Federal government requirements for modern heating equipment to achieve higher efficiencies have been with us since 1992. It has been a challenge to safely vent today's more efficient appliances with their low flue gas temperatures. The damage we see in existing masonry chimneys from these appliances and from hot water heaters venting into the same flue as the heating system has been incrementally getting worse over the past 10 years. Older masonry flues previously venting oil appliances now being used for modern gas equipment and higher efficiency oil appliances seem to be most susceptible to damage. When the existing flue has deficiencies prior to installation of the newer equipment, these conditions can be both costly and potentially hazardous, if they are not addressed when the higher efficiency equipment is installed for the following reasons:
1. Inadequate draft at the appliance resulting in:
A) Poor combustion resulting in reduced efficiency
B) Incomplete combustion resulting in CO production
C) Excessive condensation in appliance resulting in premature failure of equipment.
D) Moisture contamination of vent pipe
E) Moisture problems in brick chimney as excessive condensation "rots" the interior of the flue and leeches through walls causing damage to veneer and plaster
2. Leaking flue gases back into the home:
A) Through failed masonry units in the chimney exposed to the living area
higher in the chimney
B) Due to pressurization issues in the flue flow reversal through draft hood or Barometric damper
3. Flue may not be able to perform as intended due to size
4. Negative draft may not be sustainable due to pressurization issues when multiple appliances are installed
5. If the chimney is unlined, modern gas appliances require by code to be installed into a lined chimney
6. Missing sections of flue tile or gaps between the tile render the flue unsuitable for modern appliances
Chimney liners to heating equipment are not required by code to be insulated and the use of insulation falls onto the manufacturers instructions and the installers wish to provide the best possible performance of the new installation. Many manufacturers and, the National Fuel Gas Code, NFPA 54, recommend insulation but do not require it. However, it has been our experience that many installations still have issues when they are not fully insulated such as sweating behind the liner, which accelerates deterioration and can cause performance issues in chimneys with more than one flue. Premature failure of aluminum liner is accelerated by lack of insulation, which is also true for inferior stainless liners. Excessive condensation still can occur especially when the chimney is on an outside exposed wall of the home affecting efficiency and safe venting.
Written by Kevin Stewart, General Manager
September 1, 2006