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  1. #1
    Join Date
    Aug 2004
    Posts
    91
    After upgrading insulation and windows and replacing a 30 year old 120k NG furnace with a 75k 92% unit, my calculated heat loss went from 110,000 to 32,000 btu/hr. At a setpoint of 19C with outside temp of 5C the house will maintain 18.5-19 for several hours. The furnace cycles TWICE a day for,20-30 mins in the morning and the same in the evening. I set it back to 16 overnight.

    Now I'm wondering if the new furnace was a waste of money. With such a significant reduction in heat loss, the old furnace would have probably cycled about the same as the new one with a slightly larger fuel consumption. Before the energy upgrades the old furnace would cycle twice per hour under the same conditions. I suppose the bottom line is that furnace replacement payback is going to me much longer when combined with major energy upgrades.

  2. #2
    Join Date
    Oct 2004
    Posts
    149
    Sounds to me that maybe your furnce is oversized. I mean why a 72K furnace with a heat loss so low?

  3. #3
    Join Date
    Jan 2004
    Location
    PA
    Posts
    68,795
    You should have done the energy upgrades first, and then the load calc to get the right size furnace.

    Look at it this way, you also upgraded the reliability of your heating system also.
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  4. #4
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,432
    Originally posted by martik
    Now I'm wondering if the new furnace was a waste of money. With such a significant reduction in heat loss,

    I suppose the bottom line is that furnace replacement payback is going to me much longer when combined with major energy upgrades.
    OPEN the Doors
    so you can use that New furnace !
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  5. #5
    Join Date
    Feb 2003
    Location
    Huntsville,AL
    Posts
    4,125
    do you even need a furn?
    put a 500watt elec heater into the bath for mornings --
    bake biscuts ea morning
    harvest rainwater,make SHADE,R75/50/30= roof/wall/floor, use HVAC mastic,caulk all wall seams!

  6. #6
    Join Date
    Aug 2004
    Posts
    91
    Contractor did not want to put in a smaller furnace, there are the odd -15 days here and the next owner may want to maintain a higher temp.

    If it only runs twice a day, 4 months a year it will probably last 50 years.

  7. #7
    Join Date
    Dec 2002
    Location
    Rochester, MN
    Posts
    5,305
    At 5c degree (42f) is not very cold, but it still sounds oversized! I bet some rooms will be cold while the others are warm when it gets cold out.

    -15c, (5f) is not that cold, We get -20f (-29c) and my 60k furnace keeps up quite well.

  8. #8
    Join Date
    Jan 2004
    Location
    PA
    Posts
    68,795
    Originally posted by martik
    Contractor did not want to put in a smaller furnace, there are the odd -15 days here and the next owner may want to maintain a higher temp.

    If it only runs twice a day, 4 months a year it will probably last 50 years.

    In othee words, th contractor didn't trust your load calc, and doesn't do them himself.


    A 50,000 90% would still have given you 30% more heat then your load calc said you need.
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  9. #9
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,432
    Originally posted by cem-bsee
    do you even need a furn?

    put a 500watt elec heater into the bath for mornings --
    bake biscuts ea morning
    CEM,

    Right, that's what I do !
    Well, ONLY on select mornings, few and far between.
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

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