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  1. #1
    Join Date
    Jan 2013
    Location
    San Jose, CA
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    Default Ventilation in furnace closet

    We recently purchased a home in San Jose, CA that was built in the 50s. I'm natively from a place with basements where the the furnace always is located. However, in our home here, the gas furnace and gas water heater are located in a small utility room (in the center of the house), which is accessible via a door inside a closet. I've noticed that this utility room has both a floor vent (into a vented crawl space) and a ceiling vent (into a vented attic). Although I am sure this is the safest way to go, is it necessary? It seems like a huge amount of heat escapes through the vent. Although the vents are separated from other rooms by 2 doors, it still seems like a lot of heat can escape under the doors. I'd love to close up these vents if it won't cause other problems. I know that open combustion devices need an air source, but does this need to be into cold spaces? Note that both the furnace and water heater are "normal" top venting (low efficiency) types. Thank you!
    Last edited by svento; 01-03-2013 at 03:27 PM. Reason: Add house age.

  2. #2
    Join Date
    Sep 2012
    Location
    Boston
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    1,004

    Default Re: Ventilation in furnace closet

    they absolutely have to be well vented. the setup you have seems to be fine but there other options. you can install the upper vent through the upper wall directly to the outside instead of the attic. i can't see any benefit in moving the lower one unless the crawl space itself is not vented to the exterior at all. at for drafts, you can weather seal the utility room door so that no drafts enter the house

  3. #3
    Join Date
    Jan 2013
    Location
    San Jose, CA
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    13

    Default Re: Ventilation in furnace closet

    Thank you. I suppose you are probably right that insulating the door might be the easiest way to stop drafts. I didn't exactly say this, but I was hoping to close off the vent instead because the heater itself produces a lot of heat locally, so keeping this heat in the conditioned space made sense to me.

    I am curious why you suggest venting the ceiling vent directly outside (instead of to the attic)? Is this to eliminate putting hot air into the attic? I can't see any way it would stop heat loss, so just curious.
    Last edited by svento; 01-03-2013 at 04:34 PM.

  4. #4
    Join Date
    Jul 2010
    Location
    SoCal
    Posts
    6,767

    Default Re: Ventilation in furnace closet

    Both the furnace and the gas water heater have to be vented to the outside, not the attic. Use a separate vent for either appliance.

    The reason is CO2.

  5. #5
    Join Date
    Jan 2013
    Location
    San Jose, CA
    Posts
    13

    Default Re: Ventilation in furnace closet

    Sorry, maybe I wasn't clear: Both furnace and water heater exhausts are vented to the outside properly in ducts. What I am questioning (and calling a vent) is basically a hole with screen over it in the floor and the ceiling of the utility room.

  6. #6
    Join Date
    Sep 2012
    Location
    Boston
    Posts
    1,004

    Default Re: Ventilation in furnace closet

    dj, his concern is getting combustion air into the utility room, which is needed. he has his exhaust vent all taken care of.

  7. #7
    Join Date
    Jul 2010
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    SoCal
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    Default Re: Ventilation in furnace closet

    Quote Originally Posted by svento View Post
    Sorry, maybe I wasn't clear: Both furnace and water heater exhausts are vented to the outside properly in ducts. What I am questioning (and calling a vent) is basically a hole with screen over it in the floor and the ceiling of the utility room.
    The "holes" are to make sure there is plenty of air coming to the appliance room, especially to the furnace. Don't close them.

    If you have heat escaping out of the furnace, then you must have a leak in your system. Have you had your heating/cooling system tuned up and serviced?

    By the age of your house I can assume that you need an a/c tech or a plumber to check them out.

  8. #8
    Join Date
    Jan 2013
    Location
    San Jose, CA
    Posts
    13

    Default Re: Ventilation in furnace closet

    Ok, so I get the concept of needing combustion air... but in my previous houses the furnace was in the basement with no vent to the outside. So is the difference here simply the fact that the utility closet is relatively small in size? I guess I'm trying to understand why the combustion air need to come directly from the outside instead of coming from the living space. (Yes, I am sure in a new home with tight construction, this could lead to a problem, but the house was built in the 50s and isn't very tight.)

    And I am not sure heat is exactly escaping the furnace (it's only maybe 10 years old), but the furnace itself seems to be radiating heat just based on the fact that a large flame is burning a few inches from the surface!
    Last edited by svento; 01-03-2013 at 06:54 PM.

  9. #9
    Join Date
    Dec 2010
    Location
    Houston Texas
    Posts
    2,969

    Default Re: Ventilation in furnace closet

    The extra vents could be from days of yore when proper venting wasn't to code. Have a professional, licensed HVAC come out and tell you if your local code authority will allow you to close those vents.

    Its amazing how long old code lingers on the books. In my fair city we still are required to have a separate shut off switch for the dishwasher.

  10. #10
    Join Date
    Jul 2010
    Location
    SoCal
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    Default Re: Ventilation in furnace closet

    Quote Originally Posted by svento View Post
    Ok, so I get the concept of needing combustion air... but in my previous houses the furnace was in the basement with no vent to the outside. So is the difference here simply the fact that the utility closet is relatively small in size? I guess I'm trying to understand why the combustion air need to come directly from the outside instead of coming from the living space. (Yes, I am sure in a new home with tight construction, this could lead to a problem, but the house was built in the 50s and isn't very tight.)

    And I am not sure heat is exactly escaping the furnace (it's only maybe 10 years old), but the furnace itself seems to be radiating heat just based on the fact that a large flame is burning a few inches from the surface!
    Furnaces are hot when they are working. New furnaces are a little better insulated, but don't worry about heat loss, it's not that critical. By all means have a pro look at your system.

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