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  1. #1
    Join Date
    Jun 2010
    Location
    Tarrytown NY
    Posts
    56

    Furnace Air Intake Question

    I've had my new American Standard 2-Stage, 95% furnace installed since May and this is my 1st heating season.

    The unit is installed in the attic which has pleanty of ventilation and is sealed from the living space below. Its a downflow furnace configuration and it's working well. For December here in NY my gas usage is significantly less than December of last year even though its been much colder this year. I upgraded from an 80% single stage furnace.

    The installation looks fine based on all of the information on this site on how the unit should be installed except for one item.

    My HVAC guy didn't extend the Air Intake beyond how it is set up from the factory meaning when you open the cover of the furnace you see the air intake PVC with it's plastic screening cap. No PVC was added to extend the air intake out the side of my unit.

    When i asked my HVAC guy about this he said that it's ok to have it configured this way since the attic is open to the outside air. Also forgot to note that i also have a attic fan vent within 10 ft of the furnace so besides the normal attic vents there is this 14 inch vent to the outside air near the furnace.

    I also saw that he removed the "metal knock-out" where the air intake would enter the furnace cabinet so i can see that there are no obstructions between the furnace air intake and the attic air.

    My novice estimate is that there is enough air from the attic to satisify the furnace and i don't believe it's sucking any air from the inside of my house. I don't feel any drafts near the attic stairs or anywhere else when the furnace is running.

    I'm thinking that this configuration must be ok since the furnace is working great and very efficiently and i know i'm going to have to make sure that the existing air intake grill is vacumed and kept clean each season but is this common practice for units in the attic? Again this is a down flow furnace so its standing vertically.

    Thanks, John

  2. #2
    Join Date
    Dec 2002
    Location
    Houston,Tx.
    Posts
    15,849
    Quote Originally Posted by jrref View Post
    Again this is a down flow furnace so its standing vertically. Thanks, John
    John, just wondering, I have never seen in Houston a down flow in an attic, is there a air chase under it, with fur downs running throughout the home? I don't really know about your air intake, you probably would have to special order a condensate furnace in Houston, we just don't use them here, but I personally think the intake should exit the home, but again I don't know.
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  3. #3
    Join Date
    Jun 2010
    Location
    Tarrytown NY
    Posts
    56
    Yes, the furnace is mounted vertically with the return from the living space coming in to the top and under the furnace is the A-Coil for the A/C. This two piece arrangement is then connected (or sitting) on the main metal ductwork which then has flex branches going off to different parts of my townhome.

    I agree this must be a special application for the townhomes which i live in since we are tight on space.

    These furnace & A/C configurations have been installed in my development since 1994 and we are now replacing the units with the new 95% 2-stage furnaces and new A/C, 15 SEER single stage.

  4. #4
    Join Date
    Jun 2008
    Location
    Cincinnati, Ohio
    Posts
    2,176
    The only problem not having the air intake pipe installed to the outside is just as Mr. Bill pointed out........it's not truly outside air. HOWEVER, I have seen 90+% furnaces installed in both basements and attics without them and they work just fine.

  5. #5
    Join Date
    Jun 2010
    Location
    Tarrytown NY
    Posts
    56
    It's interresting that you mention this, not truely outside air.

    True the furnace isn't using 100% air from the outside of the house but it is using the air from the attic which is slightly warmer because of any heat loss from my living area. I'm not sure what the temperature difference is but i know it's slightly warmer. I have a very well insulated attic, R-60, but there is always some heat loss.

    I'm wondering if it's not a bad thing to have the furnace using this slightly heated air vs pulling in the cold outside air directly.

    Because the attic is so well insulated and sealed, i even have an attic tent for the attic stairway, i'm fairly certain that the furnace is not sucking any significant air from the living space.

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