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Should low temperature protection of Category 1 or 3 appliances be a code requirement?

SpeyFitterSpeyFitter Member Posts: 420
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


  • Mark EathertonMark Eatherton Member Posts: 5,582
    edited April 2013
    It WILL be code....

    Any jurisdiction falling under the control of the IAPMO organization will be required to conform to the requirements of the code, and this is but one of many that will be developed over the next two years for the 2015 code cycle.

    If you are interested in being a part of this effort, you can either join the Radiant Professionals Alliance at or go to

    The IAPMO organization is an ANSI, open consensus process, meaning you don't have to be a member of either organization in order to affect change.

    As I said, this is but one of the many changes we are proposing to the NEW 2015 Uniform Solar Energy Hydronics Code (formerly USEC), Uniform Mechanical Code, and the Uniform Plumbing code.

    In those jurisdictions where the Uniform codes are not enforced, these new regulations can be adopted as "Installation Standard Guidelines". More information can be gotten at

    In addition to writing code, the RPA is tasked with training, certifying and re-certifucation of designers, installers and inspectors responsible for delivering this work. These are in addition to the regular, ongoing education efforts, as well as our efforts to capture more work for our organization. Our work will NEVER be completely done.

    I, like you, have seen more than my share of boilers that were condensed to death, and weren't even in a situation where you'd think it'd be an issue. But it was, and it is. And the consumer gets stuck with the bill(s).

    Please visit the RPA web site for more information, and thanks for asking the question.

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
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