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    Staple Up Radiant - Old House, Is this possible? (3 Posts)

  • OldMNHouse OldMNHouse @ 11:12 AM
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    Staple Up Radiant - Old House, Is this possible?

    Ok,

    I know the answer - yes and no, it depends...  I apologize in advance for the long post, but I want to get as much detail in here as I can.

    I have an 1878 house that I bought in May 2013.  The house is essentially a two story structure of 700 sqft per story, there is also an original one story kitchen addition of 400 sqft and a closed in porch of 150 sqft.
    Shortly after I bought the home I did an energy audit which said that I needed to tighten up bypasses in the attics and spray foam the rim joist, which I plan to do.  Currently we have one air exchange per hour, and we are in MN, so this leads to a lot of heating of the house in the winter.  I imagine that if I seal most of the bypasses and add more attic insulation, this would improve the situation substantially.
    The second story has been remodeled in the last 10 years and have wall insulation, the wall insulation in the downstairs is non-existent, except for in the porch, which is fully insulated.  I also plan to add insulation in the attics to get to R-50, from current R-19.  The floor is 1" subfloor and 3/4" pine on top.

    I am hoping to do staple up radiant because I love warm floors (and my wife hates the baseboard heaters, which line the exterior walls in most rooms).

    I have not done a load calculation, but here is some data that I have.

    The house is heated with natural gas, and last winter, which was cold (lowest was -44 with wind chill),
    had an average daily use of natural gas (both stories of the house) of a
    little less than 10.5 therms/day in January and February.  The main
    floor is about 1100 square feet, so it gives me a little less than 40
    btu/hr/sqft (not taking into account that part of the 11 therms that was used
    for heating the 2nd floor (separate heating zone).
    The boiler output is 83000 BTU/hr.

    We have a total of 141 linear feet of baseboard heaters in the house --> 70000 btu @ 500 btu/linear foot.

    The main floor comprises 48000 btu @ 500 btu/linear foot, which gives me about 43.5btu/hr/sqft for the main floor.

    My wife would like to get rid of all baseboard heat, don't know if this is possible, could do one or two runtal wall radiators in strategic locations as the piping is available, but would prefer to have as few as possible.

    Now, is staple up possible?
    I heard from one company that I would need to add wall insulation before doing anything,
    another specified 7/8 PEX ($2k), and
    a third specified 1/2" PEX with extruded plates ($8k).

    What do I need?  Can I go with less heavy duty plates and save some money, or would it not get warm enough?  Of the $8k, $3k was the heating plates.

    Sorry for the long note, but I wanted to get as much info as possible crammed in.
  • Gordan Gordan @ 2:12 PM
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    Consider radiant ceilings

    That's a lot of heat loss. Even under the best circumstances a heated floor can only provide up to 35 BTU/sqft due to surface temperature limit recommendations, and yours are not the best circumstances so even that may not be attainable. 1.75" of wood is no small barrier to heat flow. To boot, the subfloor is probably cupped and there are gaps in it so contact between heat transfer plates and it might be tenuous. There's a system (UltraFin) that uses little convective plates that snap onto the PEX tube that's suspended a few inches below the subfloor in the joist bay, which would not be vulnerable to irregularities in subfloor but would require that the joist bays be sealed really well at the perimeter to prevent heated air leakage. Bare PEX tube, regardless of size, is not likely to be able to transfer enough heat to be a primary heat source in any non-superinsulated house in a Northern climate.

    And then, as I indicated in the subject, there are radiant ceilings, which are a good retrofit option. Search for that term on the site and you'll find out a lot about the pros and cons. These typically, but not necessarily, involve furring out the existing ceiling and stapling thin plates to the furring strips, snapping tubing into them, and then sheetrocking over the entire kit'n'kaboodle.
    This post was edited by an admin on September 20, 2013 2:21 PM.
  • Gordy Gordy @ 6:27 PM
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    The Math

    Is the key need to do a heat loss first.
    Probably before that tighten up the envelope first. This then will give you an accurate heat loss to design a radiant system to.

    If you do the radiant (if doable) then the envelope you will end up with an oversized heating system.

    Stay away from the 7/8 pex guy. Bigger is not better. Willing to bet the mind set is use bigger pex with no plates, and wider spacing is the same result...... its not!!

    If you can do under floor then extruded plates with 1/2" pex 8" centers is the way to go heat loss will tell all. this method will require the highest water temps near what you are running for baseboard. I'm with Gordan your pushing through a lot of wood thus rvalue to get the heat to the space.

    IF you are considering new floors then the over the top method with plates will yield more out put with lower water temps.
    Over the top methods are sandwich, warm board R, Roth panel,amongst others.

    Ceiling radiant is a wonderful option that will yield more btus per square foot output than radiant floors you can have a higher surface femp than radiant floors, but you are limited to 120* water supply temps on the sheet rock.
    And No heat does not rise hot air rises your room will be with in a couple of degrees from ceiling to floor. I have radiant ceilings. You wont have the warm floors they will be neutral.
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