We live in a mobile home in the midwest. It is July. That means it is HOT. We don't have Air conditioning, so after repairing the window screens and opening the windows and back door, anf running fans and ceiling fans, it was still HOT. So today, I installed a chimney. I got a 6 inch diameter (single wall) galvanized stove pipe with a wire screen and cover on the top. It was $2 at a yard sale, but the whole setup is $10-15 new at Menards. I got on the roof, which is metal, and traced the size of the pipe onto the roof. I cut a hole in the roof just the right size, and then cut the same sized hole in the ceiling, and shoved the chimney pipe down the hole until it was flush with the inside of the ceiling. Voila ! Now the hot air has a way to escape. (Hot air rises.) It made a 2 or 3 degree difference (maybe more) immediately. I plan to install a couple more when I get the $. I still need to anchor it and caulk around it, but it works like a charm.
Another thing- the trailer had poor air circulation between the kitchen and the rest of the house, because there was a wall between there and the living room, with only a hallway between them for air to pass through. So I cut a square hole in the dividing wall just the size of a box fan ($12 at K-Mart) and put it in the hole. It helped dramatically.

place a small fan underneath it to direct the hot air up.

excellent idea!

Thanks for the idea. Our ceiling fan (reversible) does that for us. Also, they make a fan for just that purpose that fits in the stovepipe and is thermostatically controlled for $25 or so. (There are a great deal of useful parts and accessories you can use, they are made for woodstoves, but you can adapt.)
P.S.- it is now NOTICIBLY cooler after about a half an hour.

i am seriously pondering making a cooler A/C unit if this heat doesnt break..

i have everything i need,cooler,copper tubing,pump,fan.. just need a couple fittings to make it happen.

would be perfect for knockin the heat of the day outta the room in the evenings..

OK, turns out i had the stuff to make the redneck AC system..

this is the basic design i followed..

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i worked with what i had so its a bit different. i used 1/2 inch copper tubing, a 12 volt inline diaphragm pump out of the old camper and assorted scrap pieces of the old water lines from the camper. also am substituting a 5 gallon bucket for the cooler and using a full size fan..

will try it out this afternoon and report back on how it works.. may post a pic or two of the contraption then as well..

One other thing you might look into as an alternative is an earth tube from below the house.

OK, trial run with the redneck AC was successful enough that i am going to sacrifice a cooler..

ice in the bucket lasted less than 15 minutes lol.. it was a hot one here today..

but even with that we managed to drop the temp in the room from 90 to 85 in about 30 minutes..

took a little time and tweaked the tubing to where it fit the fan a little better and drilled a couple holes in the top of a old water cooler i had here and going to give it another go late afternoon tomorrow..

west tx, i believe i will stick with my redneck AC.. 8 inch soil temp here is 86. i would have to dig down a couple feet to get cool soil and past about 8 to 10 inches here we got limestone .. swinging a pick in the crawl space in 90 degree weather is too much like work..lol

war, how much of a temperature difference did your roof vent make? worth your effort?

You guys are making me feel so bad that i live up north and have air conditioning right now.

In my Dad's house we always had an attic fan that drew all the heat up into the attic and out the windows up there, since I left home he installed ceiling fans in all the rooms, but only one window air conditioner due to the very very old wiring in the house.

the temp in the crawl space under the house would be cooler. all it would require is a a heat escape through the roof and a floor vent to the crawl space.

Hippiehillbilly- that is quite a success ! From 90 to 85 in 30 minutes is great. I had a similar drop in temp over the same approximate time, but only because the air temp in the house was that much higher than the outside air temp. When the hot air escapes, it quits when the temp inside is equal to the temp outside. This is good, but your device could actually lower the temp LOWER than the outside temp.
When I lived in a van-type motor home in Iowa, I had a dog and a cat with me. In the summer, it got up over 90 degrees for over 30 consecutive days. To keep them cool while I was at work, I bought 20# of ice every morning, put it in a plastic tub, and set the tub in front of a fan. Of course, the windows were all open too. When I got home from work, it was still cool in the motor home. It was a small area, but that worked.