Is it better to leave the AC on about 78 or to leave it off while your gone for a week then turn it on?

Question

We have a summer cabin, we're thinking of leaving the AC about 78 deg. while were gone to keep it cool. If we come up it can be almost 90 inside if we have it off then it runs non stop and never gets below 80 for the week were there. Were there on average 15 out of the 30 days a month. What do you think will cost less?

Is it easy to install a programmable thermo.? I agree with paula, it takes of time to cool everything off. Last summer when it was 90 everyday, the thing ran non stop for 5 days straight at about 80 degrees.

Ok adding more details. There is no basement there and its built on a sand base. So the vents are usually pretty warm. The AC also isnt the best out there, i believe its underpowered. There is also a glass wall with patios that gets the morning sun which raises the temp about 10 degrees. And theres no way even at night the temp is being dropped 1 degree every 10 mins when its hot out. Its pretty small and was an energy saver. We didn't think it would be that hot in northern WI.

Answer 1

The A/C should be able to remove enough heat to drop the temperature 1* every 8 to 12 minutes, or keep the temperature from climbing. If it does not, it is either undersized for the application, or it is not operating efficiently.
Do you close the window curtains when you are out of the cabin? Is there a fan in the attic to remove heat buildup? Are there trees around the cabin to provide shade? Has the filter been changed, the coils cleaned and the system tested this spring? Does it get cooler at night where you could open the windows and let the warm air out and cooler air in?
To save money (energy) you maximize your savings by not running the unit. The more it runs, the more it costs. Pulling down a living space to a comfortable temperature should not take long. Running a system all week at 78* will cost more than running a well-tuned system for only the time you are there.

In No WI, you also have humitity to condend with. Water retains a lot of Btu's. A room dehumidifier will help. Good insulating curtains on that large glass door will help. If you don't wan't to opt for a new central air unit, try some window shakers to boost your cooling capacity. An energy conserving unit will perform, has it been checked recently? You should get a 20* temperature drop across the unit, even if it can't cool down the entire cabin, it should have a temperature drop. If not, it does not have enough refrigerant to remove the heat.

If you can read and follow instructions, know some basic concepts of electricity and wiring, you can install a programmable stat yourself.

Keep Kool

Answer 2

Leaving the AC on at 78 will do nothing for you until you reduce the heat load on the inside of the cabin. The large glass area must either be reduced or the glass needs to have an ultra violet and infra red polymer film put on the inside to reduce the heat from getting in.

It sounds to like your system is underrated for the size of the cabin. So if you were to upgrade the AC system and tint the window you should get a very reasonable reduction in the temperture inside the cabin within say three to five hours upon arrival each weekend without leaving it run all week.

Have a reputable HVAC company come out and do an evaluation of the cabin. Heat/cold loss and a good glass company to check of "tinting" the windows.

With that $ cost in hand go to your utility company and find out how fast you will recover the improvements and if they offer any low interest money to do the work with and rebate programs for additional insualtion of the cabin as well.

Have fun.

Answer 3

We set our AC to 85 when we leave the home for more than 1 hr. It actually takes less than that time to cool the home down from 85 to 80. So, it you are going to be gone for longer than it would take to return the house to normal living temperatures, turn the AC up, but not off. If the in house temp does not go above 85, the AC won't turn on anyway. Same with heating in the winter, but on the other side of the temperature and thermostat scales. 65 deg when gone.

Answer 4

Depends a bit, what area/climate the cabin is in.

When I go away for several days (from Phoenix), I DO turn off the A/C.

But if you have a regular routine - like going to the cabin each weekend, you might try installing a programmable thermostat. I have one for home, that allows the house to warm up to 90F during weekdays, while I'm out at work. It cools down to 85F when I'm home in the evening & at weekends.

If you don't know when you'll be at the cabin & it's not in too hot a location, leaving the A/C off while you're away, may still be a good option - experiment & watch your electric bills.

Answer 5

It is simply not true that it saves money to leave the AC on. That has been an old wives tale for decades. If you are concerned about money, turn the unit off when you are gone. Anyone that says otherwise doesn't understand the laws of thermodynamics.

That being said, if you are concerned about the humidity and associated problems (mold growth), you could leave the AC on a high setting (maybe 83-85) so that it will run just often enough to remove humidity.

Answer 6

I don't like to turn the a/c up too much when I leave, not more then 9 degrees from the normal setting. First off when you come home you don't want to have to wait for hours for the a/c to cool off the house. Second the a/c will have to over work if you turn the unit off, because not only does it have to cool down the air, it has to cool down the sheetrock, furniture, and other sufaces in the house.

Answer 7

First off your kind of wasting energy. Second get your A/C checked out it shouldn't take five days to pull down to temp even being 90 inside thats what they are designed for. Its not running very effeciently could be low on gas have a leak anything really I would have it looked at. Don't get me wrong it will take a while to pull down to temp when its hot but a week thats just crazy. Somethings not right there.

Answer 8

makes sense to leave it running at a higher temp then having it off and making the unit work twice as hard to get the cabin cooled down

Answer 9

If you are not home, reduce the amount of work the A/C has to do for you, but that it doesn't have to re-cool, all your wall interiors, furniture etc. Leave it at a higher temp., then on return, go to your regular settings.
There are set-back thermostats out there for vacation settings too.

Answer 10

I would suggest to leave it on or like you said it would run non stop to try and cool down