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    Need advice (15 Posts)

  • Joe V Joe V @ 12:20 PM
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    Need advice

    I am replacing an old gravity furnace that is fired with oil.  Not sure what the quotes will look like for an oil to gas conversion but should it be cost prohibitive, what kind of consumption would a newer oil fired furnace have?  During the coldest month last year, we burned 375 gallons.  This bad girl heats about 5000 sqft in NY (The insulation on the outside is glass wool, not asbestos-had it tested.)
    So, just looking for a ballpark figure, what would a newer oil burning furnace burn under similar conditions. 
  • Chris Chris @ 12:51 PM
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    Your Not Going

    To find an answer to your question. Many variables come into play with estimating fuel savings. Suggest you start by having a heat loss of the structure done. Compare that loss with the current btu/hr out put of the current boiler. How oversized is it. Just properly sizing the boiler alone with give you fuel savings. What that is, don't know. Need the heat loss.

    From there its all about how efficiency is the system itself. The AFUE or boilers efficiency has nothing to do with the system only applies to the heating plant and that's not even a real number.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • Joe V Joe V @ 1:50 PM
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    Looking for info

    Right, let me rephrase the question.  What is the typical efficiency of a 1920 gravity furnace?
    50%, 60%,70%?
    I have already done a heat loss calculation on the house using Slantfins app.  It came out to 155000BTU/hr Heat loss-if memory serves.  I have no data on the furnace.  I dont think it is oversized though.  It runs a good 20-30 minutes and stays off for a nominal 50 minutes.  It keeps the house comfortable.  So does the nice warm chimney that runs up the house' center.
    I think could talk myself out of replacing it.  375 gallons on a cold month is not too terrible (the $4/gallon is).  Especially when considering its excellent reliability and the fact that none of those who came to quote even walked through the whole house or get a count of all the windows.  Why replace something that I know works for something that may not be adequate to do the job? 
  • Chris Chris @ 1:57 PM
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    Guess You Need

    To find better contractors. Why would the boiler not be adequate for the job if it's sized and installed correctly? So your burning 52,125,000 btuh per month which equates to 1,737,500 btuh per day or 72,395 btu/hr based on that 375 gallons.. Thinking you need to redo that heat loss.

    You have a high mass boiler. Lots and lots of water, thus the long off times. That's not a bad thing.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
    This post was edited by an admin on August 30, 2013 2:01 PM.
  • SWEI SWEI @ 2:26 PM
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    More information

    Do you want to try and keep this as a gravity system?  I've never seen that done before.  Not saying it's impossible, but not something a standard HVAC contractor is going to be familiar with for sure.

    A hydro-air system designed using a _very_ low speed fan might be able to pass muster.

    Old furnace is probably somewhere around 50% if I had to guess.

    155,000 BTU/hr comes to 31 BTUs per square foot.  Any way to improve the envelope on the house?  That should be your first step.

    Where in NY are you?  I'm guessing there's no natural gas available.   An air source heat pump might be your best bet.
    This post was edited by an admin on August 30, 2013 2:29 PM.
  • Joe V Joe V @ 2:54 PM
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    Hi and thanks

    No, I do not wish to keep it a gravity system.  Truthfully, never considered it.  What we are looking at is a typical Trane/Lennox/Bryant type replacement hot air furnace, variable speed blower with an air return.
    We do have natural gas in the house.  My concern is IF the oil to gas conversion pushes this project out of my budget and I decide to stay with oil and replace just the furnace, would I see a significant savings in oil consumption? 
    The caveat  though, is  the new furnace also has keep house comfortable as well as save oil. 
    Unfortunately, better insulation is not possible for a number of reasons that I won't bore you with. 
    This post was edited by an admin on August 30, 2013 2:57 PM.
  • SWEI SWEI @ 3:38 PM
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    Heat Loss

    Worth reviewing in detail before you leap.  I've never seen an old building which had literally no possible envelope improvements.

    Is there an attic?

    Do you need the basement heated?  Can you insulate under the 1st floor from underneath?

    Do the windows have thermal blinds or drapes?  That plus some infiltration reduction can make a staggering difference.

    Do check out that spreadsheet that Carl pointed you at.  Be sure to input your local prices and then adjust the efficiencies on the various types of equipment until you are comparing apples with apples.  It's an eye-opener.
  • Joe V Joe V @ 2:18 PM
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    It is not

    a Boiler.  Hot air furnace. 
  • Zman Zman @ 3:11 PM
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    Gas

    Joe,
    Check out this spread sheet www.eia.gov/neic/experts/heatcalc.xls‎
    You need to plug in your local energy rates and take a guess at efficiencies.
    For the sake of guesstimating, assuming you existing furnace is around 50-60 % efficient and a new one would be 75-80% efficient would seem reasonable enough.
    As Chris has said, size the new furnace off a heat loss calc.
    I think you will be blown away by how cheap natural gas is.
    Gas furnaces really are not that expensive
    Carl
  • Joe V Joe V @ 3:17 PM
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    Wow!

    Thanks Carl!  That spreadsheet is very enlightening!
    I was blown away!  Natural gas could be cheaper than coal!
    This post was edited by an admin on August 30, 2013 3:22 PM.
  • JStar JStar @ 4:04 PM
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    Furnace

    Natural gas is the way to go right now. Just replacing the furnace will be a whole can of worms to deal with. Either way, you'll need to redo all of the ductwork in the system. Might as well take advantage and convert to gas now. It shouldn't add a lot to the installation cost.
    - Joe Starosielec
    http://thatcherhvac
    http://facebook.com/thatcherhvac



    Guaranteed performance. Guaranteed energy savings.


    Serving all of NJ, NYC, Southern NY State, and eastern PA.

    Consultation anywhere.

    (Formerly "ecuacool")
  • Joe V Joe V @ 7:45 PM
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    why replace

    all the ductwork? they are embedded in walls.
  • JStar JStar @ 8:00 PM
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    Duct

    The original ductwork was sized to work on gravity, and may not give the desired comfort with a modern furnace and blower. The heat loss of the home, and the duct sizes will need to be carefully assessed. The duct runs will most likely be way too big. You won't have to change what's in the walls, but definitely look at the ducts in the basement.
    - Joe Starosielec
    http://thatcherhvac
    http://facebook.com/thatcherhvac



    Guaranteed performance. Guaranteed energy savings.


    Serving all of NJ, NYC, Southern NY State, and eastern PA.

    Consultation anywhere.

    (Formerly "ecuacool")
  • Joe V Joe V @ 8:43 AM
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    Thanks

    The ducts in the basement are easily accessible and can be removed and replaced with flex duct from the air handler in minutes.  I think the ductwork in the base ment are 8 inches in diameter and the longest run is 13 feet. 
    What is in the walls are not insulated which is why the system will be heat only.  Appreciate all the answers to my questions.
  • Joe V Joe V @ 8:43 AM
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    Thanks

    The ducts in the basement are easily accessible and can be removed and replaced with flex duct from the air handler in minutes.  I think the ductwork in the base ment are 8 inches in diameter and the longest run is 13 feet. 
    What is in the walls are not insulated which is why the system will be heat only.  Appreciate all the answers to my questions.
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