Pressure, pushing down on me

January 28, 2010 2:54 PM

Is an aneroid barometer affected by being indoors in air conditioning?

I'm thinking of buying an aneroid barometer, or possibly even a barograph for my house. The main criteria is going to be decorative, but I'd also like it to be accurate. I am pretty close to sea level, but we have central a/c or heating turning on and off constantly most days. Will that affect the measurements any?

posted by IanMorr to Science & Nature (3 answers total)

If your central AC is set up to force a little outside air into your living space whenever its fans are running, it will raise your indoor air pressure, as will opening a windward window. Your bathroom exhaust or kitchen exhaust fans will lower your indoor air pressure, as will opening a lee-side window. Exactly how big these effects are depends on the design of your house. The beauty of owning a barometer is that you can actually measure these effects directly, and correct for them if necessary.

Outdoor air pressure doesn't usually change terribly quickly, so the experiment is easy to do. Wait for a still day, then turn off all your fans and open a window to equalize indoor and outdoor air pressures. Write down the barometer reading. Close all your windows and turn on all your exhaust fans. Once the barometer reading has stabilized, write it down again. Turn off the exhaust fans and turn on the AC. Write down another reading.

Now you can correct your future readings, if necessary, based on which fans are operating at the time you take them. I'm guessing it won't actually be necessary, but that guess is based on much less information than your barometer can give you.
posted by flabdablet at 3:28 PM on January 28, 2010 [1 favorite]

Best answer: Not enough to make a difference. The pressure in your house with equalize with the changes in atmospheric pressure pretty much instantly, at the rate atmospheric pressure changes with weather fronts. The temperature difference between your house and the external environment also won't matter because it will actually be holding the temperature variable more constant that it would be if the barometer were outside.
posted by 517 at 3:29 PM on January 28, 2010

I "borrowed" an Altimeter that we replaced at work (I'm a [helicopter] pilot), sitting on my TV stand, and I never see a difference when I open my windows or when the AC/Heat runs. I keep the thing set at standard pressure (29.92" HG) and it just moves with high and low pressure systems that come in. Today for example it's showing 200' below sea level, as there is low pressure over the Tampa bay area.
posted by blackout at 3:44 PM on January 28, 2010