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Started By
Message
New House AC question
Posted on 8/10/23 at 9:09 am
Posted on 8/10/23 at 9:09 am
First summer in our new construction house and my units are having trouble keeping my bedrooms cold.
Kids bedrooms are on west side of the house and master is on the east. If I keep both units on 72 all day the kids bedrooms get up to 75-76 in late afternoon when sun is on that side. Unit is running almost 20 hours a day with thermostat on 72 at all times.
Mater side runs about 16 hours a day of left on 72.
South east Louisiana. AC company says units are charged up and clean.
Am I expecting too much out of a brand new house and AC in this heat thinking it should keep up?
Kids bedrooms are on west side of the house and master is on the east. If I keep both units on 72 all day the kids bedrooms get up to 75-76 in late afternoon when sun is on that side. Unit is running almost 20 hours a day with thermostat on 72 at all times.
Mater side runs about 16 hours a day of left on 72.
South east Louisiana. AC company says units are charged up and clean.
Am I expecting too much out of a brand new house and AC in this heat thinking it should keep up?
14
Posted on 8/10/23 at 9:11 am to Simon Gruber
Are the units undersized? What type of insulation?
Posted on 8/10/23 at 9:14 am to wickowick
I don’t believe so. 2650sq/ft living and we have 2 3 ton units.
Regular fiberglass insulation.
Regular fiberglass insulation.
Posted on 8/10/23 at 10:02 am to Simon Gruber
I am about to have my AC guy check my freon again. Mine are performing about like yours.
Posted on 8/10/23 at 10:11 am to Simon Gruber
Friend,
What is the outdoor temperature when your temperature rises to 76 indoors? Most A/C systems are designed for a delta temperature of 20-25 degrees. That means that if it is 100 degrees outside, your A/C is designed to keep your inside at 75-80 degrees.
That is why it is imperative for your units' health that you do not keep the thermostat at 72 if the temperature outside you are trying to reduce is 100. Running the system all day like you are reduces your A/C system's lifespan, will create large electricity bills, and is not good on the electrical grid.
It is not a popular opinion here, but set your thermostat higher. I would never recommend setting it at a greater than 20 degree difference from the outside temperature.
Yours,
TulaneLSU
What is the outdoor temperature when your temperature rises to 76 indoors? Most A/C systems are designed for a delta temperature of 20-25 degrees. That means that if it is 100 degrees outside, your A/C is designed to keep your inside at 75-80 degrees.
That is why it is imperative for your units' health that you do not keep the thermostat at 72 if the temperature outside you are trying to reduce is 100. Running the system all day like you are reduces your A/C system's lifespan, will create large electricity bills, and is not good on the electrical grid.
It is not a popular opinion here, but set your thermostat higher. I would never recommend setting it at a greater than 20 degree difference from the outside temperature.
Yours,
TulaneLSU
Posted on 8/10/23 at 10:22 am to Simon Gruber
quote:
75-76 in late afternoon
This is not abnormal on this heat, keep ceiling fans going at a higher rate in affected areas
TulaneLSU is correct on the expectations of AC units in this heat
Posted on 8/10/23 at 10:46 am to Simon Gruber
I replaced my units in my current house as soon as I moved in. I am getting very similar results as you during this wave. I really don't think what you're experiencing is abnormal.
Posted on 8/10/23 at 10:55 am to Simon Gruber
What's the thermostat showing for actual temp when the kids rooms are 75-76? Is it showing 72 for actual temp or is it above?
Also, how is it in other rooms served by the kids bedrooms unit? You could check the balancing dampers that serve each duct runout. Make sure they're fully open to the kids bedroom. If they are, you could try pinching back on dampers to areas that are comfortable. This would send more air to the kids rooms theoretically. You're still limited by duct size though. This can be tricky though, because different areas need more air at different times of day. Need plenty of air in the den for instance when everyone is awake vs when everyone is sleeping, etc. Usually its a happy medium.
One last thing. 6 tons for 2,600 sq ft. is fine. Its average for today's typical house. Its all about how well the house is insulated though. With how hot its been, the units very well just might not be able to keep up. One thing you you can do as more of an observational experiment to see how well your house is insulated is to turn off the a/c when its hot outside. The faster it warms up, the more heat is getting in.
Also, how is it in other rooms served by the kids bedrooms unit? You could check the balancing dampers that serve each duct runout. Make sure they're fully open to the kids bedroom. If they are, you could try pinching back on dampers to areas that are comfortable. This would send more air to the kids rooms theoretically. You're still limited by duct size though. This can be tricky though, because different areas need more air at different times of day. Need plenty of air in the den for instance when everyone is awake vs when everyone is sleeping, etc. Usually its a happy medium.
One last thing. 6 tons for 2,600 sq ft. is fine. Its average for today's typical house. Its all about how well the house is insulated though. With how hot its been, the units very well just might not be able to keep up. One thing you you can do as more of an observational experiment to see how well your house is insulated is to turn off the a/c when its hot outside. The faster it warms up, the more heat is getting in.
Posted on 8/10/23 at 11:06 am to brickyard
Would it matter at all if the AHU / ducts are in the attic? (slab construction)
Posted on 8/10/23 at 11:09 am to Simon Gruber
I mean this in the nicest way possible but I wouldn't judge your unit based off 102 degree temps. 72 is way too low unless your house is perfectly insulated.
Posted on 8/10/23 at 11:13 am to brickyard
quote:
What's the thermostat showing for actual temp when the kids rooms are 75-76? Is it showing 72 for actual temp or is it above? Also, how is it in other rooms served by the kids bedrooms unit? You could check the balancing dampers that serve each duct runout. Make sure they're fully open to the kids bedroom. If they are, you could try pinching back on dampers to areas that are comfortable. This would send more air to the kids rooms theoretically. You're still limited by duct size though. This can be tricky though, because different areas need more air at different times of day. Need plenty of air in the den for instance when everyone is awake vs when everyone is sleeping, etc. Usually its a happy medium.
I have sensors in the bedrooms to control AC based off the temp in the room instead of at thermostats.
The living area and kitchen in the middle of the house is always 3-4 degrees cooler then bedrooms that are on either side of house.
Posted on 8/10/23 at 11:50 am to Simon Gruber
Well, you have plenty of tonnage.
I would have to be there to diagnose.
Some things i can think of that are common in St Tamm, are :
1) cold air boxes too close to bedroom door, leaving the rest of the room unswept. When cold air exits the ceiling grille, it is being pulled to the return air. So it never sweeps the room.
2) AC guy might have done a manual J, but perhaps did not calculate each room. ( not enough air {duct size} )
3) excessive length flex duct, flex duct not pulled ( expansion) before connecting.
4) pressure boxes-
5) insufficient attic ventilation
6) not the best matching of indoor / outdoor units. Improperly fine tuned from day one.
I would have to be there to diagnose.
Some things i can think of that are common in St Tamm, are :
1) cold air boxes too close to bedroom door, leaving the rest of the room unswept. When cold air exits the ceiling grille, it is being pulled to the return air. So it never sweeps the room.
2) AC guy might have done a manual J, but perhaps did not calculate each room. ( not enough air {duct size} )
3) excessive length flex duct, flex duct not pulled ( expansion) before connecting.
4) pressure boxes-
5) insufficient attic ventilation
6) not the best matching of indoor / outdoor units. Improperly fine tuned from day one.
This post was edited on 8/10/23 at 12:03 pm
Posted on 8/10/23 at 12:04 pm to EF Hutton
Ok so you replied while i was typing the other paragraph.
So you have control dampers for each bedroom duct ?
If you are Zoned, I’m out of here. Not my cup of tea.
So you have control dampers for each bedroom duct ?
If you are Zoned, I’m out of here. Not my cup of tea.
This post was edited on 8/10/23 at 12:06 pm
Posted on 8/10/23 at 12:07 pm to yomamak
quote:
I mean this in the nicest way possible but I wouldn't judge your unit based off 102 degree temps. 72 is way too low unless your house is perfectly insulated.
I can understand this, but after the sun goes down and temperatures outside drop to around 80-85 should it take 6 plus hours for my bedroom to go from 75/76 to 72?
Posted on 8/10/23 at 12:11 pm to EF Hutton
quote:
you have control dampers for each bedroom duct ? If you are Zoned, I’m out of here. Not my cup of tea.
No it’s not zoned. I just have nest thermostats with temperature sensors in multiple rooms.
The return air is not right next to the bedrooms with issues. I’ve also tried leaving doors open and it made no difference.
Posted on 8/10/23 at 12:14 pm to Simon Gruber
Friend,
The temperature in New Orleans did not drop below 85 until 4AM this morning. This is the hottest stretch of weather in recorded New Orleans history. Tonight’s projected low is 83-85.
Yours,
TulaneLSU
The temperature in New Orleans did not drop below 85 until 4AM this morning. This is the hottest stretch of weather in recorded New Orleans history. Tonight’s projected low is 83-85.
Yours,
TulaneLSU
Posted on 8/10/23 at 12:46 pm to Simon Gruber
quote:
The living area and kitchen in the middle of the house is always 3-4 degrees cooler then bedrooms that are on either side of house.
I would go up in the attic and see what the manual damper situation looks like. You should see some kind of handle by each tap that you can adjust. This would be an easy way to see if you can improve things. Check and make sure you can't open any more for the ones serving the kids bedrooms. If all the way open, you can try pinching back in the interior area where you said is comfortable. You can be in the attic adjusting things and have your wife on a ladder in the kids bedroom with her hand up to the grille. She can yell at you if she feels any more air coming out. Do this with caution though. You don't want to pinch back too much anywhere and starve the unit for air. That would be a lot bigger problem than what you have now. I'm just talking about slight adjustments.
Posted on 8/10/23 at 2:05 pm to Simon Gruber
HVAC Design temperature for much of the Deep South is 92-94F, which means if your unit is properly sized it can maintain a set point temperature of 75 F at those outside temperatures. When temperatures are in the high 90s/low 100s, your temperature will likely creep above 75 F much of the afternoon early evening, much less maintain a temperature of 72 F. Though it sucks for this heat wave, the good news is that for the other 97% days of the year you are not going to have an oversized system, which would likely be problematic in terms of home comfort, operating expense, and HVAC operational life.
TL:TR - your units are very likely properly sized, according to manual J heat load calculations. Your HVAC company is shooting straight with you.
TL:TR - your units are very likely properly sized, according to manual J heat load calculations. Your HVAC company is shooting straight with you.
Posted on 8/10/23 at 2:26 pm to Simon Gruber
quote:
can understand this, but after the sun goes down and temperatures outside drop to around 80-85 should it take 6 plus hours for my bedroom to go from 75/76 to 72?
Your attic temperature might be as high as 130 F into late afternoon/early evening , you probably have R-8 insulated ducts running though the attic that are going to pick up attic heat, so the temperature in the supply plenum maybe substantially cooler than the temperature exiting your room supply registers. It’s important to remember that ductwork, sized properly to the tonnage, is every bit as important in home comfort as the equipment that cools and heat.
6 hours though does sound like a fairly long time time though for temperature drop from 75/76 to 72 in the evening - might the normal in this heat, but not sure.
Posted on 8/10/23 at 2:34 pm to Simon Gruber
My AC guy just left. He added a little freon for a known leak that we will address this fall/winter.
He got up at 4 AM to install two new units. Times like these I'm glad I am not crawling in attics and just in an uncomfortable 76-78 degree home.
He said that many of his calls are checking units and telling people that they're at peak performance...peddling as fast as they can.
He got up at 4 AM to install two new units. Times like these I'm glad I am not crawling in attics and just in an uncomfortable 76-78 degree home.
He said that many of his calls are checking units and telling people that they're at peak performance...peddling as fast as they can.
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