AC cannot cool below 78F

57 Replies

Hi BPers,

We have a house that was built in 1984 in Texas. The tenant claims that the AC cannot cool down below 78 F. The outside temperature was around 100 F when they claim this. The AC is running all the time. The AC man says that its common for this type of house and it only cools down to 78% of outside temperature.  The tenant claims that because the AC cannot cool below 78 F, its a safety issue for the tenant. The tenant age is in their 70s.How do i handle the tenant's complain ?

James and Shanti

Relay what the AC expert said.  If the tenant continues to complain, offer to release them from your lease and allow them to move before the first of the month (or the first of the following month) if they so choose.

James and Shanti Kandasamy - I think you need a new AC man, and possibly a new AC. I am in SC right now where it gets 100+ on a daily basis. We can get our place down into the low 70's easily. I would be complaining if I were your tenants too. 78 degrees is simply unacceptable. Get ready to shell out $$$$ if you need a new AC/heat pump. 

The house I grew up in wouldn't cool below 78 when it got really hot, really couldn't go more than 20 degrees below the exterior.  It sucked, but we lived with it for years.  That condenser was just too small for that house when it got that hot.

If your climate gets that hot for any length of time, you probably need a bigger unit.  

You can also check the attic.  If there is poor ventilation, that thing could be a 180 degrees and radiating heat into the house.   Its possible you can get attic ventilators and more insulation and be fine.  Some HVAC guys like to staple the runs to the rafters because it looks neat and tidy, but that means you are running your cold air through the hottest part of the house.  Very possible just dropping the air ducts to the floor, blowing some insulation and putting in a power attic ventilator will get you another 10 degrees.   Depends on the house construction, of course, but those things work.

you may need a more powerful unit, better insulation, attic fan, windows, etc.  Is this a new problem?  Some builders do not install the proper unit from day 1

I guess I'm cheap...I set the AC in my own house to about 81-82 degrees. 78 would be cold. Lol

17 degrees lower than outside temp, general rule of thumb.  so if its 95 degrees outside, chances are it wont go below 78 until it cools down outside.

I would think that you have a real issue with the AC unit or the house simply not being airtight enough or possibly an insulation issue. However, I would verify this by visiting the property in the middle of a hot day and running the AC. See if the house is cooling with all doors and windows closed, it should cool down in a couple of hours even on a hot day. I have had similar issues with tenants only to find out that the literally leave their front door open for short periods of time, kids running in and out.

As a Florida resident we have to deal with 100 degree temperatures and 100% humidity on a regular basis. Have your AC company actually run the calculations on your house square footage and determine if your unit is big enough. If it is, then the house is leaking somewhere, either through the windows, doors, or attic space. 

In my opinion, it is not unreasonable to have to provide your tenant with a house that can cool off to 72 degrees. Good luck and hopefully this does not cost you a bundle to fix!

I have been through this. My old house years back had 2 units but no matter what we did to it once it hit a certain temp outside it would not go below 78 inside. I am warm blooded so I can't stand it and was miserable.

The A/C guys said sometime the older models just can't keep up when it gets really hot. You can have an under sized unit or even an oversized unit.

Weather patterns have changed over the decades. So it's possible when it was installed the highest temps annually were 87. Fast forward 10 years later and you have an older unit and top temps are 95 and it can't keep up.

Make sure your thermostats are working properly as well. If a temp meter in house says 82 but thermostat is reading 78 then something is off. Thermo is generally not supposed to be off by more than 2 degrees. Digital are better than the old mercury ones.

The outside coils might need cleaning. If you can put a dollar up against it and there is no suction then it is not circulating properly usually. You can take a dollar up to your ceiling or house vents to check for air flow. There is velocity of the air and also the temp of the air. So if all the room/ hall vents are blowing and good velocity but the air is not cool enough or is warm you have a cooling issue. Need to check if freeon is fully charged.

I moved to my new house about 3 years ago and the A/C blows me out of the water keeping at 72 when it is 99 outside here in GA.  

What "type of house" is it that cannot cool down below 78% of the outside temperature?  Is it a 2 story?  They are usually hot upstairs unless the have 2 units, 1 for each floor.  An older house may need more insulation in the attic or more roof vents to let the hot air escape.  Sizing an AC can be tricky.  If it's too small then it will not keep up on the hot days,  but if it's too big then it will cool the house off too quickly, leaving it still humid.   It's not uncommon for a properly sized AC to run nonstop on the hottest days of the year, but I would still expect it to get cooler than 78 degrees.  I would definitely be getting a second opinion.  See if the utility company offers an efficiency inspection.  Some do for free or really cheap.   

Another thought is what kind of thermostat do you have.  If it is programmable with different temperatures settings for different times of the day, make sure they're not setting the nighttime or morning temperature to high.  Some people do that thinking they are saving money.  But once the temperature starts to go up outside the AC can not keep up if the house temp was already high to start with.   

You have had a lot of great post already.  I did ac repair for a few years and I have been a handy man for around 8.  You are going to have to update your ac most likely.  I would look hard to find a good ac company around town and ask them to check your duck work.  If it is old you could be cooling your attic space which nobody wants to do.  Also make the last ac technician did a proper cleaning of the inside and outside system.  Also if you have an attic fan that is not working that could cause the house to be hotter than normal.  Most likely you will need a new ac system and a new ac duct system but I would get the new ac system now and a new duct system in the winter time.  Also one last thing I would get 3 different contractors estimates on replacing the ac and duct system they should do this for free.  Good luck

Also one last thing when you replace just one part of the system you run the risk of the whole system not working properly.   If the outside condenser unit is not meant to work with the air handler or vs. versa you can run into issues with the unit not cooling at a 100%.    

I did a flip recently where we replaced windows, going from single pane aluminum to double pane vinyl. It made a massive change in how "tight" the house felt. If the AC appears to be making a proper temperature exchange, look at doors, windows, and insulation in the attic. Is your outside unit in the afternoon sun? If so, consider a sunshade as a temporary fix. Down here the sun can be a real booger at making things much hotter than ambient. Lastly, add a window unit or two in select locations to appease the tenant. Maybe the whole house can't get to 72, but a room or two can alleviate that "safety" issue.

A 20 degree differential is pretty common , .  My house cools fine until we get over 95 outside . I am lucky to get 75 degrees inside . Why ?  After 3 pm the front of my house gets dirrect sun in the hottest part of the day , my house was built in 1969 , the AC unit is 10 years old and sized correctly .  I also have a brick front , and it sucks up the heat  ( great in winter)  My front door in the late afternoon , if you touch it you will burn your hand .

It was worse until I added a vent fan in the attic and I tinted the front windows , I also have a window unit in 1 bedroom so I could balance the ductwork to send more to the living areas. 

Grab  a window unit to help things out for them .

I'd personally, replace the condenser.  But, window A/C's can help ease them during the summer months at a lesser price......short term.

I have 2 condensers in my house and the upstairs one is going.  I pumped it with refrigerant but it's still not as good as the other one.  My HVAC guy puts a temp. gauge on the vents.  One unit blows in the low 60 degree range, and the broken unit can only get down to 72 degrees.  That's the temp right out of the duct, not the room temp....

I've been told this by many an AC guy...apparently none of them understand the basic laws of thermodynamics (turn your house into a thermos and you could get it much lower than that).  What I have found is that in "general", for much of the south, AC units are not typically sized appropriately to be able to cool more than about 20 degrees ambient outdoor temperature.  This is because contractors tend to size ACs based on square footage, which is a ludicrous way to size a system that's output is measured in cubic feet per minute.  To get an accurate AC size, you have to consider the amount of cubic space, whether or not you're in direct sunlight, how the attic is vented, etc.

Here are some things to consider, I tend to focus on economic fixes:

1. A bigger unit may not help.  A unit that is sized too large for the amount of cubic space in your home will just cycle on and off more often, and that can be bad for the mechanical parts.  It also is bad for the air.  If the AC doesn't stay on long enough, it does not have a chance to remove moisture from the air.  Dry heat "feels" much better than wet heat.  I am EXTREMELY sensitive to humidity.  I can be in 80 degree house and feel fine if its dry.  A 74 degree house with high humidity makes me start to sweat.  Having the fan "on" instead of "auto" helps a bit with this in my house.  

2. Your attic may be working against you.  

2a. f the temperature in your attic is more than about 120, you have a ventilation problem (Yanks would say more than 110 and you have an issue, but this is the south we're talking about).  You want your attic to pull fresh air from outside (low part of roof) and vent out along the top (either gable vents, or ridge vents or 'turtle' vents).  This can be a really cheap fix for an "AC" problem.  There's a good article at Building Science that covers how much square footage of vents you need in the eaves vs. near the top of your roofline.  Vents in the wrong place, or not enough in the correct place (low vs. high) can cause issues.

2b. Where are the ducts?  If the ducts are in the attic, you'll be battling temperature from the start.  Duct insulation may help somewhat.

2c. What type of insulation is in the attic?  If you don't have a good thermal barrier between the attic and the ceiling, you essentially have a a heating element along the top of the living space that is eating away at your cooler air.  Adding more insulation would help and cost much less than new windows/new AC.

3. Make sure you are airtight.  If the unit is sized appropriately for the house, then consider air leaks.  Windows, doors, rim joists, etc. can all be sealed pretty easily.  Whenever I buy a rental, the first thing I do is replace weather stripping.

4. How are your windows?  If they're older aluminum/contractor grade they probably aren't very energy efficient.  Lowe's sells heat barrier film by Gila that worked pretty well for me.  Much cheaper than new windows.  Thermal curtains can also help with this.  But realize air leaks can cause much more thermal increase than radiation through the windows can.

I am a bit pragmatic about how much to spend on a rental for it to become more energy efficient.  There are other things you could do (add wall insulation, buy a bigger unit, etc.), but I didn't detail those because to me they cost too much to put in a rental.   I will absolutely pay for window film, blow in insulation in the attic, passive attic ventilation and new weather stripping, because I do most of that myself and its not hard.  But this is the south, its hot, and I will not put in new windows or a new AC (please note, I have Class C rentals, YMMV if you want to keep class A renters).  I had one tenant who liked to set the AC at 70 and the house was a 1967 energy nightmare.  I told her too bad, I was not putting in new windows or a new unit since it could reliably cool to 78, but I would let her break the lease if she wanted (she passed).

My personal house cannot cool below 78 when it hits 3 digits.  I have crappy attic insulation, crappy windows, and my house leaks like a sieve.  But 78 is good enough for me as long as the humidity stays low.  Eventually I will get around to all the energy projects on my own house....

Window units are cheap.  Get a couple and help them out until you can get a good HVAC company to fix the problem.  Make sure the attic is well ventilated.

While the system might be a problem I bet they are "old school" and turning the thermostat up and down. 

Those that have suggested that you can not get a the temp. more than 17 degrees below the outside temp. need to get a new HVAC company also.  That's saying at 100 degrees outside the inside temp would only get to 83?  Nada........

I'm live in Georgia in a house that is 34 years old and I'm low to mid 70 inside all summer long.  I can't understand you guys that like it at 78.

I had the same problem with a rental in San Antonio. I had at least four A/C contractors out that could not pinpoint the problem. Then I spent some time online and found that it was likely the insulation/ventilation.

I spent a couple of hours in the attic with my brother in law blowing some insulation into the space there, and have not had an issue since then. I did look at the ventilation as well, but this house appeared to be adequately ventilated.

There have been a lot of great suggestions and I second getting window units as a temporary measure until you can get to the actual problem. I'd also suggest monitoring the heat and humidity levels in various parts of the house. You can buy something that measures those in garden centers and big box stores. Maybe those can help pin point the problem.

I'm a Florida native and my parents seemed not to believe in AC when i was growing up, so I keep my house at 80, sometimes 78 when I want to be spoiled or when turning on the oven.