Prepared by John Gulland, Gulland Associates Inc.
For Canada Mortgage and Housing Corporation
September, 2002
The Technical Sub-Committee (TSC) for standard CSA F326-91, Residential Mechanical Ventilation Systems is working to update the standard. The complexities of the task are being managed through the formation of several Task Groups (TG) charged with addressing particular issues identified by the sub-committee. The work of two of these TGs are relevant to this project: the TG on Combustion/Depressurization and the TG on Harmonization of Standards.
The TG on Combustion/Depressurization is reviewing and refining the requirements in F326 related to protection against depressurization that can cause venting failure in combustion equipment. Although its work is not yet completed, there is a clear consensus that the test procedures set out in CGSB Standard 51.71, The Spillage Test, will, subject to detailed review and refinement, form the basis of the approach recommended to the F326 TSC.
The TG on Harmonization of Standards could not be active until clarity emerged on the general approach recommended for F326, particularly as it relates to the issue of protection against depressurization for vented combustion systems. The necessary clarity now exists. This report is intended to assist the members of the TG on Harmonization in comparing the relevant standards and in making recommendations, first to the F326 TSC, and then to the TSCs responsible for the standards under review, of changes that would be required to bring their requirements into technical agreement with those proposed for F326.
1. Through a detailed review of the relevant standards, document the approach taken in each in addressing potential problems of combustion air supply and house depressurisation.
2. Starting with the assumption that the approach proposed by the TG on Combustion/Depressurization in the current round of revisions to F326 is the most technically appropriate, identify the changes needed in the other standards to make their treatment of combustion venting and house depressurization compatible with that in F326.
3. Develop specific proposals to be eventually submitted to the various committees responsible for the standards under review.
4. Present these proposals to the Harmonization Task Group of the F326 Sub-Committee and the Coordinating Committee on Combustion Venting and make any changes identified by these groups.
5. Identify any difficulties with the starting assumption in Point 2.
This report and its appendices is intended to meet objectives 1, 2, 3 and 5.
· CSA F326, Residential Mechanical Ventilation Systems
· CGSB 51.71, The Spillage Test
· CSA B139, Installation Code for Oil-Burning Equipment
· B149.1, Natural Gas and Propane Installation Code
· CSA B365, Installation Code for Solid-Fuel Burning Appliances and Equipment
Changes in the materials and techniques of house construction over the past 25 years have resulted in reduced leakage rates of building envelopes. Throughout this period there has been much discussion within the responsible codes and standards committees concerning the use of chimney-vented combustion devices in houses of relatively air tight construction. The issues that animated these discussions include:
Underlying these concerns is the objective of acceptable performance of combustion equipment which can be defined as:
A suitable supply of combustion air for chimney vented equipment can be defined as one that is available as required from a location which is at or close to atmospheric pressure. Efforts to ensure adequate combustion air for new installations, or to correct apparent problems related to the issues listed above, have until recently focussed on providing a supply of combustion air from outdoors either directly to the appliance combustion chamber, or more commonly, indirectly to the space in which the appliance is installed. Both laboratory research and field experience have shown that these efforts to ensure acceptable performance by supplying combustion air from outdoors have not generally been successful.
Of the
five standards reviewed, three are combustion equipment installation codes
(B139, B149 and B365), one is a ventilation system standard (F326) and one is a
house pressure test standard (51.71). The five standards were reviewed for
their treatment of the issues of combustion air supply and protection against
depressurization. The results of this review are summarized in the following table.
|
|
F326 Residential Ventilation |
51.71 The Spillage Test |
B139 Oil Appliance Installation Code |
B149 Gas/Propane Appliance Installation Code |
B365 Solid Fuel Appliance Installation Code |
|
Current edition |
1991 Rev. 1993 |
1995 |
2000 Rev. 2001 |
2000 |
2001 |
|
Combustion air supply requirements |
None in the body of the standard but is
referred to in Appendix B1.12 as follows: ". . . in order to prevent venting problems,
fireplaces should be aerodynamically isolated from the dwelling unit. This might be accomplished, for example,
by supplying direct outdoor air to a fireplace fitted with tight‑fitting
glass doors." |
None |
4.4.1.1 May be installed
only where "an adequate supply of combustion air is available" 4.4.2.2 Adequacy
criteria: dwelling built to 1985 NBC or later Air supply size:
Total free area of 4.5 cm/kWh (1 in /5000 Btu/h) of the total input rating of
all oil-fired appliances within the space. |
7.1.5 "where there
is insufficient air for combustion", or the building (a) is of tight construction with a continuous air barrier, or (b) has an
equivalent leakage area of 78 in (0.05 m ) or less at a differential pressure
of 0.00145 psig (10 Pa); provide outdoor
air based on Table 7.2.2 which provides sizing criteria |
No requirements except: "4.2 Outdoor Combustion Air Ducts A duct supplying
combustion air from outdoors shall only be connected directly to the air
inlet of an appliance that is certified for such a connection." Passive supplies
are not discussed or recommended. |
|
|
|
|
|
|
|
|
Protection against depressurization
requirements |
6.3.2
Dwelling Units Incorporating Vented Combustion Appliances Conduct house depressurization test. Test is conducted with house set
up simulating winter conditions and operating selected exhaust devices.
Depressurization limit: "the value for which the appliance has been
certified by an accredited certification agency or the value specified by the
manufacturer or, in the absence of such certification or specification,
5 Pa." |
1. Purpose 1.1
"provide a method for determining whether air moving devices in a
dwelling are likely to impair normal venting of fuel-fired, vented appliances
through depressurization . . ." (includes
a range of depressurization limits based on appliance/venting
characteristics) House
set up and test procedure similar to, but with slight differences from, that
specified in CSA F326. |
4.1.5 "The
installer shall inspect the house and its mechanical systems to determine if
operation of exhaust devices could lead to levels of depressurization of the
house that would adversely affect the operation of the oil-burning appliance
and its venting system. If such is the case, the building owner shall be
informed of the situation in writing." |
7.6 Conditions Created by Exhaust Fans, Air Supply Fans, Circulating Fans, or Fireplaces When it is
determined that depressurization could be a problem "either the
condition shall be corrected or the fuel supply to the affected appliance
shall be discontinued." 7.7 Engineered Installations Outdoor air
may be supplied in other ways "if designed in accordance with
good engineering practice." |
4.1.3 Protection against Depressurization Either test house
depressurization using "CGSB Standard 51.71 or an equivalent" or
provide spillage warning using a CO detector/alarm. If required, the
makeup air system "shall conform to the requirements of provincial
regulations or, in the absence of such regulations, the requirements of the National Building Code of Canada." |
Two very different approaches are evident among these five standards:
· B139 and B149 are combustion air-centred: Their requirements assume that tight house construction will not permit natural leakage to supply combustion air. Both standards have extensive requirements for the provision of combustion air from outdoors. The problem of exhaust device depressurization is not addressed in any detail within the standards. In fact, the recognition in B149 that its combustion air and venting tables are appropriate only when depressurization of the space does not exceed – 5 Pa (Appendix C) presents installers and inspectors with a problem because the standard includes no detail on how to proceed if the value is outside this limit.
· F326, 51.71 and B365 are depressurization-centred: Their requirements assume that houses leak enough to provide combustion air, but that depressurization of a house by its exhaust devices may disrupt normal operation of chimney-vented combustion equipment. (Standards 51.71 and B365 have requirements recognizing that open or decorative fireplaces may consume enough air to affect the operation of other equipment.)
It is assumed in standards B139 and B149 that oil and gas appliances may not receive the combustion air they require if the dwelling ". . . has windows and doors of either close-fitting or sealed construction, and the exterior walls are covered by a continuous, sealed vapour barrier and gypsum wallboard (drywall) or plywood or similar materials having sealed joints . . . " (B149) or is ". . . built in accordance with the National Building Code of Canada, 1985 (or subsequent edition)" (B139). This assumption is not supported by housing research literature. The natural leakage rate of new Canadian houses is generally sufficient to supply combustion air requirements for closed combustion chamber natural draft vented equipment without inducing any significant amount of house depressurization. In addition, the usual methods of providing combustion air from outdoors are generally ineffective and may induce venting failure under certain conditions.
Combustion
air from outdoors for an appliance that is not specifically engineered to
function in this mode is normally provided indirectly through a duct that
terminates near the appliance. A direct connection of the outdoor air duct to
the appliance air inlet would be considered a superior approach except for
concerns about unintended effects on combustion. B139 provides that "An outside
combustion-air duct may be directly connected to the burner if the appliance is
so certified." B149 does not contain such a limitation, but the language
in the standard makes clear that indirect supplies are assumed through statements
such as "An outdoor air supply . . . shall be provided to either an
enclosure or a structure in which an appliance(s) is installed."
Field-installed
indirect combustion air supplies function to passively increase the
leakage rate of the building in proximity to the combustion equipment. As a
result, these supplies are more properly referred to as make-up air. The
design and sizing provisions in the standards assume that the building interior
and the area around the outdoor termination of the air supply are at or close
to atmospheric pressure. This approach has technical limitations that can
result in the appliance not having access to a suitable supply of combustion
air. These limitations include:
· As currently prescribed, indirect combustion air supplies are not adequately sized to supply the total combustion air requirements of the appliances they are intended to serve at the maximum allowable driving pressure of – 5Pa.
· Wind effects at the outdoor termination of the duct can cause significant fluctuations of the pressure in the duct which affects the flow direction and volume of air supplied to or withdrawn from the space.
· Stack effect during cold weather normally produces negative pressure at lower levels of the building where most fuel-burning appliances are installed. This stack effect can induce flow in a passive make-up air supply duct, whether or not the appliance is firing. During extremely cold weather, this stack effect-induced flow can cool the space excessively and may interfere with the performance of the appliance when it fires. Stack effect may produce a pressure difference at the appliance that exceeds the –5 Pa default depressurization limit for appliances that are not otherwise certified, a problem that can impair appliance function if its venting system runs up the outside wall of the dwelling and/or penetrates the building envelope below its highest level.
· The operation of exhaust devices may depressurize the dwelling in excess of the –5 Pa default value. The indirect make-up air supplies, as currently prescribed, cannot be expected to provide sufficient relief to prevent such depressurization.
For these reasons, passive indirect sources of make-up air are not considered a reliable means of supplying combustion air in tightly-sealed buildings. It should be noted that these limitations do not apply to relief openings in small enclosures such as furnace rooms that are designed to permit air for combustion and ventilation to flow from other parts of the building.
It is also worth noting that the test procedure described in Standard CGSB 51.71 could be used to detect situations in which the combustion air consumption of an oil- or gas-fired appliance is suspected of depressurizing the space in which it is located. This would simply involve establishing the prescribed test conditions and, instead of turning on selected exhaust devices, firing the combustion appliance and measuring the depressurization of the space.
The technical limitations of passive and even direct supplies of outdoor combustion air, combined with the knowledge that most new houses have sufficient natural leakage to supply combustion air without significant depressurization, suggest that the most effective means of ensuring acceptable performance is to determine the potential for excessive depressurization through testing and to take appropriate action based on the test findings. This general approach is reflected in standards CSA F326, CSA B365 and CGSB 51.71. The most recent set of proposed revisions to the National Building Code Section 9.32 Ventilation Systems is also generally in harmony with this approach.
The TG on Combustion/Depressurization will report to the F326 TSC on the mechanism by which agreement can be achieved between its requirements and those of CGSB 51.71, which will likely be referenced within F326. Through the sharing of information and considerable overlap in membership between the TSCs for CSA F326 and CGSB 51.71, it is expected that once both standards are reviewed and revised, agreement will be achieved.
This standard was published as a new edition in 2001. The extensive revisions made to the standard included a new Sub-section 4.1 Protection Against Depressurization aimed at bringing its provisions into close agreement with the approach taken in the most recent proposed revisions to the National Building Code of Canada, Subsection 9.32.3.8 Protection Against Depressurization. In summary, this approach involves either the testing the potential for excessive house depressurization using the CGSB 51.71 procedure and taking appropriate remedial action, or installing spillage warning devices such as CO detectors. The option of providing spillage detection and alarm is unique to hand-fed wood burning equipment and is justified by the direct involvement of the user in the combustion process and the fact that spillage from these systems is readily detected by relatively inexpensive smoke and CO detectors.
Because B365 was revised recently and its requirements in this area were brought into general agreement with the NBC, which in turn is consistent with the general approach anticipated for F326, B365 can be said to agree conceptually with F326. Once the F326 TSC completes its work and recommends a final draft for publication, some slight changes to B365 might be warranted to bring it into close agreement. At this time, no such changes can be recommended.
To bring Standards CSA B139 and B149 into agreement with
F326 will require a shift from the combustion air-centred approach to ensuring
acceptable appliance performance to the depressurization-centred approach. This
shift will involve significant reworking of Subsection 4.4 Air for Combustion and Ventilation in B139
and Section 7. Venting Systems and Air Supply for Appliances in B149
Appendix A
offers the TSC for B139 a draft set of requirements that would bring the
standard into closer agreement with F326. Appendix B offers the TSC for B149 a
draft set of requirements to assist it in shifting from the combustion
air-centred to the depressurization-centred approach to ensuring acceptable
appliance performance.
The subject
area specialist members of both TSCs will undoubtedly refine the respective
drafts of proposed changes to account for technical issues that will emerge in
the revision process. As the process evolves, the TSCs may require support from
housing specialists in dealing with the complexities of house/combustion system
interactions.
B139-00
Installation Code for
Oil-Burning
Equipment
Proposed revisions to bring CSA B139 into harmony with the CSA F326 approach to protection against depressurization.
Note: Proposed text is underlined
and deleted text is struck through.
4.1.4
When an oil-burning appliance is located within a
building, sufficient air for combustion of the oil and ventilation of the
appliance shall be supplied to the space wherein the appliance is located.
4.1.5
The installer shall inspect the house and its
mechanical systems to determine if operation of exhaust devices could lead to
levels of depressurization of the house that would adversely affect the
operation of the oil-burning appliance and its venting system. If such is the
case, the building owner shall be informed of the situation in writing.
4.4
Air for Combustion and Ventilation
Note: See also Clause 4.1.3.
4.4.1
General
4.4.1.1
Oil-burning appliances shall be installed only where
(a) an
adequate supply of combustion air is available to assure proper combustionthe
operation of exhaust equipment will not depressurize the space in excess of the
depressurization limit for the oil-burning appliance as
prescribed in CGSB Standard 51.71; and
(b) ambient air temperatures are maintained within safe operating
limits.
4.4.1.2
Oil-burning appliances shall be located in such a manner as not to
interfere with proper circulation of air for combustion or ventilation within
the space.
4.4.1.32
Protection Against Depressurization
When the building construction is such that normal
infiltration does not meet the requirements for combustion air and ventilating
air, outside air shall be introduced to the space in which the oil-burning
appliance is located. An outside combustion-air duct may be directly connected
to the burner if the appliance is so certified.
4.4.1.4
Each duct used to convey air from the outdoors
shall have
(a) a cross-sectional
area throughout its length at least equal to the free area of the inlet and
outlet openings which it connects;
(b) a minimum
dimension of 76 mm (3 in) at any cross-section; and
(c) when making
provision for outside combustion air, the intake shall not be less than 0.3 m
(1 ft) above grade level and at least 0.3 m (1 ft) above the anticipated snow
level for the location.
Note: When ducting or
ventilating openings are considered, reference should be made to applicable
building regulations.
4.4.1.5
When a damper is provided in any opening intended
to admit combustion air into the room within which the appliance is installed,
the damper shall be interlocked to prevent any burner from starting before the
damper is fully open.
4.4.2
Residential-Type Installations
4.4.2.1
For residential-type installations and similar usages, the requirements
of Clauses 4.4.2.2 to 4.4.2.97 shall
be met.
4.4.2.2
If Where an
oil-fired appliance is installed in a house built to the requirements of the National
Building Code of Canada, 1985, or a subsequent edition, the installer shall
provide
a combustion air inlet sized in accordance with Clauses 4.4.2.3 to 4.4.2.7determine
the potential for excessive depressurization of
the space by exhaust devices., or The
potential for depressurization shall be determined using the test procedure
outlined in CGSB Standard 51.71 or an equivalent.
4.4.2.3
Where the tested
depressurization exceeds the limits prescribed in CGSB Standard 51.71, the
installer shall provide to the furnace area
(room) install a mechanical air-supply system
of sufficient equivalent capacity to prevent excessive
depressurization of the space in which the appliance is installed.* If aThe
mechanical air-supply system is used, it shall be interlocked to
the oil-fired appliance or equipment and
to the largest exhaust device(s) that
induce the negative pressure. Following the
installation of the makeup air system, the test procedure outlined in CGSB
Standard 51.71 or an equivalent shall be repeated.
Note: The requirement to install an
interlocked mechanical make-up air supply is but one of the possible options.
Theoretically others could include the use of a pressure sensor, a mechanism
for pressurizing the space at appliance start-up, the use of a spillage switch
as either an appliance shut-down or signal to a mechanical subsystem and so on.
The TSC may want to consider a list of alternatives to an interlocked
mechanical supply or wording that permits other alternatives provided their
effectiveness can be demonstrated using the CGSB 51.71 test procedure.
4.4.2.4 Documentation
Where a makeup air
system is installed to control the building pressure in accordance with Clause
4.4.2.3, its performance
characteristics and maintenance requirements shall be documented and provided
to the building owner.
4.4.2.4 Good Practice
Mechanical make-up air
supply systems shall be sized, fabricated and installed in accordance with good
practice, and supplier's instructions where available. The principles and procedures described in
the following references are deemed to represent good practice:
(a) HRAI Design and Installation Manual for
Residential Mechanical Ventilation Systems;
(b) HRAI Residential Air System Design Manual;
(c) ASHRAE Handbook, 1987, HVAC Systems and
Applications, Chapter 10 — Air Distribution Design for Small Heating and
Cooling Systems;
(d) ASHRAE Handbook, 1988, Equipment,
Chapter 3 — Fans;
(e) ASHRAE Handbook, 1989, Fundamentals,
Chapter 33 — Duct Design.
4.4.2.5 Minimum Supply Air Temperature — Ducted
Heating Devices
Where outdoor air is
introduced to a warm air furnace or other ducted heating device, it shall be
tempered and/or mixed with return air so that the temperature of the air
entering the device is not less than 15.5°C unless otherwise
recommended by the manufacturer of the device.
Design shall be based on the outdoor winter design temperature and a
return air temperature of 20°C.
4.4.2.6
An outdoor air intake
duct shall be insulated to prevent condensation on the outside of the duct from
the point where it passes through the building envelope to the point where the
supply air is introduced into the living space or is tempered to above the dew
point temperature of the room air. Such
ducts shall have insulation with an RSI value conforming to applicable
regulations but not less than 0.5.
Joints in the ducts shall be sealed, and the insulation shall have, on
its outer surface, an airtight and vapour‑retardant membrane.
4.4.2.7
The distance from the
bottom of an outdoor air intake opening to finished grade or to any nearer and
lower permanent horizontal surface shall not be less than 450 mm or the
depth of expected snow accumulation, whichever is greater, except that where
the opening is protected from snow accumulation, this clearance may be reduced
to 250 mm.
4.4.2.8 Outdoor Air Intake Shut-off
Outdoor air intake
openings which have been installed to meet the requirements of
Clause 4.4.2.3 — shall be equipped
with an automatic means of preventing airflow when they are not required to be
open.
Note: In unconfined spaces
in buildings of conventional frame, brick, or stone construction built prior to
the requirements of the National Building Code
of Canada, 1985, and not subsequently
significantly air-tightened, infiltration is normally adequate to provide air
for combustion and some ventilation; however, there may be notable exceptions.
Houses built in accordance with the National Building Code
of Canada, 1985 (or subsequent edition),
with extensive exterior stucco coating, or with a sealed vapour barrier or
other similar air sealing technique, will often be sufficiently airtight so
that there is not sufficient air for both combustion and venting the products
of combustion of an oil-fired appliance, or for replacing the air vented by
other exhaust devices within the house.
4.4.2.3
Where an appliance is located in an unconfined
space in a building having insufficient infiltration, additional air for
combustion and ventilation shall be obtained from outdoors or from spaces
freely communicating with the outdoors. Under these conditions, permanent
opening(s) shall be provided so that the total air received through these
openings will be at least as much as would be admitted by openings having a
total free area of 4.5 cm /kWh (1 in /5000 Btu/h) of the total input rating of
all oil-fired appliances.
4.4.2.94
An appliance that is located in a confined space and that obtains all of
its air for combustion and ventilation from within the conditioned space of the
building shall be provided with two permanent openings, one near the top of the
enclosure and another near the bottom. Each opening shall have a free area of
not less than 19.5 cm /kWh (1 in /1000 Btu/h) of the total input rating of all
appliances in the enclosure, freely communicating with interior areas that have
in turn adequate infiltration from the outside. (See Figure 2.)
4.4.2.5
An appliance that is located in a confined space
and that obtains all of its air for combustion and ventilation from outside the
building shall be provided with two permanent openings, one near the top of the
enclosure and another near the bottom. Each opening shall communicate directly
or by means of ducts with the outdoors or to such spaces (such as a crawl
space) that freely communicate with the outdoors, and shall be sized in
accordance with Clause 4.4.2.6. (See Figure 3.)
4.4.2.6
The requirements of Clause 4.4.2.5 shall be met by
one of the following methods:
(a) vertical duct(s)
with a free area of not less than 5.5 cm /kWh (1 in /4000 Btu/h) of the total
input rating of all appliances in the enclosure;
(b) horizontal
duct(s), with an equivalent length of less than 15 m (50 ft), having a free
area of not less than 11 cm /kWh (1 in /2000 Btu/h) of the total input of all
appliances in the enclosure; and
(c) air openings that
communicate directly with the outdoors, having a free area of not less than 5.5
cm /kWh (1 in /4000 Btu/h) of the total input rating of all appliances in the
enclosure.
Note: Duct runs that are
primarily horizontal and that have an equivalent length greater than 15 m (50
ft) should be sized accordingly larger to provide the same air flow as would be
provided by the requirements of Clause 4.4.2.6(b).
4.4.2.7
An appliance located in a confined space that
obtains its combustion air from outdoors and ventilation air from within the
conditioned space of the building shall be provided with two openings for
ventilation, located and sized in accordance with Clause 4.4.2.4, and a
combustion air supply sized in accordance with Clause 4.4.2.3.
4.4.3
Louvres and Grilles
In calculating free area as specified in Clauses
4.4.2.3 to 4.4.2.6, consideration shall be given to the blocking effect of
louvres, grilles, or screens that protect openings. Screens used shall be not
smaller than 6 mm (1/4 in) mesh and shall be readily accessible for cleaning.
If the free area through a design of louvre or grille is known, it shall be
used in calculating the size of opening required to provide the free area specified.
If the design and free area are not known, it shall be assumed that wood
louvres have 20–25% free area and metal louvres and grilles have 60–75% free
area.
4.4.4
Commercial and Industrial Equipment
For commercial and industrial equipment, permanent
facilities for supplying outside air shall be provided in accordance with the
following:
(a) For furnace or boiler rooms adjacent to outside
walls and where combustion air is provided by natural infiltration from the
outside, there shall be a permanent air supply inlet having a total free area
of not less than 1.5 cm /kWh ((1 in /14 000 Btu/h) (65 cm (10 in ) per US
gal/h)) of total input rating of 22 the burner or burners,
and in no case less than 75 cm (12 in ).
(b) For furnace or boiler rooms not adjacent to
outside walls, the combustion air shall be supplied in a manner acceptable to
the authority administering this Code.
(c) When ducts are used, the inlet air duct shall
terminate in a location where the freeze-up possibility of steam or water pipes
and electrical or mechanical equipment is reduced to a minimum.
4.4.5
Specially Engineered Installations
The size of combustion air openings specified in
Clauses 4.4.2.3 to 4.4.2.6 may not apply when special engineering methods, such
as mechanically supplied combustion air, approved by the authority
administering this Code, assure an adequate supply of air for combustion and
ventilation.
B149.1-00
Natural Gas and Propane
Installation Code
Proposed revisions to bring CSA B149 into harmony with the CSA F326 approach to protection against depressurization.
Note:
Proposed text is underlined and deleted text is struck through.
7.
Venting Systems and Air Supply for Appliances
7.1 General
7.1.1
The requirements of Clause 7.2 shall apply to central heating furnaces,
boilers, and hot water heaters; space heaters and
fireplaces.
7.1.2
The requirements of Clauses 7.2 to
7.5 inclusive shall not apply to a direct
vent appliance.
7.1.3
Interference with the air
supply for an appliance shall
be prohibited.
7.1.4
Air supply shall be provided in
accordance with
(a) Clauses 7.2 and 7.3 when either an appliance
or a combination of appliances
has a total input of up to and including 400 000
Btuh (120 kW);
or
(b) Clause 7.4 when either an appliance
or a combination of appliances
has a total input exceeding 400 000 Btuh (120 kW).
7.1.5
When an appliance
other than a central heating appliance
or a domestic water heater is installed in a
location where there is insufficient air for combustion, provisions shall be
made to provide an air supply sized
in accordance with Table 7.2.2A or 7.2.2B.
7.1.3
Appliances shall be
installed only where
(a) the operation of
exhaust equipment will not depressurize the space in excess of the
depressurization limit for the appliance as prescribed in CGSB Standard 51.71;
and
(b) ambient air
temperatures are maintained within safe operating limits.
7.1.4
Appliances shall be
located in such a manner as not to interfere with proper circulation of air for
combustion or ventilation within the space.
7.2 Protection
Against Depressurization
7.2.1
Residential Installations
For residential-type
installations and similar usages, the requirements of Clause 7.2
shall be met.
7.2.2
Engineered Installations
For systems with input
exceeding 400 000 Btuh (120 kW), other
means of providing protection against depressurization may
be used if designed in
accordance with good engineering practice, subject to the
approval of the authority having jurisdiction,
7.2.3
Where an appliance is installed
in a house built to the requirements of the National Building Code of
Canada, 1990, or a subsequent edition, the installer shall determine the
potential for excessive depressurization by
exhaust devices of the space in which the appliance
is installed. The potential for depressurization shall be
determined using the test procedure outlined in CGSB Standard 51.71 or an
equivalent.
7.2.4
Where the tested
depressurization exceeds the limits prescribed in CGSB Standard 51.71, the
installer shall install a mechanical air-supply system of sufficient capacity
to prevent excessive depressurization of the space.* The mechanical air-supply system shall be
interlocked to the natural gas- or
propane-fired appliance or equipment
and to the largest exhaust device(s) that induce the negative pressure.
Following the installation of the makeup air system, the test procedure
outlined in CGSB Standard 51.71 or equivalent shall be repeated.
Note: The requirement to install an
interlocked mechanical make-up air supply is but one of the possible options.
Theoretically others could include the use of a pressure sensor, a mechanism
for pressurizing the space at appliance start-up, the use of a spillage switch
as either an appliance shut-down or signal to a mechanical subsystem and so on.
The TSC may want to consider a list of alternatives to an interlocked
mechanical supply or wording that permits other alternatives provided their
effectiveness can be demonstrated using the CGSB 51.71 test procedure.
7.2.5 Documentation
Where a makeup air
system is installed to control the building pressure in accordance with Clause
7.2.4, its performance characteristics and maintenance requirements shall be
documented and provided to the building owner.
7.2.6 Good Practice
7.2.6.1
Mechanical make-up air
supply systems shall be sized, fabricated and installed in accordance with good
practice, and supplier's instructions where available. The principles and procedures described in
the following references are deemed to represent good practice:
(a) HRAI Design and Installation Manual for
Residential Mechanical Ventilation Systems;
(b) HRAI Residential Air System Design Manual;
(c) ASHRAE Handbook, 1987, HVAC Systems and
Applications, Chapter 10 — Air Distribution Design for Small Heating and
Cooling Systems;
(d) ASHRAE Handbook, 1988, Equipment,
Chapter 3 — Fans;
(e) ASHRAE Handbook, 1989, Fundamentals,
Chapter 33 — Duct Design.
7.2.6.2 Minimum Supply Air Temperature — Ducted
Heating Devices
Where outdoor air is
introduced to a warm air furnace or other ducted heating device, it shall be
tempered and/or mixed with return air so that the temperature of the air
entering the device is not less than 15.5°C unless otherwise
recommended by the manufacturer of the device.
Design shall be based on the outdoor winter design temperature and a
return air temperature of 20°C.
7.2.6.3
An outdoor air intake
duct shall be insulated to prevent condensation on the outside of the duct from
the point where it passes through the building envelope to the point where the
supply air is introduced into the living space or is tempered to above the dew
point temperature of the room air. Such
ducts shall have insulation with an RSI value conforming to applicable
regulations but not less than 0.5.
Joints in the ducts shall be sealed, and the insulation shall have, on
its outer surface, an airtight and vapour‑retardant membrane.
7.2.6.4
The distance from the
bottom of an outdoor air intake opening to finished grade or to any nearer and
lower permanent horizontal surface shall not be less than 450 mm or the
depth of expected snow accumulation, whichever is greater, except that where
the opening is protected from snow accumulation, this clearance may be reduced
to 250 mm.
7.2.6.5 Outdoor Air Intake Shut-off
Outdoor
air intake openings which have been installed to meet the requirements of
Clause 4.4.2.3 — shall be equipped
with an automatic means of preventing airflow when they are not required to be
open.
7.2
Air Supply Determination for Central Heating Furnaces, Boilers, and Hot Water
Heaters
7.2.1
An outdoor air supply sized
in accordance with Clause 7.2.2 shall be provided to either an enclosure
or a structure in
which an appliance(s) is installed when the structure
either
(a) has windows and doors of either close-fitting
or sealed construction, and the exterior walls are covered by a continuous,
sealed vapour barrier and gypsum wallboard (drywall) or plywood or similar
materials having sealed joints; or
(b) has an equivalent leakage area of 78 in (0.05 m
) or less at a differential pressure of 0.00145 psig (10 Pa) as determined by
the recognized Canadian fan depressurization test procedure.
7.2.2
Except as permitted in Clause 7.2.3, the free area
of the outdoor air supply required
by Clause 7.2.1 shall be determined from Table 7.2.2A for an appliance(s)
having a draft control device and
from Table 7.2.2B for an appliance(s) not
having a draft control device,
using the total input of all appliances in
either the structure or enclosure.
If an appliance with a draft
control device and an appliance
without a draft control device are
installed within the same structure or enclosure,
the required free area of the air supply opening
shall be the greater of either (a) that required by Table 7.2.2A, using the
total input of only those appliances having
draft control devices;
or
(b) that required by Table 7.2.2B, using the total
input of all appliances.
7.2.3
An outdoor air supply shall
not be required for a single water heater with an input of 50 000 Btuh (15 kW)
or less where there are no other appliances within
either an enclosure or structure
that require an air supply.
7.2.4
An outdoor air supply sized
in accordance with Clause 7.2.5 shall be provided to either an enclosure
or a structure in
which an appliance(s) is installed when the structure
is neither constructed as described in Clause
7.2.1(a) nor complies with Clause 7.2.1(b).
Table 7.2.2A
Combustion/Dilution Air Requirements for Appliances
Having Draft Control Devices When the Combined Input Is Up to and Including 400
000 Btuh (120 kW) and the Structure Complies with Clause 7.2.1 (a) or (b)
(See Clauses 7.1.5, 7.2.2, and 7.21.2.)
______________________________________________
Table Deleted
______________________________________________
*For total inputs
falling between listed figures, use next largest listed input.
†These figures are
based on a maximum equivalent duct length of 20 ft (6 m). For equivalent duct
lengths in excess of 20 ft (6 m) up
to and including a maximum of 50 ft (15 m), increase
round duct diameter by one size.
7.2.5
The free area of the outdoor air
supply required by Clause 7.2.4 shall be determined from
Table 7.2.5A for an appliance(s)
having a draft control device and
Table 7.2.5B for an appliance(s)
not having a draft control device,
using the total input of all appliances in
either the structure or enclosure.
If an appliance with a draft
control device and an appliance
without a draft control device are
installed within the same structure or enclosure,
the required free area of the air supply opening
shall be the greater of either
(a) that required by Table 7.2.5A, using the total
input of only those appliances having
draft control devices;
or
(b) that required by Table 7.2.5B, using the total
input of all appliances.
Table 7.2.2B
Combustion Air Requirements for Appliances NOT
Having Draft Control Devices When the Combined Input Is Up to and Including 400
000 Btuh (120 kW) and the Structure Complies with Clause 7.2.1 (a) or (b)
(See Clauses 7.1.5, 7.2.2, and 7.21.2.)
______________________________________________
Table Deleted
______________________________________________
*For total inputs
falling between listed figures, use next largest listed input.
†These figures are
based on a maximum equivalent duct length of 20 ft (6 m). For equivalent duct
lengths in excess of 20 ft (6 m) up
to and including a maximum of 50 ft (15 m),
increase round duct diameter by one size.
Table 7.2.5A
Combustion/ Dilution Air Requirements for
Appliances Having Draft Control Devices When the Combined Input Is Up to and
Including 400 000 Btuh (120 kW) and the Structure Does NOT Comply with Clause
7.2.1 (a) or (b)
(See Clause 7.2.5.)
______________________________________________
Table Deleted
______________________________________________
* For total inputs falling between listed figures,
use next largest input .
† See
Table 7.2.2A for acceptable approximate round duct equivalent .
Table 7.2.5B
Combustion Air Requirements for Appliances NOT
Having Draft Control Devices When the Combined Input Is Up to and Including 400
000 Btuh (120 kW) and the Structure Does NOT Comply with Clause 7.2.1 (a) or
(b)
(See Clause 7.2.5.)
______________________________________________
Table Deleted
______________________________________________
* For
total inputs falling between listed figures, use next largest input.
†See Table 7.2.2A for
acceptable approximate round duct equivalent.
7.2.6
Installation in an enclosed space
When Where an appliance(s)
is located within an enclosure and,
permanent openings sized and located in accordance with Items (a) and (b) below
are
shall be supplied to allow
communication between the enclosure and the rest of the structure,
the total volume of the structure may
be used to determine air supply requirements,
provided that the structure is
not constructed as described in Clause 7.2.1(a) and does not comply with Clause
7.2.1(b).
Otherwise, the volume of the enclosure
shall be used.
(a) In all cases, an opening shall be provided that
shallOpenings to permit the free flow of air between the
enclosure and the rest of the building shall
(i) have a free area of not less than 1 in per 1000 Btuh (2225
mm per kW) of the total input of all appliances within the enclosure;
and
(ii) be located not more than 18 in (450 mm) or less than 6 in (150 mm)
above floor level.
(b) When one or more appliances are equipped with draft
control devices, an additional opening shall be supplied having the same
free area as the opening required in Item (a), and the opening shall be located
as near the ceiling as practicable, but in no case lower than the relief
opening of the lowest draft control device.
7.3
Air Supply Openings and Ducts
7.3.1
Except as specified in Clauses 7.3.3 and 7.3.4, a
duct shall be used to provide the outside air supply required
by Clauses 7.2.1 and 7.2.4. The duct shall
(a) be of either metal or a material meeting the
Class I requirements of ULC Standard CAN/ULC-S110;
(b) communicate directly with the outdoors;
(c) be of at least the same cross-sectional area as
the free area of the air supply inlet
opening to which it connects; and
(d) terminate within 1 ft (300 mm) above, and
within 2 ft (600 mm) horizontally from, the burner level
of the appliance having the largest
input.
7.3.2
A square- or rectangular-shaped duct shall only be
used when the required free area of the air supply opening
is 9 in (5800 mm ) or larger, and when used, its smaller dimension shall not be
less than 3 in (75 mm).
7.3.3
An opening may be used in lieu of a duct to provide
the outside air supply to an appliance(s)
as required by Clauses 7.2.1 and 7.2.4, and the opening shall be located within
1 ft (300 mm) above, and 2 ft (600 mm) horizontally from, the burner
level of the appliance having
the largest input.
7.3.4
Certified combustion air supply equipment may be used in lieu of
a duct to provide the outside air supply to
an appliance as required in Clauses
7.2.1 and 7.2.4.
7.3.5
An air supply inlet
opening from the outdoors shall be equipped with a means to prevent the direct
entry of rain and wind, and such means shall not reduce the required free area of
the air supply opening.
7.3.6
An air supply inlet
opening from the outdoors shall be located not less than 12 in (300 mm) above
the outside grade level.
7.4
Air Supply Requirements for Appliances Having a Total Input Exceeding 400 000
Btuh (120 kW) (See Clause 7.1.4.(b).)
7.4.1
Ventilation of the space occupied
by an appliance and equipment
shall be provided by an opening(s) for ventilation
air at the highest practical point communicating with
outdoors. The total cross-sectional area of such an opening(s) shall be at
least 10% of the area required in Clauses 7.4.2 and7.4.3, but in no case shall
the cross-sectional area be less than 10 in (6500 mm ).
7.4.2
When air supply is
provided by natural air flow from the outdoors for natural
draft, partial fan-assisted, fan-assisted, or power
draft-assisted burners,
there shall be a permanent air supply opening(s)
having a cross-sectional area of not less than 1 in per 7000 Btuh (310 mm per
kW) up to and including 1 million Btuh, plus 1 in per 14 000 Btuh (155 mm per
kW) in excess of 1 million Btuh. This opening(s) shall be either located at or
ducted to a point not more than 18 in (450 mm) or less than 6 in (150 mm) above
the floor level. This air supply opening
requirement shall be in. addition to the air
opening for ventilation air required
in Clause 7.4.1. See also Clauses 3.1.4 and 3.1.5.
7.4.3
When air supply is
provided by natural air flow from outdoors for a power burner
and there is no draft regulator, draft
hood, or similar flue gas
dilution device installed in the same space, in addition to the opening for ventilation
air required in Clause 7.4.1, there shall be a
permanent air supply opening(s) having a
total cross-sectional area of not less than 1 in for each 30 000 Btuh (70 mm
per kW) of the total rated input of the burner(s),
and the location of the opening(s) shall not interfere with the intended
purpose of the opening(s) for the ventilation air referred
to in Clause 7.4.1. See also Clauses 3.1.4 and 3.1.5.
7.4.4
When air is provided by natural air flow from
outdoors into a location containing both types of equipment
described in Clauses 7.4.2 and 7.4.3, the
cross-sectional area of the opening(s) shall not be less than the total
required cross-sectional area for both types of equipment
when calculated in accordance with either Clause
7.4.2 or 7.4.3, as applicable. This air supply opening(s)
requirement shall be in addition to the air opening for ventilation
required in Clause 7.4.1. See also Clauses 3.1.4
and 3.1.5.
7.4.5
When an air supply duct
is used to meet the requirements of either Clause 7.4.2 or 7.4.3, its discharge
opening shall be located where there is no possibility of cold air affecting
steam or water pipes and electrical or mechanical equipment.
7.5
Air Supply Dampers, Louvres, and Grilles
7.5.1
The free area of an air
supply opening required in Clauses 7.2 and 7.3 shall be
calculated by subtracting the blockage area of all fixed louvres, grilles, or
screens from the gross area of the opening.
7.5.2
Apertures in a fixed louvre, grille, or screen
shall have no dimension smaller than 0.25 in (6 mm).
7.5.3
Neither a manually operated damper
nor manually adjustable louvres shall be used.
7.5.4
An automatically operated damper
or automatically adjustable louvre shall be
interlocked so that the main burner cannot
operate unless either the damper or
louvre is in the fully open position.
7.5.5
An automatic combustion air damper installed
in the air supply within a dwelling
unit shall be certified.
7.6
Conditions Created by Exhaust Fans, Air Supply Fans, Circulating Fans, or
Fireplaces
When it is determined that the operation of another
appliance or other equipment,
including an exhaust fan, air supply fan,
or circulating fan, adversely affects the venting, combustion, or burning
characteristics of a gas appliance,
either the condition shall be corrected or the fuel supply to the affected appliance
shall be discontinued.
7.7
Engineered Installations
Subject to the approval of the authority
having jurisdiction, outdoor air
supply provision, other than those described in Clauses
7.2 and 7.3, may be used if designed in accordance with good engineering
practice.
7.8
Air Supply by Mechanical Means
7.8.1
When the air supply is
provided by mechanical means, an air flow sensing device shall be installed. It
shall be wired into the safety limit circuit of the primary safety control to
shut off the gas in the event of air supply failure.
When an appliance is
not equipped with a combustion safety
control, the restoration of the gas supply shall be by a
manual reset device.
7.8.2
When all the air supply is
provided by a make-up air heater and
the appliance is interlocked with
the heater, the requirements of
Clauses 7.1 to 7.6 inclusive shall
not apply.