Need help deciding on Vitodens 200
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  1. #1
    Join Date
    Aug 2007
    Location
    Sudbury, Ontario, Canada
    Posts
    20

    Need help deciding on Vitodens 200

    I have a 15 year old cast iron mid-efficiency boiler (HydroTherm 125,000 BTUH input) heating a small ~950 sq ft 1 1/2 story house with cast iron radiators. The boiler stops firing on very cold days on high water temperature (boiler shutoff set @ 205 F), but keeps the house warm since I've removed wooden decorative enclosures around main floor radiators. I've been told the large pipes feeding the radiators were installed originally for natural convection circulation, before circulating pumps were invented.

    The Vitodens 200 DHW supply should be adequate for our 2 people, one bath house, but I'm worried whether I can get a condensing boiler to run in condensing mode. The last time I had a Viessmann contractor look at our house he said that cast iron radiators need to be matched up with cast iron boilers. This had a somewhat logical ring to it, but I'm a technically oriented guy and I require a more technical answer. His comments killed my ambition to pursue a condensing boiler.

    I'm trying to revisit the suitability of the Vitodens 200. But, I don't want to spend all that money and find out that I can't get the return water temperature down low enough to operate in condensing mode.

  2. #2
    Join Date
    Oct 2009
    Location
    God's country - Shenandoah Valley, VA
    Posts
    339
    Quote Originally Posted by satwar View Post

    The last time I had a Viessmann contractor look at our house he said that cast iron radiators need to be matched up with cast iron boilers. This had a somewhat logical ring to it, but I'm a technically oriented guy and I require a more technical answer. His comments killed my ambition to pursue a condensing boiler.
    .
    Eliminate this contractor from your list: he doesn't know what he's talking about!

    Mod/cons work great with converted gravity systems if done right. In fact, it's probably the best scenario for a replacement. The large mass from the rads and piping will produce a "natural reset" that will cause the boiler to operate in the condensing mode most, if not all, of the time.

    Make sure a load calculation is done (manual J or equivalent) and the boiler is sized to that, not the rating of the old boiler. Calculate the EDR (rad sizing) and set the reset curve to match. Make sure the system is thoroughly flushed and a strainer is installed at the boiler's return. Follow the manufacturer's piping and installation instructions and you'll have one of the most comfortable and efficient systems around.

    Also, consider having your contractor install TRV's to control each rad.

    If you send me a p/m, I can send you a helpful article.

    Make sure you choose the right contractor. He's 98% of the equation! That cannot be over-emphasized. A good hydronics pro can take any brand of mod/con and make it run like a Mercedes. A knucklehead will mess up the best boiler made, including a Viessmann.
    Bob Boan


    ​You can choose to do what you want, but you cannot choose the consequences.

  3. #3
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,597
    Cast iron rads and outdoor reset work great together. you'll have low return temps most of the year. Should save you lot of money on your annual heating bill. Size the boiler to the homes heat loss, not the radiators.
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  4. #4
    Join Date
    Aug 2007
    Location
    Sudbury, Ontario, Canada
    Posts
    20
    Quote Originally Posted by bobboan View Post
    If you send me a p/m, I can send you a helpful article.
    How do I send you a p/m ?

  5. #5
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,597
    Only Pro members have PM abilities.
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    How many times must one fix something before it is fixed?

  6. #6
    Join Date
    Aug 2007
    Location
    Sudbury, Ontario, Canada
    Posts
    20
    Very encouraging, that's very good news. Too bad I can't see that article. I'll spend some time doing the heat loss with HVAC-Calc, as I'm pretty sure there's no installer in my city that will do it himself

  7. #7
    Join Date
    Aug 2007
    Location
    Sudbury, Ontario, Canada
    Posts
    20
    Some good news. I found an installer in my city from the Viessmann web site. He's the first installer I've found that seems to talk sensibly. He says that cast iron radiators are the perfect heating element for a condensing boiler, and that a cast iron boiler is about the worst choice.

  8. #8
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,597
    Congrats.
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