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condensing vs. conventional right application

Bobbyd2727 Member Posts: 27
Trying to decide between the condensing boilers and the conventional cast iron boilers.  While the condensing boilers like the system 2000 sound greatly efficient, are they the right application for a 3000 square foot house with vaulted ceilings and hot water baseboards?  What concerns me is with my old dunkirk boiler it takes an hour to raise the temperature one degree when it is below freezing outside and that is with 160 degree water running through the baseboards. Don't these condensing boilers gain their efficiency with lower temperatures?  We vaulted the ceilings in the kitchen and den after we bought the house and the old heating system was already in.  I can't increase the baseboard coverage since those rooms are on a slab.  Size of kitchen plus den is 25 x 18 and there is 24 ft of baseboard. Rest of house has eight foot ceilings with plenty of baseboard.  What would the best boiler for this situation???


  • icesailor
    icesailor Member Posts: 7,265

    The reason your cathedral ceiling rooms don't work is because you increased the heat loss but didn't increase the radiation. If you raise the high limit setting on the boiler to 180 degrees, it will heat faster and better. As far as adding baseboard, where you don't have enough to add more, you need to know what the output on the baseboard is. Take Slant-Fin, the most popular. At 180 degrees, the cheapest is #15 that produces App. 550 BTU's per foot. Nest which is more popular is #30 at 600 BTU's per foot. Last is #80 at 750 BTU's per foot. So, if you should happen to have #15 baseboard, you can get an additional 200 BTU's per foot by changing the baseboard. This is just an example.

    I'm not commenting on the difference between CI and Mod-Con other than to say that if your system was designed for 180 degree water and are running it at 160 without you mentioning any problems, you could possibly have long periods where you don't get condensing. I'm not comfortable with the claimed longevity of Mod-Con boilers. They could be more expensive in the long run. I haven't seen a lot of old Weil McLain GV Gold boilers croaking and being replaced. But Weil McLain just came out with a GV Gold 90%+ that is the same bomb proof cast iron boiler that can be direct vented with PVC and has heat recovery in the exhaust to suck any available heat out of the exhaust and put it into the return water. It comes with all the P/S pumps installed and a SS HX. It looks like a nice unit. You just can't hang it on the wall. And it isn't an aluminum block.

    A new boiler isn't going to make those rooms warmer. Only a change in radiation will do that. What's wrong with the old one?
  • Bobbyd2727
    Bobbyd2727 Member Posts: 27
    old boiler should it be replaced??

    the old boiler is a dunkirk cast iron about forty years old,  It just uses too much oil.  I have a programmable thermostat that I set back to 62 degrees at night and during the day, back up to 67 from 3 to 10 p.m.  and it uses btween 1100 to 1200 gallons a year other than that with yearly tuneups no problems at all. I have a high speed beckett burner.  I'm really debating if i should change it.
  • icesailor
    icesailor Member Posts: 7,265
    Boiler Replacements:

    Those 40 YO Dunkirks have a value on the shore as boat moorings in mud. More valuable than the scrap. It ran like crap when new with a 1725 RPM burner and runs just as bad with the AFG. They leak air like an old rotten tubeless tire. The first house I built myself in 1963 came with one as a un-assembled home from Grossmans Lumber in New England.

    If you are considering gas, the new Weil-McLain GV 90+ would be a plug and play for you. It comes all piped to where you just connect the supply and return and vent it with PVC. Or use Inoflue PE venting because there is no PVC manufacturer who approves of Sch 40 PVC pipe and fittings for any other use but drain, waste and venting of waste and water.  NOT exhausting gas appliances.
  • Bobbyd2727
    Bobbyd2727 Member Posts: 27
    gonna change it

    I can't use gas too far to plumb it at a reasonable cost looking for another oil boiler.  So you think maybe i'll save 30 to forty percent with lets say a buderas g215 or a burnham mpo??  thanks for your advice!!
  • Steamhead
    Steamhead Member Posts: 16,889
    First thing to do

    is a heat-loss calculation. You may find your present boiler is way oversized for the house. This is pretty common and always wastes fuel.

    Then select a boiler based on the calc results. For best efficiency and ease of service, go with a 3-pass boiler such as:



    Burnham MPO

    Slant/Fin Eutectic



    Weil-McLain Ultra Oil

    There are probably some I didn't mention but these come to mind.

    Also, the System 2000 based on the rave reviews it gets. This is a steel boiler but unlike the usual cheapo steel boilers out there, this one does very well.
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
  • chapchap70
    chapchap70 Member Posts: 139
    edited February 2012
    System 2000 is not condensing

    The System 2000 is a low mass boiler that purges the heat out of the boiler to cut fuel use.  The amount of time needed to heat up a room with baseboard depends mostly on water temperature and amount of baseboard in the room; not on the boiler.  I am assuming that you have a flow rate of 4 plus gallons per minute and the loops are not too much over 100 feet.

    Even though I installed large System 2000 boiler set up with 257,000 BTU output for a church, I had to raise the water temperature to 200 degrees to get enough heat into the 2 baseboard zones that can only give an output of about 7500 BTUs.  The much larger sanctuary and basement zones heat fine.  (air handlers)

    The only way to remedy this is to install more baseboard in the room or replace with higher output baseboard.  Since the large boiler only contains 7.5 gallons of water, (the one you would probably need holds 2.5 or 4 gallons depending on your heat loss) there are fuel savings to be had.  Purging the heat from the baseboard zones only gets the temperature down to about 175 after the call for heat has been satisfied.  If the air handler is the last zone calling, the purge gets the temperature down to about 125.

    see system2000.com for more info how this boiler works.
  • icesailor
    icesailor Member Posts: 7,265
    Heat Loss:

    There are different piping strategies to get around your example of low temperature at the end of a zone. Reverse Return comes to mind. Allthe supplies are connected to the supply. The rerrns are connected to the return back to the boiler.
  • Mac_R
    Mac_R Member Posts: 117

    I like condensing boilers.  The Buderus GB125BE is a beautiful boiler.  The thing that I find is the price of those systems including the chimney lining can make them pricey.  If you are doing direct vent then it is not so bad.  One of the most important things with a condensing boiler is controlling the Delta T.  For that you need to use a smart circulator.  I always use the Taco Delta T 008 on my jobs.  Tell it you want a 30 degree Delta T and it will keep it.  A Delta T is the temp difference between the supply and return lines.  With a condensing system you need to maintain at least 20 degrees in order to take full advantage of the condensing.  If you are not condensing then you don't have a condensing boiler.  Then why spend the money.  A lot of guys out there will tell you to use the three speed Grunfoss circulators.  They are a fixed speed pump and will do nothing for you.  The pump needs to change the rate that it moves the water around the system based on the needs of the house.  The more heat loss the more water we need to move.  The lower the heat loss the less water we need to move.  Sounds simple.  It is.  There is a lot of math involved with a new system.  Make sure your contractor understands everything about the system.  The boiler is just a small peace of the puzzle.  You are going to buy the Bentley.  Now don't go to Walmart and buy the tires.  
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