Condensing Furnace Venting Part 2: Evaluation of Same-Chimney Vent Systems for Condensing Furnaces and Natural Draft Water Heaters.

摘要

In 1987, the National Appliance Energy Conservation Act prescribed the first federal minimum energy conservation standard for natural gas furnaces at an annual fuel utilization efficiency of 78%, effective January 1, 1992. One of the techno-economic issues that has prevented higher furnace efficiency standards since then is the lack of cost-effective, simple, and safe solutions that enable condensing furnaces and atmospheric combustion water heaters to vent through the same existing chimney. Part 1 of this two-part report series, published in October 2014, documents the issue, prospective solutions, and a test laboratory established to evaluate prospective venting solutions. This part 2 report documents the updated prospective solutions (because they have evolved since part 1 was written), the methodology for experimentally evaluating prospective solutions, and results of the evaluations. The fundamental issue is that higher furnace efficiency standards would require the use of condensing furnaces; and when existing noncondensing furnaces are replaced and the costs of modifying the venting systems considered, it is unclear whether this requirement is cost effective in all applications. It might be possible to reuse existing vertical vents as chases for new condensing furnace venting systems. If not, where physical constraints and codes allow, it might be possible to install new horizontal side-wall vent systems. Where these options are not feasible, running new vertical vents through buildings and roofs would be an alternative, albeit at additional cost. The most challenging application is when the existing noncondensing furnace and a draft hood–equipped atmospheric combustion water heater are commonly vented up the same chimney and a side-wall vent for the new condensing furnace is not an option. Cost-effective, commercially available solutions that enable condensing furnaces and atmospheric combustion water heaters to vent through the existing vertical chimney are needed.