I have a 58 year old house in Arlington, Va., with a 32 year old Carrier gas furnace and a 20 year old Carrier air conditioner.
Both units have worked fine in the five years I've owned the house and have required no work apart from checkups and replacing a fuse on the A/C.
My utility bills aren't outlandish considering the age of the equipment and that I've got old single-pane double hung windows and 2400 square feet (including finished basement). My electric bill peaks at $150 in the summer (compared to $50 in April/October) at $.09/KHW, and the gas bill peaks at $250 in the winter (compared to $30 in the summer for hot water and the stove) at $1.26/therm. I've got a programmable thermostat and set back to 60 at night in winter, though my wife is home with the little one so I don't set back during the day.
The furnace is my primary concern. The latest tech to look at it said the heat exchanger is fine and didn't recommend replacement. But with a 2-year old in the house and another on the way sometime in the near future, I don't want to take chances with CO or with a winter outage.
I'm thinking of the following system:
12 SEER 2-stage A/C
92% 2-stage/variable speed furnace.
I'm sure the existing A/C can't be more than 6 SEER and the furnace 60% AFUE, so I'm getting a big boost there, but it looks like I'll get more bang for the buck saving money on utility bills by getting the 93% vs. the 80% rather than going higher above 12 SEER on the A/C.
One other thought is a heat pump. I assume that equipment costs will be a bit lower, and I compared my gas/electric rates, and it appears as though the heat pump will be cheaper, at $.94 per therm output versus $1.35 per therm output from gas.
Input 1 therm
Marginal $/Therm $1.26
$/Therm Output $1.35
Marginal $/KWH $0.09
$/Therm Consumed $2.64
$/Therm Output $0.94
I hadn't really considered a heat pump until doing this calculation, but is seems as though it might be cheaper, although the gas would win for comfort.
I'm replacing most of the windows this summer with high-efficiency Marvin windows.
I just can't decide whether to replace stuff now before it breaks and the 13 SEER rule goes into effect, or wait it out and wait for failure. I'm also looking for thoughts on gas versus heat pump in my climate at my rates.
Thanks for any advice.