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Radiant Floor Heating/copper pipe in slab heating upgrade


QUESTION: I have a 1954 mid-century ranch with hydronic heat-in ceiling upstairs(set within 1 1/2" plaster), in floor w/in bathrooms and within a 4" monolithic concrete slab in the basement.  Currently, I have a 1990s-era cast iron Weil-Mclain, mid-efficiency(80%) boiler with, what I think is, 1/2" soft copper tubing running throughout.  While the basement is very comfortable, I think it both terribly inefficient(no-sub slab insulation) and likely doomed to ultimate failure from the surrounding concrete.  

So, my initial thoughts are to lay some amount of rigid insulation, maybe 2 or 4" on top of the existing slab.  Then lay modern hydronic/Pex style tubing on top of this, finally finishing the new "subfloor" off with carpet.  At the same time, I would likely upgrade my boiler to a modern, high efficiency unit.  Basement wall insulation would also be done at the same time.

Does this seem like a reasonable plan to increase efficiency/reduce my natural gas bills, but still maintain the basement comfort I enjoy? The above is not a DIY-project in my book!

Thanks for your advice.

Badger Boiler FLR radiant drawing
Badger Boiler FLR radi  
ANSWER: There were many homes built just after WWII with radiant ceilings such as yours. As you know, comfort is extraordinary. Here in Richfield, MN we have hundreds of otherwise modest homes with wonderful radiant ceiling panels installed by plumbers-of-old and plastered over in the typical fashion of the day.

We use the same technology today and just finished a new radiant ceiling installation in St.Paul, MN in a 100 year old house where kitchen appliances and a huge island took up all the available floor area, leaving us with the radiant ceiling option.

We consult on many old radiant heating systems, many of which were inspired by Frank Lloyd Wright's eccentric taste for natural/local building products, stone in particular. FLR liked concrete and used it extensively, but knowing how cold it can be, used steel and copper pipe to keep both slab and structure warm.

As with our advice on FLR homes, the first thing for yours is a new wall-hung, high efficiency condensing boiler with built-in outdoor reset. This is the best way to save money on the fuel bill in any old home heated with radiant floors, ceilings or even cast iron radiators. The new boiler will take advantage of the radiant mass of these older systems making them more comfortable while lowering fuel bills by as much as 50%--common.

The proper application of this technology should also prolong the life of older copper radiant systems embedded in ceiling or floor, since the water temperature delivered will gradually increase and decrease with the weather. Less stress, longer life. Some of the old copper and iron pipe radiant systems installed 1930-1960 corrode from the outside in, but many suffer from neglect of the inside "boiler" water quality. All should be flushed (once), cleaned and treated with approved chemicals by qualified technicians.

"While the basement is very comfortable, I think it both terribly inefficient(no-sub slab insulation) and likely doomed to ultimate failure from the surrounding concrete."

Perhaps. We find that the copper pipe in basement slabs tends to fail in a slow and singular fashion. That is, you may notice the water pressure dropping over time, less than a year. This will also happen in old baseboard heating systems served from sub-slab copper running from room to room. We find that a single loop will fail, followed by it's siblings in indefinite in order and timing. You may anticipate failure but we still service many radiant floors and snow melting systems in service for more than 50 years and a few as long as 80. No need to panic.

As for "terribly inefficient"; it depends. Our early (circa 1980's) radiant floor heating and snow melting systems installed  with polybutylene tubing were often installed over bare ground with predictably long "charging" times. That is, it took awhile to heat up the ground before the room or snow got warm. For space heating this is typically an one-time annual event the cost of which is time an a few dollars in most cases. The typical heat load in an un-insulated "dry" basement is about a third of the upper levels. If the rim-joist is foamed and the walls furred and insulated the load is even lower.

Definitely start with the condensing boiler.

If you are determined to fix what is not broken, I would look to several products on the market designed to serve what seems to be a growing trend to "finish" the basement. If we can't tear up the old concrete we will use a pre-insulated radiant panel designed for this purpose and cover it with any reasonable flooring e.g. solid wood, tile, carpet with thin pad, etc.

You are very lucky to have a heated slab in your basement, as it is one of the very few ways to make a basement in the Midwest truly dry and comfortable.

As every successful radiant floor heating systems starts with a Manual 'J' heat load analysis and experienced specification, you will want to start with a good hydronic design. And by-all-means, insulate the cold side of any radiant floor you can.

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

QUESTION: Thanks for very much for your insight.

As an aside, I worked for two summer at Taliesin, Frank Lloyd Wright's home in Spring Green, WI in the 1990s.  The beauty of his home contrasted with the incredibly complex, and often poorly performed engineering, that allowed the aesthetic qualities to succeed.  While, I'm happy to live in a home inspired(at least the heating system) by him, I could never live in one his homes, the maintenance requirements are often astronomically expensive.

Thanks again.

Yes, I too reveled at the contrast of aesthetic comfort and dire lack of creature comfort, akin to sitting in one of Frank Lloyd Wright's chairs. I could have given him a hand had I been born a bit sooner. I was in 2nd grade in Avoca, just up the river, a few miles in 1962.

I also got a kick out of standing in his "corner" fireplace and looking up to blue sky, thinking what my stonemason grandfather would have said about it (can't be repeated here). Suffice to say, FLR did not know or perhaps care what a smoke shelf was. It brought a whole new meaning to "breezeway".

Thank you for sharing.  

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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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