Originally posted by wyounger
First, I am stunned at your gas consumption for February, given the climate and having an ancient furnace. It must be well insulated!
--Actually I think it's appaling how little insulation it has! Built in 1952 when they didn't do much insulating. On the plus side I replaced the old drafty pathetic aluminum windows with current "new construction" windows. Low E, Argon gas etc. That quickly patched 10 holes. (including a really bad Bow window). We also have a programable thermostat and use it effectively adn we don't keep the house very warm in the winter ~66/67 degrees at most, 62 at night.--
Don't assume usage based on equipment sizing. You can run a 120kBTU burner half the time or 60k burner all the time, and the gas consumption is equal. That said, with everything else being equal, you will get better efficiency using the smallest equipment that can get the job done- so you would waste less heat out the flue with the 60k burner than the 120k burner. A heating system that's too large for the job will not achieve its rated efficiency.
---So the old Singer unit probably isn't even hitting the 60% AFUE then. From the way you are laying it out my assumptions on how to calculate the savings were way off. I pulled the 2003/4 heating season, & the 2004/5 season and ran the usage numbers and we were at 585 & 584 for those 2 periods. (Hey were real consistent!) Now I will try to use your forumla and see what kind of savings we may see.
----Wow from 585 down to 390!
If your old unit was 60% efficient, and you upgrade to a 90% unit... let's use your February 2005 data as a test case. How much heat did the house actually use, and how much went up the flue?
120 therms = 12,000,000 BTU (1 therm = 100,000 BTU)
12,000,000 * 60% = 720,000 BTU went into the house.
To put 720,000 BTU into the house with a 90% efficient furnace, you need 720,000 BTU / 90% = 800,000 BTU, or 80 therms of gas consumption. From there you should be able to figure the cost savings, given your gas rates (and how they may be changing...)
I can think of very few cases in your part of the country where getting an 80% furnace really makes sense. You're on the right track with a high efficiency unit. Dual fuel is not a bad idea, either, since you're going to be replacing the outdoor unit anyway. In that system you use a heat pump for heating whenever it's above freezing outside, and use a regular furnace when heating when it's below freezing. In nonfreezing temperatures heat pumps are much cheaper to run than any sort of fossil fuel furnace. There's not much price difference to get a system set up for dual fuel when you're already replacing the AC unit and coil, so it won't be hard to recover the extra cost in utility savings. This setup is all the rage this year, with natural gas rates rising so quickly.
--Cost is a real significant factor as I will have to borrow to pay for the unit. The dealer who was in never mentioned dual fuel.---
We can't address your price question directly. I would agree that you aren't comparing apples to apples at this point. That's just one more reason you should get more than one bid!
---I realize that is a forum rule which I why I kept any actual prices that is was quoted out of my posting. Still, as a consumer I find it amazing that the pricing information on HVAC is as "tight" as it is. I am going to get at least 2 other quotes, including a Trane dealer as well in the mix. The other question I had posed was more of a Value question. Does it make sense that a 2 ton Carrier A/C unit would cost twice a 3 ton Concord unit does? Essentially can you go with a lesser name and still get a reliable unit and save some, or are you really gambling on the lesser name?----