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  1. #1

    mod/con sizing & more ?s

    Hi, I'm new here. I have a 60 year old oil boiler cast iron radiators & a 20 yr old, 80g eletric water heater . I want to switch to gas mod/con & indirect water heating.

    I did a heat loss calc using the slant fin site, (guessed at a few things, temp 0*F, no wall insulation). I came up with ~69k btu/hr.

    I've talked to a few contractors, 4 suggested Buderus wall hung, one Weil Mclain. Of those 2 would go with the 106k Buderus, 1 the Buderus 84k, 1 the W/M 80k, still waiting on 1, not hopeful. All based sizing on size of radiators, 1 I asked about heat loss hasn't bid, hmmm. W/M is 20% higher, others close in price.

    2 more questions: Most suggested a Super Stor 45g or similar, 1 the W/M 40 plus tank-in-tank style (not the W/M boiler guy ). I'm sure either is more than enough except for visitors. Any opinions on these 2 styles or brands?

    Then there's the pvc venting, according to 1 guy Buderus requires 1ft above ground, no higher. Another says it's ok to add a "snorkle" to raise it up another ft. I live in central Mass & we get snow often over a foot so it might be nice not to have to remember to shovel out the vent. Is that OK, unwise, warranty voiding?

    Thanks in advance

  2. #2
    Join Date
    Aug 2007
    Location
    WI
    Posts
    1,116
    Quote Originally Posted by centralma View Post
    Hi, I'm new here. I have a 60 year old oil boiler cast iron radiators & a 20 yr old, 80g eletric water heater . I want to switch to gas mod/con & indirect water heating.

    I did a heat loss calc using the slant fin site, (guessed at a few things, temp 0*F, no wall insulation). I came up with ~69k btu/hr.

    I've talked to a few contractors, 4 suggested Buderus wall hung, one Weil Mclain. Of those 2 would go with the 106k Buderus, 1 the Buderus 84k, 1 the W/M 80k, still waiting on 1, not hopeful. All based sizing on size of radiators, 1 I asked about heat loss hasn't bid, hmmm. W/M is 20% higher, others close in price.
    If your heat loss calc is reasonably accurate, I would not go bigger than 80k btu.

    2 more questions: Most suggested a Super Stor 45g or similar, 1 the W/M 40 plus tank-in-tank style (not the W/M boiler guy ). I'm sure either is more than enough except for visitors. Any opinions on these 2 styles or brands?
    Do you fill a big bath tub or whirlpool? If so, you may need more. If not, 40 gallons should be plenty. Both indirects are good, but the tank in tank style is better if you have very hard water with no softener. Found that out the hard way.

    Then there's the pvc venting, according to 1 guy Buderus requires 1ft above ground, no higher. Another says it's ok to add a "snorkle" to raise it up another ft. I live in central Mass & we get snow often over a foot so it might be nice not to have to remember to shovel out the vent. Is that OK, unwise, warranty voiding?
    Usually you should be one foot above the anticipated snowfall.

    Thanks in advance

  3. #3
    Join Date
    Jan 2004
    Location
    PA
    Posts
    68,795
    The Ultra 80 can mod down to 16,000 BTUs. So it is a good choice for getting long cycles at mild outdoor temps.
    Either of the 2 indirects will be fine.
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  4. #4
    Thank you both, I appreciate the help.

  5. #5
    Join Date
    Mar 2003
    Posts
    7,326
    it is claimed that the tamk in tank style heats your domestic more even;y and easily due to the larger contact area as opposed to a coil in tank style. Whatever floats it for you will work just fine. I do not know if you guys up there have access to it yet, but Triangle tube makes an all in one unit called the excellence that uses a foiurteen gallen instantaneous tank right in the boiler cabinet. These are in high demand as they come prepiped and controlled for domestic priority, outdoor reset etc. and are very price competitve. I have sold a bunch for both residential and commercial projects and love these things.

  6. #6
    Thanks, flange. All my hot water use is on the opposite side of the basement from the boiler, ~30 ft. I don't want to wait & waste water (had a ranch house once) so I had asked about having the indirect tank where the current water heater is located. None suggested a different or better way so I don't think an all in one would work for me easily.

    Maybe I should redo my heat loss calc, does 69k btu/hr seem ball park to you? 1500sq ft cape, replaced windows. Are they sizing for the indirect demand?

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