AC during a heat wave

[Music Lover]

It's easier and cheaper to maintain a set temperature than to bounce it up and down a few degrees.

Not always. If the AC temp is raised and the house warms to the new set temp and stays there for a while less energy is used because the difference between outside and inside is less. The same applies to lowering the temp in heating season.

It's just basic physics.

And really, it's not that hard to raise or lower the temperature.

 

[GenXguy]

Not always. If the AC temp is raised and the house warms to the new set temp and stays there for a while less energy is used because the difference between outside and inside is less. The same applies to lowering the temp in heating season.

It's just basic physics.

And really, it's not that hard to raise or lower the temperature.

You're right. It's better to lower it. I do it all the time, and it keeps the bills more reasonable than if I keep the AC cranked. There's an old wives tale that keeping it set to the same temperature all the time, even when you're not home, saves money. But it doesn't.

Keeping the temperature 78 degrees overnight (with fan on) and about 80 during the day is perfectly acceptable to me.

 

[TheWizard]

You're right. It's better to lower it. I do it all the time, and it keeps the bills more reasonable than if I keep the AC cranked. There's an old wives tale that keeping it set to the same temperature all the time, even when you're not home, saves money. But it doesn't.

Keeping the temperature 78 degrees overnight (with fan on) and about 80 during the day is perfectly acceptable to me.

The best example of when it DOES pay to keep the temperature set to the same number is in winter with a heat pump supplemented by electric resistance heat, especially if you can't disable the electric resistance function.

For most other (linear) systems, it works better to adjust the temperature set point appropriately when you're going to be gone for a few days, etc...

 

[NW-Bound]

The walls will not support mini-splits as it is post and beam construction with plaster and lath.

There are indoor evaporator units that are floor mounted, flush against the wall.

There are also units that are recessed into the ceiling with just the grill showing.

 

[NW-Bound]

I am currently up in my high-country home at 7000'. Yesterday, the high reached 89F (32C), and the low is 57F (14C).

It felt a bit warm in the late afternoon, so I turned on the central AC. Nope! The compressor did not run. Its capacitor had gone bad. Oh well! Good thing that the humidity was so low, the dew point was 6F (-14C)!

It cooled down quickly after sunset, so the evening was not uncomfortable at all. And the night was really cool.

 

[Calico]

Central NC.
Current outside temp: 102
Current heat index: 110
Current AC setting: 76

At night I set the AC at 72; any warmer and I find it difficult to sleep.

 

[audreyh1]

I am currently up in my high-country home at 7000'. Yesterday, the high reached 89F (32C), and the low is 57F (14C).

It felt a bit warm in the late afternoon, so I turned on the central AC. Nope! The compressor did not run. Its capacitor had gone bad. Oh well! Good thing that the humidity was so low, the dew point was 6F (-14C)!

It cooled down quickly after sunset, so the evening was not uncomfortable at all. And the night was really cool.

Oh that darn capacitor! Fortunately an easy fix.

Those temps sound lovely to me. I’m glad you made it back up to your mountain home.

 

[GenXguy]

Oh that darn capacitor! Fortunately an easy fix.

Those temps sound lovely to me. I’m glad you made it back up to your mountain home.

Yeah, I had one fail in a 20+ year old central air unit just two or three years ago. If I turned the fan manually, it would start up, but not the compressor. Cost me less than $15 to fix it myself.

I added a couple window units since then and am using them quite a bit, giving them a good workout while they're under warranty and taking the load off the central air, completely shutting it off most of the time.

 

[NW-Bound]

There's no place around here in the boondocks to get a replacement cap for the AC. I am leaving for the metro home tomorrow, and will get a replacement there to bring up the next time I come up to the 2nd home.

And next time, if I remember, will bring my AC service kit with the pressure gauge. I want to check the R22 pressure, and to get some refrigerant to top off if the pressure is low. My main house central AC also runs on R22, so some spare R22 may come in handy.

 

[ncbill]

There's no place around here in the boondocks to get a replacement cap for the AC. I am leaving for the metro home tomorrow, and will get a replacement there to bring up the next time I come up to the 2nd home.

And next time, if I remember, will bring my AC service kit with the pressure gauge. I want to check the R22 pressure, and to get some refrigerant to top off if the pressure is low. My main house central AC also runs on R22, so some spare R22 may come in handy.

IIRC, RS-44b is a drop-in replacement for R-22.

 

[Surewhitey]

I personally like it at 76 & running a dehumidifier to reduce the humidity. We run fans too. If we go to 74 or lower, it seems to push the humidity from condensation... Our unit is likely just too large for the home...

 

[NW-Bound]

IIRC, RS-44b is a drop-in replacement for R-22.

There's a lot of conflicting info regarding adding RS-44b to an R-22 system. There's one vendor who says it's been done in Europe for years, with no harm.

However, RS-44b is more expensive than R-22 in the US.

 

[RetiredAt55.5]

I personally like it at 76 & running a dehumidifier to reduce the humidity. We run fans too. If we go to 74 or lower, it seems to push the humidity from condensation... Our unit is likely just too large for the home...

Sounds like the system's too large, if you need to also run a dehumidifier.

The system must be cycling on and off too frequently.

 

[Surewhitey]

Sounds like the system's too large, if you need to also run a dehumidifier.

The system must be cycling on and off too frequently.

Yeah, we installed it new after buying the home. Later we found it had insulation added to the exterior walls via little holes in the brick grout & it's too efficient now. We run a dehumidifier, especially the humid days & try to stay ~50%...

 

[MichaelB]

DW is a hot wife so we keep the A/C at 74 during the day and 72 at night.

Our A/C died a few weeks ago the day before a heat wave started. We survived and are now the proud parents of a new heat pump with a hybrid furnace for the cold Chicago winters.

 

[Aerides]

I don't know many men who are comfortable when it's 77°F indoors during the summer, and I don't know many women who aren't cold when it's 64–66°F. There are always exceptions.

In S. Fla, DH and I keep our AC set at 77 and we're both comfortable when that's maintained. Anything below 80 is still ok if needed. Barefoot, tees, shorts most of the time for both of us. AC manages the humidity to about 50-55 most of the year.

Heat comes on in the winter if it's below 70. Everything else is managed by clothing.

 

[Jerry1]

The electric came back on last night. What a relief.

 

[RetiredAt55.5]

In S. Fla, DH and I keep our AC set at 77 and we're both comfortable when that's maintained. Anything below 80 is still ok if needed. Barefoot, tees, shorts most of the time for both of us. AC manages the humidity to about 50-55 most of the year.

Heat comes on in the winter if it's below 70. Everything else is managed by clothing.

My son in St. Pete had a problem in his apartment this past winter, when Florida had a "cold" spell into the 30's.

Evidently, some housing down there doesn't have much of a heating system. Plus, since moving down there 5 years ago he has "acclimated" to the warmer climate.

 

[Aerides]

Yes we don't have specific heating in florida. We just put the AC on heat and it blows warm air. This past Winter was the closest since at least 2010.

 

[FD1000]

In S. Fla, DH and I keep our AC set at 77 and we're both comfortable when that's maintained. Anything below 80 is still ok if needed. Barefoot, tees, shorts most of the time for both of us. AC manages the humidity to about 50-55 most of the year.

Heat comes on in the winter if it's below 70. Everything else is managed by clothing.

Great if it works for you. It doesn't work for us. We both wear very light shorts and t-shirts/sleeveless shirts and thongs. As I said before, I don't mind sweating outdoors, but not indoors.

Just for context: building guidelines generally recommend setting thermostats between 73°F and 76°F to maximize energy efficiency. In every workplace I've been in, the thermostat was typically set between 72°F and 74°F. The employees ranged in age from their 20s to over 70. Most of the men were comfortable at those temperatures, while most of the women were not.
The above suited us in the summer. In the winter, we have 68 during the day and 63 during sleep.

 

[audreyh1]

Yes we don't have specific heating in florida. We just put the AC on heat and it blows warm air. This past Winter was the closest since at least 2010.

The new house has a heat pump as part of the AC and hoping it works well as it’s rare we drop below 33 degrees outside and then only briefly. Otherwise it defaults to resistive heat which is what we have in the old house and is quite expensive.

 

[Slim11]

At 72 indoors, I'd need a freaking sweater! Ha!
Put a mister on your condenser (outside A/C unit). That will pre chill the air from 100 degrees by several degrees.

This is have to try. 100degrees temps, my account couldn't keep up. Most of that is on the house not the ac. Cathedral ceilings , ranch home, home built in 1950, so no insulation or good venting

 

[NW-Bound]

I kept records of electric bills going back 10 years. In Aug 2015, I used a total of 2,697 kWh, for an average of 87 kWh/day. The average temperature of the month was 95.8F (35.4C). The bill was $348.44, and the effective rate was 12.9c/kWh.

In 2025, with the 3 minisplits and the DIY solar power with battery storage, my grid consumption in August was 1,100 kWh, for an average of 35 kWh/day. The average temperature of the month was 97.6F (36.4C). The bill was $146.24, for an effective rate of 13.3c/kWh.

The effective rate was not increased much for 10 years, from 2015 to 2025. This year there is a bigger increase, and I am waiting to see what it will be for August.

 

[Sunset]

Oh that darn capacitor! Fortunately an easy fix.

.....

I've repaired my A/C twice now as the capacitor blew when it was really hot. That's twice in 20 years.
So now I have a spare sitting on the water heater so I don't have to try to find one on a hot day.

 

[reneeh63]

Summer I keep the daytime temp at 78 with a ceiling fan in the main living room and that feels fine as long as the humidity is under control (less than 50-ish%). Night temp is 75 (ceiling fan in bedroom) and a/c has been running except in the earliest morning hours during this crazy heat spell. When it cools off decently overnight I love to open up the house for a few hours first thing in the morning but that's not possible in the worst of the summer, especially given the humidity.

Winter is 72 daytime and 66 night but we dress for the weather and I enjoy a good comforter! Electricity is cheap here, but not cheap enough.