Date of Publication: June 30, 2025 [2022.03.V-02.C]
Subject: Drain Water Heat Recovery Unit (DWHR) Installations in Houses with Septic Systems 2024 OBC Update
Summary of Updates: No changes to recommendations or references.
2024 Ontario Building Code [O.Reg 163/24 Amended to 5/25] Reference(s):
Article 12.2.1.2. of Div. B
Supplementary Bulletin SB-12, Chapters 1 and 3
Incoming Request:
In a home that uses a septic system, the sanitary building drain is typically located at the mid-point of the basement foundation wall (approximately 3 to 4 feet above the basement floor) which leaves an insufficient amount of space above the drain to install the DWHR unit in a vertical position as per the specifications of the Standard CSA B55.2. This may not be discovered until inspection of the plumbing rough-in, making enforcement particularly contentious.
Are Drain Water Heat Recovery (DWHR) systems required to be installed in a residence with a septic system?
Executive Summary:
Single story homes on septic may not provide enough vertical space for correct installation of DWHR units, which are required for all energy efficiency compliance options except “other” (Energy Star and R-2000). Early identification of this potential problem will assist building officials and applicants in finding a compliant solution.
Discussion & Considerations:
In a two-storey house with bathrooms on the second storey it will be possible to install a DWHR in a vertical position in order to meet the OBC and the CSA standard by locating the unit on the first floor. In a single storey house, this will only be possible where the lot is a “walk-out” and the septic tank is located such that the building drain exits in the building low enough to allow a vertical installation. In other cases it will be impossible to install a DWHR correctly.
One possible solution is to install a sewage ejector at the lowest level of the basement floor to pump up the shower waste to the elevation of the building drain. However, this is not a real solution both in terms of energy use and long-term maintenance.
Since both the prescriptive and performance (modeling) compliance options require use of a DWHR, another solution is to use the “Other Acceptable Compliance Method” (Energy Star or R-2000) as described in Subsection 3.1.3. of Chapter 3 of SB-12, and do a trade off of the DWHR for another energy efficiency feature. Until such time as the Code is revised to remove the prescriptive requirement for a DWHR in both the prescriptive and performance compliance paths, a house will have to be either Energy Star or R-2000 compliant in order to eliminate the need for a DWHR.
Risk/Benefit Analysis:
Although this guidance does follow the intent and wording of the code, the risk of requiring the “Other Acceptable Compliance Method” for all homes where a DWHR cannot be installed is not insignificant. It is an additional cost for an applicant, and is very likely seen as an unnecessary expense by designers, builders and homeowners. When building officials are perceived to be inflexible and unable to provide solutions, it is an extra burden for staff and the municipality as a whole. Building officials may want conduct research into energy efficiency trade-offs for a DWHR to and suggest an Alternative Solution Proposal where appropriate.
Final Recommendation:
Building officials should communicate very early in the review phase that a DWHR may not fit in the vertical space between the first floor showers and the horizontal building drain where a house has been constructed on a septic system. This will give the applicant an opportunity to look for solutions. Inspectors should bring this concern to the builder at the earliest stage possible.
Disclaimer:
This guidance document is intended to assist building officials by gathering relevant information to interpret the OBC Act and the prescriptive requirements of the Ontario Building Code, and is intended to be a best practice aid for building officials.
The views expressed within this guidance document should not be considered as the official interpretation of legislated requirements based on the Ontario Building Code, as the final responsibility for interpretation rests with the local Authority Having Jurisdiction.
The views of this advisory committee should not be construed as legal advice.