central A/C vs. window unit A/C.....

[rnch]

what do ya'll think would result in a lower electric rate?

1. central a/c, cooling the entire house, set at 74 degrees

2. central a/c set at 78 degrees for the entire house, one window unit keeping one small office/bedroom, doors closed, cooled to appx. 72 degrees?

we are assuming both units (window and central) are brand new and are the higher efficiency models.

inquiring minds want to know!

this has been a topic of intense discussion at work...it's STILL hot & humid here in nawlinz.

 

[jnevin]

The window ones eat electricity. My last house was old and didn't have central air, and the window unit jacked my bill up, over $100 per month for a 1200 sq ft house. I have central air at my new house. It's completely exposed and has the sun blaring on it all day. The house is more than twice the size and my biggest bill was $70 this summer.

 

[Y_lifter]

Central AC is gonna have huge up front costs that must be spread across the
life of the unit and infrastructure. Plus the electric..

Window units would be good if you intend to use them in one room for sleeping
and not the whole house. Whole house using a window unit usually means that
the unit Never cuts off 24x7 due to it struggling to cool that much air, plus you won't get any circulation or warm return air as you would with a central unit.

Personally, I would get a central AC system installed as it boosts the value of the house, lasts much longer, if much more efficient in cooling the whole house, circulates and filters the air better and removes way more humidity.

.........Waiting for GL to post up the truth..

 

[Y_lifter]

PS..

I have always had central AC in the houses since childhood that I can recall.
Maybe since 1970..

 

[Scotsman]

Also get a bigger central ac unit than the bare minimum. Whatever the cubic footage of your place is make sure the unit is designed to cool more space than that. It will cool faster and not have to work as hard to do it. Typically installers recommend that you get one that just barely covers your needs.

Cheers,
Scotsman

 

[feisty11975]

500 sq ft per ton on a central...if you are over per ton then the unit will run more, causing of course, a higher electricity useage!

Window units are ok if cooling a small space like a bedroom or home office.

 

[Y_lifter]

^ repost

 

[heatherrae]

The new model of central air is very efficient but expensive to purchase. It would be way more efficient than the window shaker/central air combo you are envisioning.

 

[feisty11975]

^ repost

Hey damnit...I specified how much sq ft per ton...I did not see that anywheres in this thread.

My bf has his own a/c-heating company so I have learned a lil bout this subject.

 

[rnch]

the coffee pot debate at work is centering on one item...the monthly electric bill amount...and which option would give a lower dollar electric bill in the a/c months down here.

installation costs of the various units not withstanding....which option do ya'll think would give a lower dollar electric bill in the summer months?

 

[samoth]

Moved to math forum.

 

[heatherrae]

the coffee pot debate at work is centering on one item...the monthly electric bill amount...and which option would give a lower dollar electric bill in the a/c months down here.

installation costs of the various units not withstanding....which option do ya'll think would give a lower dollar electric bill in the summer months?

The new high efficiency central air units.

 

[Scotsman]

the coffee pot debate at work is centering on one item...the monthly electric bill amount...and which option would give a lower dollar electric bill in the a/c months down here.

installation costs of the various units not withstanding....which option do ya'll think would give a lower dollar electric bill in the summer months?

Logically thinking about it:

One has one A/C unit and one has Two, even though the temp setting would be different you probably will have a higher bill with the two cooler set up. Although the larger unit would no longer have to cool one room, you also will loose circulation by closing that room off for the use of the small cooler.

Just think of it this way will it be less power usage to use the larger cooler 10% or so more, or to have a smaller cooler running 100% as much as the larger cooler if not more to maintain the lower temp in it's room.

Cheers,
Scotsman

 

[Y_lifter]

You would need to know the amount of watts electric the central ac blower and compressor unit used per hour, compared to each window unit * the number of units needed to cool the Sq footage.

Assuming both would be running the same amount of time per month. Which is a bad assumption since the central AC is gonna be way more efficient in running/cooling in hours needed to be run per day..



.... still waiting on GL to respond, as well as Feistys man dood..

 

[Cutiebaby]

If I could go central I would! Window ac's suck

 

[gonelifting]

A lot of misinformation on this thread.

First I will say...

Fiesty, your boyfriend is wrong. I don't care if he's a contractor. Maybe you misunderstood him, then I'll let it slide. There is no "rule of thumb" when sizing an AC for a house. 500sf/ton or whatever. You need to do a load calculation on the house individually asd each house is built and insulated differently. It's called a Manual J. That is the main one among others.

Do NOT oversize AC. If AC is too big, then you will not remove enough humidity in the air and it will be cool but very muggy/clammy in the house. The temp will get down to 72 in 10 minutes and you'll still feel clammy. The longer the AC runs, the more latent load (humidty) it will remove. You WANT that.

If an AC system is designed properly, on the hottest day of the year (in the design) the unit should run all day long. That is a good thing. Generally installers put in systems which are too big and have these short cycling problems. They don't run long enough to remove humity but DO get down to the temp desired, then shut off. The cycle is repeated all day long with poorer comfort.

If properly sized, the unit will be far smaller than once perceived the "right" size, thus using less electricity because of smaller motors blowers, etc... and better comfort.


To answer your question... it depends on the outside temp. Just a guess, I would say keep the window unit off.

Try Kill-A-Watt. I have a couple of them. You plug anything into them and it tells you exactly how much money you're spending on electricty over a period of minutes, hours days, weeks etc... $25 each.

 

[ZKaudio]

gonelifting come put in a new ac for me, I want some hi tech sh*t.

 

[gonelifting]

Just fyi...

I have the Kill-A-Watt thing plugged into my Window AC (10,000 btu)AND dehumidifier (65pint) at the same time in my basement. In a month's time about one month AGO, they both combined used $1.55/day. The temp was set at 72 and the humidity at 45%.

 

[Y_lifter]

A lot of misinformation on this thread.

I KNOW you weren't meaning mine Gladys..

 

[gonelifting]

I KNOW you weren't meaning mine Gladys..

lol No, just what I pointed out.


Also, if the system is already installed in the room where the window unit will be running, then just vclosing the "vents" (supply registers) will not really save much in the way of energy consumption. The system as awhole will not run as it was designed, thus run LESS efficiently.

 

[Y_lifter]

Window Units = Ghetto cooling

 

[digimon7068]

The window ones eat electricity. My last house was old and didn't have central air, and the window unit jacked my bill up, over $100 per month for a 1200 sq ft house. I have central air at my new house. It's completely exposed and has the sun blaring on it all day. The house is more than twice the size and my biggest bill was $70 this summer.

My house is four bedrooms. . .I have two window units upstairs. . .set them on 74 degrees and left them run all summer. . .my bill was never more than $70 per month. That said. . .next spring we're going to upgrade our furnace and I'm gonna get central air then too. . .I just like central air better. . .much more comfortable plus it doesn't have to "catch up". . .

 

[ZKaudio]

I have a vacation home in az, the temps in summer are up to around 115... I looked into some geothermal whatchamajiggy awhile back that looked VERY cool. The elect bill is around 180/month even when I'm not there.. Is there anything super high tech that could minimize my cooling costs?


(sry to threadjack)

 

[Scotsman]

On the oversize thing it works here in Colorado where the humidity isn't really a factor (avg peak summer hum. is ~30%)I should have specified that.

Cheers,
Scotsman

 

[gonelifting]

People who live in a milder temp area should really look into a heat pump while getting an AC unit installed. They work down to 30 degrees or so in the winter, so a place like Florida or anywhere really that doesn't get too cold can benefit greatly from them by not using natural gas or oil but instead use the AC system but in heat mode.

When it gets colder than the (very roughly) 30 degrees, it swithces automatically to the backup heat strips or your normal fuel like gas or oil. Very efficient, depending on your electricity rates.

Same exact thing as AC but with the added "heat pump" option. Ask about it. Not much more money.

 

[Y_lifter]

I have a vacation home in az, the temps in summer are up to around 115... I looked into some geothermal whatchamajiggy awhile back that looked VERY cool. The elect bill is around 180/month even when I'm not there.. Is there anything super high tech that could minimize my cooling costs?
(sry to threadjack)

RADIANT BARRIER

 

[gonelifting]

I have a vacation home in az, the temps in summer are up to around 115... I looked into some geothermal whatchamajiggy awhile back that looked VERY cool. The elect bill is around 180/month even when I'm not there.. Is there anything super high tech that could minimize my cooling costs?


(sry to threadjack)

Yes, radiant barrier is the cheapest, most bang for your buck thing you can do. I mean $500 cheap.

The Geo thing you're talking about is very expensive. I know you don't care!! lol But that IS the most efficient thing you can buy. There really is no better than that out there unless you go solar or something. Geo, properly done is the best. period.



"properly done" get a very good contractor. Go to that site I sent you and they are all pros that would love to point you to a knowledgable contractor that knows his shit. It's not a diy site.

 

[ZKaudio]

My parents are having a custom home built out there and I've been urging them to put more time into their cooling system, and the overall efficiency of their building, but they just don't care. I do care about costs, if it's like 30k for the system, it would take some serious time to warrant the sunk costs during installation...making it probably not worth it.

 

[gonelifting]

My parents are having a custom home built out there and I've been urging them to put more time into their cooling system, and the overall efficiency of their building, but they just don't care. I do care about costs, if it's like 30k for the system, it would take some serious time to warrant the sunk costs during installation...making it probably not worth it.

Ohhhh, I thought it was an existing house. If it's new, you should look very carefully at insulating properly. Foam insulation is great. There are other ways of getting the job done, cheaper, but the foam allows for less mistakes from the contractor. Insulating very well that does not allow air to infiltrate the home is HALF the battle in terms of energy efficiency in the structure. An airtight home allows an even smaller unit to be installed thus having less energy bills, more comfort due to less temp swings fro outside air getting in to disrupt etc... "airtight" house. Look into both those things and you'll be golden.

 

[Y_lifter]

Fond Memory of my childhood

"Close that door, I'm not cooling the whole Neighborhood"