High-Efficiency Boilers and Direct Venting
Today’s modern world is full of examples of technological advancement, and the plumbing/mechanical industry is no exception. From toilets to water heaters, there is new technology being incorporated into the design/production of products and materials every day. This necessitates the need for the modern technician to evolve and learn each new product as it hits the market. High-efficiency water heating for space heating and domestic hot water supply (high-efficiency boilers) is a prime example of this industry advancement. Unfortunately, there are many examples of improper and poor installation practices of high-efficiency boilers, with the operation and lifespan of these systems suffering greatly when this happens. One of the most common installation errors can be found with the intake and exhaust vent piping.
Most high-efficiency boilers and water heaters use what’s called, “Direct Venting,” which means the exhaust and intake are piped/ducted to outside air. If done correctly, this design eliminates variables that can negatively impact the efficiency of the combustion process, as it does not take much to de-rate a unit that has an efficiency rating of upwards of 95%. The gains from installing a direct vent high-efficiency gas-fired boiler or water heater can be quickly negated if this part of the system is incorrectly installed.
For this type of appliance to maintain its efficiency, it must convey flue gasses outward and fresh oxygenated air inward at specific minimum/maximum velocities and volumes. Aspects of installation that might affect these volumes and velocities include the vent piping’s nominal diameter, developed length, and pitch. Every manufacturer will include a set of instructions that provides this necessary information to reference during installation. It usually will offer a table or chart to provide nominal pipe size, maximum developed length of vent piping, fitting take-offs, authorized piping material, etc. Reference the tables below, which are from the installation and operation manual of a LAARS MagnaTherm boiler. Always follow these specifications to guarantee proper operation.
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