Canadian Contractor

Dave Gray   

Under Pressure, Part 2 of 2

Renovation Contractor

As we make homes tighter, we increase the risk of dangerous combustion gas build-up

As we make homes tighter, we increase the risk of dangerous combustion gas build-up

By Marshall Leslie

Now that most residential construction spending in Canada is devoted to renovations, homeowners are aware that building envelope improvements, mechanical upgrades, and new appliances are among the biggest expenditures they can make. The payoff from new windows, doors, furnaces, range vents, fireplaces, water heaters, and air sealing is improved comfort. If not done properly however, all that effort will pose a health risk if a build up of combustion products occurs in the house.

Combustion products in the house can come from gas, oil, or wood appliances and heating devices, and occasional leaks from an attached garage. They pose a health risk if make-up air is not supplied in the right amount, and fans and dryers cause depressurization, to the point where appliance vents are reversed and combustion devices spill their products indoors. Depressurization happens when the air pressure inside a house is lower than it is outside.

Renovated houses with air-sealed building envelopes, window and door replacements, and new HVAC systems may experience this problem. It’s a problem that a spokesman for the Canadian Association of Fire Chiefs in 2017 suggested had caused the deaths by carbon monoxide poisoning of at least 50 people in Canada every year.


Following the solutions and recommendations of a Canadian voluntary standard – CSA F300-13 Residential depressurization – could stop that from happening. This Canadian Standards Association publication is for everyone that sells or installs gas-, oil-, and wood-burning appliances or ventilation equipment, renovators, inspectors, home improvement dealers, utilities – even the DIY crowd.

In 25 pages, F300 describes how to perform two alternative types of assessment. One calculates predicted house depressurization using floor area, exhaust flows, and geographic location, and can be performed with or without a blower door test. The second is a step-by-step field test performed under light wind conditions, with detailed preparation – exhausts off, openings sealed, furnace and basement open. A manometer (it measures the difference in pressure between two points) is required.

F300 was developed with the use of materials provided by HRAI Canada and has been used in some of its educational offerings. The BC Technical Safety Council references F300 in its guidelines for the gas services industry. Enbridge Gas Distribution encourages homebuilders and mechanical and heating contractors to use F300 to identify potential safety problems when renovating, when exhaust fans are installed or exchanged, and when installing or replacing gas or oil appliances.

Gary Sharp, the Director of Renovator Services for the Canadian Home Builders’ Association (who writes elsewhere in this magazine) states: “When a home is made tighter, it may affect how the mechanical systems work. It is important to ensure that the combustion equipment is operating as intended by receiving adequate combustion air and fully exhausting the products of combustion. The F300 Standard provides a method to identify when residential depressurization may cause a health risk and provides solutions to prevent or mitigate the build-up of combustion products in the house. It is important that this be used and understood by all involved in the renovation.”

John Goshulak is Vice-President of sales and marketing at Weil-McLain Canada, a heating system manufacturer. He chaired the F300 technical committee that wrote the 2013 standard and will lead the reconstituted committee when it soon meets to incorporate proposed changes. He points out that the F300 committee worked hard at putting together the original standard. He believes the ongoing work of the reconstituted committee will be to “take this message and deliver it to the end users…in a clear and straightforward manner.” Using simple tools “like worksheets, software programs, and smartphone apps that will make evaluating the potential of depressurization within a home much easier.”

There’s an app for many home design and building product plans, calculations, submissions, and presentations. The codes and standards world however has been limited to apps that search documents and other forms of reference. Putting copyright material on a phone or tablet has not happened much because it is a traditional revenue source for standards development organizations and governments. So making information about residential depressurization that is user friendly, tested, and accessible will be an important objective for the next F300 committee.

Copies of CSA F300-13 “Residential depressurization” may be purchased at the CSA Group’s online store:

Marshall Leslie served as Vice Chair of the Technical Committee on Residential Depressurization. He is a Toronto-based building products consultant, and chairs the housing committee of the Consumers Council of Canada.


Stories continue below

Print this page

Related Stories