We're in PA and have a cape cod style house that runs hot on the second floor. What has worked primarily for us, is I set the programmable thermostat controller to run the HVAC fan on low (instead of auto) an hour before we go to bed so that the air upstairs and throughout the house mixes. I also shut all the doors upstairs as I feel like this helps, although I don't know if it actually does. We also have ceiling fans in the upstairs bedrooms which helps to feel cooler, although I feel like we mostly use them at the start of summer on those first few hot days. Good luck.

This isn't uncommon and the reason is always the same, inept contractors. IDK which but the one that installed unit or the one you have trying to fix it don't know their business. If you have the desire and determination, I'll attempt walking you though tests to get some idea of why this is. No silver bullet , just hit and sweaty work inside attic.

If "power vents in secound floor" means supply vent booster fans, that's about all you can do unless you boost return. I wouldn't go to extremes with present system, I'd add a mini-split upstairs.

2nd floors invariably have a higher heat gain than first floors - if for no other reason than the hot air from downstairs travels............... up! Assuming your ductwork is adequate, zoning could help, provided it is done correctly (of which 99% of zoning systems are not). First of all, make sure the dampers in your ductwork are set for Summer (more cool air going upstairs) in the summer, and Winter (more warm air going downstairs) in the winter. If this doesn't work, try to find someone who knows what they are doing with zoning. And if you can't find someone that gives you a warm-and-fuzzy on zoning, get a minisplit and/or ceiling fans.

" My AC unit has been checked several times and is large enough and functioning correctly. "

Seems an oxymoron is afoot. lol"

Hi, Genevieve,

" I have a 1,600 sq foot home and cannot keep the second floor cool. My AC unit has been checked several times and is large enough and functioning correctly."

This suggests that the folks making the assessment have defined the "system" boundaries to include only your evaporator and condenser units. They may indeed be operating as designed. However, the entire HVAC "system" includes the evaporator, the condenser, the duct work, the blower, and the controls which condition and distribute conditioned air to the various living spaces. Your "system" is not maintaining comfortable conditions on the 2nd floor, so, by definition, it is not working correctly.

I infer from your description that you have a single air handler distributing air to both the 1st floor and 2nd floor without zoning, and which is controlled by a single thermostat. That's a tall order when the heating and cooling loads can vary a lot--both during the course of a single day and seasonally. Here are two suggestions to improve comfort without a major overhaul or adding an additional system(s.):

1. There should be balancing dampers installed which allow you to vary the air flow to the 1st floor and 2nd floor (sktn77a refers to them in their post above.) Adjusting them to increase the air flow to the 2nd floor and decrease the air flow to the 1st floor should improve comfort on the 2nd floor. You may need to adjust them seasonally.

2. If the system is controlled by a single thermostat located on the 1st floor, it has no idea what the temperature is on the 2nd floor. You can swap the thermostat for one which allows inputs from remote sensors and install one or more remote temperature sensors on the 2nd floor. This would allow you to control the system based on 1st floor conditions when occupants are mainly on the 1st floor, and based on 2nd floor conditions when occupants are mainly on the 2nd floor. That option will likely result in over-cooling and over-heating of one level, but that's the penalty without zoning.

Well said.

You do not have enough detail to understand the issue and offer advice. Otherwise you are just guessing and throwing money at things unless you try to zero in on a predominant reason:

• "Checking" the HVAC appliances to make sure they are functioning is only a small part of the equation. It may be designed/installed insufficiently, say you only have a single return in the hallway. Or say flex duct in the attic is pinched.
• "Reinsulating the attic" without detail may not be sufficient. The R value, type, location of insulation, and climate has an effect on comfort and attic performance.
• Just noting you have soffit and ridge vents may not be sufficient. Say, inadequate total amount of passive venting. Say, soffit vents are actually perforated panels installed over old plywood with no actual holes in the plywood. Say, a ridge vent in a short length hip roof that doesn't provide enough high venting.
• The style of house and 2nd floor design may have an effect. Say a 1/2 story, over a garage, or a two story Living Room with all south/west facing windows open to the 2nd floor.

In any case, a solar or electrically powered attic exhaust fan does not "fix" what most laypersons think they need to fix - they can actually cause harm to your house by creating condensation and mold in the attic. An attic's temperature is naturally going to be anywhere from 20d-40d higher than outside. The issue with comfort below is that you pinpoint everything that contributes to that comfort to separate you from a hot attic.

Ordinarily I'd agree with everything you said 3onthetree but people come to Houzz for silver bullets, not a list of things they can do to help diagnois/solve their problems.

"Ask not what you can do for yourself".

The "problem" you're describing is common to all multistory houses. ALL. Look up "stack effect" to understand why.

The only real solution that works is to have two separate heating/cooling systems for the house. Each with its own ducting not connected to the other. One for the upstairs, one for the downstairs. If the upstairs is hotter, turn it on or set it to a lower temperature than the one for downstairs. Without separate systems, in one of my homes, I need to run the A/C long enough for the upstairs to reach the desired temp, as at night before bedtime. Doing so makes the downstairs colder than we prefer but that's the solution.

Zoning rarely works well or reliably.

@klem1:

"If you have the desire and determination, I'll attempt walking you though tests to get some idea of why this is. No silver bullet , just hit and sweaty work inside attic."

Also @klem1:

"people come to Houzz for silver bullets, not a list of things they can do to help diagnois/solve their problems."