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Should low temperature protection of Category 1 or 3 appliances be a code requirement?
When a Category 1 or Category 3 Gas Boiler (typically made with a steel or cast iron heat exchanger designed to run above 140 degrees F) starts up cold it will condense for a period of time. A little bit of flue gas condensation is not going to kill one of these boilers in most cases, BUT extensive flue gas condensation, especially in systems used in very intermittent situations with large volumes of water that need to be brought up to temperature, will impact the longetivity of one of these boilers negatively, and I would argue in some cases could cause a dangerous situation which could cause flue gas spillage or potential fire.
There are a few different ways to design low temperature protection into the hydronic side to ensure these boilers do not condense - 1) A "Shunt Pump," which bypasses a percentage of the supply water back into the return inlet of the boiler. 2) A 3 way mixing valve which blends some of the supply water back into the return to ensure the boiler return is above 135-140 F 3) Other hydronic designs, for example a primarly secondary system with higher flow rates on the primary side always ensuring some of the supply water is put into the return, etc.
I'm curious why this is not a code requirement, or if it is a code requirement in your area, I'd be interested in hearing what the exact codes or standards are.
Class 'A' Gas Fitter - Certified Hydronic Systems Designer - Journeyman Plumber