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My house gets very hot on some days. I don't have a central AC system, and cannot install it because the house is a rental. I have to make do with various floor fans and portable AC units. There are several doors to the backyard with shady, cool spots. However because the layout is a bit complicated, I am having trouble about the optimal arrangement of my fans (and what additional fans to budget for).

I have some ideas about how I would like the air to move, but I need to have a way to see how it is actually moving so I can optimize my fan placement. What is a low cost way of measuring this?

  • Searching online has turned up many guides about measuring airflow through ducts of a centralized AC system. If only I had that problem! :)
  • Simply trying one fan setup and seeing what parts get cooler is not precise enough. There's not enough temperature differential across my house for me to feel it precisely, it would take too long and besides the temperature is not stable over time.
  • I tried walking around with a strip of toilet paper, but it doesn't have enough precision for a good measurement.
  • I could throw some kind of confetti in the air, which would solve my problem, but my wife would kill me when she sees the mess.
  • I have a room scenter that vaporizes an oil/water mixture. It looks like thick white smoke coming out of the machine, and goes about 1-3 ft before dissipating. In theory I could try to turn it on and carry it around, but it seems a bit of a hassle. Didn't work -- the smoke it makes is too faint and too turbulent.
  • I could purchase some kind of anemometer. However my fans are cheap and it's not like I have high winds blowing through my house either way, so I don't know if I will have trouble finding a sensitive enough anemometer that is not very expensive.
  • I could purchase a pressure meter, but I suspect that the pressure differential will be too small for a cheap one to work.
  • I could purchase a smoke machine, which apparently start at $30. Then try putting it in different rooms. Among other things though, would this trigger the fire alarm or stain the walls in any way?

Surely this must be a common enough problem, that there is some standard method or technique to see where the air is going?

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The best way to see air flow is to use a fog there are commercial cans really expensive or if your grocery store has dry ice buy a pound, when you get home , put some warm water in a pan and put a chunk of the dry ice in the water, as the heat breaks the dry ice down a cloud of non toxic smoke that will leave no residue is released.

I used to put a couple bowls of water on the porch and in a fish pond (no fish) on Halloween, as long as there was no breeze the fog looked really cool and the kids loved it , we needed to check ventilation on some process benches and I used some pvc pipe water and dry ice to make the smoke in a clean room and check flow , putting the dry ice in a pan with warm water will do the same and makes it easy to see how the air is moving.

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  • This sounds like the best fog method assuming you can obtain dry ice. For anyone who decides to try it, please be aware that dry ice makes a lot of CO2, and if you're in a small space with poor ventilation there's a risk of suffocating yourself. I can't explain it fully in a comment but do research safe handling before trying. It should not be dangerous in a small amount and with good ventilation, though. – Bege1986 Aug 16 at 20:57
  • Every time you exhale aprox 5% Co2 to suffocate your self in a small room 10x10 it would take more than 10 lbs and that would not suffocate you but give you a headache so no even in a normal bedroom room a few lbs of dry ice poses absolutely NO risk. Safeway and other stores have dry ice available in my area maybe not in big cities but in rural areas it is quite common, you have more chance of frost bite with dry ice than anything else., just to explaine dry ice IS co2 in a solid form it doesn’t create it it is Co2. you first would notice is rapid breathing because Co2 triggers breathing. – Ed Beal Aug 16 at 22:12
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Whenever I want to check airflow I use a candle and see where the flame is pointing.

In your case I would:

  1. Create a rough plan of your apartment
  2. Take and light a candle
  3. Walk to a position where you want to "measure" the airflow
  4. Standstill and wait for candlelight to settle
  5. Note air movement direction on the plan
  6. Repeat a meter or so away from the first spot
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Use painter's tape to hang a bunch of crepe-paper streamers from the ceilings and doorways. Make the streamers long enough to nearly touch the floor to be sure they're catching all the breeze being created by your fans.

You should be able to quickly see which way the air is moving and how far each fan is pushing the air.

Don't forget that while you're setting up to push cool air from the shady spots inside or chilled air from the portable AC units around, that it's not a bad idea to pull air from cooler places to warmer places and to put fans in windows pointing out to pull the warmer air out of the house, too.

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