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New Construction Layout Advice

styxplo Member Posts: 49
I'm building a 1740 square feet timber frame with an addtioinal 1460 squre foot basement for a total of 3200 square feet. in Ohio The house is wrapped with 6-1/2" SIPS on the walls and 12" SIP roof panels. The basement is poured with ICF's and 2" foam under the slab. It has 6 embedded PEX circuits with 9" spacing and each run around 280'. The main floor has the master bedroom, great room, and kitchen which are on floor joists with 3/4" decking. This will be staple up PEX with aluminum heat plates. The dining room is also on the main floor, but it is poured concrete over Light Deck with embedded PEX, The 2nd floor is a loft (2 bedrooms and a bathroom) with an 1-1/2" tongue and groove floor which is also the ceiling to the main floor so there is no space between them to run any mechanicals. I'm going to use some type of radiators up there. I used loopCad to help design the heating system. My heat load is 49,201 btu/hr. with a design temp of 7 degrees. I think this might be a little low. The front wall in the great room is all windows and the ceiling is close to 25' tall

Sooo my thoughts so far:
The basement and the dining room have to be on a mixing valve to lower the temp for the embedded in concrete PEX. Not sure how to zone this since the dining room (1-230' run of PEX) will be on the main floor thermostat and the basment will all be on its own thermostat.

The main floor joist system uses I-joists and LVL's. The LVL's call out a very specific spot where you can drill which isn't going to make it easy to run the staple up PEX. Its pretty much divided into 4 equal sections like a plus sign. I was thinking of having each section on its own manifold. Would it be better to run the supply and return to each manifold in series or to take each one back to the boiler loop on its own supply and return? Should I use Pex or copper for the supply and return piping?

I was going to have the master bedroom on the main floor as its own zone. The heating load is 8600 btu/hr so I'm thinking I'm going to need a buffer tank for the small zone. Is this over complicating (added expense$$) things? Would I be better to just keep it in the main floor zone and not have the buffer tank?

The loft bedrooms are going to need radiators. I haven't figured out what is better suited, baseboard or wall mount. The loopCad required water temp for the main floor is 130 degrees. So my water temp will be fixed to that for the loft. which style is better suited to lower water temps. I was thinking thermostatic radiator valves and variable pump for this zone?

Any advice / thoughts is appreciated

Thanks Mark


  • Zman
    Zman Member Posts: 7,334
    Have you calced the required SWT for each area. You may be able to run the whole thing at 130 and use a mod-con boiler with outdoor reset.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • styxplo
    styxplo Member Posts: 49
    LoopCad came up with 92 fro the basement (embedded slab) 126 for the main floor (staple up) and 130 for the main floor dining room ( 4" concrete with embeded PEX). From everything I've read the last SWT seems way to high for concrete in the dining room. I'm using either panel radiators or baseboard for the loft bedrooms. What I've read about panel radiators and baseboard pretty much stop the derrating on the spec sheets at 140 degrees. Thats kind of where I was getting the 140 from.

    I've been reading a lot of the idronics issues and watching many episodes of coffee with Caleffi. I came across an article in PME and a part in coffee where they used panel radiators and stepped down the tempersature for the other emitter types using proportinal mixing valves. This allowed them all to follow the outdoor reset curve with no "smarts" I really like the idea ,but when they did the poll only 3% said they used proportinal mixing valves. do you have any experience with this?

    I think I've answered some of my other questions too.

    The dining room embedded pex will be tied into the basement for the correct SWT but will have a zone valve tied into the main floor thermostat

    I'm going to run a seperate supply/return to each manifold for the staple up. Makes more sense afterI gave it some thought.

    I did the math for the buffer tank sizing. It came out to 10.7 gallons. I'm going to go with a 30 gallon because that seems to be about the smallest anyone offers. Can you oversize a buffer tank??

    Hopefully I'm heading in the right direction

    Thanks Mark
  • hot_rod
    hot_rod Member Posts: 16,334
    Yes the buffer does add cost and control complexity. I don't know of any exact formula to help decide when a buffer makes sense. Every system performs differently. Most would agree a minimum 10 minute run cycle is a good idea for any boiler.

    I think that manual mix valve tracking with ODR is an underutilized method. And you have the ability to throw an actuator on it if you want more control later on.

    6 &12 gallon electric tanks are fairly easy to find for buffers. But you do need to adapt the connection sized. No harm in oversizing a buffer.

    Boiler Buddy has an 18 gallon buffer with 1-1/4 connections. They have a sizer on the website. www.hotwaterproducts.com
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Jolly Bodger
    Jolly Bodger Member Posts: 209
    that temp for dining room PEX does seem high. but it is all based on spacing and required BTU per Square Foot needed. what is the spacing?
  • styxplo
    styxplo Member Posts: 49
    The load for that room is 5800 btu. There are a lot of windows. The tube spacing is 9”. I was thinking that you had to keep the SWT for PEX embedded in concrete closer to 100
  • Jolly Bodger
    Jolly Bodger Member Posts: 209
    It's all based on the spacing and how many BTUs you need. Room load (5800) divided by SQFT of floor with radiant tubing. give your BTU demand per SQFT. Then look on the 9" spacing curve for that point will tell you the SWT you need. This of course is the MAX needed at design temp.