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  1. #1
    Join Date
    Mar 2005
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    Built an addition and added radiant heat in basement - looking for recommendations\approaches to heat this space.

    Old space heated by a Weil-McLain HE-6 boiler (Input BTU 167K/Output 137K). Approximately 18 yrs old. 4 zones with 154 feet of baseboard. Sq ft of original space (sans basement = 2,767 sq ft). Old space is 2x4 construction R13 walls. I also have a AMTROL\Boilermate indirect water heater.

    Added radiant tube to basement (in slab for addition and slab on slab for old space). I have 1,200 linear ft of 1/2" PEX in slab\slab on slab. 600 linear ft of 1/2" PEX staple up for kitchen tile floor and 600 linear ft of 7/8 PEX in slab to heat garage. I've been told that this totals to something around 77K BTU required for heating. All of this tubing lacks Oxygen barrier. Basement is approx. 2,621 sq ft.

    The new addition is heated by force air via coils (both of which have a capacity of 45k BTU). New space is 2x6 with closed cell foam (R7/inch) insulation. R25/walls and R40/attic. New area is approx. 2,000 sq ft.

    I did Heat Loss calc with the Slant Fin Hydronic program and total Heat loss (BTU/HR) is about 96,998.

    My questions are:
    - Do you recommend that I keep the radiant heat on a separate system? Would you recommend tankless (e.g., Takagi or Munchkin) for this application?

    - Should I replace the old boiler and size a new unit for both the baseboard and force air? My assumption is that as a side benefit I could go with a modulating type that would help during non-Winter months for hot water.

    - Should I leave the old unit and add a new unit for both the radiant and forced air?

    Thanks for your help.

  2. #2
    Join Date
    Jan 2004
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    You should concider the munchin, since you don't have an o2 barrier, and yes you can size it for the whole house.
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  3. #3
    Join Date
    Feb 2003
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    That 96K does not include the original BB right and Amatrol? It looks like you need around 80K just for the old BB? With a single new boiler, you'll still need to run high temp for indirect and BB, so I don't see much condensing going on. Getting a second smaller boiler for the radiant might be more efficent, but you keep the old WH running all year long for HW. Since your buying a boiler anyway, I'd get a munchkin or Ultra. Only cost a grand oe so to upsize the boiler now rather then buying a 2nd one in a few years when the W-M goes. Is the Amatrol going to be replaced?

  4. #4
    Join Date
    Mar 2005
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    Thread Starter
    Thanks for the replies. The 96K includes the original BB and new areas but not the Amtrol.

    I was thinking that a second smaller boiler just for radiant may make more sense. My other concern is that the PEX has no O2 barrier and I've heard that sometimes cast iron corrosion is a problem so I have concerns with mixing the radiant and BB.

    I'm not sure if I should replace the Amtrol. If I go with an Ultra it may make sense to keep it (not sure). Alternatively, if I go with the Munchkin for the radiant I could move the Hot Water to that unit.

    Seems expensive to fire up the old WM in the spring\summer\fall just for HW. So far the old WM has been reliable but I guess it's just a matter of time before it goes. My local HVAC guys seem to shy away from the Ultra (they say serviing is very complex).

    Just wanted to make it clear that I'm a homeowner but my local HVAC guys will do the job. I'm just trying to figure out what my best options are before I start writing checks. Given the way gas prices are climbing I want to make sure I'm making the best decision. Thanks for your help.

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