Hot water heating renewal series: Building code and safety issues
By Alan Sutton
A Building Code is a set of rules that specify the minimum acceptable level of safety for constructed objects. The public interest for health, safety, and specific economics issues, are safeguarded through the issuance of a Building Code. Through these documents, governmental authorities require mandatory compliance to building related practices which are considered safe and economically prudent.
By Alan Sutton
Standards are accepted procedures that are normally used to evaluate the performance of a system or an individual component and typically specify the exact ways in which to perform the test or evaluation.
Guidelines are similar to Standards but are developed in a less stringent manner and generally reflect what may be considered the state-of-the-art in the industry from a committee of experienced industry practitioners.
Although there are many issues faced by a design engineer with respect to hot water heating plants and building codes and safety issues, our discussion will be restricted to dealing with asbestos management and liner selection for flues and chimneys.
Asbestos laws in Ontario, which are regulated by the Ontario Ministry of Labour, became more stringent in 2005. A burden of duty is placed on the building owner to know where the asbestos is before starting heating plant construction or retrofit. Further, the building owner must be able to demonstrate compliance with survey requirement documented. Most building owners prefer to have an asbestos specialist remove the material before handing the job site over to the mechanical contractor. When a boiler room is remediated of asbestos, the asbestos specialist will produce a report certifying that the space is clear and demolition or construction can proceed.
All boilers need to be fitted with a vent to safely carry the flue gases out of the building. Boiler efficiency is tied to venting requirements — the more efficient the boiler, the more difficult the venting. The gas code defines boiler categories, which indicate type of operation and required venting construction. This area has become more and more complex in recent years with the wide variety of more efficient boilers coming on the market. The rules are becoming stricter and at the same time harder to understand:
|Boiler Category||Definition||Performance||Venting Permitted|
|I||Operates with a negative or neutral vent pressure, non-condensing.||Not Gas Tight. Not Water Tight. Not Corrosion Proof.||B-Vent (double wall for burn protection). Galvalume or similar metal. Unsealed, site assembled from pre-made parts without fabrication.|
|II||Operates with a negative or neutral vent pressure, condensing. Condensation occurs in the flue, but not in boiler.||Water Tight. Corrosion Proof.||BH-Vent. Certified under ULCS-636 for the application. Double wall for burn protection within boiler room. Single-wall for chimney liner. Double-wall sections may be insulated or have air gap only. SS-316L or SS-AL29-4C stainless steel inside, which will not corrode on exposure to condensate. SS-430 outer wall for corrosion resistance under boiler room ambient conditions. Site assembled from pre-made parts without fabrication.|
|III||Operates with a positive vent pressure, non-condensing.||Gas tight.||Same as Category II.|
|IV||Operates with a positive vent pressure, condensing.||Gas Tight. Water Tight. Corrosion Proof.||Same as Category II.|
The BH-vent solution works well in penthouse boiler rooms, where the flues are short. There is a cost premium, but it’s not great compared to the overall cost of the project. The real price-vs-performance concern comes in with basement boiler rooms and the question about lining existing chimneys. A chimney liner prevents acidic flue gases from condensing on the clay liner and causing it to fall apart.
A chimney without lining may or may not result in desired draft characteristics. For a retrofit project, a chimney is likely to be oversized relative to boiler draft requirements, especially if overall plant capacity has been reduced. This situation will result in excess draft, which will cause excessive negative pressure at the boiler breaching. This effect essentially vacuums heat out of the boilers, reducing operating efficiency. Barometric dampers are suggested to control this, but observed behavior shows that dampers open wide in very cold weather, when the plant is at its hottest, so the draft is essentially uncontrolled.
If the chimney is already lined and calculations show excessive draft (more than about –5.0 in. wc.), there are basic ways to improve the situation:
- Install an additional large barometric damper in the common flue near the entry into the chimney. Note that increased air flow through the boiler room will result and potential for heat loss from low-level piping may require additional insulation to be installed.
- For non-condensing boilers, put a cap on the top of the chimney, reducing the exit opening, and decreasing the draft rate.
- Install an automatic draft control damper.
I hope this article gives readers some insight into the factors that can enter into heating plant performance. In future articles in this series, we’ll be covering issues owners will encounter when renewing older plants, such as domestic hot water, flue venting, and plant sizing for best value.
Alan Sutton, B.A.Sc., MBA, LEED AP, General Manager with Efficiency Engineering Inc. in Cambridge, specializes in energy efficiency and control of central plants. He can be reached at firstname.lastname@example.org.
Relevant Hot Water Heating Plant Codes
• National Building Code
• Ontario Building Code
• Ontario Fire Code
• National Fuel Gas Code
• Canadian Electrical Code
• Ontario Hydro Electrical Safety Code
• Ontario Gas Utilization Code
• Canada Plumbing Code
• CSA B51 –[M1991] Boiler, Pressure Vessel, and Pressure Piping Code
• CSA-B214 Installation Code for Hydronic Heating Systems
• SMACNA Guidelines
Other articles in this series:
Hot water heating renewal series: Boiler efficiency
Hot water heating renewal series: plant monitoring and control