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  1. #1

    replacing gravity furnace

    Hi all. I am replacing an old gravity furnace in my 2000 square foot home in LA. I plan to replace it with a high efficiency gas furnace. The old unit has asbestos and I have someone to remove it safely. My questions relate to different suggestions from different installers.

    Regarding ducts and returns.

    One company suggested cutting new heating vents in floors throughout the rooms and using the existing old vents for returns plus another large return. Said this is the best route for quiet and if I decide to add A/C someday.

    Another company said I could use one large return only and cut in new vents.

    Finally one suggested one large return and use the existing vents to deliver heated air. That seems like the most reasonable, least destructive and probably least expensive route.

    What would I want to consider in terms of functionality, noise, efficiency?

    Other questions are about 2 stage or variable blowers, put coil in now for later A/C addition, and sizing the furnace.

    Help with any and all would be great as it is getting a little chilly here with no heat.

    Thanks

    Walter G

  2. #2
    Join Date
    Jul 2009
    Location
    Columbia, MD
    Posts
    3,830
    To get the advantage of 2 stage or variable speed you will need properly sized ducts that wont produce over a TESP of .5" w.c.

    I like returns in all the rooms. This will provide the MOST comfort. 1 big central return works and is cheaper but, isn't the most comfortable way to do it.

    Can you take some pictures of the old beast before it gets ripped out?

  3. #3
    I grew up with steam radiators, then gravity for 20 years. Never had forced air. So when you say "more comfortable" what do you mean? More even heat in the house? more or less blowing of air? more noise at vents or at return?

    Thanx

  4. #4
    Join Date
    Jul 2009
    Location
    Columbia, MD
    Posts
    3,830
    you will have more even heat thru the house if you have returns in all the living areas.

    there are some smart people that should chime in like teddybear i think is his name and others. sorry guys cant remember everyone.

    if you close a bedroom door and only have a supply in the room it wont heat or cool properly. there needs to be a return in the room as well to keep the air changing. once your pressurize a room with so much heat you cant maintain the temp until you have something to draw it out.

    i hope this paints a picture for you.

  5. #5
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
    Posts
    2,626
    Quote Originally Posted by drpsych View Post
    Hi all. I am replacing an old gravity furnace in my 2000 square foot home in LA. I plan to replace it with a high efficiency gas furnace. The old unit has asbestos and I have someone to remove it safely. My questions relate to different suggestions from different installers.

    Regarding ducts and returns.

    One company suggested cutting new heating vents in floors throughout the rooms and using the existing old vents for returns plus another large return. Said this is the best route for quiet and if I decide to add A/C someday.

    Another company said I could use one large return only and cut in new vents.

    Finally one suggested one large return and use the existing vents to deliver heated air. That seems like the most reasonable, least destructive and probably least expensive route.

    What would I want to consider in terms of functionality, noise, efficiency?

    Other questions are about 2 stage or variable blowers, put coil in now for later A/C addition, and sizing the furnace.

    Help with any and all would be great as it is getting a little chilly here with no heat.

    Thanks

    Walter G
    The first bid is the best and probably the most expensive. The second bid is good (if the one RA is large enough) and probably a little less than #1.
    The last bid works (better on heat than A/C) and has to be the cheapest.

    2-stage and variable speed is like black and white. Go with the VS motor and 2-stage heating.

    Do not put the A-coil on now. It'll lock you in to a certain brand. There is no justification to that (except for the contractor trying to push it).

  6. #6
    Thanks for the replies. Right now money is tight so I think I will go with the cheaper set up. The only rooms that may have doors closed have 1 1/2" gap under the doors due to old carpeting. Will that help keep the rooms from having to much pressure?. Also does any one have opinions on the Trane XV95 XR95 furnaces? Any input is appreciated.

    Thanks Walter G

  7. #7
    Join Date
    Sep 2005
    Location
    Atlanta GA area
    Posts
    21,015
    Trane is probably at the top of cost for equipment.

    Installation is more important than equipment brand.
    GA-HVAC-Tech

    Quality work at a fair price with excellent customer service!

    Romans Ch's 5-6-7-8

    2 Chronicles 7:14

  8. #8
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
    Posts
    2,626
    Quote Originally Posted by drpsych View Post
    Thanks for the replies. Right now money is tight so I think I will go with the cheaper set up. The only rooms that may have doors closed have 1 1/2" gap under the doors due to old carpeting. Will that help keep the rooms from having to much pressure?. Also does any one have opinions on the Trane XV95 XR95 furnaces? Any input is appreciated.

    Thanks Walter G
    You'll probably find that the doors will suck closed if almost closed. In other words, the gap under the door is not enough but better than nothing.

    A variable-speed, IMHO, has many advantages. If you're trying to save money, don't do it there.
    Last edited by George2; 12-04-2012 at 05:21 PM. Reason: added infomation

  9. #9
    Join Date
    Feb 2009
    Location
    Fox Lake IL
    Posts
    442
    I have seen gravity furnace vents on the inside walls if yours is that way have them cut new ones on the out side wall..

  10. #10
    Join Date
    May 2004
    Location
    south louisiana
    Posts
    3,160
    La. or L.A.
    ducts & furnace in crawlspace?

    in La. we usually don't have returns in every room.
    as long as air has dedicated pathway to return to cenrtally
    located return it isn't an issue.
    dedicated pathways include jump ducts..transfer grills
    or more expensive would be return from each room
    back to central return.

    putting some of that $$ into sealing ducts is a good move
    if they use mastics and not duct/foil tapes to seal leakage.

    you have no ac now? (can't be La.!) and will be doing addition
    to house when?

    best of luck
    The cure of the part should not be attempted without the cure of the whole. ~Plato

  11. #11
    We live in West LA and rarely feel the need for AC. But we would like the option down the road, so I am going with the 2 stage variable speed furnace and having the coil attached at the same time. I have seen their work and they did use the foil tape for sealing.

  12. #12
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
    Posts
    2,626
    Quote Originally Posted by drpsych View Post
    We live in West LA and rarely feel the need for AC. But we would like the option down the road, so I am going with the 2 stage variable speed furnace and having the coil attached at the same time. I have seen their work and they did use the foil tape for sealing.
    I would not attach the A/C coil at the same time as the furnace install. You'll be locking yourself into the particular brand and it could effect the efficiency rating (and rebates/tax credits). There is no advantage to doing it now, especially if money is (still) tight.

  13. #13
    Join Date
    Dec 2007
    Posts
    4,685
    Los Angeles or Louisiana, which LA?
    The Food Stamp Program, administered by the U.S. Department of Agriculture, is proud to be distributing the greatest amount of free meals and stamps EVER.
    Meanwhile, the National Park Service, administered by the U.S. Department of the Interior, asks us to "Please Do Not Feed the Animals". Their stated reason for this policy "... the animals become dependent on handouts and will not learn to take care of themselves."
    from an excerpt by Paul Jacob in Sun City, AZ

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