I had to deal with this issue for years head-on as my home gets direct sun for 8 hours needing me to have the A/C on during the long summer days & nights full blast. I then noticed that even so, on 100-112 degrees, the A/C would only keep temp at 84 degrees. A power outage would necessitate a cool-hotel room. As to what to do?

1. I shut all window blinds before sun comes keeping the cool in.

2. Keep A/C in top operating condition. Change filter often

3. I put insulation in the attic. Months later, added more extra

4. Did wall insulation too

5. You can install an attic fan. When turned on, it blows all hot air out of attic in minutes. Works very well. Noisy when on & shakes home. It works!

6. They have heat resistant paint for roof tiles that repel heat. Choose color

7. I did install turbine wind-driven fans

8. Look into possibility of shade trees planted to shelter the home

9. Also installed attic foil which bounces the heat right back to the roof

In Texas we simply use A/C Zone units with Texas size compressors... LOL

You have great advice here, Will.  We hit 98 yesterday. Thankfully today should be cooler in the mid 80's.  I keep all blinds shut and lights off. 

Seems Richie Alan Naggar really thought this through!  Lots of great suggestions there!

Heat rises and it can become stifling in older homes. Closing off some first-floor register vents can help push more air to the second floor. If that doesn't work, I'd consult an HVAC professional for more advice, Will.

We deal with both high temps and high humidity but condos are a bit different since roof/attic improvements are not possible. 

What we do is...

Keep the blinds closed

Install ceiling fans in all bedrooms, living area, kitchen

Check the humidity levels. We invested in a portable dehumidifier years ago and it makes a huge difference in the comfort level, even if the inside temp is 80*. We use it when the humidity level is uncomfortable and after we shower to keep the level down.

Keep some floor fans handy to use on those nights when the a/c is working too hard.

Have your a/c serviced each year at the start of the season. If it's old, replace it with one that is more energy efficient. When we had our 14 seer installed a couple years ago, we found that not only did it cool better at the same temp but our electric bills are lower.

Make sure your a/c unit is the right size for your house. The a/c guy I use also services my PM rentals and when he replaced a 2nd floor unit, recommended 2-1/2 ton instead of the 2 ton that it had previously. He said that is one of the most common things he sees, units that are not powerful enough for the property.

Do not use the oven during a heat wave. If you must, use it first thing in the AM or late at night. I use a slow cooker, stovetop meals, microwave, cook on the grill outside or just serve cold meals when it's too hot to heat up the kitchen. Takeout or eating out is another option.

Same with laundry, the washer will increase humidity levels and the dryer heats up the house so either run them early AM or late night. I prefer later in the day when electricity is cheaper.

How's your attic insulation? That's where I would start besides all the other great suggestions.

Lots of great helpful tips that I plan to use too. We bought a sun blocking film at Home Depot in Palm Springs did our windows down there and brought it home and did our windows here and it really make a difference.

Invite me over, I always bring the cool. 😎

Attic fans are a must Will Hamm . If the upper floor is a sleeping area and the home doesn't have central air I would have to have a window air conditioner myself. Good circulation is so important. I have fans (3) running in my basement 24/7 every day of the year... I hate stale air.

Move to Maine! You need a vacation home. 70 degrees average summer temp, 19 degrees average winter.

Will, with a two story home, a zoned HVAC system is the way to go, and many  homes to be zoned can use existing duct work.  We had three zones for our home:  upstairs, kitchen/DR, and great room/master suite.  They guaranteed that the upstairs would be within 3 degrees of the downstairs settings.  Sure enough they were spot on and that was achieved with just using the great room thermostat and not the upstairs one at all.  We have been very pleased.

Lots of great suggestions in other areas!

I had the spray foam insulation done in my Attic and it has really helped in my 2 story house. Maryland even provides a tax break for doing this energy saving method.

We switched to dual zone heating and it's been a game changer.

Same hot here in the Valley, back to A/C living. 

Here are some thoughts and what I've done in my single story home:

Dual-pane windows where you can, shades where you cannot (it's a noticeable difference when the shades are down, even on dual-pane windows).  I got the silhouettes, so some light still comes through.

Attic fan, mine is solar powered and I got a tax credit for it.  Reduced my attic temp by a solid 15-20 degrees.

Heat reflective sheeting under the roof.  When I was installing it, the areas where it was done were considerably cooler than the areas where it was not done.

Attic insulation, I went with the R30 stuff.  Overkill.

I remodeled my house and put sound deadening insulation in the exterior walls.  R-13 only, but also helps block the noise from the birds and owls at 3am...  Only in the two rooms that had the area exposed though.

LED bulbs in the house instead of incandescent.  They put out 1/4 of the heat.

Beyond that, whole house fans are supposed to do wonders.  Open the windows when it's cool out and bring that air into the house and attic.

We do not use AC in our 1880s home but love that it was built to withstand extremes in the weather.  We too have ceiling fans in all the bedrooms, an attic fan, blinds drawn during the hot sun, huge shade trees planted but our windows are situated to provide cross ventilation and our home is built of triple brick to keep cooler in summer and cozy in the winter.  The dehumidifier in the cellar removes the humidity all year long. 

Cooking is a killer in the summer months so we use the grill a lot but mainly eat cooler summertime meals:  We like to eat seasonally and locally. 

I think Richie Alan Naggar has this one well covered.

I'd say swamp coolers but not in CO. Sometimes we close the blinds on the windows. We also had new windows, double pane, with Low E and argon gas providing more energy efficiency. 

Here in Florida, the correctly operating AC has a differential of between 12 and 20 degrees. More than that creates damaging condensation. CO many not have the RH issues experienced in FL.
I suggest at the first opportunity go to Harbor Freight and purchase the 20:1 digial temperature gun. Map the temperature from the air handler at to every vent. Helpful to know how the ductwork is laid out. Typical temp increase is +1 degree for every 10 feet.
Big changes between vents suggest a issue up there where no one wants to go.

Next map the ceiling. Fix the HotSpots or pile on more insulation.

Calculate the 'volume' in house with the capacity of air handler, compressor and filter (HEPA affects exchange) to efficiently cool and dry the conditioned air. 
1 Ton for 750 SF (5200 cubic feet) is estimated here in FL.

Air intake vents. Need a big one in EVERY ROOM.
Attic ventilation. Forced, not passive ventilation may create positive results. However, you MUST insure the integrity of the core otherwise forced attic ventilation will suck the cold air out of the house. Dead duct runs sealed with foam. Outlets sealed. Attic completely sealed from living quarters.
Lastly, zone air conditioning. A split works well, and those wall shakers have come a long way.

I've always wanted to construct a GIANT picnic pavilion over my house. For some reason the city doesn't like that idea. Now I'm considering the artistic deployment of artist SAILs to create shade for most of the day.

After these have been exhasted, the soluton get REAL expensive. Windows and doors, subdeck spray foam.

We have a 2 story house. I think for starters it matters how the ductwork is set up. Then, insulation would come into play. I recently had my HVAC serviced and my very experienced technician said to keep the downstairs 1 degree cooler than the upstairs. He also said if the upstairs needs circulation just turn the fan setting on for a few minutes. My husband works upstairs in the bonus room which is the warmest room in the summer and I work downstairs in the front of the house in my office. I like it cool (74 degrees) and he wears a pullover indoors all summer. That's the best advise I have to give you Will Hamm.

Excellent suggestions by Richie Alan Naggar. Then again , a road trip may be fun! 

Close all lower level vents in rooms you are not using

You could get a stand-alone A/C unit for upstairs.

We have separate zones. Units in the attic cool the second floor. 

AC is nice, however if you dont have it or dont want to use it then open a window downstairs, and another upstairs at the other end of the house, insert a fan to suck the hot air out of the house.

My mother's tried and true method involved opening windows at night to allow cool air into the home and then at early morning, to close everything up - including the blinds and curtains, to keep heat and sun out.  This worked when we had no air conditioning. 

Hi Will- we've had 100 degree temps here and the back of our home gets some western exposure. We shut our blinds late afternoon and it makes a huge difference. Our A/C guy suggested keeping the upstairs unit 10 degrees warmer than the lower unit. 

Use a window unit, save on a/c at the same time.

I have a three story investment property and the top level would never cool down sufficiently so I added a fan-lamp.  No complaints ever since it was added.

Whole house fans. Radiant Heat Barrier in attic. Solar attic exhaust fans. Tint some of the windows.

We're up in the 100s here, and my attic/whole house fan has been great.  Run it in the morning to bring fresh air in, AC doesnt kick in til ~2-3pm most days, and run it again in the evening when the air cools down.

Blocking out sunlight works too, but I like a bright home and it's good for most plants.  

If certain windows get a ton of sun at a certain time of day, closing blinds or putting shrubs to create shade in front of them works some, too.