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  1. #1
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    Nov 2010
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    90% furnace & combustion air - what gives

    I have a 10 year old Carrier 58MSA series 110 - this is a 90% furnace yet it does not provide for outside combustion air ( of course it is direct vented ). I wonder if anybody has connected it directly to the outside for the combustion air ?

    I would be interested to find out what changes took place to allow 90+ furnaces to directly use outside air ?

  2. #2
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    Apr 2010
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    southern california
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    I assume you mean a two pipe system. The biggest change was the burner compartment and door, maybe a slightly different inducer fan assembly. Mfgs. like Rheem ,you can pipe the intake or let it draw from the space.

  3. #3
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
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    Quote Originally Posted by euroboy View Post
    I have a 10 year old Carrier 58MSA series 110 - this is a 90% furnace yet it does not provide for outside combustion air ( of course it is direct vented ). I wonder if anybody has connected it directly to the outside for the combustion air ?

    I would be interested to find out what changes took place to allow 90+ furnaces to directly use outside air ?
    I've sold Bryant/Carrier since 1981. They used to be only a 2-pipe install.

    Many of the other manufactures gave the choice (1 or 2 pipes) to the installers. Guess which way they choose?

    So, some years ago, (I don't think it's been 10 years already) Carrier gave us the choice. I assume it was something to do with the design, but I don't remember.

  4. #4
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    Nov 2010
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    Canada
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    Thanks for the info - by choice do you mean there were two different units and one would order as needed for a given install ?

    Looking at the install manual they do not refer to being able to do a 2-pipe setup.

    I be interested to find out if there was a retrofit kit, or parts from newer units could be used to make this a 2-pipe setup. What is the main difference between 1 and 2 pipe systems in the furnace design ?

  5. #5
    Join Date
    Dec 2010
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    The Quad-Cities area (midwest).
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    Quote Originally Posted by euroboy View Post
    Thanks for the info - by choice do you mean there were two different units and one would order as needed for a given install ?

    Looking at the install manual they do not refer to being able to do a 2-pipe setup.

    I be interested to find out if there was a retrofit kit, or parts from newer units could be used to make this a 2-pipe setup. What is the main difference between 1 and 2 pipe systems in the furnace design ?
    It's the same furnace for all manufactures when it comes to deciding on a one or two pipe installation.

    The furnace you have will accept a combustion air pipe. The advantage is that it minimizes contamination and makes your home tighter.

    Call a qualified Bryant/Carrier dealer and they will (hopefully) know how to do it.

  6. #6
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
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    Sidebar:

    I say hopefully because the largest Carrier dealer in our area installed a furnace and the termination looked like a bull's horn.

    The homeowner had to put a piece of plywood between the pipes to keep the furnace going.

    I asked the homeowner if they bought the plywood or did he have to?

    It was meant as a joke, he didn't think it was funny.

  7. #7
    Join Date
    Nov 2010
    Location
    Ontario, Canada
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    61
    There are many reasons and advantages to pull the combustion air from outside. Just out of curiosity, why do you want to?

  8. #8
    Join Date
    Aug 2004
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    S.E. Pa
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    6,175

    Cool

    *direct vent* is two pipes--one in/ one out. A single pipe is a *power vent*.

    You should have a two pipe to minimize cold air infiltration and provide reliable MUA and not depressurize the CAZ.

  9. #9
    Join Date
    Nov 2010
    Location
    Canada
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    Currently it is a 1 pipe connection, and I would like to make it 2. The part I don't understand why in the first place the furnace would be installed with 1 - in my case it would take only about 6' of PVC pipe, and with all the benefits of dual connection.

    This brings up a question - would a good pro always install as a 2 pipe system ( provided the furnace allowed for it ), or are there valid reasons why only connect the power vent to the outside ?

  10. #10
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    Apr 2010
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    southern california
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    Quote Originally Posted by hearthman View Post
    *direct vent* is two pipes--one in/ one out. A single pipe is a *power vent*.

    You should have a two pipe to minimize cold air infiltration and provide reliable MUA and not depressurize the CAZ.
    I do not quite agree with your definition.Direct vent implies that all necessary combustion air is obtained from either an attic, crawl space, or outside via piping directly from one of these areas to the appliance and all flue gases are discharged to the outside atmosphere. Power vent refers to a gas appliance which depends on a mechanical device to provide a positive draft within the venting system.

  11. #11
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    Apr 2010
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    Quote Originally Posted by euroboy View Post
    Currently it is a 1 pipe connection, and I would like to make it 2. The part I don't understand why in the first place the furnace would be installed with 1 - in my case it would take only about 6' of PVC pipe, and with all the benefits of dual connection.

    This brings up a question - would a good pro always install as a 2 pipe system ( provided the furnace allowed for it ), or are there valid reasons why only connect the power vent to the outside ?
    To answer your question no, it depends on the conditions which exist for each location. The second pipe is bringing air into the appliance , it is no different than taking air from the space around the appliance if code permits. All gas fired appliances require combustion air to mix with the fuel being burned and to also allow products of combustion to vent to the outside. Mechanical codes allow different scenarios of where to obtain this air from. The only argument in your case may be the possible energy savings from not drawing air from the surrounding space or the infiltration of cold air into the building by not direct venting. The other plus for direct venting is obtaining air which is not contaminated from the outside ,which will help protect the heat exchanger from failure due to any chemicals which may be in the enclosed area. Never store chemicals around a furnace.

  12. #12
    Join Date
    Aug 2004
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    S.E. Pa
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    Cool

    Quote Originally Posted by acwizard View Post
    I do not quite agree with your definition.Direct vent implies that all necessary combustion air is obtained from either an attic, crawl space, or outside via piping directly from one of these areas to the appliance and all flue gases are discharged to the outside atmosphere. Power vent refers to a gas appliance which depends on a mechanical device to provide a positive draft within the venting system.
    2009 IRC Ch 24 Definitions:
    "Direct Vent Appliances-Applainces that are constructed and installed so that all air for combustion is derived directly from the outside atmoshere and all flue gases are discharged directly to the outside atmosphere."

    Since we are talking about a 1 0r 2 pipe 90%+ vented with PVC, that makes this a mechanically vented appliance with a positive vent pressure. Therefore, in order to be a *direct vent* an appliance needs a second pipe for intake air from the outdoors as defined by the gas code.

    Now, there are *direct vent* appliances that do not power vent because they are a thermosyphoning sealed loop balanced system. However, without the sealed loop and CAT III or IV, it would have to be mechanically or power vented.

    Do you still disagree?

  13. #13
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    Apr 2010
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    southern california
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    Quote Originally Posted by hearthman View Post
    2009 IRC Ch 24 Definitions:
    "Direct Vent Appliances-Applainces that are constructed and installed so that all air for combustion is derived directly from the outside atmoshere and all flue gases are discharged directly to the outside atmosphere."

    Since we are talking about a 1 0r 2 pipe 90%+ vented with PVC, that makes this a mechanically vented appliance with a positive vent pressure. Therefore, in order to be a *direct vent* an appliance needs a second pipe for intake air from the outdoors as defined by the gas code.

    Now, there are *direct vent* appliances that do not power vent because they are a thermosyphoning sealed loop balanced system. However, without the sealed loop and CAT III or IV, it would have to be mechanically or power vented.

    Do you still disagree?
    I agree with everything about direct vent. But power vent is always forced mechanical draft and should not be confused with induced mechanical draft. There are a lot of people that see an inducer fan in their furnace and believe it is power vented which is not always the case. I know that you know the difference , but most homeowners do not. I am in agreement on CAT III AND CAT IV.

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