I am just speculating. I do not know what you call "HUGE". My 2,000 SF split level home in Raleigh averages $95.00/month during the month of June. I know folk who pay $250.00 per month.

I do not know what you have the thermostat set on. If you set it on 70 degrees, the system might run all the time. But, I feel certain that it is not the age of the AC unit. It could be that you are cooling more than the conditioned space (interior space). Maybe there is duct leakage in the attic.

The thing sitting out back is the condensing unit. A complete replacement system is the condensing unit, a line-set, evaporator coil, and the furnace (or air handler). All of that is controlled by a thermostat. The thermostat should be digital.

I would charge approx. $2,500.00 to replace a condensing unit, the line set, the evaporator coil and possibly a digital thermostat for a 925 sf condo. The condensing unit should be a one and a half ton or a two ton unit.

We would refuse to install a new outdoor unit on a 1974 vintage indoor coil. That's like going to a car dealer and buying a new car but asking for the transmission to be taken out of your 1974 Impala. It's all a matched system. That car would be a mess with a clunker 3 speed Turbohydromatic in it just like a new high efficiency condensing unit would not peform well with an ancient evaporator coil. Sure you'd get cool air but probably not save much money.

With the prices some dealers charge, the new equipment will be dead and replaced before saving operations money, over the cost of repairing old equipment.

As I gat older, I relize that new is not always better. It is just newer. Many people fell better with new over old. I don't have this mindset.

Thanks for the replies. Like I said, I'm trying to figure this stuff out on my own so your advice is very much appreciated.

As to the second response, I don't really understand how the different parts work together; I'm trying to research it before I call and get prices from people. I understand what you are saying however. That's why I'm asking if I need to replace just the condenser that's outside or also need to do something in the attic where the new furnace is.

As for what I consider huge for a monthly bill, my bill in the summer is $300+. Considering that I have one floor 925 sf condo, use the new energy efficient light bulbs, have all new energy efficient appliances, am not home most of the time, and when I'm home I don't have a lot of lights on, that's a lot of money for one month's electric bill. If I don't use the air conditioner at all, my bill is about $55 a month. So I know it's the air conditioner that's doing this. Oh...I also had an energy audit done three months ago and it was determined that the place was not leaking anywhere. The duct work is fine, the windows are newer, etc. The audit was very good.

Yes, newer is not always better, but good lord, there has got to be something better than what I have now in terms of efficiency and costs.

Thanks again!

One thing you did not tell us was what do you have the unit set on and what do you do during the time you are not there?

I live in a 1750 sqft house. I have poor attic insulation. Most days of the summer are at 100f. I adjust the thermostat to cool to 78. I use ceiling fans which give a simulated 75 degrees. If I were to drop the thermostat to 75 without the fans, My bill would double from $250 to 500. I have older equipment, that is very efficient to operate under these conditions. I monitor the power usage periodically during the summer for many years. Newer equipment will cost more to operate for sure. This year I will replace the coil and outdoor cabinet, but I will keep the compressor in the beginning. The compressor is 23 years old. I want to see how long it will last.

What I am saying is, you should not replace the condenser (outdoor unit) without replacing the evaporator coil (indoor coil attached to the furnace) and the line-set. The only equipment in the attic is the new furnace and the indoor coil. The coil has no moving parts.

Consider this:

The outdoor condenser pulls 13 amps of current (12 amps for the compressor & 1 amp for the fan). The voltage is 208 volts. Thus the amount of electricity it uses is 2,704 watts per hour (2,704/1000 = 2.704 kWh) of electricity. In New Haven, CT electricity cost was 11 cents per kWh in 2006. So, 2,704 watts x $.11 per kWh equals $.298 per hour worth of electrical usage. If your system ran 8 hrs. per day at $.298 per hour, the cost of electricity would be $2.38 per day. That would equal $71.52 for one month.

The blower on the furnace draws 5 amps of current at 115 volts for a total of 575 watts or .575 kWh of electricity per hour. For 8 hrs. at a cost of $.11 per kWh that equals $.51 per day. At 30 days that would be $15.18 for the month.

Outdoor unit cost $71.52 plus the furnace blower cost of $15.18 equals $86.70 of electricity usage for the month, or $2.89 per day.

Now, if I use your electricity charges of $305 (with A/C) per month minus $55 (without A/C) per month, that equals $250 of monthly A/C usage. $250 divided by $.11 per kWh equals 2,273 kWh of electricity usage each month or 75.77 kWh per day.

In conclusion, if your system draws 13 amps plus 5 amps and the electrical rate is $.11 and your cooling bill is $250.00, then your A/C unit is running 23 HOURS PER DAY.

BOB, did I do the math right?

Daiseycat3, if the thermostat setting is low, the system might run for 23 hours per day.

I agree with all those telling you to replace the entire system (other than your furnace, which is new) - 20+ year old equipment won't match up with a new condenser to save you much

$2500 to replace it all would be an EXCELLECT price - I predict you'll get bids of nearly twice that

Sounds like you really NEED a modern digital programmable thermostat so you can cut the system back for periods when you're not there. If you're comfortable with 76 or 77 degrees when you're home, program the thermostat for about 85 degrees to kick in just before you leave and then have it switch back to 76 or 77 about 15 or 20 minutes before you're scheduled to return home - Just switching to a modern thermostat and programming it smartly could probably save you $75 of that $300 you're spending. Replacing the condenser, lineset and evaporator could probably save you another $75

IF you could get the system replaced for $2500 and if it saves you $75 a month for 6 months of the year, then it would pay for itself in about 5 or 6 years - It would also raise the resale value of your condo by a couple grand if you were to ever consider putting it on the market

Don

Daisy:
What temperature do you keep the thermostat set to when you are not home in the summer? When you are home? What floor is the condo on?

Remodeler:
11 cents/kw-hr sounds too cheap for CT. The 13 amp draw that you use in your example may be off by a factor of 2 as it is an early 70's vintage. We don't know the size of the unit or the power consumption.

Can't tell you how much I appreciate all the info!

To answer some questions: 1) I do have a new thermostat that I can set for different times of day. When I leave in a.m. it goes to 85 degrees and then at about 5 pm it sets back to 78. About 11 pm when I go to bed it goes to 70 only because I can't sleep if it's too warm (again, in this condo, air doesn't move that well). So I think my temps are good - I'm always hot so for me to put thermostat on 78 when I'm home is good for me. I'd love to set it on 60!

If I know I'll be gone more than them normal 8 hours, I keep it on 85 and "hold" it there until I get home. I also have cats and while I don't want ot spend to keep them cool, the fact is I can't go above 85 or it will definitely effect them.

I also use a ceiling fan on my vaulted ceiling in living room when I'm home, and that does help - probably why I can keep temp so high without wanting to kill myself.

Condo is all one floor. We have crawlspace/basement underneath that is newly insulated/wrapped. Like I said, they did an energy audit and said the place was in excellent shape as far as no leaks, etc.

I now understand what you mean by replacing the part in furnace area...I didn't know all the diff parts but you all did a nice job of explaining it to this still-learning single lady!

IS IT POSSIBLE that my electric meter is "off" or maybe needs to be checked? Someone suggested that. Will the electric company come out and check it for me? (Although they have no reason to; they are making money off me!)

Again, I REALLY appreciate all your advise and explanations!

Normally if an electric, water or gas meter is incorrest, it is to the residents favor. If the spinning disc has bad pivots, it will run slower. This means less recorded usage. If the water vanes are stuck, this means free water. The same with the gas meter. If a meter were rebuilt wrong, it could be reading high, but not normally from usage.

Running the thermostat to 70 is expensive. Install a ceiling fan over the bed and leave the stat at 80. You will save a lot of money this way. Turn off the electric blanket.

Bob, Thanks for info. Maybe I won't call the electric company - my bill may go up! ; )

Don't use the electric blanket in summer!

thanks for everyone's help...really helped me to understand things. Maybe I should leave things as they are for now and hope we have a cool summer.

Daisy:

I think your setback temperature is too high at 85. You are going from 85 to 78 to 70 in one day - that's a 15 degree swing on a hot day. I would try 80 to 76 to 72 for a week or so and see how it feels. You cut your swing in half. I agree with Bob on putting a ceiling fan above the bed - the bedroom doesn't get stuffy when the a/c shuts off with a celing fan running. The 15 degree swing coupled with the 70 degree setpoint is why your summer electric bill is so high.

Garyg, thanks for the info. The more you explain it the more I understand what you are saying. I will adjust the temps to what you suggested and try that.

As for ceiling fan in bedroom, I was thinking of doing that but a couple issues...the heat/air vent is smack in the middle of the ceiling which is where you'd normally put a fan. Plus I can't have anything blowing directly on me (long story; have a condition affecting the nerves in my face; wind/breeze causes horrendous pain in my face, so I have to stay away from things that blow on my face.)

Thanks again!