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  1. #1
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    Default Boiler Installation Advice

    I could use some feedback. On a five year old house, there is a Weil McLain Gold GV5 (series 4) boiler. It is horizontally vented, with plenty of combustion air ventilation. Our elevation is about 7,200 feet.

    In the installation instructions on page 12 it states "Installations above 5,500 feet altitude must be direct vent if sidewall vented."

    Boiler Link

    I interpret this to mean that the intake air must be piped directly to the boiler, not using pass through combustion air vents. We've been going around about this, and today Weil McLain originally said it was okay as is (not direct vented), and then changed opinion and said it must be direct vented.

    1: Am I misinterpreting the definition of direct vent? It seemed pretty clear to me, but maybe not.

    2: What would be the reason for requiring it at 5,500 feet for sidewall vented units, but not below?

    3: Have any of you run across type of statement this in any other boilers or Cat IV furnaces? The customer service tech at WM seemed genuinely surprised when I pointed out that sentence in the installation instructions. The plumbing supply house that sold the boiler didn't seem to be aware of it either.

    Hopefully I haven't left anything out, but if so, let me know and I'll fill in the blanks.

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    Jim Robinson
    New Mexico, USA

  2. #2
    Join Date
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    Default Re: Boiler Installation Advice

    IMO - Direct vent means connection to the exhaust side of the boiler with a vent pipe that exhausts to the exterior of the building. The pipe size, number of fittings and maximum length of run to meet boiler manufacturers requirements.

    Direct vent means that it is separate from other appliances and does connect with other flues or chimneys.

    The inlet air can be from open space within the home (with volume requirements) or piped from exterior, depending on type of direct vent appliance and manufactures installation instructions.


  3. #3
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    Default Re: Boiler Installation Advice

    Ken's statement of 'direct vent' is basically what I would also have written. His is the standard definition that I am aware of.
    I am not aware of anything that ties 'direct vent' and the combustion air source to each other as part of the definition. Your combustion air could either come from the interior or exterior. Unless the unit uses a concentric vent pipe system, I'm really missing your question.
    Since we don't have altitude around here, at least not natural, not sure about this. All the install manuals I have read refer to the need to change the orifice on the gas valve at higher altitudes.
    I read through portions of the manual. It definitely sounds like a concentric pipe set-up for your elevation. My guess is that this is necessary due to air pressure issues with potentially running a vent or combustion pipe up 2 stories at high altitude. Did you buy the high altitude conversion kit? Sounds like it has a different pressure switch and probably a gas valve orifice.

    Last edited by Markus Keller; 12-10-2010 at 07:36 AM. Reason: add info
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  4. #4
    David Bell's Avatar
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    Default Re: Boiler Installation Advice

    Quote Originally Posted by Jim Robinson View Post
    I could use some feedback. On a five year old house, there is a Weil McLain Gold GV5 (series 4) boiler. It is horizontally vented, with plenty of combustion air ventilation. Our elevation is about 7,200 feet.

    In the installation instructions on page 12 it states "Installations above 5,500 feet altitude must be direct vent if sidewall vented."

    Boiler Link

    I interpret this to mean that the intake air must be piped directly to the boiler, not using pass through combustion air vents. We've been going around about this, and today Weil McLain originally said it was okay as is (not direct vented), and then changed opinion and said it must be direct vented.

    1: Am I misinterpreting the definition of direct vent? It seemed pretty clear to me, but maybe not.

    2: What would be the reason for requiring it at 5,500 feet for sidewall vented units, but not below?

    3: Have any of you run across type of statement this in any other boilers or Cat IV furnaces? The customer service tech at WM seemed genuinely surprised when I pointed out that sentence in the installation instructions. The plumbing supply house that sold the boiler didn't seem to be aware of it either.

    Hopefully I haven't left anything out, but if so, let me know and I'll fill in the blanks.
    The GV boiler is meant to be a direct vent boiler. The atmospheric pressures above 5500' may play havoc with the pressure switch that proves combustion fan if not direct vented resulting in nuisance calls for no heat. The use of a concentric kit is the best solution. I have seen furnaces and boilers require kits for high altitude conditions.


  5. #5
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    Default Re: Boiler Installation Advice

    The define their definition of direct vent on page 14 of the installation instructions.

    The only things I could think of were something with the atmospheric pressure or that they wanted the incoming air to be as cold as possible. The customer service tech wasn't very helpful. The fact that it would be okay according to them at 5,400 feet, but not at 5,600 is kind of arbitrary also. The run of the horizontal exhaust would play a big factor, I would think.

    Jim Robinson
    New Mexico, USA

  6. #6
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    Default Re: Boiler Installation Advice

    Do you have the required high altitude kit? And the "Vent Supplement" that was supposed to be included with the boiler?
    "If the boiler installation is at high altitude (over 5,500 feet) make sure to
    obtain and install the high altitude kit. Obtain the high altitude kit and
    review the instructions included. Note the venting restrictions and input
    reductions at altitudes over 5,500 feet."

    "GV boiler controls automatically reduce input with increasing altitude. See Table 1 for
    estimated input at altitude as a percentage of sea level input. Multiply the boiler sea level input by this percentage to obtain the estimated high altitude input. Note that the length of the venting system will also have a minor impact on input. Refer to the vent supplement for further information.
    No modifications to the boiler should be necessary for installations up to 5,500 feet above sea level. For higher elevations, the air pressure switch must be changed to a special high altitude switch. Refer to the high altitude kit instructions, manual Section IId. Note that the gas valve outlet pressure must be checked (and adjusted if necessary) in accordance with manual Section VIIf."


    "At altitudes above 5,500 feet, GV boilers can be sidewall vented only when
    using direct vent (ducted combustion air). GV boilers can be vertically
    vented in any of the configurations shown in the vent supplements. Refer
    to vent supplements for more detail."

    As others have mentioned, since the boiler makes automatic adjustments based on altitude, having outside combustion air would help keep the unit from adjusting based on pressure differential between indoors and outdoors. This would likely not be an issue at lower altitudes but would screw with proper operation at your altitude.
    When in doubt, follow the instructions. The do refer to combustion air as direct venting and the exhaust venting as direct exhaust venting.

    Jim Luttrall
    www.MrInspector.net
    Plano, Texas

  7. #7
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    Default Re: Boiler Installation Advice

    You are absolutely correct Jim Robertson, and "great catch" by the way.

    I'm going to disagree with both Ken A. and Markus K. They're both describing "direct exhaust venting" not "direct venting".

    Your manual and mfg refer to the National Fuel Gas Code, (NFPA 54) and the ANSI standard number for same (ANSI Z223.1) which IS the National Fuel Gas Code (NFPA 54). That is your source of definitions, conditions, specifics, that the mfg is referencing. You can view it on-line for free at NFPA.org. You will have to register at the site, you may register without joining NFPA as a member. I've given step by step instructions for viewing NFPA standards and codes on-line for free many times before. When you view the "list of standards and codes", NFPA 54 (they're in numerical order) is what you want.

    To be "direct vent"(ed) an appliance must be #2 below. #1 is required and #3 is a given with this type of equipment, whether or not it is installed in a "direct vented" manner. Some DV or condensing equipment may be installed without #2 below, but when it is, it is no longer a "direct vented" installation. IOW, sealed ducted/vented combustion air from the outdoors to the sealed combustion chamber is the critical componant of "direct venting".

    "Direct vent" means generally,

    1. Sealed combustion chamber

    2. Sealed ducted/vented combustion air from the outdoors to the combustion chamber on the same plane and in relative proximity within requirements and conditions as the

    3. Sealed ducted/vented exhaust.

    Although this may be accomplished by concentric venting, it is neither required, nor always the best way to do so, even through the wall, it depends (IOW separate inlet and exhaust vents - sealed - are acceptable, but they should/must originate/terminate on the same plane).

    Usually, these units operate under positive pressure, exhaust but not always, sometimes its more of a push-me/pull-me exhaust/combustion air.

    As far as the question as to "why" at higher altitudes ...

    Winds at higher elevations (suddenly effecting pressures), prevailing and otherwise, extremes of sudden wind/pressure changes, topography, all have their effect as well.

    Higher altitude air less dense, "thinner" air, and lower available oxygen. Generally, higher altitudes equal lower mean "pressure" than at sea level.

    This is one of the reasons why units are adjusted for lower fuel delivery/flow at firing point at higher altitudes to assure as-complete-as-possible combustion. 5,000 or 5,500 feet is also the usual adjustment point for power venting/control/pressure systems adjustment as the chamber also has to be more readily evacuated from the products of combustion (again the air is "thinner" so concentrations of other gases within become more critical by volume). Fuel such as NG can be devalued for example and/or adjustments at the burner controlling (reducing) the fuel rate to be presented for combustion.

    Boiling point of water lower, etc. all effects the "science of combustion" just as it effects the "art of cooking/baking" at higher altitudes.

    Note, not just adjustments at the flow of fuel, but, "A special high altitude pressure switch" must be installed to replace the factory installed pressure switch at installations above 5500 ft.

    It becomes more critical with the "thinner air" to assure proper combustion - the "room for error" becomes tighter between a combustion appliance and a CO producer.

    Combustion air temperature doesn't play a factor really in a DV boiler or furnace. The combustion chamber is sealed. Heat is transfered via a HE. The fuel when combustion occurs releases the same heat irrespective of the air temperature of the combustion air. The actual water content of the combustion air effects minimally - the condensate volume is mostly determined by the characteristics of the fuel combusted.

    Last edited by H.G. Watson, Sr.; 12-11-2010 at 06:58 PM.

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