The idea that the wood floor needs air flow is nonsense. The biggest issue with wood floors occurs when the humidity is low. You don't have that problem in the summer months.

Does this house have a basement? If it does then you may be able to install dampers in the supply trunks for the first floor. This will help balance the air flow between the floors. You should not completely shut off the flow to the first floor as it could cause too much air pressure on the the furnace blower.

If you can't install dampers then try covering the first floor vents. There are magnetic vent covers but they only work on metal registers. You may have to tape a cover over the vent or come up with some other creative solution.

Utilize a powered recirculating duct in a stacked closet from first to second floor . But it sounds like the builder installed an barely adequate budget system, and that needs fixing no matter what.

Running the fan constantly tends to raise the humidity level and makes you feel more uncomfortable. Did the flooring installer tell you what humidity range you need in order for the floor not to warp? Is this manufactured flooring and if it is have you read the manufacturer's guidance on humidity?

Short term fix = air conditioning units in the upstairs + dehumidifiers running throughout the summer. This will work for a few years. Which is the amount of time you will have to save money to upgrade your HVAC to include whole home air conditioning+humidistat (dehumidifier/humidifier...whatever is needed for your location...you see where I'm going with this?).

Dehumidifiers have been used as a 'poor man's air conditioner' because it pulls moisture out of the air making it feel 'cooler' on the skin (your sweat evaporates faster making you feel cooler). You will need to empty the reservoirs twice/day. You will do this with each room because each room will require a dehumidifier and and/or an air conditioner (portable air conditioners have to be vented to the outside OR they have small reservoirs that can be emptied 2-4 times per day).

Again, you will purchase all these units so that you can buy enough time to save enough money to purchase the whole-home upgrade...if you don't go to all this trouble (and costs) you will most likely lose your new hardwoods to warping. Wood can handle a LITTLE bit of humidity abuse...but it can only take it for a short time. After that, the warping is permanent.

I'm sorry you are finding this out AFTER you installed the hardwoods. Personally, if I had the ability to finance it, I would go ahead and have the HVAC upgraded BEFORE the summer. That way you don't waste money on multiple air conditioners and multiple dehumidifiers...and all the electricity it takes to run them 24/7 through the summer (not to mention all the buckets of water you will have to cart back and forth to the bathroom every day).

Have you considered just calling in an HVAC pro (perhaps the one that installed) to come in and look? They may be able to help adjust dampers or other solutions to better balance out the flows between two floors. (I'm assuming this is an existing system and they haven't been called in)

I would suggest a $20 hygrometer from Amazon to check your relative humidity in the home. It sounds like is part of the concern. That way you will know if the floors are in their happy zone. Thats usually 35% to 55%.

A two story home with one AC will always have a design challenge to over come when temps start climbing.

The simple reason is mostly science and physics. Cool air falls and hot air rises.

If the temp is 70 degrees on lower level, the thermostat satisfies and shuts the system off.

You go upstairs and it's a balmy 80 degrees up there / some cases worse. Might be as bad as 85. The thermostat has no clue how hot it is upstairs. (Move the thermostat to upstairs and the down stairs becomes a meat locker and cooling bills require a brinks armed truck to collect your utility bill.) < means you pay for it one way or another.

Comfort: no two people are alike. Some like 80 degrees some like 70. If you like 70 and you want 70 through out your house, that is either going to cost you some design dollars or a lot of frustration.

Choices: The most cost efficient method is zoned AC. This is not considered cheap, and more often than not it's put in with junky control boards, has static pressure issues which will cause further damage to the system and possibly the controls.

The other problem with a zone system is trying to cram too much cooling into spaces not large enough to handle it. Realize this is very scientific and relates to things you can't see such as 'air flow'.

400 CFM (cubic feet per minute) per ton of air conditioning. If you have a 5 ton air conditioner that is 2000 CFM of air per minute for a unit that size. (Size means capacity).

So if you select the zone system choice, your work is cut out for you. There is a myriad of junk on the market and worse yet those junk dealers that install it because they know going in that cost is a big hurdle. (so let's install something that needs replacing every 5.5 years or so.)

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Another way to zone: install dedicated equipment to cool the upstairs area. The problem with this is: that most people add more AC to the home. Leave the existing system because cost is even more to have to rip this older system out and replace it too.

Then the home is over cooled. The system(s) are oversized for the structure do not run properly (short cycle) which can cause a myriad of failures the worst of which is inadequate oil return to the compressor. (leads to compressor failure)

Other problems with this scenario is damp musty problems develop in the home because the AC's do not run long enough to pull humidity from the home.

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With that said: zoning for AC and heat can work. I have zoning in my own home. I don't quote zone systems on the cheap. I quote them so they will work for years and years and years with rarely any trouble.

It's not uncommon for me to stumble across zone systems installed by others with myriad problems, not working properly, causing system failures and the list goes on and on.

Realize I stumbled across many of these zone system problems 'before' I installed a zone system in my own home. Most zone systems rarely make it to year 6 before needing replacement. The system I installed in my home is 12 years old and still going strong. Design is very important as well as equipment that you are trying to control via a zone system.

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what causes flooring to warp? moisture. too wet. What causes flooring to crack? dryness. too dry.

With that said, I'm not a flooring expert. But these are common sense things. (an engineered wood floor product) is probably designed to over come a lot of these problems.

If you bought a regular wood floor product? time will tell. Any wood product naturally expands and contracts so some of the problems with wood floors is due to installation of the product. If there wasn't enough room for the floor to expand, this can cause it to buckle (warp up & crack).

I service the Katy, Texas area.

Here's a video (embedded below) I made '5 YEARS AGO' covering HVAC zone systems for 2 story structures. Realize the website 'PAGE' this video points to is no longer in operation. People don't want to spend the $$ to do it right. They would rather complain about how junky things are and don't work as advertised with the cheaper junk options others sell... yada, yada, yada. I leave the video up as a 'see I told you so' type moment.

The video does a good job of explaining the problem if you're unaware and curious. OR you have a similar problem with your home. Again I service the Katy, Texas area.

I agree with Ray on this one. Low humidity is a problem for wood flooring, There are millions of homes in the US with wood floors. Many have humidity levels consistently above 50% in the summer. Your flooring guy is making excuses about installing register vents that can't be adjusted. He should have discussed this with you before installing the floor.

The relative humidity is the key. I'll reiterate the recommendation to purchase a thermo hygrometer. In fact I put one in my Amazon cart yesterday. It has three remote sensors so you could have the base unit on your main floor, a remote in the basement, upstairs and outside.

https://www.amazon.com/gp/product/B00FX8ZGOO/ref=ox_sc_act_title_1?smid=A2ANVX7C75D1I&psc=1

Close the vents on the first floor and monitor the temperature and humidity. If the humidity is in the 40-60% range you and the floor was installed properly you should have no issues.

Closing vents at registers often times create system turbulence with in the HVAC duct system this doesn't do anything good.

The reason this happens is that air takes a path (duct work) that is available. That duct work maybe 20 foot or more long. At the end of that duct, the register is closed and the air rams into the closed grill has to turn around and go back. IE: turbulence.

The system is 18 years old and you've always done it, but now have problems? I can only guess here as to what is going on.

People often say 'I've always done this and never had a problem.' But you have a problem now. The thin line of 'Experience'.

Just because you seem 'to get away with' doing something for an extended period of time, doesn't mean it wasn't causing damage.

With that said, the damage is probably already done (however long you've been doing what you've been doing has finally caught up to you is my thin veiled guess.) But 18 year old system is due to replace anyway. National average AC life is about 15 years.

In terms of homes being build now with zone systems... all the ones I see are junk rarely if ever installed properly and most likely last in the realm of 5.5 to 6 years. Builders build, move on to the next build.

If you're looking for 'Service' after the fact of the home being built do your research. Builders in my experience are not equipped to service prior installations.

They build and margins are thin. First sight of trouble with the building market and most go under.

So if it's any consolation it's probably good that your builder didn't install a zone system 18 years ago. But now, there's even more junk on the market that is more or less worthless garbage in terms of zone systems controls, dampers, design flaws and so on.

But as you know... there is a big market for 'cheap' these days. If you don't like the term cheap substitute it for 'inferior'.

My opinion is based on 24 years of 'doing' this for a living. Most don't like my opinion and that's ok. I fix air conditioning problems. No matter how hard I try, I can not fix people.

Anyone can do 'air conditioning'. All that's required is knowing 25% of what this job entails. 75% of the AC problems encountered come from where?

Not knowing what you shouldn't do.

I service the Katy, Texas area.

Austin Air Companie - Awesome explanation!