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