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Radiant floor design-2 temp or keep at 1

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Mosherd1
Mosherd1 Member Posts: 70
edited December 2022 in THE MAIN WALL
Completely gutting and remodeling my mothers split lever house.  It’s located in Northwestern Il-the land of forced hot air. I’ve done the heatloss/load calcs.  The house I will have a two stage 75,000 btu furnace, the heatloss came in around 64,000 if memory serves. The ductwork will be zoned into 3 zones, basement, main level (kitchen, living, dining) upper (bedrooms and bathroom). My mother has always lived in old cold drafty 4 square farms houses, and most recently a ranch built on an uninsulated slab.  She’s in her late 70’s and really likes my heated floors. The boiler will be a triangle tube solo 110 ( the smallest they offer) on ODR. The basement will be  HWBB, zone 1. The main level will be, radiant floor with 3/4 plywood subfloor with 3/8” engineered hardwood, zone 2. The upper level will be radiant floor with 3/4” plywood subfloor, carpet pad and plush carpet. Except the bathroom it will be 3/4” plywood, 1/4” denshield and ceramic tile.  The basement BB will be sized for 120 degree water, the main level should also need around 115-120 water, but I’m thinking the upper level will need close to 140 water. Would you run everything at 120 ODR, and let the furnace cycle on that zone if the floor can’t keep up, or set the boiler for 140 ODR and use a manual 3 way valve to mix the other two zones down lower to track with the ODR?  I know the bathroom floor might be on the high side of allowable design temps, but I’m a little short on enough floor space in there and am planning on a 2ft electric baseboard heater to meet the load if needed.   I figure it’s a bathroom and if the floor is a little hotter than normally allowed it will still be comfortable.

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  • Mosherd1
    Mosherd1 Member Posts: 70
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    The furnace is mainly there for air conditioning.  The furnace was only slightly more expensive than purchasing just an air handler. And I’m kind of a fanatic about having back up mechanical systems. 
  • hot_rod
    hot_rod Member Posts: 22,353
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    The toughest load may be the radiant with pad and plush carpet. With the load calc number, see what that room will require for SWT

    For bathroom supplemental consider an electric towel bar, they are crowd pleasers and can add just enough extra for designnconditions.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Mosherd1
    Mosherd1 Member Posts: 70
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    @hot_rod if memory serves the load call came out to 23 btus per square foot, which seams a little high.  I need to look at those numbers again, since I did the load calc, we ended up removing all the drywall, I foamed the edge of every stud with Great Stuff, all holes in the upper and lower plates, caulked the sill plates to the subfloor, foamed the back of every exterior electrical box, and used damp spray cellulose to reinsulate. And it’s newer double pane windows. I haven’t done the math yet to figure out what the SWT will need to be with the carpeting. 
  • hot_rod
    hot_rod Member Posts: 22,353
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    Again, just another rule of thumb, keep SWT within 15 degrees of one another to avoid a second temperature zone. You can tweak a bit by tightening tube spacing in the high loads areas, maybe 6” in the high load areas.

    That is the nice thing about using radiant load and design software, you can adjust those variables in the program to maximize a design. Tube spacing, loop length, gpm flow rate can all be played with to get the end result before you install any tube. A skilled design will look for those small adjustments to bring SWT for all the zones as close together as possible, KISS

    There are some radiant friendly carpet pads, lower r-value that could be considered. How plush does a bedroom carpet need to be when little of it is even available to walk on😚, for example
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Mosherd1
    Mosherd1 Member Posts: 70
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    Thank you for the input @hot_rod. It’ll be staple up with plates on floor joists 16” OC, so I can’t really get more than 2 runs per bay. I don’t have access to computer design, I get to do it the old school way with paper and pencil. And I’m good with that, it makes one understand how each variable can affect another. Much like learning how to use an old school 35 mm camera before using a modern day DSLR camera. I’ll push for  lower “r” value carpet pad, but my mom and fiancé (an interior design by trade) are pushing for a nice thick dense high quality carpet.