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Radiant Floor Heating/floors not warm enough with PEX below the floor


I had my plumber install a triangle tube prestige 110 boiler in my old house with the stand up radiators systems is awesome but I have a kitchen,1/2 bath and a sunroom without these radiators. I figured okay new boiler why not install some staple up pex underneath in the unheated crawl spaces. I had a spare zone and pump coming off the new boilers manifold so I ran a 3/4 pex supply/return 15' away to a 3 port 1/2" manifold and ran 3 100' circuits to rooms controlled via 1 t-stat. The max temp I'm getting at floor level is 73 deg. I've set the boiler min CH to 140 and max 180 which puts my target temp. around 150. The new manifolds are very hot and the boiler is showing good temps on the feed and return and the boiler satisfy and shuts off.Should I have just skipped the manifold and made a 300 zone? The flooring is 3/8 tile 1/2 ply and 3/4 flooring ( is all this material to much resistance for the heat to penetrate? ) the 1/2 pex is in single run 10" bays with continuous heat transfer plates a Mylar type reflective breathable barrier and 8" of unfaced insulation. There are 2 air vents 1 in the 3/4 return to boiler and 1 at a high point in the return furthest away from all pex and boiler. This is most defiantly not an efficient system how do I get more floor heat at less temp and less cycle. Thanks for your help Mark C.

Badger Radiant Designs
Badger Radiant Designs  
Every proper radiant floor heating system starts with a proper room-by-room heat load analysis performed on dedicated software. Once the heat loads are known the appropriate radiant panel system can be specified.

Do you have any of this information?

We have a local distributor here in Minneapolis that "designs" bare-tube or "suspended" PEX sub-floor radiant systems for many misguided heating contractors. The results are predictable and reflect your own experience.

We get called out on these system regularly and after measuring, noting floor construction and insulation below the floor. We often end up specifying heavy aluminum heat transfer panels, upgrading the insulation and hope to lower the design water temperature to take advantage of the condensing boiler.

These zones are usually the smallest and have the highest heat loads keeping the boiler running hot and cycling; two things that should be avoided in any hydronic heating design, but more especially when employing the incomparable condensing boiler.

It is also likely that the Triangle Tube 110 is too big for the total load, which means it will be cycling on and off more than it should in the shoulder months when outdoor reset and modulating flame save the most energy and offer the best comfort. When you raise the design temperature the boiler and distribution system performance, both comfort and fuel economy goes down.

This type of system is one of the most challenging to design and install. Seek an experienced professional that designs his own systems.  

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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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