Hello all, new to this forum. I have a home built in 2006, just shy of 2100SF. My AC unit is 3.5 tom 13 SEER, problem is, in the summer, my house will get up to 80 degrees in the afternoon and forget about turning on the oven! It will not begin to cool off until somewhere in the neighborhood of about 8 PM, I have had several different AC companies come out and look at the unit and am told it is sized properly and running as advertised. Electric bill is routinely 300/month. Could someone please direct me as to what to look at next? This has been going on for years. I was deployed to Afghanistan and where it was 130 degrees outside, my tent was 80 degrees inside! Hard to believe they have better technology that we do. Please help! Thank you

 

Welcome to the forums and thank you for your service!

Check in the attic for both voids or settled insulation and obstructed ventilation. You should have soffit vents [intake] and then vents at/near the ridge or gable ends to exhaust some of the hot attic air.

 

Assume you are taking the steps to keep the house closed up during the day to minimize the heat load that the AC is being asked to cool.

If the system is properly sized as all the companies have stated what are they saying is the reason it's not functioning properly?

 

I work in South Florida. From what I've seen over the years is no matter what someone says is big enough, no matter what fancy load calculations they did, if you don't have a system sized to 500 square feet per ton, you will often have the problem you are having. 2100 square feet should be at least 4 Tons, and since there is no 4 and a half Ton units, 5 Tons is also an option. The heat and humidity in the Florida summer leads to me getting several calls a week with the same problem you are having. What you can do is make sure you have the proper insulation installed in the attic. Seal off any potential outside air leaks. Also check for any leaking ductwork in the attic.

 

Also look at window placement/orientation. If you have windows facing east/west you could be getting significant heat from the sun beating in, especially the west side from afternoon sun. We were just at our daughter's in Brevard County over the holiday weekend and I installed reflective window tint on the west-facing sliding glass doors out the back of her bedroom./ She called me the other day to tell me there was a noticeable difference in temperature.

$300/month! Yikes!. Ours runs about half that on the FPL averaging plan, i.e. about $1800/year.

 

If you find a solution..please let me know! We are in SW Florida and have the same issue. (It's been going on for 4 years...this year it's driving me crazy!!) We had an ac company out and our supply duct was replaced with a 16 inch duct and he claims that our coil has a leak but it's on backorder right now...I'm hoping that by doing both it will help some. My house cools great at night and early am
..around noon the temp begins to rise and doesn't stop until after 6..then it decreases. We are also considering having tint installed. We have no leaks in our ductwork.

 

What size unit? 16" round is good for around 1,000-1,200 CFM, depending on if its flex or metal duct. Which is enough air for up to 3 tons capacity

 

I know nothing about size of A/C but have lived in both Fl and AZ and if you can lower humidity it will feel cooler. Here in NC I can drop temp one degree and will lower humidity and make house comfortable.

 

Hard to tell what the size of the supply is as it seems like it is wrapped in insulation, i can tell that it is a flexible line however. I have heard any number of reasons why the unit cannot cool the house but no one has agreed with what I think and that is the unit is too small. I have heard the ducting is too small not allowing the air to drop down through the diffusers and at the end of the run it is shaped incorrectly allowing warmer air to double back into the cooler air, they have said I cannot expect any more that a 20 degree split from the outside to inside temperature, one fella wanted to install some sort of blower attachment to the unit, any your lad told me I need to shade my outside unit (cant remember the name of that particular unit), most tell me they cant find anything wrong. My houses faces east and I have a sliding glass door on the west side which I have applied reflective tint to as well as bolting a fabric gazebo to the concrete patio to shade the door. I pulled all the paperwork from the original installer and as I was looking through the manual J load calculation, I could not find anywhere where the sliding glass door, the window in my front door or the window above my front door were accounted for. I have an insulation contractor coming out this week to inspect his end of the deal and will move forward from there. If I were to replace my unit with a 5 ton, any idea of what the cost might be, I am assuming the ducting will need to be replaced as well. Also, would I be running the risk of the unit short cycling if I up size to a 5 ton? Thanks for everything thus far.

 

The unit being too small was my first non professional thought but if that was the case wouldn't the techs have said something ?? That is a costly fix

 

I dunno...doesn't seem THAT small to me. My place in VA was right at 2150, 2 story built in 1990 (energy star for the time), 3 ton 10 SEER worked fine except for the loft area and that was just a convection issue. Our temps were pretty darn hot and humid also. Mid 90's common in summer. Think my highest bill then was around $250-275? But also had electric clothes dryer, spa out back, and used the DW constantly. Prices have gone nowhere but up of course. That might be $450 now.

Is the OP using a setback on his stat during the day or is it a constant and the unit just can't keep up even though it runs all afternoon?

 

Got any plants for shade?
Is the house 1 story or 2 story?
What color is the roof?
Which direction does the long side of the house face?
Any porches or awnings?


Wild guess- 1 story house, black roof, no shade, lots of windows, wide side faces due south, AC unit is sitting in the sun?

 

I tried using a programmable thermostat to have the temp increase to 78 while we were gone and come down to 75 when we returned, problem was, when we returned, the unit was not able to get the temp down to 75 until sometime after 8 pm or later.

 

1 story house, black roof, tree in the corner of the house but doesn't provide much shade, longer side faces east, ac unit is on the North side of the house and yes it is in the sun for a good amount of the day, front door faces east with the sliding glass doors facing west, I installed a large gazebo on the back patio to shade the sliding glass door

 

I installed blinds on every window in the house and keep them closed 24/7, reflective tape installed on sliding glass door, doors remained closed unless absolutely necessary, thermal curtains hung in front of sliding glass door as well

 

The average A/C unit according to national testing is only 59% efficient...!
Everything needs to be checked, plus actual Btu/hr delivered to the rooms.

Check the 'indoor' humidity level & the temp-drop split & list it here...!

Does the system have LOW AIRFLOW TO THE ROOMS?

You always want the highest static pressure on the supply-side at the diffusers to the rooms, while at the same time, as much as possible, reducing as much ‘resistance’ or pressure drops in the rest of the supply-side, which also includes low pressure drop fittings in all of the supply side ductwork to optimize pressure at the supply-side diffusers.

You want to greatly reduce the airflow ‘resistance’ on the return-side to produce more static pressure and CFM airflow on the supply-side. Any airflow needlessly restricted on the Return-Air side reduces the air availability to the blower wheel blades, which reduces the blower wheel performance and the increase the airflow through the evaporator coil and to & from all the rooms.

You should also always have branch duct dampers installed so you can adjust the airflow balance, for example, to 2nd floor areas, where that is a problem.

Reducing all the return air ‘resistance’ possible on the return-side making any ductwork optimally as large as possible, plus return-air filter areas as large as possible to reduce all return-side resistance and pressure drops possible, which will optimize supply-air CFM both to and from the rooms.