unaware of the potentially hazard-
ous situation that has been created by the dryer and ex-
haust mismatch.
Each change in direction increases the duct's resis-
tance to air flow, which reduces the velocity of the air
flow. As discussed in the commentary for Section
504.6, the lower velocity will allow lint particles in the
dryer exhaust to drop out of the airstream and collect in
the duct, usually near the bend in the duct or a low point
in the duct. As the lint builds up in the duct, the efficiency
of the dryer will be reduced and eventually the volume
of lint will become a potential fire hazard.
Because of poor planning, dryers are often installed in
locations that require excessively long duct runs, often
with multiple changes in direction. Whether the distance
is 25 feet (7620 mm) or some distance specified by the
manufacturer, duct bends (fittings) will significantly re-
duce the allowable length and must be accounted for in
the installation and at the time of inspection. It is not un-
common to find installations that cannot comply with this
section or its exception. In those cases, the dryer must
be relocated or a condensing (ductless) dryer must be
used. Condensing dryers do not have an exhaust duct,
are extremely energy efficient, use an air-to-air heat
exchanger to condense the water vapor extracted from
the clothes and pump the condensate to a drain or store
it in a removable reservoir.
5_24 2003 INTERNATIONAL MECHANICAL CODe COMMENTARY
SYSTEMS
Another option is clothes dryer booster fans, which
would have to be approved by the code official, be-
cause the code does not have an allowance for them.
The code does not currently address booster fans be-
>" cause the dryers are not currently listed for use with
booster fans, booster fans do not currently interlock
with the dryer to prevent dryer operation in the event of
booster fan failure and booster fans will likely be in-
stalled in locations where the building owner/occupant
will not be aware of the fan and its operational condition.
504.6.2 Rough -in required. Where a compartment or space for a
'domestic clotbes dryer is provided, an exhaust duct system shall
be installed in accordance with Sections 504.6 and 504.6.1.
y To assist in the inspection process, this section requires
installation of a dryer exhaust duct rough -in that com-
plies with Section 504. Practically all homes will have a
clothes dryer, making a proper exhaust duct system a
very important part of any dryer installation. The intent
of this section is to make sure that a code -complying ex-
haust duct system is installed and inspected prior to oc-
cupancy and the eventual installation of the dryer. The
exhaust duct requirements of Section 504.6.1 (without
the exception) are intended to make the exhaust duct
system rough -in compatible with any of the typical do-
mestic clothes dryers that are likely to be installed. The
exception to Section 504.6.1 will require a specific
rough -in and appliance.
504.7 Commercial clothes dryers. The installation of dryer ex-
haust ducts serving Type 2 clothes dryers shall comply with the
appliance manufacturer's installation instructions. Exhaust fan
motors installed in exhaust systems shall be located outside of
the airstream. In multiple installations, the fan shall operate con-
tinuously or be interlocked to operate when any individual unit
is operating. Ducts shall have a minimum clearance of 6 inches
(152 mm) to combustible materials. Clothes dryer transition
ducts used to connect the appliance to the exhaust duct system
shall be limited to single lengths not to exceed 8 feet (2438 mm)
in length and shall be listed and labeled for the application.
Transition ducts shall not be concealed within construction.
❖ The code classifies clothes dryers into two categories:
Type 1 and Type 2. Type 1 clothes dryers are primarily
used in the family living environment and do not have
the capacity or generate the amount of heat necessary
to dry large volumes of clothing. The scope of this sec-
tion does not regulate Type 1 clothes dryers.
. Type 2 clothes drying appliances and exhaust ducts
are designed for the higher volumes, temperatures and
frequency of use found in public access and commer-
cial laundries. Type 2 dryers must be installed in accor-
dance with the manufacturer's instructions. These
dryers are tested to the appropriate safety standard for
the appliance, and the manufacturer's installation in-
structions convey the information needed to duplicate
the installation configuration that was tested and found
to meet the requirements of the safety standard. The
manufacturer's installation instructions are evaluated
504.6.2 — 504.7
by the agency responsible for testing the appliance
and, therefore, the instructions will prescribe an instal-
lation that is consistent with Section 304.1, which ad-
dresses the installation of all mechanical equipment.
Common exhaust systems for multiple dryers must be
designed and engineered in accordance with the
equipment and the appliance manufacturer's installa-
tion instructions (see Figure 504.7).
The potential fire hazards associated with Type 2
clothes dryers are similarto those of Type 1 clothes dry-
ers (combustible lint, debris and high temperatures).
However, the complex exhaust systems, intense heat,
and larger volume of combustible lint and combustion
by-products associated with commercial dryers call for
additional safety requirements (see commentary, Sec-
tion 504.5).
Commercial and multiple -dryer installations can rely
on a single exhaust fan to.prevent back pressure, over-
come duct friction and induce the proper flow within the
common exhaust system. Figure 504.7 shows a
four -unit installation with the exhaust tan located at the
roof level. This section requires that exhaust fans for
Type 2 clothes dryer installations be operated continu-
ously or be interlocked to operate when any individual
unit is operating.
it is possible to exhaust multiple Type 2 dryers
through a common duct -system, such as a common
riser or common manifold serving groups of adjacent
units. This configuration will usually require an exhaust
fan to prevent back pressure and to overcome static
pressure in the duct system. In such installations, the
common duct system will be connected to the inlet side
of an exhaust fan and the fan will be located at the duct
system termination to the outdoors.
The motor of the exhaust fan must be positioned out-
side of the exhaust airstream so that lint, debris and
condensation do not accumulate in or on the motor.
This requirement is generally satisfied by belt -driven
fans with externally mounted motors. Location in the ex-
haust stream could result in deterioration and failure of
the motor, as well as a fire hazard associated with the_
accumulation of combustible fibers in contact with a
motor that may be hot enough to cause ignition. Failure
of the exhaust fan motor could result in an unsafe oper-
ating condition for the dryers served by the fan.
Where multiple dryer units vent to a common venting
system using a common fan, the common exhaust fan
must operate when any one or more of the individual dryer
unit(s) are operating. This can be achieved in two ways.
The first, continuous exhaust fan operation, is not
desirable and is rarely done because of increased en-
ergy usage and the unreliability of the design. Continu-
ous operation without interlocks (fan supervision) is not
reliable because the dryer units would not respond to or
be "aware" of an exhaust fan failure. Any mechanical
failure of the exhaust fan or opening of an over -current
protection device could create an unsafe condition. The
same is true of Type I dryers using booster fans.
The second and preferred method is to install ex-
haust fan supervision interlocked with each dryer unit
2003 INTERNATIONAL MECHANICAL CODE COMMENTARY 5-25