Seeking input: Does your central AC have trouble keeping up in this heat?

[woo me with science]

We just replaced a central AC unit. The old one was powerful. Even on very hot days, it cooled perfectly and quickly.

It recently died after a good, long run. We replaced it with the unit recommended by the AC service company we use.

The new one is struggling to keep up. Today it was over 100 in our area, with a heat index in the 110's.

The thermostat was set to 70, anticipating the heat. When we woke up this morning, the temps were fine, and the AC obviously had cooled the house well during the night. However, by mid-afternoon the house was at 78 degrees, and it remained there through the evening. The house is cooling again now that the sun has been down a while.

The house has also seemed more humid since putting in the new unit. This is the unit our service recommended as a good quality and value, based on our house size.

Did we just have an exceptionally good unit before? Is this sort of performance normal for a normal-grade air conditioner mixed with this level of heat, or should I be calling the service?

[demmiblue]

1. I just had a new unit put in last year, and have had no problems (100 degrees yesterday).

However, I don't think I can help you out too much... I usually set mine somewhere between 75-78.

Prior to the new unit, I do remember calling my heating/cooling company because the temp inside my house would not go below 78-79 degrees. They did comment that, due to the excessive heat and humidity, the temperature may not be able to go down any lower (turns out I did have issues with the unit, though). Family members did not have this issue, and I did not have this issue in the past.

I am wondering if they really did put in the appropriate air conditioner for your square footage. I guess more knowledgeable people will chime in.

Either way, I would still call the service company on such an expensive purchase.

Good luck!

:hi:


P.S. My new unit was a little more expensive than the basic unit that they said I needed. I also do not know the quality of my previous unit.

[woo me with science]

3. Thank you for responding.

Hearing your experience does help. I have been trying to get as much feedback as possible from friends and neighbors, too.

I just did a quick google search and found some AC conversations with comments to the effect that most units are designed to cool a certain number of degrees below the outside temperature...so maybe I shouldn't expect a temp. of 70 on really hot days.

I will probably still call them sometime soon (while it's still under warranty) to ask some more questions and hear what they say. I"m sure they have their hands full this week with units that are dead in this heat.

I do miss the old unit.

[demmiblue]

5. Another thought:

Is your unit running during the day as you would expect for your set temperature?

When I got my new unit, I also got my first programmable thermostat. I tried setting it on one of the energy saving programs, but soon found that it didn't suit me (too hot at times, especially when I was home during the day), so I would turn it down. Being new to the programmable thermostat, I assumed it would stay at that temperature (kind of like a permanent forced override). It didn't... I guess I should have read the manual! Needless to say, I don't use the preset features anymore.

[Capn Sunshine]

25. Another nother thought

Did you sign up with your power company for decreased amps when demand is high for a price break? Also, the newer coolants are much greener but just not as efficient at abnormally high temps I'm told.

[freshwest]

2. I'm thinking they didn't put in the right BTU for your space. They may not admit it though.

Do you have anything to cool the coils outside, some people use some water to pre-cool; and do you have ceiling fans?

They won't reduce the humidity, but it will feel cooler. I'm not sure, but I remember that when they won't cool or make as dry of air indoors it's because they calculated it wrong. Under or over in cubic footage, can't remember which one.

The air conditioner needs to work longer to draw humidity out of the air. Do you have any way to check what the new electricity usage is running, like how fast the meter head is spinning?

Anyway not an expert, but that's what I remember, it has to be working hard or it won't pull the humidity out. Good luck.

[woo me with science]

4. We haven't tried to cool the coils.

A couple of rooms have fans, but not the main ones. Thanks for the idea - I should probably be running them.

I do remember that the guy recommended this lower efficiency unit for exactly that reason: because it was better to have it running longer to remove the humidity.

It does seem to me that it is running pretty constantly. The humming is louder than with the older unit, too.

I think I will call. Thank you for giving me some things to think about when planning this conversation.

[freshwest]

12. BTW, remember that you have to block the air flow to rooms you're not using (intake and output) to..

Focus the cooling in the rooms for the heat sensitive. You've probably got another month or two of this heat (IDK where you are) to deal with so it's kinda like a siege. This would be a good season to go all raw food, haha! No cooking, just salads and fruit. Or do your cooking outside with a solar oven. (Just a couple of hints to stay cool and save money.)

[hobbit709]

6. 70°? Damn that's cold. I keep mine at 78°

How well is the house insulated and sealed? That makes a big difference. Make sure the filters are clean.

Rule of thumb. For every degree lower, expect to add 5% onto your electric bill.

[woo me with science]

9. I know. We have some hot weather-sensitives here.

Partly I have been putting it so low because it is having such a hard time keeping up in this heat wave. I want it to start out cooler than usual in the morning, so it won't rise as far in the afternoon.

But you definitely have a point about the bill. :P

[mnhtnbb]

7. Just had the a/c guy out to check unit for our rented garage apartment

and he told me that most units are designed to handle 20 degree difference--so if it's 100
outside don't expect the unit to be able to cool to 70.

70! You are going to have one whopping electric bill. We are set at 77 and I run
ceiling fans WHEN IN THE ROOM. A ceiling fan won't lower temperature, just cools
your skin to make it feel like a lower temp. Turn on when in room; turn off when you leave room.

You can expect to reduce your electric bill 6-8% for every degree you raise the thermostat
when running a/c.

[woo me with science]

10. Okay, that 20 degrees thing sounds like what I found online last night..

and is reassuring. I would hate to think the brand new unit was not doing its job.

Unfortunately, our ceiling fans are in the rooms we don't use much during the day.

Usually we keep it at about 73. I have been putting it lower at night this week, because of the rise in temp. during the day. I wanted to start out lower.

Thanks very much for responding. This is exactly the type of feedback I was looking for.

[Kaleva]

24. Outdoor temp doesn't affect the A/C though.

Except in extreme conditions. If the outdoor temp is 100 degrees and the house temp climbs to that during the day, then one has a very serious insulation problem. If the inside temp is 80 degrees or so, the the A/C ought to be putting out 60 degree air or so right at the plenum.

I don't have A/C in my home and when we had several days of very hot weather, the temp in the house remained about 78 degrees except for one upstairs bedroom that is exposed to the sun from morning till evening and that room's temp did climb to 84.

[TorchTheWitch]

8. my window units have had trouble keeping up

Normally they do a great job on only half capacity, but yesterday it was soooooooo hot I had to run them full blast and it still isn't quite enough. It's ok, but I'd be happier if it was just a wee bit cooler. I cranked up the big floor fan all the way in addition to the window units for the doggie since he's covered with hair and I'm not so it must be more uncomfortable for him than me. Usually I just have it on low in addition to the a/c, well, just because he likes the fan so much ("aaahhhhhhhhh, air blowin' on mah big belleh!"). This was also the first time since I've lived here (and I've been here for something like 6 years) that I ever needed to use the downstairs wall unit a/c just for me. The few times I've put that one on before it was really for a guest's comfort rather than mine. It's been so long since I used it at all I actually had to figure out how it worked all over again.

Moral of the story I guess is that with this ghastly heat I think any a/c unit would be struggling to keep up.

[woo me with science]

11. I think you are probably right.

Today is somewhat cooler than yesterday, and already I can see a big difference. It is a lot cooler in here than it was at this time yesterday.

Good luck with the window unit. Our last house had a bunch of window units that we used depending on which room we were in. Some of them were fantastic, and others just did not do the job.

Thanks for the response. :)

[TorchTheWitch]

16. What a difference a day makes!

Thankfully, today is a good 10 degrees or more cooler and less humid, and my window units are doing much better. Still have them running a bit higher than usual, but we've had a relatively cool summer so far this year until this heat wave from hell kicked in a few days ago. Doggie even moved away from the direct line of air from the fan, so I turned it down back to the usual lower speed. I don't need the downstairs wall unit on at all today. I don't know why, but my house stays really cool in the downstairs level all summer. The two window units upstairs are just the little $99 ones, but they do a great job of keeping the whole upstairs pretty cool. It's cooler up here now in the heat of the afternoon today with them running a little bit higher than the usual half capacity than it was last night at 3am with them running full blast.

Man, last night was hot and muggy as hell. Felt like my house got transferred into the Amazon jungle in August without my knowing it... I expected to go out in the backyard and see all kinds of dew dripping vines and ferns climbing all over the house, and I'd have to hack out a spot for the doggie to pee and poo with a machete while he hunted giant python instead of the usual carpenter bees eating the neighbor's fence.

I much prefer the window units over central air. It's WAY cheaper, and for some reason I don't get any breathing trouble or dried out mucus membranes and sinus problems like I always did when I lived in a place with central air. The window units are a bit noisy, but I rather like that sort of "white noise".

Anywho... glad to hear that you seem to be getting more sufficient cooling out of your a/c unit as well. I really think it might just be this miserable heat and damn near any kind of unit would be struggling to keep up. Thank goodness it's not so bad today.

[RebelOne]

13. I live in a mobile home with two window units.

One is in the living room and the other is in my back bedroom. Both do a very good job cooling even though the temps have been in the high 90s. In fact, yesterday, the outside thermometer read 99 degrees and it was really cool inside.

[pitohui]

14. well check the thermostat but the humidity comment is troubling...

we set our central AC on 80 degrees but it still keeps the humidity low over the entire house

i would tend to think if the house is too humid there is something wrong

[LaurenG]

15. I think something is wrong with your unit

It shouldn't be cooling "down" to 78 unless its way too small for your square footage. One of the units at work did this and it turned out it had a slow freon leak. Maybe you could have the people who installed it check it out.

[crispini]

17. If you keep it too low and run it too much

you could very well freeze up your system. If it's running all the time it could have iced over the compressor. I don't think there's any cure as AC is not designed to run all the time. I'm not sure what to tell you as I keep mine at a balmy 85 (just enough to take the edge off). Maybe consult a professional?

[Tuesday Afternoon]

18. ^this^

[Curmudgeoness]

19. Central AC! What's that? Pant pant pant.

This is the second summer in a row that temps here have been unbearable for more than a few days at a time. If this because commonplace, I will have to find out what central a/c is. Dying here!

[seabeyond]

20. my house has not been under 85 in a couple months. mine certainly does not keep up

i have fans on ceiling in every room, and mobile fans in bedroom and kitchen

granted, they say... house too big for one unit. heater does not get my back room either. but last year, i was cold all the time with AC. not this year. not once

[blueamy66]

21. You set your AC at 70???????

Holy crap, your electric bill must be freaking huge!

Here in AZ, I keep mine at 82 during the day and 80 at night...and need a blanket for the 80.

If I kept my air at 70, my bill would be over $400 a month.

[RebelOne]

22. I keep my window units at 60 or 65

and 70 at night. And my electric bill has never been over a hundred dollars. But in the winter, I use electric heaters (cause my furnace has not worked in years), and my electric bill has been astronomical.

[RebelOne]

26. Just received my new bill and it is $99.

And my two units are on all day and night at 60 to 70 degrees.

[Kaleva]

23. Your house being more humid then before is a concern

I routinely recommend under-sizing the A/C because the longer it runs, the more humidity it will extract from the air. An over-sized unit will often cool the home down fast but it wouldn't have the chance to remove the excess humidity.

Is it much more humid in your area then usual? A/C has to decrease latent heat before it can decrease sensible heat. Is there a steady stream of water coming from your condensate drain? Is your A/C running non-stop during the day and do you have an idea how much it's running during the night?

If you can, check the suction line (it's the larger copper tube) going into your outdoor unit. When the unit is running, it ought to be cold or at least very cool to the touch and any exposed copper ought to be sweating on humid days. With the A/C still running, the air being blown out the top of the outdoor unit ought to feel much hotter then the surrounding air.

A/C ought to be able to drop the return air temperature about 15-18 degrees. If your house temp is 78, then the output air from your indoor coil ought to be around 60 degrees. Does the air from your registers feel quite cool?

While the unit may be sized properly, it may have a low charge but you can only find out for sure by calling the A/C company back as they have the gauges to check the pressures.

[erinlough]

27. Just for information

I just put in a geothermal unit. The price is about double the cost of a traditional furnace/air conditioner, but the savings are real. My bill is 1/2 what it was with a traditional furnace and the heat and air conditioning is very comfortable. If anyone wants more info let me know, but I wish I had done this a long time ago.