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Radiant Floor Heating/Add new zone for radiant slab to existing boiler


Mr. Audetat,

I have a Burnham 204HNSL-BEI2 boiler controlled by a single thermostat which currently serves about 1400 square feet of living space via copper pips and varying sizes of baseboard fixtures in the various rooms.

I'm building a 24x26 garage addition with radiant heat in the slab. A contractor is installing the appropriate amount of radiant pex loops in the slab, and I'm planning on finishing the installation by connecting the radiant pipes in the slab to my existing boiler (the boiler is about 20 feet away from where the radiant pipe will connect). I believe I need to add a zone to my existing boiler along with a heat exchanger to separate the glycol system that heats the slab from the rest of the home baseboard fixtures, but I'm still learning about what is required in order to help me plan the work. Can you help me determine what supplies I need for this work. Let me know what additional information you need from me (or pictures of the existing setup which may help) in order for you to provide any assistance you're willing to offer.

Assuming you have secured a Manual 'J' heat load for the house and new garage to assure the existing boiler will handle both loads, to add a new radiant slab zone to an old cast iron boiler you need a sub-assembly including a plate heat exchanger to isolate propylene glycol from the heat medium of the boiler system. Further, you will need a mixing valve or other control system to protect the cast iron boiler from condensing.

You must pay careful attention to the type and concentration of anti-freeze--boiler-grade propylene glycol is the only choice here--and prepare to maintain it each season.

There are several ways to protect the boiler while improving comfort and efficiency including simple by-pass piping, mixing valves and injection. Which is right for you is determined by the existing piping, load factors and budget.

You may forward all the details and pictures of the existing systems to  

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Morgan M. Audetat


Radiant panel heating design, including floors and ceilings, European wall panels and snow melting for residential and light commercial buildings..............................................................-Master of Steam and Hot Water,City of Minneapolis....................................................--- Master Plumber, State of Minnesota...........


30 years..... Charter Board Member - Radiant Panel Association, former manufacturer of condensing boilers, former national distributor of radiant floor products, son and apprentice of mechanical & plumbing contractor. Current mechanical/plumbing contractor specializing in hydronic based, integrated HVAC systems. Radiant floor heating/cooling. Snow Melting. Condensing Boilers. Indirect water heaters. System design, consulting and technical training world-wide. Licensed contractor, designer, installer and consultant.

B.S. University WI 1981 CONTINUING EDUCATION: Viessmann Condensing boiler and Solar water heating certification 2010, N.D.S.U. Lead Worker RRP certification 2010, Knight condensing boiler certification 2009, Wrightsoft Manual J CAD certification 2009, RPA Designer & Installer Certification 2008, Nate Hydronic/Forced Air Certification 2008, Uponor/Wirsbo advanced design school certification 2007, Buderus Wall-hung certification 2007, Power Limited License (low voltage controls) 40 CE credits 2005, Basic Hydronic Certification IPEX & Northern Alberta Institute of Technology 1998, Charter Board Member - Radiant Panel Association 1994, Residential Off-Electric to Hydronic Conversion Heating School Canadian Hydronics Council 1994, B&G Little Red School House 1993, Rood Utilities (now Auburn Technical Institute) Oil Burner School 1993 ,Tekmar Controls residential and commercial 1993, Division Manager and Advanced Hydronic Seminar Instructor for the first Exclusively Hydronic Radiant Floor Distributor in the USA 1990, Hydronic Radiant Heating Association Workshop participant with Richard c. Bourne, PE spring 1988, Master Plumbing, Hydronic, Solar Course Red Rocks Community College 1987.

Awards and Honors
2009 System Showcase Award - Radiant Panel Association

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