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Radiant Floor Heating/tankless water heater problem radiant floor heating uneven radiant floor heating wirsbo zone valves


QUESTION: I have radiant heating installed in my house and it is embedded in the concrete floor with nothing on top of the concrete (stained concrete floor).  The system is generating uneven heating on the floor where I can have warm floor in one spot and ice cold spot just a feet away from it.  Is this normal?  If not, could you help me answer what the cause might be for this uneven heating?

ANSWER: Dear David, I think the cold spots in your radiant floor heating system being caused by the concrete stain...just kidding. The cause is likely an air locked PEX loop "circuit". Any competent radiant floor contractor can use his infrared thermometer to confirm the flow at the manifold. If the radiant floor manifold has flow meters, this will be an indication by not conclusive evidence that you have proper flow.

Please let me know how it sorts out.

---------- FOLLOW-UP ----------

QUESTION: Thank you for your response to my initial question, sorry that it has taken me this long to respond with further results of my problem.
I finally got a floor heating specialist to come and look at my system (five zone Wirsbo brass manifold with solenoid control valves operated by a Taco controller and a Rannai water heater).  After testing the system he came up with the following problems.
1.   Two of the control vales are not working at all, the signal is coming from the controller but they do not actuate.
2.   On one of the functioning zones that openís when triggered (the longest loop in the system) has a flow problem, when the valve opens and water flows it is not strong enough to start the recirculating pump.
3.   The current recirculating pump may not be adequate for our long runs, operates at 2GPM.
4.   Propane gas pressure was too low.

The following is the suggested fix for the problem.
1.   Replace the old manifold with one that has flow meters, balancing valves, and an air bleed valve.
2.   Replace circulating pump with one that operates at 4GPM.
3.   Replace the Rannai controller that will allow us to raise the water temp above 120 degrees.

I am all for this, if it will take care of the problem, if you have any comments, Iím all ears. Thank you again for your advice.

         Dave Komsak

You failed to mention that your radiant floor system was driven by a tankless water heater. See my many comments on this practice in previous posts.

Tankless water heaters add another level to an often confusing and unfamiliar aspect of radiant floor design and installation.

As you have correctly surmised, a tankless "water" heater is normally fired with a water flowing from a faucet. This flow will vary with manufacturer and model. When used as a boiler, the tankless water heater's need for minimum flow must be considered and pumps, pipes and controls specified accordingly.

The tankless water heater gives you a fixed temperature presumably at design (the water temperature needed to heat your home on the coldest day of the year). In all but the coldest month this temperature is not needed so the result is less "on" time (cooler floors) and higher fuel bills.

The old Wirsbo zone valves or "actuators" can be a headache. You must install and adjust them properly to make them work. Your plan sounds like a good one but the flow you have the flow you need are in question. How do you know what the current flow is and what you need.

Flow can't be guessed and required flow is a question of radiant floor tube or loop, number length and the load of the house.

If the water give out, consider a real condensing boiler and gain the benefit of a weather sensitive control which, will lower you fuel bills and keep the radiant floors warmer more of the time.  

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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 íJí 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 Ė 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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