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  1. #1

    Planning for future furnace replacement

    Hello all,
    I have a 2900 split level square foot house in Warroad, MN that was built in 1997. The heating and air conditioning is original to the house, so I’m starting to look at options for replacing the furnace and possibly the A/C at some point in the next couple of years and want to know what I should consider talking to contractors about. According to the MN Department of Labor and Industry, the design temps are -29F winter and 83F drybulb/67F wetbulb summer (http://www.dli.mn.gov/ccld/pdf/sbc_1323.pdf), at least for commercial buildings.
    Existing equipment:
    90% Armstrong Air 100,000 BTU single stage furnace operating on LPG Model GUK100D14-1B
    2.5 ton Trane A/C SEER 10. R-22 refrigerant.
    Current fuel and electricity rates:
    LPG $1.45/gallon
    Regular Electricity: $0.119 / kWHr
    Off Peak Electricity: $0.058 / kWHr (utility controlled, can be on or off at any point during the day depending on the utility’s system load and cost of power. Typically on for at least 12 hours a day during the week and on all day on weekends/holidays during normal weather)

    Option 1: Replace furnace with a 2 stage furnace. Leave existing A/C alone until it fails.
    Option 2: Replace furnace with a 2 stage furnace as in option 1 and replace A/C at the same time.
    Option 3: Replace furnace with a modulating furnace like a Carrier Infinity type. Leave existing A/C alone until it fails.
    Option 4: Replace furnace with a modulating furnace like a Carrier Infinity type as in option 3 and replace A/C at the same time
    Option 5: Replace furnace and A/C with a gas/heatpump hybrid system
    Option 6: Replace furnace and A/C with a gas/heatpump hybrid system and add a modulating electric plenum heater like an Electro-MN Electro-Mate operating on off peak electricity.
    Option 7: Geothermal heat pump. Probably not in the cards due to up front cost, but possibly worth looking at with utility rebates and tax credits.

    Thanks for any advice

  2. #2
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,301
    I'd think a 1 or 3 is a wise move. In your cool climate, a 15 year old Trane is just getting broken in

  3. #3
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    7,446
    I would change both the heat and ac out and the same time no matter what you do. With your electric rates a high hspf rated heat pump with resistance back up would probably be cheaper than propane. I'm sure one of the numbers guys will be along in a bit to crunch them for you. A dual fuel set up would be nice but its quite a bit more cost up front and like I said will likely be more expensive to operate than a heat pump with electric backup. Geothermal would be a great way to go but like you said upfront cost is high especially when you have to drill wells or horizontal trenches. There is a 30% no cap tax credit for geothermal install that I'm pretty sure is still in effect.

  4. #4
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    7,446
    If you decide against a heat pump and just replace with another furnace I would leave the old ac until it fails bc it probably doesn't get used much in your climate. In run time it is probably the equivalent of a 4 year old ac in the southeast where I'm at.

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