Volume 24, number 2, september 2010

Saving is not a crime!

In many natural gas boilers, the energy lost up the chimney can be significant. Adding an automatic vent damper to the exhaust vent can turn out to be an efficient and very cost-effective measure.

The aim in using such a device is to be able to limit surplus air. Too much excess air will lead to:

  • reducing the temperature of the fumes ahead of the exchanger and reducing the difference in temperature between the fumes and the surface of the exchanger, which is the principal heat transfer agent;
  • increasing the flow rate of the fumes, reducing the time of contact between the fumes and the exchange surface, resulting in a greater quantity of energy being vented that is not recovered.

Watch out! While the advantages of such a practice seem attractive, limiting the combustion air in a boiler can nevertheless be risky. The incomplete combustion of natural gas, along with allowing an unused capacity of fuel to escape, will lead to:

  • carbon monoxide forming, which can be a major health risk;
  • the exchanger clogging with soot, which acts acting as a barrier to heat exchange.

These two phenomena interact. In the short term, the boiler will no longer be able to meet heating needs, it will not last as long, and it will have a tendency to overheat. The integrity of the appliance will deteriorate; eventually, it will cease to function or will be a fire risk, even cause gas poisoning.

So, given these basic principles, the importance of not impairing the safe venting of combustion products is obvious. In fact, modifying any appliance could turn out to be dangerous! It is important that any modification be carried out by competent workers using certified materials and be done according to design principles recognized as safe.

Clause 8.26 of the Natural Gas and Propane Installation Code (B149.1) authorizes the use of an automatic vent damper under certain conditions. In many cases, this authorization goes against certifying that a boiler conforms to the Code for the Field Approval of Fuel-Related Components on Appliances and Equipment (B.149.3).

Given the risks inherent in an obsolete practice and the importance of efficiently managing energy, the Régie du bâtiment du Québec (RBQ) has clarified this practice.

The RBQ agrees with the installation of automatic vent dampers, without requiring a complete, new approval of the appliance according to Code B149.3 in force, if all the following conditions are respected:

  1. It is a Category 1 gas appliance.
  2. The appliance has an approval tag affixed on premises by a recognized certification organization or by the RBQ.
  3. An engineer or contractor with the appropriate licences must submit the documents needed for analysis (drawings, list and description of components, etc.) to a certification organization recognized by the Building Code.
  4. The installation of dampers must conform to the requirements of Clause 8.26 of Code B149.1 and  Clause 9.6.2 of Code B149.3.
  5. Only the modification of the appliance by the addition of a damper is authorized.
  6. A letter from a recognized certification organization with the number of the file or tag certifying that the installation does not compromise the existing approval must be retained by the organization.  
  7. A permanent plate or tag with indelible markings must be affixed alongside the approval tag (see (2)).
  8. A declaration of the work must be produced and sent to the RBQ for each installation.

Other considerations and obligations:

  1. Make sure that the appliances to be fitted with an automatic vent damper have not been modified since their initial approval.
  2. The owner is responsible for maintaining and using an appliance in accordance with the provisions of the Québec Safety Code. Thus, any modification of an approved appliance, except as concerns the installation of these dampers, annuls its initial approval.
  3. The manufacturer’s installation instructions must also be respected for each installation.  
  4. In the case of approved appliances that were certified on site, the addition of a duct damper must be recognized by the appliance manufacturer. If this practice is not yet included in the installation manual, the manufacturer must specify the conditions of use and installation.
  5. The RBQ does not recognize as acceptable the installation of a damper on a certified appliance unless the contractor can demonstrate that all the manufacturer’s requirements have been met.

We recommend that you read with the complete text and follow the recommendations of INFO-RBQ dated March 2010 covering modulating dampers to control the venting of combustion products.

(Note: In French only.)

Charles Côté, Eng.