Hourly cost of air conditioning?

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penumbra
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Hourly cost of air conditioning?

Post by penumbra »

We have a 25 year old a/c unit providing reasonably effective cooling for a 3000 sq ft house... a little noisy but effective. Serviced once 5 years ago with no problems found. We have a single story, only modestly well insulated home in coastal California. Hottest days get up to about 90 degrees for the afternoon/early evening. Trying to determine if it would pay to upgrade the system. It uses about 5 kw/hr, which at our rate of $0.23/kWh, is about $1.20/hr. On about 20 days per year, we run it for 6 hours or so. I know there’s quite a variety of systems out there, but can someone give me an idea about how much energy/hr a new system uses? Companies I’ve spoken to are incredibly evasive about getting estimates. Thanks in advance..
AlohaJoe
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Re: Hourly cost of air conditioning?

Post by AlohaJoe »

My A/C is 1.5 HP. That means 1.5 HP/hour, which is 0.11 kWh. Then multiply that by your rates.

Of course, that's the maximum. How much it actually runs would depend on the room layout, the temperature chosen (mine is set at 73F), the insulation, and so on. I can understand why companies would be reluctant to give out estimates when they don't know all those factors.

My A/C costs me around $25/month to run for 270 hours. (approximately 9 hours a night, every night).
runner3081
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Re: Hourly cost of air conditioning?

Post by runner3081 »

Here is a single data point for you.

Going from a 20 year old unit to a new one with a 14 SEER rating has dropped our bill significantly. We are seeing a monthly reduction of $80-$100 with the same indoor temp settings and pretty similar weather (during peak season June, July, August, Sep).
killjoy2012
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Re: Hourly cost of air conditioning?

Post by killjoy2012 »

This is one of those cases that if it's not broke, don't fix it (or replace it).

Sure, if you buy a new central AC, it'll operate at a higher efficiency and lower electrical cost than what you have today. But even if it was 50% more efficient, at 120 HOURS of use per year.... vs. $3-6k for new equipment. If your operating cost went from $1.20/hr to $0.60/hr, that's a $72 savings per year. It takes a long time to get back $3-6k at $72/year.
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ClevrChico
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Re: Hourly cost of air conditioning?

Post by ClevrChico »

A modern a/c unit and blower motor would probably knock about 1/3 off your energy costs. Payback would take a while. :-)
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whodidntante
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Re: Hourly cost of air conditioning?

Post by whodidntante »

AlohaJoe wrote: Sun Sep 09, 2018 10:30 pm My A/C is 1.5 HP. That means 1.5 HP/hour, which is 0.11 kWh. Then multiply that by your rates.
1.5 HP is 1.1 kW
28fe6
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Re: Hourly cost of air conditioning?

Post by 28fe6 »

I put an hour meter on my AC unit so I can check it daily and determine it's duty cycle. Multiply by amps measured by a clamp-on hour meter to get cost. My biggest take-away is set the thermostat a couple degrees higher during hot summer days. It makes a big difference.
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Re: Hourly cost of air conditioning?

Post by graviteer »

As others have pointed out, you say that you run your air conditioner very little ($144/year). A new unit will cost several thousand dollars. It's not possible for the improved efficiency of the new unit to recover its cost, even if it too lasts 25 years.

Even so, it may be wise to replace the unit before it fails. Then you can have the work done on your schedule, during the off-season, when your HVAC contractor is relatively idle. Otherwise there's a fair chance that, somewhere down the road, you'll suffer the inconvenience of being without AC for an extended period during the hottest part of summer.
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penumbra
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Re: Hourly cost of air conditioning?

Post by penumbra »

OP here. Thanks for your responses. Very helpful! Welcome further comments. :happy
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mmmodem
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Re: Hourly cost of air conditioning?

Post by mmmodem »

Realize that HVAC companies are not being evasive. They don't know what your usage is and therefore cannot give you an estimate. It's like asking your dealer how much it costs to drive a mile in X sedan. They don't know If you're driving highway or city or our how much you pay per gallon. Therefore, they don't have enough information to determine what your cost per mile will be. Same with central AC. It will cost more to cool your home at 95 degrees than at 85 degrees. Your AC will cost more per hour on a hot day than on a cooler day as it will be power cycling less often. My wife and I like different temperatures so even on the same system and same home, the usage costs will vary for the person.

If you really want to determine the difference in the costs are with the upgrade, look at the efficiency of your model in the SEER rating and compare to the efficiency of the one you may buy. Also realize the SEER rating is an apples to apples comparison for a situation that may not be applicable to your usage. In other words, YMMV.
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Re: Hourly cost of air conditioning?

Post by adamthesmythe »

With infrequent use of the AC, I personally would not replace until the unit is unrepairable.
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RickBoglehead
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Re: Hourly cost of air conditioning?

Post by RickBoglehead »

penumbra wrote: Mon Sep 10, 2018 9:56 am OP here. Thanks for your responses. Very helpful! Welcome further comments. :happy
What further comments could there be? You run your system 120 hours a year. Killjoy2012 and graviteer laid it out quite clearly. Let's assume it was FREE to run.

$1.20 / hr x 6 hours per day x 20 days per year = $144 a year

$3,000 system (probably low estimate) / $144 = 20.8 year breakeven

My rough cost to run two units on a hot day is $10 a day. During a hot summer, we might run it 30 days, so that's $300. Still a ten year payback if it was free, which it's not.
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keystone
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Re: Hourly cost of air conditioning?

Post by keystone »

I typically don't believe the claims that you'll get your money back, although I am sure there are some exceptions.

I have a 26 year old Rheem and got it serviced about 5 years ago. The technician told me that it was a great system and I should get several more years out out of it. Then he mentioned that if I upgraded to a new system I would get my money back because of improved efficiency. I figured the cost of a new system installed would run about $5K, but my entire electric bill at it's highest is only around $100 with my current system. So I figured that even if I saved $20 per month in the summer, it would take me about 80 years to recoup my investment.
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Re: Hourly cost of air conditioning?

Post by Smoke »

Been there myself with this issue,
If you are certain you will be staying in the home for many years, replace it with a new more efficient unit.
If you don't know if you will move or not leave it alone, it still works.

I weighed this 25 yrs ago with an old Amana unit that at that time was 22 yrs old and still working, no seer rating with that unit Amana's best guess was "6". I replaced it.
Things I considered, repair costs, replacement unit costs, and my heaviest concern was the timing of exactly when the old unit would give up the ghost.
At the either coldest day of the year (heat pump) or the Hottest day of the year. Tennessee.
It would of course quit then and on a weekend ( yes I would have to live with "the family" during that time and never hear the end of it)
How long it would take to repair or replace when it quit.

Feeling lucky? Keep it.
Worrying every time you think about it? Replace it.
Nothing lasts forever, and prices go up every year for new units.
Money saved by waiting will only cost more by postponing the inevitable.

Just my 2 cents :)
Arguing for the sake of arguing is something I am not going to engage in.
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flossy21
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Re: Hourly cost of air conditioning?

Post by flossy21 »

The coolant for the older units is being phased out due to environmental concerns.

"As of 1 January 2020, the chemical HCFC-22, which a principal component of the trade-named refrigerant “Freon,” will no longer be produced in or imported by the United States."

Basically once that older unit develops a leak and needs more coolant you are going to be paying more and more for the coolant because it will become more and more scarce. Demand goes up, supply goes down, Prices go up.

You are good until 2020 but after that you'll be on borrowed time.
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Re: Hourly cost of air conditioning?

Post by nesdog »

We are just going down this road. Our AC is nearly 40 years old, original to the house! It works....kinda... and doesn't get used as much as our upstairs one. However we don't want to scramble when it breaks in mid-winter or the heat of another Socal summer.

Since we will stay in the house for a lot more years, we are replacing it. One less potential headache and added efficiency.
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Re: Hourly cost of air conditioning?

Post by Valuethinker »

flossy21 wrote: Mon Sep 10, 2018 1:47 pm The coolant for the older units is being phased out due to environmental concerns.

"As of 1 January 2020, the chemical HCFC-22, which a principal component of the trade-named refrigerant “Freon,” will no longer be produced in or imported by the United States."

Basically once that older unit develops a leak and needs more coolant you are going to be paying more and more for the coolant because it will become more and more scarce. Demand goes up, supply goes down, Prices go up.

You are good until 2020 but after that you'll be on borrowed time.
Is there a substitute chemical? There has been for some of these for other CFCs I believe, I believe.
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RickBoglehead
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Re: Hourly cost of air conditioning?

Post by RickBoglehead »

keystone wrote: Mon Sep 10, 2018 12:42 pm I typically don't believe the claims that you'll get your money back, although I am sure there are some exceptions.

I have a 26 year old Rheem and got it serviced about 5 years ago. The technician told me that it was a great system and I should get several more years out out of it. Then he mentioned that if I upgraded to a new system I would get my money back because of improved efficiency. I figured the cost of a new system installed would run about $5K, but my entire electric bill at it's highest is only around $100 with my current system. So I figured that even if I saved $20 per month in the summer, it would take me about 80 years to recoup my investment.
So, to make sure we understand, an 80 year payback is not acceptable to you? :shock:

Consumer Reports used to (I don't get it anymore) push the idea of replacing an old refrigerator due to improved efficiencies. This was before a new refrigerator cost as much as a car used to. I did the analysis, saw an 18 year breakeven, and didn't do it.

Went to a solar panel presentation a few years back, when the city was pushing a program that they said was amazing. Listened to the presentation, found all the "we can't guarantees" including what the utility company would pay for excess electricity, and did my analysis. It went beyond the life of the expected panels.
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Re: Hourly cost of air conditioning?

Post by Valuethinker »

RickBoglehead wrote: Tue Sep 11, 2018 8:36 am
So, to make sure we understand, an 80 year payback is not acceptable to you? :shock:

Consumer Reports used to (I don't get it anymore) push the idea of replacing an old refrigerator due to improved efficiencies. This was before a new refrigerator cost as much as a car used to. I did the analysis, saw an 18 year breakeven, and didn't do it.
I don't know what new fridges in the USA cost, but in Europe they cost around USD 600-800. We have a Bosch (upper middle kind of appliance here) and it was around the low end of that.

https://www.amazon.com/Kenmore-61212-To ... 609&sr=1-2

tells me $700 US?

So. As much as a car used to? Not in real dollars (or pounds). Been a long time since a car cost less than £500 (GBP). Did you simply mean that fridges are fancier?

I think the difference CR now v. CR then is the dramatic improvements in fridge efficiency. That began nationally about 1992. It came as a result of research done at National Energy Labs and legislative initiatives in California in particular.

A 1985 fridge in the USA burned about 2000 kwhr pa or $240 pa at rough average retail price (twice that in some places).

A modern US fridge (which is bigger) burns something around 550 kwhr. So say about $60-70 pa.

The move from the one to the other would payback in around 4 years? Or say your current fridge does 1100 kwhr thus saving is around $65-70/ yr and 10 yr payback.

Thus, further gains in efficiency will be marginal. The drop in consumption has been so dramatic.

If your fridge was made after about 2002, I think, the gains in early replacement are not worth it. One of the things GWB signed into law (I think in his second term) was a major improvement in the energy efficiency of appliances, across the board.
Went to a solar panel presentation a few years back, when the city was pushing a program that they said was amazing. Listened to the presentation, found all the "we can't guarantees" including what the utility company would pay for excess electricity, and did my analysis. It went beyond the life of the expected panels.
One always has to run the numbers. I am not sure what the "expected life" of panels is, though, because there are 25+ year old panels out there, still producing (although there is decay on output). Inverters last less time-- 10-15 years.

Agree the price of sale of surplus electricity is key for most people.

Saving electricity is usually the cheapest form of generation.
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RickBoglehead
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Re: Hourly cost of air conditioning?

Post by RickBoglehead »

People are spending in excess of $2,000 for a frig today. Of the 107 listed on Costco's site, 79 are $1,000 or more, 42 are $2,000 or more. I said "as much as a car used to". My first car cost that much.

Clearly appliances are much more efficient today. I did the analysis back before the efficiency change, and my payoff was like 9 years.

I look at financial payoff for everything. I do let "do what's right" come into the equation when appropriate. In August 2009, the US rolled out a program called "Cash for Clunkers". That program incentivized people to turn in older vehicles and get a rebate from the government for the purchase of a new vehicle. The trade-in was made non-functional, and sent to the scrap yard. We bought a hybrid vehicle that even with the incentive had a dubious payoff at 5 years with assumptions on gas prices (which were sky high at the time - sky high for the US anyway). DW is a big "leave no footprint" thinker, so we bought it. Gas went down, and I never did go back and analyze how much we saved (maintenance was very low). Earlier this year I ordered a PHEV (plug-in hybrid electric) to replace it, which is cheaper than buying a hybrid-only model, or a gas model (that we would buy, base gas model no one would buy). Our estimated annual savings on fuel is under $300.

Back to the OP's topic - you're never going to save enough with your usage to pay for this. When it can't be repaired, or repairs are very expensive, then replace it. Note that repairs can often be diagnosed via some quick Googling. I have replaced two capacitors, one ignitor, and a exhaust fan, all with some Google research and a few videos. A repairman might charge $200 to replace a $12 capacitor that is basically plug and play.
Last edited by RickBoglehead on Tue Sep 11, 2018 10:53 am, edited 3 times in total.
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Re: Hourly cost of air conditioning?

Post by keystone »

RickBoglehead wrote: Tue Sep 11, 2018 8:36 am So, to make sure we understand, an 80 year payback is not acceptable to you? :shock:
If the new unit has a chance at lasting 80 years, then I might be persuaded. :happy
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Re: Hourly cost of air conditioning?

Post by RickBoglehead »

keystone wrote: Tue Sep 11, 2018 10:45 am
RickBoglehead wrote: Tue Sep 11, 2018 8:36 am So, to make sure we understand, an 80 year payback is not acceptable to you? :shock:
If the new unit has a chance at lasting 80 years, then I might be persuaded. :happy
"We guarantee it"! Of course they won't be in business in 80 years.
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Valuethinker
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Re: Hourly cost of air conditioning?

Post by Valuethinker »

RickBoglehead wrote: Tue Sep 11, 2018 10:41 am People are spending in excess of $2,000 for a frig today. Of the 107 listed on Costco's site, 79 are $1,000 or more, 42 are $2,000 or more. I said "as much as a car used to". My first car cost that much.
Oh indeed, and my father's Morris Minor cost £500 ;-). As I said, a long time ago. I think his Pontiac Lemans cost $3k (1978). So we could compare that to a $2k fridge now ;-).

So there's 2 things going on there:

- (dramatically) improved energy efficiency
- bigger fridges, which are therefore offering greater service value to the owners (must be, because people want them)

Taking energy efficiency on 2 fridges of very different sizes is like buying a BMW to replace a Ford Mondeo because it has better fuel economy and then complaining of a long payback ;-).
Clearly appliances are much more efficient today. I did the analysis back before the efficiency change, and my payoff was like 9 years.
The efficiency has been moving fairly constantly - there was not one efficiency change. So it really does depend on how old the fridge being replaced was.

It's a fairly constant refrain here that replacing an old fridge, or chucking the ancient "beer fridge" that sits in the garage, saves $10-20 pcm on electricity bills. But if your current fridge was made after 2000 that's unlikely.
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Re: Hourly cost of air conditioning?

Post by lomarica01 »

OP when you say you run the AC for 6 hours does that mean the compressor is running for 6 hours, or the thermostat is set and the AC compressor will be turned on as needed over a 6 hour period. Most likely the latter so it seems like this makes a huge difference in how you are calculation the costs.
I just compare my monthly bills in summer to spring and fall when no ac is used to get the approximate costs.

Based on this with even say a 50% increase in efficiency my payback for a new unit was well over 10 years. In addition I believe older products seem to be better built and will last longer. It is quite possible a new AC would not even last the payback period as many have a warranty of say 5 years.
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