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Radiant Floor Heating/natural gas boiler for small garage radiant slab


I'm wondering if their is a natural gas solution to a small heat load garage slab in Bemidji, Minnesota.  All of the gas boilers I've looked at provide much higher outputs than I need.  I know Electro makes a mini-boiler that would fit nicely, but I have natural gas available.  Here are my numbers:

-400 sq.ft shallow frost-protected slab, R-19 walls, R-40 ceiling, 2" EPS foam under slab and surrounding the thickened edge.

-2 runs of air barrier PEX @150' each.

-Insulated 8'x9'garage door, no windows.

Heating small garages, additions or even some of the newer well insulated SIP,ICF, and cabins up north all present loads to small for even the smallest condensing boilers. Even with a 5 to 1 turn-down ration the lowest output available will still likely short-cycle on many of these applications, "bumping off the bottom" as the boiler reaches design temperature in a few minutes and must shut down entirely or overshoot the temperature it has targeted.

The answer is mass. You must have stored water for micro-zones or very small total loads if allowed to call the boiler to fire independently of other zones. These systems should be carefully designed for optimum performance.

I do not design system in this venue, but will be happy to review your plans if you send them directly to me.

Radiant Floor Heating

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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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