BCAB 1980 - Heat-recovery ventilators in a mechanical ventilation system

Heat-recovery ventilators in a mechanical ventilation system

Project Description

The project is the design of an alteration to an existing house containing one dwelling unit.

It is proposed that the mechanical ventilation system design include two heat-recovery ventilators (HRVs), one for each of the upper and lower floor areas.  Each HRV will have an exhaust and intake on an exterior wall and will supply fresh air to bedrooms and exhaust from bathrooms.

Applicable Code requirements (BCBC 2024)

Sentence 9.32.3.1.(1), Division B, Required Ventilation

(1) Every dwelling unit that is supplied with electrical power shall be provided by (sic) a mechanical ventilation system that conforms to

(a) CAN/CSA-F326-M, "Residential Mechanical Ventilation Systems,"

(b) this Subsection, or

(c) for ducted mechanical ventilation systems serving more than one dwelling unit in a house with a secondary suite including their common spaces, the mechanical ventilation system shall comply with this Subsection or Part 6.

Sentences 9.32.3.2.(1 and 2), Division B, Design and Installation

(1) Aspects of mechanical ventilation systems not specifically described in this Subsection shall be designed, constructed and installed in accordance with good practice such as that described in the ASHRAE Handbooks and Standards, the HRAI Digest the HRAI Residential Mechanical Ventilation Manual, the Hydronics Institute Manuals and the SMACNA Manuals.

(2) Exhaust fans and supply fans shall be installed in accordance with this Subsection and the manufacturer’s instructions.

Sentence 9.32.3.3.(1), Division B, Mechanical Ventilation System Components

(1) A mechanical ventilation system shall include:

(a) a principal ventilation fan system that

(i) provides supply air in accordance with Article 9.32.3.4., and

(ii) includes an exhaust fan that conforms with Article 9.32.3.5.,

(b) the kitchen and bathroom exhaust fans that are required by Article 9.32.3.6., and

(c) if the building includes a heated crawl space, the components that are required by Article 9.32.3.7.

Sentence 9.32.3.4.(4), Division B, Ventilation Systems Supply Air

(4) Where the principal ventilation system is a heat-recovery ventilator, the heat-recovery ventilator shall

(a) provide supply air through dedicated ducting to

(i) each bedroom,

(ii) each floor level without a bedroom, and

(iii) each ancillary space described in Subclause (2)(a)(iii), and

(b) draw exhaust air, through dedicated ducting,

(i) from one or more indoor inlets, at least one of which is located at least 2 m above the floor of the uppermost floor level, and

(ii) at the capacity rating of the heat-recovery ventilator, which shall be no less than the air-flow rate specified in Table 9.32.3.5.

Sentence 9.32.3.5.(1), Division B, Principal Ventilation System Exhaust Fan (excerpt)

(1) A principal ventilation system exhaust fan shall

(a) run continuously, and

(b) provide at least the air-flow rate specified in Table 9.32.3.5.

Sentence 9.32.3.6.(1), Division B, Kitchen and Bathroom Exhaust Fans

(1) An exhaust fan that provides at least the air-flow rate specified in Table 9.32.3.6. shall be installed in

(a) every kitchen, and

(b) every bathroom or water-closet room, unless the bathroom or water-closet room is served by the principal ventilation system exhaust fan that complies with Article 9.32.3.5.

Decision being appealed (Local Authority’s position)

Only one mechanical ventilation system is permitted per dwelling unit.  A system which includes two HRVs is not Code-compliant.

In some cases, the Code explicitly permits multiple components (e.g. multiple kitchen and bathroom fans) but in some cases the Code limits that component to one (e.g., one mechanical ventilation system and one principal ventilation system exhaust fan).

Neither the referenced standard nor the documents regarding good practice provide any guidance for installing more than one HRV in a single dwelling and they provide no guidance on how to balance them.

Appellant's position

In this existing house, two HRVs are necessary to overcome complex ducting limitations and avoid excessive duct run lengths from one floor to the other.

Two HRVs can be used provided that the minimum total ventilation requirements are satisfied, air is supplied to and exhausted from the appropriate rooms, and the system is properly balanced.

Appeal Board Decision #1980

The Board reverses the decision of the local authority.

It is the determination of the Board that the Code requirements related to a mechanical ventilation system can be satisfied in a system that includes two HRVs.

Reason for decision

A mechanical ventilation system will include multiple pieces of equipment and components, such as those listed in Sentence 9.32.3.3.(1), Division B.  All of the pieces and components, together, comprise a mechanical ventilation system.  The Board interprets that where the Code stipulates that a mechanical ventilation system must include a certain sub-system (e.g., a “principal ventilation fan system” as in Clause 9.32.3.3.(1)(a), Division B) or a certain piece of equipment (e.g., a “principal ventilation system exhaust fan” as in Sentence 9.32.3.5.(1), Division B) it does not prohibit the installation of two such sub-systems or pieces of equipment.

In this case, each HRV must distribute air on the floor area it serves in compliance with Sentence 9.32.3.4.(4), Division B, and the minimum air-flow rate for each HRV can be determined from Table 9.32.3.5., Division B, for the floor area served by that HRV.  Other rules, such as those located in the various Articles in Subsection 9.32.3., Division B, apply.

It is the responsibility of the owner (or their designated contractor) to find and follow good practice in the design and installation of the system, such as is described in the referenced standard or guides, so that the Code minimum ventilation rates are achieved.

Don Pedde
Chair, Building Code Appeal Board

Dated:  September 4, 2025