ASHRAE Journal - November 2014 - 14

TECHNICAL FEATURE

6.5.7.1.2 Conditioned supply air delivered to any space with a
kitchen hood shall not exceed the greater of:
a) the supply flow required to meet the space heating or cooling load
b) the hood exhaust flow minus the available transfer air from
adjacent spaces. Available transfer air is that portion of outdoor ventilation air not required to satisfy other exhaust needs, such as restrooms,
and not required to maintain pressurization of adjacent spaces.
The rationale behind this requirement is to capitalize on available transfer air (that originated as outside
air and has already been heated or cooled) as a contribution to the replacement air requirement of the
exhaust hood, potentially reducing the size and energy
consumption of the dedicated makeup air (MUA) unit.
In some cases, transfer ducts and/or fans may be incorporated within the design to meet this requirement. In
other cases a dedicated MUA unit may be a more costeffective option and the designer may need to argue
that the transfer air was not "available" from a practical
perspective. This is particularly true when the occupancy schedule of the adjacent space is not in sync with
operation of the exhaust hood.
Section 6.5.7.1.2 applies to the design of all CKV systems, regardless of airflow capacity, while the following
requirements apply only to CKV system design where
the exhaust rate exceeds 5,000 cfm (2360 L/s).
6.5.7.1.3 If a kitchen/dining facility has a total kitchen hood
exhaust airflow rate greater than 5,000 cfm then each hood shall
have an exhaust rate that complies with Table 6.5.7.1.3. If a single
hood is installed over appliances with different duty ratings, then
the maximum allowable flow rate in each section of the hood shall
not exceed the Table 6.5.7.1.3 values for the appliance duty ratings in
that section of the hood. Refer to ASHRAE Standard 154-2003 for
definitions of hood type, appliance duty, and net exhaust flow rate.
The 5,000 cfm (2360 L/s) threshold was established to
exempt smaller restaurants where the cost-effectiveness
of the energy efficiency requirements could be challenged. The "facility has a total kitchen hood exhaust
airflow rate greater than 5,000 cfm" statement replaced
"Individual kitchen exhaust hoods larger than 5,000
cfm." This prevented the addition of multiple hoods or
hood sections individually operating beneath 5,000 cfm
(2360 L/s) to avoid the energy saving methods and specifications required in 6.5.7.1.3 and 6.5.7.1.4. for larger
capacity systems.
The exhaust airflow rates in Table 6.5.7.1.3 are 30%
below the minimum airflow rates in ASHRAE Standard
154-2003 Ventilation for Commercial Cooking Operations, for
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TABLE 6.5.7.1.3 Maximum net exhaust flow rate, cfm per linear foot of hood
length. (From Standard 154-2003.)
TYPE OF HOOD

LIGHT DUTY
EQUIPMENT

MEDIUM DUTY
EQUIPMENT

HEAVY DUTY
EQUIPMENT

EXTRA HEAVY DUCT
EQUIPMENT

Wall-Mounted
Canopy

140

210

280

385

Single Island

280

350

420

490

Double Island
(Per Side)

175

210

280

385

Eyebrow

175

175

Not Allowed

Not Allowed

Backshelf
Pass-Over

210

210

280

Not Allowed

Exception: a) At least 75% of all the replacement air is transfer air that would otherwise be exhausted.

unlisted hoods. While the IMC still recognizes unlisted
hoods, this airflow limitation in Standard 90.1 effectively
outlaws unlisted hoods (for systems greater than 5,000
cfm [2360 L/s]). ASHRAE research has shown that hoods
listed per UL Standard 7108 and tested per ASTM/ANSI
F17049 have exhaust rates that are at least 30% less than
those of the unlisted hoods. The following discussion
delves into this aspect, presenting third-party performance data for a number of hood designs.
Certification bodies (CBs) list and label exhaust hoods
that operate with commercial cooking appliances and
a fire extinguishing system according to Standard UL
710 Exhaust Hoods for Commercial Cooking Equipment.8 The
Standard includes a construction section and performance section. The construction requirements ensure
the hood's integrity during a fire and fan failure. The
performance section ensures the hood's ability to capture and contain the cooking effluent and products of
combustion under actual cooking conditions. However,
in some cases, the cooking challenge may not be as
"challenging" as some real-world conditions. As a result,
the ASTM Kitchen Ventilation subcommittee of F26 Food
Service Equipment took on a project to develop a test
method9 using enhanced flow visualization techniques
to determine the capture and containment exhaust rate
for different appliance lines and exhaust hood configurations. This test method was used as the foundation of
past CKV research projects7,10,11,12 as well as a basis for
ongoing evaluation of high-performance hoods.13
Figure 2 presents the results of third-party testing
for eight different designs of 10 ft (3 m), "listed" wallcanopy hoods in comparison with a generic "unlisted"
hood operating over a heavy-duty appliance line (twovat fryer, under-fired boiler and convection oven) in
ASHRAE Journal - November 2014

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