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When this shows up on the exam
The HVAC House exam leans hard on Section 9.32: the principal ventilation fan range, the kitchen and bathroom exhaust rules, make-up air, and the outdoor air table for furnaces. Small Buildings repeats the ventilation questions and adds fireplace and chimney numbers from Sections 9.21 and 9.22. Most questions give you a house description and ask for one number in L/s, m² or mm. The trap is usually a missed condition, not the arithmetic.
The method
- Count the bedrooms. Table 9.32.3.3 is read by bedroom count only. Over 5 bedrooms, the prescriptive path does not apply (OBC Div. B 9.32.3.1.OBC Div. B 9.32.3.1. Required Ventilation(1) The heating-season ventilation required by Clause 9.32.1.2.(1)(b) shall be provided by a mechanical ventilation system complying with (a) good practice such as that described in CAN/CSA-F326-M, "Residential Mechanical Ventilation Systems," (b) for dwelling units with 5 or fewer bedrooms, the balance of this…).
- Read the min and max for the principal fan. Each row gives a minimum and a maximum normal operating exhaust capacity in L/s (OBC Div. B 9.32.3.3.OBC Div. B 9.32.3.3. Principal Ventilation System(1) The principal ventilation system shall incorporate the following components: (a) a principal ventilation fan complying with this Article, and (b) except as permitted by Article 9.32.3.6., provision for the introduction of outdoor air to the dwelling unit, in conformance with Article 9.32.3.4. or 9.32.3.5. (2) The…). The installed fan must fall inside that band.
- Check the supplemental exhaust. A kitchen needs a fan of at least 50 L/s, unless the principal fan intake is the only one and it is in that kitchen, or the principal fan has a kitchen-switched high rate of at least 2.5 times the table minimum. Every bathroom or water-closet room without a principal intake needs at least 25 L/s (OBC Div. B 9.32.3.7.OBC Div. B 9.32.3.7. Supplemental Exhaust(1) Except as provided in Sentences (2) and (3), a supplemental exhaust fan with a rated capacity not less than 50 L/s shall be installed in each kitchen. (2) A supplemental exhaust fan is not required in a kitchen where the only exhaust air intake for the principal ventilation fan is located in that kitchen. (3) A…).
- Check make-up air. If the house has a fuel-fired space- or water-heating appliance that is not direct-vented or mechanically vented, every other exhaust device needs a make-up air fan rated from 100% to 110% of its exhaust capacity, unless an exception in Sentences (6) to (8) applies. The principal fan is exempt only while it runs at or below the table maximum (OBC Div. B 9.32.3.8.OBC Div. B 9.32.3.8. Protection Against Depressurization(1) This Article applies to (a) dwelling units that contain a fuel-fired space-heating appliance or fuel-fired water-heating appliance of other than direct-vented or mechanically vented types, and (b) ancillary spaces that contain an exhaust device, where the space is not within a dwelling unit in a house with a…).
- Check how outdoor air gets in. Through a furnace: compare the fan with Table 9.32.3.4, which allows linear interpolation (OBC Div. B 9.32.3.4.OBC Div. B 9.32.3.4. Ventilation Systems Used in Conjunction with Forced Air Heating Systems(1) Where outdoor air is to be introduced to the dwelling unit through a forced air heating system, the provision of outdoor air shall comply with this Article. (2) Where the actual normal operating exhaust capacity of the fan installed to satisfy the requirement for a principal ventilation fan exceeds the maximum…). Exhaust-only: the circulation fan must be rated at least 5 times the principal fan capacity (OBC Div. B 9.32.3.6.OBC Div. B 9.32.3.6. Exhaust-Only Ventilation Systems(1) A ventilation system with no provision for the introduction of outdoor air to the dwelling unit may only be used where the dwelling unit (a) contains no solid-fuel-burning appliance, no fireplace of other than direct-vented type, and no other fuel-fired space- or water-heating appliance of other than direct-vented…).
- Non-heating season. Natural ventilation uses Table 9.32.2.2 (a fixed area or a percentage of floor area). Mechanical ventilation without cooling needs one air change per hour; with cooling, add the room rates of Table 9.32.2.3 (OBC Div. B 9.32.2.3.OBC Div. B 9.32.2.3. Non-Heating-Season Mechanical Ventilation(1) Where a habitable room or space is not provided with natural ventilation as described in Article 9.32.2.2. and is mechanically cooled, its non-heating-season mechanical ventilation system shall (a) have the capacity to exhaust air from inside the room or space, or to introduce outdoor air into that room or space…).
- Fireplaces and chimneys. Add hearth extensions and clearances in mm, and convert the 100 mm combustion air duct to an equivalent area if the duct is not round.
Worked example 1: principal fan, kitchen and bathrooms
A 4-bedroom house has a natural-draft gas water heater. The principal fan draws from the kitchen, the main bathroom and the ensuite. A powder room has no principal intake. A 150 L/s range hood is planned.
| Step | Work | Result |
|---|---|---|
| Fan band | Table 9.32.3.3, row "4", min and max columns | 26 to 38 L/s |
| Kitchen exemption | 2.5 x 26 L/s | high rate of 65 L/s, kitchen switch |
| Powder room | no principal intake, so supplemental fan | 25 L/s |
| Range hood make-up air | 150 L/s to 150 x 1.10 | 150 to 165 L/s |
The principal fan running at, say, 30 L/s needs no make-up air because 30 L/s is not above the 38 L/s maximum (OBC Div. B 9.32.3.8.OBC Div. B 9.32.3.8. Protection Against Depressurization(1) This Article applies to (a) dwelling units that contain a fuel-fired space-heating appliance or fuel-fired water-heating appliance of other than direct-vented or mechanically vented types, and (b) ancillary spaces that contain an exhaust device, where the space is not within a dwelling unit in a house with a…). When the fan runs at its 65 L/s high rate, it is above the maximum, so the exemption no longer covers it in that mode. Raise this with the designer.
Worked example 2: outdoor air through the furnace
The house is in a location with a January 2.5% temperature of -10°C. The measured return airflow upstream of the outdoor air connection is 214 L/s and the principal fan is 26 L/s.
- Furnace airflow under Clause 9.32.3.4.(3)(a): 214 + 26 = 240 L/s.
- Table 9.32.3.4, -10°C block, 15°C mixed air column: the 200 L/s row gives 44 L/s and the 300 L/s row gives 66 L/s.
- Interpolate (permitted by Sentence 9.32.3.4.(4)): 44 + (40/100) x 22 = 52.8 L/s.
- The 26 L/s fan is below 52.8 L/s, so no tempering of the outdoor air is needed (OBC Div. B 9.32.3.4.OBC Div. B 9.32.3.4. Ventilation Systems Used in Conjunction with Forced Air Heating Systems(1) Where outdoor air is to be introduced to the dwelling unit through a forced air heating system, the provision of outdoor air shall comply with this Article. (2) Where the actual normal operating exhaust capacity of the fan installed to satisfy the requirement for a principal ventilation fan exceeds the maximum…).
Sentence 9.32.3.4.(2) works with a 15°C mixed air temperature or the furnace maker's minimum return air temperature, whichever is less. This example assumes the maker gives no lower value, so the 15°C column governs.
If the fan had exceeded the limit, the system would need tempering, or would have to move to Article 9.32.3.5 or CSA F326.
Worked example 3: non-heating-season ventilation
An unfinished basement inside a dwelling unit measures 9 m x 12 m. Table 9.32.2.2, "within a dwelling unit" rows, gives 0.2% of the floor area (OBC Div. B 9.32.2.2.OBC Div. B 9.32.2.2. Non-Heating-Season Natural Ventilation(1) The unobstructed openable ventilation area to the outdoors for rooms and spaces in residential buildings ventilated by natural means shall conform to Table 9.32.2.2. (2) Where a vestibule opens directly off a living or dining room within a dwelling unit, ventilation to the outdoors for such rooms may be through…).
- Floor area: 9 x 12 = 108 m².
- Required area: 108 x 0.002 = 0.216 m² of unobstructed openable area.
A windowless den, 3.0 m x 3.6 m with a 2.4 m ceiling, is not mechanically cooled. It needs one air change per hour (OBC Div. B 9.32.2.3.OBC Div. B 9.32.2.3. Non-Heating-Season Mechanical Ventilation(1) Where a habitable room or space is not provided with natural ventilation as described in Article 9.32.2.2. and is mechanically cooled, its non-heating-season mechanical ventilation system shall (a) have the capacity to exhaust air from inside the room or space, or to introduce outdoor air into that room or space…).
- Volume: 3.0 x 3.6 x 2.4 = 25.92 m³, so 25.92 m³/h.
- Convert: 25.92 x 1000 L / 3600 s = 7.2 L/s.
Worked example 4: fireplace hearth, combustion air and chimney
A masonry fireplace has a 1,000 mm wide opening and a fire chamber floor 350 mm above the hearth.
- Base hearth depth: 400 mm in front of the opening, measured from the facing (OBC Div. B 9.22.5.1.OBC Div. B 9.22.5.1. Hearth Extension(1) Except as required in Sentence (2), fireplaces shall have a noncombustible hearth extending not less than 400 mm in front of the fireplace opening measured from the facing, and not less than 200 mm beyond each side of the fireplace opening. (2) Where the fire chamber floor is elevated more than 150 mm above the…).
- Elevation over 150 mm and up to 300 mm adds 50 mm. The 50 mm above 300 mm adds another 25 mm. Depth: 400 + 50 + 25 = 475 mm.
- Width: 200 mm beyond each side, so 1,000 + 2 x 200 = 1,400 mm.
- Combustion air duct: at least 100 mm diameter or equivalent area (OBC Div. B 9.22.1.4.OBC Div. B 9.22.1.4. Combustion Air(0.1) Every solid fuel-fired fireplace, including a factory-built fireplace, shall have a supply of combustion air from outdoors in accordance with Sentences (0.2) to (1). (0.2) The combustion air shall be supplied by a noncombustible and corrosion-resistant supply duct. (0.3) The supply duct shall have (a) a diameter…). Area = 3.1416 x 50² = 7,854 mm². A 75 mm deep rectangular duct needs 7,854 / 75 = 104.7, so 105 mm wide.
- The interior masonry chimney needs 50 mm to combustible framing, but flooring and subflooring need only 12 mm (OBC Div. B 9.21.5.1.OBC Div. B 9.21.5.1. Clearance from CombustibleMaterials(1) The clearance between masonry or concrete chimneys and combustible framing material shall be not less than, (a) 50 mm for interior chimneys, and (b) 12 mm for exterior chimneys. (See Note A-9.21.5.1.(1)) (2) A clearance of not less than 150 mm shall be provided between a cleanout opening and combustible material…).
Common mistakes
- Using the maximum column of Table 9.32.3.3 for the 2.5 times kitchen rule. The multiplier applies to the minimum.
- Counting a den or office as a bedroom, or missing a basement bedroom.
- Adding a bathroom fan where a principal intake already serves that bathroom, or forgetting the kitchen fan when the principal fan draws from several rooms.
- Allowing make-up air from 90% to 110%. The code allows no less than 100% and no more than 110%.
- Forgetting to add the principal fan to the measured return airflow before entering Table 9.32.3.4, or rounding to the lower row instead of interpolating.
- Applying the 5 L/s and 10 L/s room rates to a room that is not mechanically cooled. Uncooled rooms use one air change per hour.
- Leaving m³/h unconverted. Divide by 3.6 to get L/s.
- Using 2% or 4% for spaces within a dwelling unit. Those rates are for spaces outside dwelling units.
- Using the 12 mm flooring clearance for chimney framing, or the 12 mm exterior chimney value for an interior chimney.
- Adding 200 mm in total to the hearth width instead of 200 mm on each side.
- For supply ducts (OBC Div. B 9.33.6.8.OBC Div. B 9.33.6.8. Clearances of Ducts and Plenums(1) Reserved. (2) Where the plenum clearance is 75 mm or less, the clearance between a supply duct and combustible material shall (a) be equal to the required plenum clearance within 450 mm of the plenum, and (b) be not less than 12 mm at a distance of 450 mm or more from the plenum, except that this clearance may be…), applying the reduced clearance without a shielding bend or offset.
Find it fast in the code PDF
Bookmark Division B > Part 9 > Section 9.32, then search:
- "normal operating exhaust capacity" for Table 9.32.3.3 and the fan rules.
- "kitchen exhaust" for the high-rate kitchen exemption.
- "outdoor make-up air" for Article 9.32.3.8.
- "Linear interpolation is permitted" for Table 9.32.3.4.
- "one air change per hour" for uncooled mechanical ventilation.
- "Unfinished basement space" for Table 9.32.2.2.
For fireplaces, bookmark Section 9.22 and search "hearth extending" or "equivalent area". For chimneys, Section 9.21 and "combustible framing material". For supply ducts, Section 9.33 and "plenum clearance".
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Based on the official 2024 Building Code Compendium on ontario.ca.
© King's Printer for Ontario, 2024. Reproduced with permission.
OBC Div. B 9.32.3.1. Required Ventilation
Open OBC Div. B 9.32.3.1. in the code viewer(1)The heating-season ventilation required by Clause 9.32.1.2.(1)(b) shall be provided by a mechanical ventilation system complying with
(a)good practice such as that described in CAN/CSA-F326-M, "Residential Mechanical Ventilation Systems,"
(b)for dwelling units with 5 or fewer bedrooms, the balance of this Subsection, or
(c)Part 6.
(2)Mechanical ventilation systems complying with the balance of this Subsection shall incorporate at least the following components:
(a)a principal ventilation system complying with Article 9.32.3.3.,
(b)supplemental exhaust fans complying with Article 9.32.3.7., and
(c)protection against depressurization in accordance with Article 9.32.3.8.
OBC Div. B 9.32.3.3. Principal Ventilation System
Open OBC Div. B 9.32.3.3. in the code viewer(1)The principal ventilation system shall incorporate the following components:
(a)a principal ventilation fan complying with this Article, and
(b)except as permitted by Article 9.32.3.6., provision for the introduction of outdoor air to the dwelling unit, in conformance with Article 9.32.3.4. or 9.32.3.5.
(2)The principal ventilation fan shall be capable of operating at an exhaust capacity complying with Table 9.32.3.3., referred to hereinafter as the "normal operating exhaust capacity." (See Note A-9.32.3.3.(2))
(3)The requirement for a principal ventilation fan may be satisfied by a single fan, by the exhaust side of a heat recovery ventilator, or by a group of fans, provided all fans in the group are controlled simultaneously by a controller complying with Sentences (5) to (7). (See Note A-9.32.3.3.(3))
(4)The components of the principal ventilation system shall be approved by their manufacturer for continuous operation.
(5)The principal ventilation fan shall be controlled by a manual switch located within the living area of the dwelling unit and clearly marked ventilation fan. (See Note A-9.32.3.3.(5))
(6)If all controls serving the principal ventilation fan are in the "off" position, the principal ventilation system shall not operate.
(7)The requirement for a manual switch stated in Sentence (5) can be satisfied by a manual override incorporated in a dehumidistat or other automatic control, provided
(a)the automatic control is located within the living area of the dwelling unit, and
(b)the manual override is clearly marked ventilation fan.
(8)Where the principal ventilation fan is controlled by a dehumidistat or other automatic control in addition to the manual switch required by Sentence (5), the manual switch shall be capable of activating the fan regardless of the setting of the automatic control.
(9)Where an exhaust air intake for the principal ventilation fan is connected directly to the return side of the duct system of a forced air heating system or other forced air distribution system, it shall be connected, where applicable, not less than 1 m upstream from the connection of the outdoor air supply duct required by Sentence 9.32.3.4.(5).
(10)Exhaust air intakes for principal ventilation fans located in kitchens, bathrooms and water-closet rooms shall be located in the ceiling or on the wall not less than 2 m above the floor. (See Note A-9.32.3.3.(10))
OBC Div. B 9.32.3.7. Supplemental Exhaust
Open OBC Div. B 9.32.3.7. in the code viewer(1)Except as provided in Sentences (2) and (3), a supplemental exhaust fan with a rated capacity not less than 50 L/s shall be installed in each kitchen.
(2)A supplemental exhaust fan is not required in a kitchen where the only exhaust air intake for the principal ventilation fan is located in that kitchen.
(3)A supplemental exhaust fan is not required in a kitchen where the principal ventilation fan draws from that kitchen and other rooms, provided
(a)the principal ventilation fan can be switched to a high exhaust rate equal to not less than 2.5 times the minimum normal operating exhaust capacity specified in Table 9.32.3.3., and
(b)the high exhaust rate of the principal ventilation fan, as described in Clause (a), is activated by a manual switch in the kitchen labeled "kitchen exhaust."
(4)Where an exhaust air intake for the principal ventilation fan is not located in a bathroom or water-closet room, a supplemental exhaust fan with a rated capacity not less than 25 L/s shall be installed in that bathroom or water-closet room.
(5)Where the intake for a supplemental exhaust fan other than a cooking appliance exhaust fan serving a cooktop is installed in a kitchen, it shall be installed in the ceiling or on the wall at not less than 2 m above the floor.
(6)A supplemental exhaust fan required by this Article shall be controlled by a manual switch located in the room served by the fan.
(7)Where a kitchen or bathroom is exempted from the requirement to install a supplemental exhaust fan by virtue of Sentence (2) or (3), the principal ventilation fan shall be controlled by a manual switch located in the kitchen or bathroom and wired in parallel with the manual switch required by Sentence 9.32.3.3.(5).
(8)Where a supplemental exhaust fan required by this Article is controlled by a dehumidistat or other automatic control in addition to the manual switch required by Sentence (6), the manual switch shall be capable of activating the fan regardless of the setting of the automatic control.
OBC Div. B 9.32.3.8. Protection Against Depressurization
Open OBC Div. B 9.32.3.8. in the code viewer(1)This Article applies to
(a)dwelling units that contain a fuel-fired space-heating appliance or fuel-fired water-heating appliance of other than direct-vented or mechanically vented types, and
(b)ancillary spaces that contain an exhaust device, where the space is not within a dwelling unit in a house with a secondary suite and where the house with a secondary suite contains a fuel-fired space-heating appliance or fuel-fired water-heating appliance of other than direct-vented or mechanically vented types.
(2)Except as provided in Sentences (6) to (8), any mechanical air exhausting device, other than the principal ventilation fan operating at a rate not greater than the maximum permitted by Table 9.32.3.3., shall be provided with outdoor make-up air supplied by a fan rated to deliver outdoor air to the dwelling unit at a rate
(a)not less than the exhaust capacity of the device, and
(b)not greater than that exhaust capacity plus 10%.
(3)An outdoor make-up air supply fan required by Sentence (2) shall be wired so that it is activated whenever the device for which it supplies outdoor make-up air is activated.
(4)The outdoor make-up air required by Sentence (2) shall be
(a)introduced to a normally unoccupied area in the dwelling unit, or
(b)tempered to at least 12°C before being introduced to occupied areas or to a supply duct system.
(5)If the outdoor make-up air required by Sentence (2) is not tempered upstream of the supply fan, the supply fan required by Sentence (2) shall be approved by the manufacturer for the handling of untempered outdoor air.
(6)The provision of make-up air as described in Sentence (2) is not required in a dwelling unit with solid-fuel-burning appliances, where all other fuel-fired appliances are direct-vented or mechanically vented.
(7)The provision of make-up air as described in Sentence (2) is not required if it can be shown using the test procedures in CAN/CGSB-51.71, "Depressurization Test," that the maximum depressurization levels to which fuel-fired space- or water-heating appliances and their venting systems will be exposed will not exceed the limits set out in CAN/CGSB-51.71 for the categories of fuel-fired appliances and venting systems installed in the dwelling unit.
(8)The provision of make-up air as described in Sentence (2) is not required for mechanical exhausting devices operating a subfloor depressurization system installed for the purpose of reducing the risk of radon ingress.
OBC Div. B 9.32.3.4. Ventilation Systems Used in Conjunction with Forced Air Heating Systems
Open OBC Div. B 9.32.3.4. in the code viewer(1)Where outdoor air is to be introduced to the dwelling unit through a forced air heating system, the provision of outdoor air shall comply with this Article.
(2)Where the actual normal operating exhaust capacity of the fan installed to satisfy the requirement for a principal ventilation fan exceeds the maximum outdoor airflow permitted by Table 9.32.3.4. for a mixed air temperature of 15°C or exceeds the minimum acceptable return air temperature specified by the manufacturer of the furnace, whichever is less, then either
(a)the system shall incorporate a means for tempering outdoor air introduced to the heating system ducts so that a mixed air temperature of 15°C or the minimum acceptable return air temperature specified by the manufacturer of the furnace, whichever is less, is achieved when the outdoor air is at the January 2.5% temperature and the indoor air temperature is 22°C, or
(b)this Article shall be considered to be no longer applicable and the mechanical ventilation system shall comply with either Clause 9.32.3.1.(1)(a) or with Article 9.32.3.5.
(3)For the purposes of Table 9.32.3.4., the furnace airflow shall be determined
(a)by operating the forced air heating system's circulation fan at the rate chosen to satisfy Clause (9)(a) when measuring the return airflow in the furnace return air plenum immediately upstream of the connection of the outdoor air supply duct required by Sentence (5) and then adding this return airflow measurement to the actual normal operating exhaust capacity of the fan installed to satisfy the requirement for a principal ventilation fan, or
(b)by using the manufacturer's rated flow for the furnace for 150 Pa static pressure and the wiring configuration necessary to achieve the flow specified in Clause (9)(a).
(4)Linear interpolation is permitted in using Table 9.32.3.4.
(5)An outdoor air supply duct shall be installed between the outdoors and the furnace return air plenum and shall be connected
(a)not less than 3 m upstream of the plenum connection to the furnace, as measured along the length of the duct, or
(b)through an acceptable mixing device installed in the return air plenum.
(6)The outdoor air supply duct required by Sentence (5) shall incorporate a flow-regulating damper.
(7)Where the outdoor air supply duct required by Sentence (5) is not connected to an outdoor air supply fan, it shall be connected downstream of all return branch connections.
(8)Where the outdoor air supply duct required by Sentence (5) is connected to an auxiliary outdoor air supply fan, the auxiliary outdoor air supply fan shall be
(a)approved by the manufacturer for the handling of untempered outdoor air if it will be handling untempered outdoor air,
(b)approved by the manufacturer for continuous operation, and
(c)designed to provide an outdoor air supply flow within ± 10% of the actual normal operating exhaust capacity of the exhaust fan installed to satisfy the requirement for a principal ventilation fan.
(9)The principal ventilation fan control required by Sentence 9.32.3.3.(5) shall be wired in such a way that
(a)activation of the principal ventilation fan automatically activates the forced air heating system's circulation fan to provide an airflow not greater than the space-heating airflow,
(b)where applicable, activation of the principal ventilation fan automatically activates the auxiliary outdoor air supply fan described in Sentence (8), and
(c)the auxiliary outdoor air supply fan does not operate when the principal ventilation fan is not operating.
(10)With the principal ventilation fan operating at its normal operating exhaust capacity, the airflow in the outdoor air supply duct shall be measured and the flow-regulating damper required by Sentence (6) shall be adjusted and permanently fixed so that the airflow in the outdoor air supply duct is within ± 10% of the actual normal operating exhaust capacity of the principal ventilation fan.
(11)The airflow measurements required by Sentences (3) and (10) shall be done using a method accurate to within ± 15% of the flow rate being measured.
(12)All connections between the ventilation system and the heating system shall be in accordance with Articles 9.33.4.1. and 9.33.5.2.
OBC Div. B 9.32.3.6. Exhaust-Only Ventilation Systems
Open OBC Div. B 9.32.3.6. in the code viewer(1)A ventilation system with no provision for the introduction of outdoor air to the dwelling unit may only be used where the dwelling unit
(a)contains no solid-fuel-burning appliance, no fireplace of other than direct-vented type, and no other fuel-fired space- or water-heating appliance of other than direct-vented or mechanically vented types, and
(b)has a forced air distribution system with a circulation fan with a rated capacity equal to at least 5 times the actual normal operating exhaust capacity of the fan installed to satisfy the requirement for a principal ventilation fan, a supply side that complies with Sentences 9.32.3.5.(10) to (12), and a return side that complies with Articles 9.33.6.12. and 9.33.6.13.
(2)Except as provided in Sentence (3), where an exhaust-only system is installed, the principal ventilation fan control required by Sentence 9.32.3.3.(5) shall be wired in such a way that, where applicable, activation of the principal ventilation fan automatically activates the circulation fan of the forced air distribution system required by Clause (1)(b) at its rated capacity.
(3)Interlocking the forced air distribution system's circulation fan with the principal ventilation fan as required by Sentence (2) is not required where the forced air distribution system is equipped with a control that automatically activates the circulation fan at user-selected intervals.
OBC Div. B 9.32.2.3. Non-Heating-Season Mechanical Ventilation
Open OBC Div. B 9.32.2.3. in the code viewer(1)Where a habitable room or space is not provided with natural ventilation as described in Article 9.32.2.2. and is mechanically cooled, its non-heating-season mechanical ventilation system shall
(a)have the capacity to exhaust air from inside the room or space, or to introduce outdoor air into that room or space, at a rate conforming with Table 9.32.2.3., or
(b)comply with Subsection 9.32.3.
(2)In applying Clause (1)(a),
(a)at least one bedroom in each dwelling unit shall be designated as the master bedroom,
(b)air change rates for any combined living/dining or family/dining space shall be determined as if the spaces were individual rooms,
(c)where a basement incorporates rooms of the types designated in Table 9.32.2.3., the assigned air change rate for each room shall be as specified for those types of rooms,
(d)basement areas used for other purposes that exceed 2/3 of the total basement floor area shall be assigned an air change rate of 10 L/s,
(e)basement areas used for other purposes that are 2/3 of the total basement floor area or less shall be assigned an air change rate of 5 L/s, and
(f)other habitable rooms, other than spaces intended solely for access, egress, storage, or service equipment, shall be assigned an air change rate of 5 L/s.
(3)Where a habitable room or space is not provided with natural ventilation as described in Article 9.32.2.2. and is not mechanically cooled, the non-heating-season mechanical ventilation system shall have the capacity to exhaust indoor air from the room or space or to introduce outdoor air to that room or space at a rate of one air change per hour.
(4)A non-heating-season mechanical ventilation system shall be designed and installed in conformance with good practice such as that described in the ASHRAE Handbooks and Standards, the HRAI Digest, the Hydronics Institute Manuals and the SMACNA Manuals.
OBC Div. B 9.32.2.2. Non-Heating-Season Natural Ventilation
Open OBC Div. B 9.32.2.2. in the code viewer(1)The unobstructed openable ventilation area to the outdoors for rooms and spaces in residential buildings ventilated by natural means shall conform to Table 9.32.2.2.
(2)Where a vestibule opens directly off a living or dining room within a dwelling unit, ventilation to the outdoors for such rooms may be through the vestibule.
(3)Openings for natural ventilation other than windows shall provide protection from the weather and insects.
(4)Screening shall be of corrosion-resistant material.
Show all 12 articles
OBC Div. B 9.22.5.1. Hearth Extension
Open OBC Div. B 9.22.5.1. in the code viewer(1)Except as required in Sentence (2), fireplaces shall have a noncombustible hearth extending not less than 400 mm in front of the fireplace opening measured from the facing, and not less than 200 mm beyond each side of the fireplace opening.
(2)Where the fire chamber floor is elevated more than 150 mm above the hearth, the dimension of the hearth measured perpendicular to the plane of the fireplace opening shall be increased by not less than
(a)50 mm for an elevation above 150 mm and not more than 300 mm, and
(b)an additional 25 mm for every 50 mm in elevation above 300 mm.
OBC Div. B 9.22.1.4. Combustion Air
Open OBC Div. B 9.22.1.4. in the code viewer(0.1)Every solid fuel-fired fireplace, including a factory-built fireplace, shall have a supply of combustion air from outdoors in accordance with Sentences (0.2) to (1).
(0.2)The combustion air shall be supplied by a noncombustible and corrosion-resistant supply duct.
(0.3)The supply duct shall have
(a)a diameter of not less than 100 mm or equivalent area, and
(b)an exterior intake for entry of air from the outdoors.
(0.4)The supply duct shall contain a tight-fitting damper that shall be located close to the interior outlet and be operable from the room containing the fireplace.
(0.5)The operating mechanism shall clearly indicate the actual position of the damper.
(0.6)The interior outlet shall
(a)be located as close as possible to the opening in the face of the fireplace, and
(b)be designed to prevent embers from entering the supply duct.
(1)Where a supply of combustion air is provided directly to the fire chamber of a fireplace, including a factory-built fireplace, the installation shall comply with the "Outdoor Air Supply" requirements provided in CAN/CSA-A405-M, "Design and Construction of Masonry Chimneys and Fireplaces."
OBC Div. B 9.21.5.1. Clearance from CombustibleMaterials
Open OBC Div. B 9.21.5.1. in the code viewer(1)The clearance between masonry or concrete chimneys and combustible framing material shall be not less than,
(a)50 mm for interior chimneys, and
(b)12 mm for exterior chimneys. (See Note A-9.21.5.1.(1))
(2)A clearance of not less than 150 mm shall be provided between a cleanout opening and combustible material.
(3)Combustible flooring, subflooring and ceiling finishes shall have not less than a 12 mm clearance from masonry or concrete chimneys.
OBC Div. B 9.33.6.8. Clearances of Ducts and Plenums
Open OBC Div. B 9.33.6.8. in the code viewer(1)Reserved.
(2)Where the plenum clearance is 75 mm or less, the clearance between a supply duct and combustible material shall
(a)be equal to the required plenum clearance within 450 mm of the plenum, and
(b)be not less than 12 mm at a distance of 450 mm or more from the plenum, except that this clearance may be reduced to zero beyond a bend or offset in the duct sufficiently large to shield the remainder of the supply duct from direct radiation from the furnace heat exchanger. (See Note A-3.6.5.6.(2))
(3)Where the plenum clearance is more than 75 mm but not more than 150 mm, the clearance between a supply duct and combustible material shall be
(a)equal to the required plenum clearance within a horizontal distance of 1.8 m of the plenum, and
(b)not less than 12 mm at a horizontal distance of 1.8 m or more from the plenum, except that this distance may be reduced to zero beyond a bend or offset in the duct sufficiently large to shield the remainder of the duct from direct radiation from the furnace heat exchanger. (See Note A-3.6.5.6.(3))
(4)Where the plenum clearance is more than 150 mm, the clearance between a supply duct and combustible material shall be
(a)equal to the required plenum clearance within a horizontal distance of 1 m of the plenum,
(b)not less than 150 mm within a horizontal distance between 1 m and 1.8 m from the plenum, and
(c)not less than 25 mm at a horizontal distance of 1.8 m or more from the plenum, except that this distance may be reduced to 8 mm beyond a bend or offset in the duct sufficiently large to shield the remainder of the supply duct from direct radiation from the furnace heat exchanger. (See Note A-3.6.5.6.(4))
(5)Where a register is installed in a floor directly over a pipeless furnace, a double-walled register box with not less than 100 mm between walls, or a register box with the warm-air passage completely surrounded by the cold-air passage, shall be permitted in lieu of the clearances listed in Sentences (2) to (4).