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Radiant Floor Heating/plaster cracking hydronicradiant ceiling


cracks in hydronic radiant heat ceiling
cracks in hydronic rad  
cracks in ceiling
cracks in ceiling  
QUESTION: Margan, Thanks goodness for the internet! You are the first person to acknowledge that this type of heat is pretty darn good - I have it in a spare room built on a slab that is my TV room in my 1940s house. I'm not sure but am guessing this room was put on in the 60s. I have had two problems in this room - both related: one is the cracking and dropping of small pieces of plaster (photos attached - not extensive but ugly and threatening) plus some roof problems with leaking during extended phase of ice damming. I called a good roof contractor who recommended I insulate the roof in the room - to help solve the ice damming plus help with the tremendous disparity in temperature between the low parts of the ceiling (where the cracks are) and the outside temperature. Indeed, after the work was done, I have seen very minimal cracking so that must have been part of the problem. I would like to sell the house but want to get this problem not only cosmetically solved but also be able to state on the seller's statement that I have done my best to alleviate the underlying issue. Can you me? thanks!

ANSWER: Cathy,

I have long been an advocate of radiant ceiling heating systems. As you know the comfort is extraordinary and the concept is not a new one. Where radiating walls or floors is not practical, or in some cases even possible, I look toward heaven for the answer.

We often use radiant ceilings to supplement a radiant floor design where the floor area is not sufficient to overcome the heat loss on the coldest days of the year. Sometimes it is a matter of incompatible floor coverings or inaccessible spaces that motivated us to heat from above.

Radiant ceilings responsive, efficient and comfortable if designed and installed correctly.

When working on older copper tubed radiant systems “plastered in” as yours was, we consider the quality and quantity of insulation above the radiant ceiling panel and the temperature of the water being supplied. Both can have a significant effect on system efficiency and the longevity of your plastered ceiling. We find many systems, especially those showing visual striping or deterioration known as calcification, we seek to lower the operating temperature and use outdoor reset (ODR).

As it appears you have already addressed the former your focus should be on the latter.
A lot has happened in the last 10 years in the hydronic industry and one of the best is the epic increase of performance that the condensing boiler industry has main. The most important improvement, as it relates to your question, is the addition of ODR as standard equipment on every condensing boiler sold in the USA today.

ODR “resets” the water temperature supplied to any type of hydronic radiation to satisfy the thermostat determined by an inverse relationship between outdoor air temperature to indoor boiler water temperature. In short, the water temperature delivered to your radiant ceiling is no more or less than is required. The result is a radiant panel that is on more and costs less to operate.  

The added advantage of outdoor reset to radiant ceiling operation is the lower temperature differentials the ceiling will be subject to. This should reduce the cracking of ceiling plaster while saving you money.

Most of the early radiant ceilings, circa 1935-1965 will were driven by cast iron boilers operating at 180° and mixed down to 120°F. If yours is running hotter you will want to have it adjusted by a professional , perhaps using a mixing valve already is place, and recommend a condensing boiler to the next owner. They will be glad you did.

Finally, I would note that your photographs lack striping, a clear sign of excessive delivered water temperature. I would be sure that the ceiling is not suffering from excessive moisture or high temperature differentials as your ice damming might explain.

Thank you for asking.

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

QUESTION: What a resource you are Morgan! Thank you so much - this is well written and well explained. One last question about the repair part:  what sorts of steps, tools and special preparations should I be asking my contractor to use when we go about repairing the ceiling (to show to potential buyers) I am assuming there are perhaps some recent innovations in the plaster world that can handle any fluxes in temperature. I would like to be able to say "that the work we did "will stay done" for some time to come..." By the way, when the time comes to do this work, I would like to have my contractor call you. At that time I would like to pay you an hourly consulting fee if thats OK with you! You are so helpful!

You are most welcome.

Any old-school plaster man will know what to do. The key is controlling water temperature.

You may send a floor plan calling out window size and quality with room height and dimensions. From this we perform an ACCA Manual 'J' heat load using purpose-built radiant software. From this information we can  determine the design water temperature required to heat the home with your old copper radiant ceiling.  

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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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