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Radiant Floor Heating/radiant slab heat insulation high propane bills


My friend built a new home after a tornado destroyed her old one. Its less than 3 years old. Radiant heat was installed in a (slab house ). they used a 50 gal propane heater for a boiler (it never shuts off)her propane bill was over 400.00 a month last year. The house is 1500 sq ft plus garage. They did not use insulation on the sides at all. The insulation used was a type of blanket in a roll. 2 runs are shut off because of leaks. she has pictures of the pour and some of the pex tubing is 8-10 inches deep. Is there any thing she can do to fix this? I listed everything i saw wrong, but does it matter. she has a daughter and grand daughter that live with her the heating was for the little girl due to respitory issues it would be great if something was overlooked and be a simple fix

Folks who contact us with stories of radiant slabs and high fuels bills almost always suffer from a lack quality and/or quantity of insulation.

The insulation-blanket-under-slab guys bank on the R-value of the ground, which is considerable in some areas (around R-10 per foot if sandy and dry) but just like in the old days when we didn't know any better, heating up a couple of feet of dirt may take a week or more. That's a lot of cash up front, like heating a pool first time in spring. For commercial buildings the ROI and operating costs may work out, but this is never the case in residential light-commercial construction and especially unwise if the building is set back or turned down for any length of time.

The blanket insulating tarps etc. are for the lazy and the stingy and perhaps for the misinformed - to be kind.

I know, New Years resolution...trying to be nice. yuk

Your case is unfortunately not unique as I recently saw insulating blankets for sale and recommended at under-slab radiant applications by legitimate, otherwise knowledgeable distributors of radiant floor heating products here in Minneapolis. It makes me nuts!

Our minimum specification for radiant slab (space heating or snow melting) insulation here in Minnesota is 2" of rigid extruded polystyrene (XPS) under-slab and perimeter.

I would need more information about your installation and location to specify the cure, but offhand I would start by installing XPS around the perimeter of the existing slab to a vertical depth of 2 feet, followed by an ACCA Manual 'J' heat load analysis reflecting this improvement. This would indicate the proper size propane condensing boiler, the installation of which could cut the fuel bill in half.  

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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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