That's a beautiful staircase, very nice.

The fans in reverse may help. There is no harm in trying it. Do you have a return vent in the basement? You can also try running the fan from the thermostat. If you have a variable speed furnace or air handler you could set it to the lowest speed. This may raise the humidity level in the house depending on your location.

We are in Colorado so raising humidity is NOT ever a problem. Thanks for the input.

It is not likely to help. The basement is where you will most easily detect a change since that has a stable temperature. Put a thermometer down there. Turn off the AC and get a stable temp. Then turn on the fans (not AC) and see what happens.

Are you in a radon area?

We don't have Radon, we had it checked before purchasing the house and it was fine.

Good idea, we could start with one fan and see what happens.

Warm air rises, cool air falls. It's not unusual for architectural features, created for appearances-sake only, to cause problems with other aspects of a structure. You've got a superhighway (an attractive one) linking the bottom and top of a multi-story house, air is going to move.

Separate systems top and bottom might help deal with it somewhat, but the physics and the pathway won't change. Opening windows to create an upflow might be feasible at some times of the year but doing that defeats having AC, and won't help at all in the winter.

Snidely, could ceiling fans running in reverse on the top floor pull some air up? We don't want to install another AC unit.

I don't think ceiling fans are going to be of any use. An upward blowing ceiling fan in the stairwell isn't going to be drawing air from more than a few feet away. The sucked up air will hit the ceiling a few feet above it, warm the air more (likely the ceiling is warmer than the house because of a hot attic in the summer time), and then spill off downward from the ceiling. If you switch directions, the stream off a downward blowing fan is going to be mostly blocked by the landing and the stair treads. And through it all, warm air will rise and cold air will fall, the problem is caused by an open stairwell top to bottom and only one system to handle three floors with different requirements.

I wonder if better balancing of supplies or changes to returns would do much ? If you had a separate system upstairs to handle the heat that's gonna rise no matter what, you could use a milder setting for the first two levels so your basement wouldn't be so cold.

Does this happen in the winter too?

Thanks for your help Snidely. The basement is cold all year long (even in the back to back over 100 degree days we've had this week), but the main level and upper floor is comfortable in the winter and not terrible in the summer, just somewhat warmer. However, the vent in my basement office does not seem to have any heat coming out of it, the contractor who finished the basement admitted a problem, but never came back to fix it, I suppose we will need to hire someone else to fix that issue. The rest of the basement is slightly cooler in winter than the rest of the house but not dramatically so.

How about a whole house fan? We had one in our last house which was much bigger than this house and had the opposite problem in a way, each floor was very closed off. I didn't want one here because the area we should install it in is visible from the front door, and they are not attractive. However, in the last house I would open the basement door and turn the attic fan on to pull the cool air up.

This house is about 750 ft in the basement, 1200 on the main floor and 1200 on the upper level.

I think whole house fans have fallen out of favor for a few reasons. One of which is, you essentially throw all your air/wall sealing and attic insulation efforts and money out the window when you install a leaky louvered opening in the ceiling of your house/floor of the attic. Because of attic venting, that opens the interior of your house to outside air 365 days a year, just like having windows you can't close. It's a dumb thing to do.

From your description, your system is deficient during both heating and AC seasons. Your layout and insistence on sticking to just one system may limit just how much can be done.

But in any event, having rooms with poor air flow suggests that you need the services of a capable and reliable HVAC contractor. Someone who can diagnose your problems and propose solutions. I'm just a fellow homeowner who can share experiences, I'm not the knowledgeable expert you should be consulting.

Good luck.

OK, you are in low humidity CO. You have large diurnal temp changes. You have three stories. If you open windows in the basement and on the top floor, the stack effect should draw air through the house very well. The question is, will it be enough to keep you cool without the AC. Combining the AC with open windows is not a good idea.

This type of cooling works very well in your climate in a well-insulated house with large thermal inertia. A whole-house fan will be more useful in your climate than in a hot-humid climate with low daily temp swings.

No mention of which level your return or returns are on. You really need an upper level return to help pull that hot air out. No heat in the basement office? Could be flex duct has come loose and as such you are dumping unrestricted air into your basement ceiling. This could be why your basement stays so cool and this would rob needed pressure and flow from the rest of the system. My plan would be to fix that duct problem first then figure what else can be done. Make sure there are no problems elsewher in the ducting as well. Once I was working in a crawl space (I am not an A/C tech) and I found the clients flex duct for the return completely off. For a long time she had been drawing air from her crawl space!

I have a similar situation but I had high windows installed at the stop of the stairwell. If I install a fan there, would it pull up the hotter, lighter air and blow it out? I had hoped the basement air would come up naturally and cool a bit in summer, but I forgot that it's heavier. The house is perfect in winter but summer is hot because we have a lot of west facing windows that soak in afternoon sun. Thanks.

We have the same issue, but only 2 rooms upstairs. We have a window fan to push air out from up there, closed the registers in the basement and left the returns open. However, I think that the air flow is still lost along the way. I found a Register Booster Fan online and I am hoping putting one of these in each room upstairs will help. Basically, close all registers on basement and first floor and allow this to help create a low pressure upstairs to aid in the air flow. Has anyone used one of these?

Ok,first nice stair design,2nd that's a losing battle trying to solve that air flow issue with diy techniques it won't work,Hot air always wins in huge 2-3 story homes.all the windows,wood flooring(cause people refuse to believe hardwood floors hold and give off heat when their warm),attic heat ect...conventional Ceiling fans can only cover so much space. I have walk around in 2 story huge newly build million dollar homes made with top knotch building materials running 2 units and the upstairs would still be stuffy, cold air is always going to sink..unless you put marble on all the upstairs walls & ceilings , lol..that's a lose lose situation.you would just be throwing money away,and professionals know that.But hey,,they won't tell you..

I have similar situation with second floor heat verses walk-out basement coolness , open staircase also an Defiant wood burning stove on second floor., I'm still under construction and added 2 separate insulated 8" flex ductwork with inline T8 Infinity fan motors , digital thermostat/humidistat controlled, from 2nd floor vaulted ceiling area directly to basement . Each fan will put out 807 cfm, this will give me positive pressure basement and negative pressure on second floor providing a continuous convection balancing temperatures. I can also run it during summer time balancing the cooler basement air with 2nd floor warmer air all separate from the central air-conditioners at each level.