Page 2 of 7 FirstFirst 1234567 LastLast
Results 14 to 26 of 88
  1. #14
    Join Date
    Apr 2008
    Posts
    14
    Quote Originally Posted by air311 View Post
    If the furnace was in the house when you bought it, then you ain't really losing out by putting a new one in. The difference between a 80% and 90+% is a big one. I'd replace the whole system and put in matching components.
    Sure I am, I'm losing the thousands of dollars a new furnace would cost me. And I would only be gaining the $100-200 or so I would save each year. Doesn't add up.

  2. #15
    Join Date
    Jun 2007
    Location
    The Twilight Zone
    Posts
    2,964
    Quote Originally Posted by jaguar36 View Post
    That may be all well and good for the initial setup, but what happens when next year (or even next month) the prices for gas and electricity have changed? I'm not gonna be calling the contractor every few months to come adjust the change over temp, so is that something that I could do myself?
    You can start at 32F change-over, and go down from there.

    If you go too low, the heat pump will run constantly while the house temperature drops. If it drops 2 degrees, the auxillary heat (gas furnace) will kick on and run the house to the setpoint temperature.

    Yes, you can change the change-over temp yourself.

  3. #16
    Join Date
    Apr 2008
    Posts
    14
    Quote Originally Posted by Jopopsy View Post
    Okay, so can somebody tell me what the conversion factor is for Propane?
    I don't know much about propane, but according to Ye Olde Wikipedia, its 91,600 BTU per liquid gallon.

  4. #17
    Join Date
    Jun 2007
    Location
    The Twilight Zone
    Posts
    2,964
    Quote Originally Posted by air311 View Post
    If the furnace was in the house when you bought it, then you ain't really losing out by putting a new one in. The difference between a 80% and 90+% is a big one. I'd replace the whole system and put in matching components.
    The difference between 80% and 95% is 15%. If he upgraded the furnace, he would be saving 15% of the cost of natural gas for his heating bill. If he uses the heat pump for primary heat, the gas furnace would only be for back-up.

  5. #18
    Join Date
    Jun 2007
    Location
    The Twilight Zone
    Posts
    2,964
    Quote Originally Posted by jaguar36 View Post
    I don't know much about propane, but according to Ye Olde Wikipedia, its 91,600 BTU per liquid gallon.
    Propane is one of the most expensive heating fuels.

    Cost for 1 million btus from Propane at $2.50 gallon, 80% efficient furnace:
    (1,000,000 / 91,600) x 2.50 / .8
    = $34.11

    Ouch.

  6. #19
    Join Date
    Mar 2008
    Location
    Jackson, NJ
    Posts
    176
    So the propane formulat would be:

    (1,000,000 / 91,600) * Cost of Propane / Efficiency of Furnace

    Cool.

    I will set up a spreadsheet and update the variables yearly in order to establish my set point. I will obsess over these newfound figures to the chagrin of my poor wife.

  7. #20
    Join Date
    Jan 2008
    Location
    Wisconsin
    Posts
    1,125
    Quote Originally Posted by jaguar36 View Post
    Sure I am, I'm losing the thousands of dollars a new furnace would cost me. And I would only be gaining the $100-200 or so I would save each year. Doesn't add up.
    $100 to $200 each year? A 90+ plus furnace should save more than that, way more if matched with a heat pump. I'm a fan of matching all components of a system, so that's why I would suggest replacing the furnace. You're going to have to replace it down the road eventually, and when you do you'll have an older heat pump or A/C system that will have to be matched with a new furnace. Might be cheaper in the long run to replace it all at once.

  8. #21
    Join Date
    Mar 2008
    Location
    Jackson, NJ
    Posts
    176
    Quote Originally Posted by gary_g View Post
    Propane is one of the most expensive heating fuels.

    Cost for 1 million btus from Propane at $2.50 gallon, 80% efficient furnace:
    (1,000,000 / 91,600) x 2.50 / .8
    = $34.11

    Ouch.
    Yep. That's why my builder is putting in a 92.5% furnace and that's also why I'm going Duel Fuel Heat Pump / propane backup. Thanks to this board.

  9. #22
    Join Date
    Jun 2007
    Location
    The Twilight Zone
    Posts
    2,964
    Quote Originally Posted by Jopopsy View Post
    So the propane formulat would be:

    (1,000,000 / 91,600) * Cost of Propane / Efficiency of Furnace

    Cool.

    I will set up a spreadsheet and update the variables yearly in order to establish my set point. I will obsess over these newfound figures to the chagrin of my poor wife.
    That is the cost of 1 million btus using propane gas. You can compare it to 1 million btus of heat from oil, heat pump, straight electric, woodstove, pellet stove, etc to compare the fuel costs.

  10. #23
    Join Date
    Jun 2007
    Location
    The Twilight Zone
    Posts
    2,964
    Quote Originally Posted by Jopopsy View Post
    Yep. That's why my builder is putting in a 92.5% furnace and that's also why I'm going Duel Fuel Heat Pump / propane backup. Thanks to this board.
    You are smart using propane only as back-up. I would run that heat pump at outdoor temps into the 20's before switching over to propane.

    Good luck.

  11. #24
    Join Date
    Nov 2006
    Location
    Montana
    Posts
    134
    Quote Originally Posted by jaguar36 View Post
    That may be all well and good for the initial setup, but what happens when next year (or even next month) the prices for gas and electricity have changed? I'm not gonna be calling the contractor every few months to come adjust the change over temp, so is that something that I could do myself?
    That doesn't matter. There is a point where your HP will no longer keep up with the heat demand of the house. As the outdoor temperature drops, the heat pump heating Btus drop. Using your average cost of fuel in the initial calculation will offset changes in utility rates. It would take a considerable change in utility cost to warrant a change in the cross-over temperature setting.

    Of course, it can happen. I always recommend yearly maintenance and if there is a huge change in utility pricing, I just pull out the graph from my customer file and replot the temp setting and make an adjustment...no biggie.

    Sure, you can fiddle with the temp setting. But it will take a month to know if you cost yourself money.

  12. #25
    Join Date
    Nov 2006
    Location
    Montana
    Posts
    134
    Quote Originally Posted by gary_g View Post
    I would run that heat pump at outdoor temps into the 20's before switching over to propane.

    Good luck.
    Based on what?

  13. #26
    Join Date
    Mar 2008
    Location
    Baltimore MD and Ridgebury PA
    Posts
    542
    Quote Originally Posted by air311 View Post
    $100 to $200 each year? A 90+ plus furnace should save more than that, way more if matched with a heat pump. I'm a fan of matching all components of a system, so that's why I would suggest replacing the furnace. You're going to have to replace it down the road eventually, and when you do you'll have an older heat pump or A/C system that will have to be matched with a new furnace. Might be cheaper in the long run to replace it all at once.

    Why would it save way more if matched with a heatpump? If matched with a heatpump then the gas furnace would be used far less due to only being used as the backup heating source. If the heatpump is properly sized then that should be a relatively small amount of time. Lets say the gas provides 20% of the heat during the winter. You'd only be saving 15% (tops) of the energy cost on a system that is only used 20% of the time.
    I have probably used 250-300 gallons of oil this winter (it is my secondary heat)... at $3 per gallon it cost me $900... 15% of this is $135... not worth it.

Page 2 of 7 FirstFirst 1234567 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