AboutMorgan M. Audetat Expertise Radiant floor heating. Snow Melting. Boilers. Indirect water heaters. Tankless water heaters. Current owner BadgerBoilerService.com Minneapolis based mechanical contractor specializing in Mod/Con based, integrated heating systems. System design, consulting and technical training world-wide.
Currently designing hot water based heating and snowmelting systems for spaces ranging from 50 to 50m square feet. Consulting fees start at $500.00US
Experience 30 years. Organizations: Charter Board Member - Radiant Panel Association, former manufacturer of the first American-made, wall-hung, sealed combustion condensing boilers, son and apprentice of mechanical & plumbing contractor.
Continuing Education: Uponor/Wirsbo advanced design school 2007, Power Limited License (low voltage controls) 40 CE credits 2005, B&G Little Red School House 1993, Tekmar Controls residential and commercial 1993, Division Manager and Advanced Hydronic Seminar Host for the first Hydronic Radiant Floor Distributor in the USA 1990, Hydronic Heating Association Workshop participant with Richard c. Bourne, PE spring 1988, Master Plumbing/Hydronic/Solar Course Red Rocks Community College 1987.
Education: B.S. University WI 1981, 26 yrs. continuing education.
Licensed CO, MN & WI. Home Inspection license WI exp.
Awards and Honors: Radiant Panel Association System Showcase Award 2008
My momma's favorite son.
Past/Present Clients: References upon request.
Expert: Morgan M. Audetat Date: 6/29/2008 Subject: Uninsulated slab radiant heat - retrofit
Question Well, Morgan, it looks like I just made a very costly mistake. I just bought a tiny 440 sq ft house (started as a garage) in central Wisconsin to live cheaply in during my retirement. It has an uninsulated slab on an uninsulated block foundation. My plan was to install 3" poly against the foundation walls starting a few inches above the slab level down to the frost line and super insulate the house. Then install radiant floor heat. Keep in mind that I need cheap heat bills because I live on a small fixed income. Now that I bought this place, I think I'm in big trouble.
I just read your answer to "Can't Get house above 66 degrees" in Wisconsin. His problem is similar although my system is not yet installed. You told him to put 2" on the foundation walls down 2 feet and THEN OUT 4 FEET. I thought my plan would be good but I defer to your expertise. It may be a problem getting out 4 feet with deck, trees, well pipes, etc. But if that's what I have to do then so be it.
I have conversed with radiant companies and determined that sales is their primary goal...NOT cost to run efficiency. Some have told me that I should put the electric matt right on the slab. I don't believe that for a minute. Even with the off peak .059 rate I think my heat bill would be WAY higher than I can afford. Other companies suggest putting down sheet insulation on the floor and then installing hot water radiant. This makes more sense to me. I even considered installing WarmBoard, even though it is a subfloor product, over a vapor barrier and insulation. It's thick, has a reflective surface and a laminate can be placed right on top of it without a pour. Health problems require that I be warm. Financial problems require a relatively cheap heat bill. Within reason, upfront costs are not as critical as the monthly operational cost.
So, Morgan, what's your take on this problem? Don't close on the house and lose my earnest money? Or...can I, SOME WAY, heat this little house comfortably without going broke?
Thanks a lot for reading and any help you can give.
Mike
Answer I insulate four feet down, out or in with 2" closed cell polystyrene: this to fight the frost. I like to go two feet down and next to the foundation to allow for proper drainage and future gardening. This can usually be done by hand (ALWAYS CALL BEFORE YOU DIG!) and then have an excavator drag out the four feet horizontal. A 1/4" fall away from the foundation would be nice.
The rest of your plan sounds fine. I would use a small Mod/Con with a built-in domestic hot water heater such as BAXI LUNA, Laars Mascot or NTI's Trinity. Both will give you wall hung, sealed combustion, nearly silent operation at 92%+ efficiency!
As for the sandwich or dry radiant floor: Rehau's Raupanel™, Uponor's Qwik Trak™ or Watts Radiant's SubRay® will serve you well. Don't worry about insulating below the panel as the concrete itself presents an R4 in resistance and the soil below the concrete typically resists temperature at an Rll or so, per foot of earth. There is controversy over these simple facts but it is unwarranted as the science is clear.
