Page 1 of 2 12 LastLast
Results 1 to 13 of 15
  1. #1
    Join Date
    May 2007
    Posts
    8

    Direct Vent vs. Non-Direct Vent

    Can anyone tell me the benefits or difference between a direct vent furnace setup compared to non-direct vent furnace? With direct vent would this eliminate the stale/stuffy air during the cold winter season? I bought a Goodman GMH95 series and before the installation I am considering is the modification to direct vent since my old furnace does not have this setup.

  2. #2
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,058
    Are you installing it yourself.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  3. #3
    Join Date
    May 2007
    Posts
    8
    Quote Originally Posted by beenthere View Post
    Are you installing it yourself.
    No I"m not. I"m at the stage where I am looking for the contractor.

  4. #4
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,058
    Direct vent will not eliminate stale stuffy air feeloing.

    Done as a proper 2 pipe system, it won't draw cold unconditioned air into your house like a natural draft furnace.

    If the furnace is sized right, it will have longer run cycles, and eliminate stagnate air problems, weather direct vent or not.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  5. #5
    Join Date
    Sep 2001
    Location
    kalamazoo,mich
    Posts
    2,174
    I bet you must've brought a real big furnace to heat your house up, real quick.
    Have you hugged the Earth today?
    Donny Baker rules

  6. #6
    Join Date
    May 2007
    Posts
    8
    Quote Originally Posted by chucko615 View Post
    I bet you must've brought a real big furnace to heat your house up, real quick.
    No sir I did not. I researched the model of my old furnace and size and compared it to the newer unit. So it is roughly matched. Correct size matters either heating or cooling.

  7. #7
    Join Date
    Sep 2001
    Location
    kalamazoo,mich
    Posts
    2,174
    How do you know that your old furnace wasn't over-sized? Many older furnaces are.
    Have you hugged the Earth today?
    Donny Baker rules

  8. #8
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,058
    More likely then not, the old furnace was over sized.

    What your research didn't tell you. Is that your new furnace requires more air flow then the old one did.

    Hopefully, the contractor you find to install it for you, will know this, and know what duct corrections you will need to have done. To keep from damaging the new furnace.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  9. #9
    Join Date
    Nov 2005
    Posts
    1,350
    What we are trying to tell you is that direct vent has basically nothing to do with indoor air quality. Direct vent deals with combustion air and nothing else.
    You may have a short cycling issue?
    You may need some sort of ERV?
    Hard to tell with the information given.
    I STARTED WITH NOTHING, AND I STILL HAVE MOST OF IT!

  10. #10
    Join Date
    Jul 2007
    Location
    Beautiful, Philadelphia, the City of Brotherly Love!
    Posts
    1,096

    If you bought the same sized furnace as the original, then it is oversized.

    Your original furnace used natural draft to vent the furnace and was maybe 70% efficient, new furnaces are at least 80% efficient, that is if they use the same chimney as your original. A direct vent is usually vented with PVC and are rated at 90% or better.

    Let's do the math, 100,000 btu at 70% AFUE = 70,000 btu output
    at 80% = 80,000 btu, at 90% = 90,000 btus. So the same furnace at 90% has an output of 20,000 btus more.

    Now to make things worse, when your house was built, it probably was not as tightly built, over the years with new insulation, windows, doors, weather stripping, and lower temperature setting, your house may require much less heat.

    In the old days installers did not use Manual J as it required math skills, it was much easier to use a rule of thumb.
    My boss from many years ago used 40,000 btus per floor, with the basement loss of 10,000 btus, these figures represented output values. So a 1 story house got 50,000 btus, and a 3 story got 160,000 btus. On many we occasions twined furnaces to achieve these numbers. If the house was as he said scary big, he used 60 btus per square foot as his sizing method.

    Nice thing about time, I have changed many of these furnaces, on one occasion I removed two twinned 175,000 btu furnaces and replaced them both with one 125,000 btu 92% furnace. The heating bill on this house when from $1200 a month to $300.

  11. #11
    Join Date
    Apr 2007
    Location
    Vancouver, BC
    Posts
    53

    Closely related question

    Not meaning to hijack the thread, but this does closely relate to the original question:

    A family member moved into a brand new house this month with a 90%+ furnace.

    When I looked in the furnace room, I noticed only one PVC pipe was hooked up to the furnace (exhaust). There was a spot for the combustion PVC to hook up but it wasn't. Instead there was (what I can assume is) an intake duct that comes down and opens up right beside the furnace.

    Isn't it normal to run a second PVC for combustion air? This house doesn't even have a gas hot water tank, its electric. So it didn't seem logical to me.

    I guess the answer to this would be the answer for the original poster.

    Thanks.

  12. #12
    Join Date
    Jul 2004
    Location
    Massachusetts
    Posts
    6,837
    Quote Originally Posted by codywatkins View Post
    Not meaning to hijack the thread, but this does closely relate to the original question:

    A family member moved into a brand new house this month with a 90%+ furnace.

    When I looked in the furnace room, I noticed only one PVC pipe was hooked up to the furnace (exhaust). There was a spot for the combustion PVC to hook up but it wasn't. Instead there was (what I can assume is) an intake duct that comes down and opens up right beside the furnace.

    Isn't it normal to run a second PVC for combustion air? This house doesn't even have a gas hot water tank, its electric. So it didn't seem logical to me.

    I guess the answer to this would be the answer for the original poster.

    Thanks.

    Some manufactures do allow a 2-pipe 90+ gas furnace to be single piped. Usually that involves some sort of intake pipe being installed and open to the basement. This style of installation does of course, eliminate the "sealed combution" feature of the furnace and also requires makeup air for the home, since all combustion air will be taken from inside the home. Our company is in snow country and we NEVER install a 90+ with only one pipe. The biggest advantage, IMO, with 2-pipe is that if the exhaust vent gets buried in snow, so will the intake. That will shut down the furnace and be an inconvenience but that's it. No carbon monoxide issue. Absent that fresh air intake, CO is still a potential problem if the exhaust vent gets obstructed. However, this issue has nothing to do with the original post.
    If YOU want change, YOU have to first change.

    If you are waiting for the 'other guy' to change first, just remember, you're the 'other guy's' other guy. To continue to expect real change when you keep acting the same way as always, is folly. Won't happen. Real change will only happen when a majority of the people change the way they vote!

  13. #13
    Join Date
    Jul 2004
    Location
    Massachusetts
    Posts
    6,837
    Quote Originally Posted by max7687 View Post
    Can anyone tell me the benefits or difference between a direct vent furnace setup compared to non-direct vent furnace? With direct vent would this eliminate the stale/stuffy air during the cold winter season? I bought a Goodman GMH95 series and before the installation I am considering is the modification to direct vent since my old furnace does not have this setup.
    As some have suggested, an oversized furnace can create hot/cold issues in a home. The hot air comes on during a call for heat and is distributed likety split into the home at some very high BTU/hour rate, shutting down the T-stat in rather short order. A nice 2-stage furnace, properly sized for the home goes a long way toward minimizing any such problem. But I suspect your may have another issue.

    The other issue could be dryness in the home. This is a direct result of heating the air in your home. When the air is heated the RELATIVE humidity drops. That is, the air becomes less dense but the amount of moisture in the air is unchanged. Since the air can now hold more moisture compared to when it's at a lower temperture, the amount of moisture actually in the air is relatively less than the air could hold if it were at its saturation point. The solution to this problem is to add a humidifier to the system. Humidifers come in different sizes, just like furances. When sizing a humidifier, the air exchange rate through the home must be taken into consideration. For homes or individuals who need/desire a lot of moisture in the air, I'd recommend a steam humidifier with an automatic flushing cycle. Having a furnace with a variable speed blower motor allows you to run the blower 24/7 at minimal electrical expense and take full advantage of whatever humidifier type you select.
    If YOU want change, YOU have to first change.

    If you are waiting for the 'other guy' to change first, just remember, you're the 'other guy's' other guy. To continue to expect real change when you keep acting the same way as always, is folly. Won't happen. Real change will only happen when a majority of the people change the way they vote!

Page 1 of 2 12 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event