I currently have a N.G./A/C setup for a 2200ft2 house in MD. 80K BTU Trane 90% single stage furnace that is 12 years old using combustion air from the basement, not outside. The A/C is an XE 1200 12 SEER unit that is starting to have failures. Blower motor last year and Starting capacitor this year. The house is 12 years old as the system is original.
My goal is to eventually replace everything with a dual fuel HP/N.G. setup, but I can not afford to do it all at once. My A/C bills are high at almost $0.16 / kWh. I estimate 600-700 kWh for A/C peak during the hottest months in the summer. FLA on my A/C is 17 amps, which I verified during normal running. I just installed the Honeywell IAQ stat to solve some of the humidity and airflow issues in the house and it has worked fantastic so far so I have decided to go full out with 2 stage heating and 2 stage heat pump with variable speed.
I am thinking that since I want to end up with a 16-18 SEER HP using a dual stage copland compressor that I need to install a variable speed ECM furnace first. I have read that the amp draw on these high efficiency HP's can be as low as 6-7amps on the first stage only, which should be a big improvement over 17 amps. I have looked into retrofitting the current Trane furnace with ECM, but it makes no sense financially or practically. My main goals here are to make a serious dent in the kWh spent on A/C and also lower my heating costs. N.G was $1.67/ therm last month and other than a short break for a month or two I think it is headed even higher in the next few years. I am 99% sure my furnace was oversized at 80K because the stupid installer ran 3/8" warflex to it and I didn't catch the problem until 10 years later when I finished the basement and changed it to 1/2" warflex to supply the full BTU's. Manuals show that the 3/8" line should have only been providing 40K BTU's. I am right to think about changing out the furnace with a VS unit first and then go for the high efficiency HP next year if I need to break up the expenditures over 2 years? I will look at Trane again, but the Goodman GMV95 series 70K unit seems like a very good unit at a great price. Please comment on my plan or any other advice.
My assumptions are that I will get some savings this winter (approximately 10%) from:
1. 95% unit vs. 90%.
2. 2 stage burner running at lower stage vs. single stage burner.
3. Properly sizing unit to 70K from 80K.
4. ECM blower running at more efficient speed vs. PSC motor.
In summer I should get better humidity control from VS blower and lower blower motor amp draw until I install 2 stage higher efficiency HP.