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  1. #1
    Join Date
    Oct 2005
    Posts
    3
    We will have a new gas-fired boiler installed (either the Slant Fin Galaxy at 82.7% AFUE or the Viessmann Vitogas-50 at 83.7% AFUE) in our 2000 sq. ft., 98,000 heat loss home. We have hot water heating and cast iron radiators.

    The contractor we're considering does not want to install Outdoor reset, as he says that this would cause overheating. What is the risk of overheating caused by this control? Can anything be done to prevent this? Can we boost the efficiency of our boilers by adding outdoor reset? The heating guys are offering one high-efficincy boiler, but it is not practical because in case of breakdown, replacement parts will have to be shipped from overseas. Any help would be appreciated, Thanks.

  2. #2
    Join Date
    Jul 2001
    Location
    Gold Coast of Connecticut
    Posts
    4,582
    I would not reset a boiler which is already running close to the point that the flue gas is going to condense. If you want an outdoor reset i believe you need a condensing boiler.
    Aire Serv of SW Connecticut- Gas heat, dual fuel and central a/c systems installed and serviced

  3. #3
    Join Date
    Nov 2001
    Location
    Moose Jaw, Saskatchewan, Canada Occupation:Interprovincial Plumber, Commercial Gasfitter Interests:
    Posts
    2,412
    YES, you want outdoor reset. For every 3 degrees you can drop the water temp you save 1% on your fuel costs. The right control will reset the temps between a minimum and maximum that you select.
    Go to tekmarcontrols.com for more info. Look for a tekmar 256. It will not cause your boiler to overheat.
    I love my job, but paydays Thursday

  4. #4
    Join Date
    Apr 2002
    Posts
    11,808
    Usually 83% is the magic number where you could be getting condensation, so these boilers probably do have a condensate drain. I have not searched these models out, but just a hunch.

    The boilers will have a manual, and that manual will tell you the minimum return temperature to stay above.

    The tekmar that has been recommended in this thread by mr. pickering, when properly set up will have that boiler running hot for a high heat output out of your rads in the dead of winter and will lower the water temperature as the winter gets milder.

    It can be set up to avoid to low of a return water temperature, and will save you operating costs.
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  5. #5
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,074
    On non condensing boilers, we set the min water temp to 140, they work good that way.

    Outdoor reset doesn't cause over heating, your contractor doesn't unserdtand the control, or its operation.
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  6. #6
    Join Date
    Jan 2002
    Location
    New Hampshire
    Posts
    1,285

    87% is the threshold for condensing

    That's why gas and oil boilers will be made of a non-rusting metal at efficiencies higher than that.

    With a typical 20% excess air, the condensing temperature of the metal would be 136 for natural gas; 130 for LP gas, and 123 for #2 oil.

    Here at Slant/Fin, we require a minimum return temperature to the boiler of 130 F.

    A reset control WOULD benefit your situation. You can call me at Slant/Fin Tech Service, if you like, at 800 873 4346.

    Noel Murdough

  7. #7
    Join Date
    Sep 2004
    Posts
    654
    Look into a similar reset device distributed by Beckett....the Heat Manager. Apparently, it works like a reset control but does not use an outside sensor and is very easy to install. Said to save at least 10% on fuel costs too.


  8. #8
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,074
    Originally posted by casturbo
    Look into a similar reset device distributed by Beckett....the Heat Manager. Apparently, it works like a reset control but does not use an outside sensor and is very easy to install. Said to save at least 10% on fuel costs too.

    Its just a timer that delays the next burner cycle.
    They save at milder temps, but don't do much when it gets to 20 or less.

    An outdoor reset still limits the water temp at 20 and 10, depending on the amount rads, or baseboard.

    Microtherm came out with the same thing years ago.
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  9. #9
    sounds to me the contractor u pick dont really understand how control works maybe u should get 2nd opinion

  10. #10
    Is this system zoned or just one thermostat ? and where is the boiler located ?

  11. #11
    Join Date
    Oct 2005
    Posts
    3

    Tekmar

    There is only one thermostat and the boiler is in the basement. We have no radiators in the basement. Thanks for all of your replies, I will be looking into the Tekmar control.

  12. #12
    Join Date
    Sep 2004
    Posts
    654
    Originally posted by beenthere

    Its just a timer that delays the next burner cycle.
    They save at milder temps, but don't do much when it gets to 20 or less.

    An outdoor reset still limits the water temp at 20 and 10, depending on the amount rads, or baseboard.

    No, the HeatManager is not a timer. It has a sensor that can figure out boiler heat load and from that, configure the burner firing cycles to better match the heat loss the boiler is going to overcome. It is considered equivalent to the Tekmar, but less complicated and less money to install.

  13. #13
    Join Date
    Nov 2001
    Location
    Moose Jaw, Saskatchewan, Canada Occupation:Interprovincial Plumber, Commercial Gasfitter Interests:
    Posts
    2,412
    I haven't used the HeatManager, but the tekmar 256 is not complicated. It gives warm weather shut down, and the reset is a true curve, not a straight line reset, adjusted for the type of heat emitter used. I think that outdoor reset would beat load usage when the outdoor temp swings are large. Many manufactures are now using tekmar branded to their own names.

    BTW, the Slant Fin Galaxy is one tough little boiler.
    I love my job, but paydays Thursday

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