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Radiant Floor Heating/Combi, Boiler or Furnace retrofit


Mr. Audetat,

I have read many of the posts to this forum and thank you for a great service.  Here is my particular problem.

We built our retirement home in West Michigan 2001 and decided to use open loop geothermal because there was no natural gas available and propane was too expensive.  Now electric rates have increased significantly (about double, $.015/kwhr) and natural gas is at our driveway (but will cost us $7500 to get it to the house).   I have decided to investigate if it is time to change to natural gas for heating and DHW.  We also like the feel of “warm floors” and would consider radiant hydronic for the main floor.   I see three   possible choices:  1) NG furnace/air conditioner  and a NG DHW; 2) NG hydronic and separate NG DHW; 3) NG “combi” using either a high efficiency tank type water heater and heat exchanger or a NG boiler with indirect DHW tank.  In any case, I would like to go with a high efficiency type system.

Our house has 1800sqf main level and 900sqf finished basement and is well insulated and the 34,000BTU Geo has done at good job at keeping the house warm in our cold winters.  If we go hydronic, the Geo would provide the cooling and when it fails it would be replaced by an air conditioner.  We also have a “gas log” direct vent fireplace (24,000BTU -80%) in the basement that we use to heat the family room for several hours 3-5 nights each week in the winter.

For the hydronic options, I have access to about 60% of the main floor to install ½” pex w/plates and this covers most of the area we normally live in (excludes part of the living room, one unoccupied bedroom and one seldom used bathroom).   (The floor is ¾” OSB sub-floor with either vinyl or carpeting above.)  I also could place a hydro/air heat exchanger in the current Geo plenum (we run the ECM fan 24/7 on low speed) to get a bit more heat distributed.

The direct vent from one appliance can probably go straight up from the basement through the roof through a small chase, but a second vent path may be somewhat difficult because of a large deck and other existing building conditions.

What are your thoughts on the hydronic system options?  (I know that I need a manual J to get a proper design, but this information provided will get us in the ballpark).  It seems like a good solution to use the tank type water heater if it would be efficient, reliable and have a reasonably long life.  Is the Phonix hot water heater worth the extra cost for modulation over the Polaris?  Another benefit of a stainless steel tank may be not having a small amount of “smell” to the hot water due to some iron content in our well water because there are no anodes.  

I don’t know what system may be the most cost effective, but with stable NG costs, rising electric costs and a Geo that may need service or replacement soon, I need to have a plan.  The high cost to pipe NG to the house is a big factor but replacing a Geo is very expensive also.  I have read with interest about the “combi” systems installed in Minnesota as part of the MBPA but have found little recent information on the many systems installed now.   How many of the 300 systems are now installed and is one particular configuration better?    

Thanks again,

Natural gas is hard to beat for space and water heating. It is commonly a third the cost of propane of electricity and it appears it will remains so for some time.

You are also correct in assuming a condensing storage type water heater is a good fit for comb-water and space heating loads like you describe. We have many thousands of such systems in the Minneapolis area going for a couple of decades now. Most are low-efficiency units but the space savings for heating basements and DHW (the most common application) is settled business.

We upgrade many such systems with high efficiency condensing water heaters like the Polaris and Phoenix you mentioned. Each has advantages depending on the application and specific space and DHW loads.

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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