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This is probably very easy to answer, but I'm working on a project where I need to heat a chamber (insulated Styrofoam container), and my option to heat it is essentially a hair dryer, as a heat gun outputs too much and would melt it since I do not have access to a variable temp heat gun.

My question is that if I have a hair dryer blowing hot air into the box, I likely need some sort of escape vent or area for air to be removed so that it does not become too pressurized, correct? I first thought about completely sealing it so the hot air doesn't escape but I'm guessing that wouldn't be a good choice if there is no place for the air to escape.

Also, sorry if this isn't the correct place to ask this but I hope it's an easy question :)

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Hair dryers are typically similar power compared to heat guns, maybe higher, though the air flow is usually a lot higher. Somewhere in the 1500-1800W range for North American ones, which is about as much juice as you can get out of a standard 120VAC outlet.

If you block off the air flow from either one, the internal thermal protection will (should) trip to prevent the case from melting (in either case).

So, yes you need to allow the air to escape, but if it is well insulated and the heat is not controlled the air temperature will likely eventually rise to a high enough temperature to melt the styrofoam etc. That will depend on the size of the chamber and the heat capacity of whatever is in it. To keep that from happening you will need to use the hair dryer and keep the air flowing as freely as possible so it does not get too hot. It may still get too hot if you can't keep the air flowing freely enough.

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  • \$\begingroup\$ Yep I'm planning to make an incision for air to escape, currently I did a few rudimentary tests and found that air can escape through the lid as it's not a good seal. Thanks for the help. I am aware of the melting point / glass transition temp of the styrofoam (glass transition temp in this case is my main concenr) and I have a temperature sensor so none of these should be major concerns fortunately. When it reaches a desired temp I'll be shutting off the hair dryer and hopefully maintain the temperature for the most part for at least ~30 seconds \$\endgroup\$ – David Brevik Jul 20 '18 at 22:41
  • \$\begingroup\$ @DavidBrevik - If hot air can escape, cold air must be entering - conservation of mass and all that. And be aware that, when the air first reaches max temp any object in the chamber will not have reached that temperature. You'll need a (possibly considerable) amount of time to heat whatever it is you're working on. \$\endgroup\$ – WhatRoughBeast Jul 21 '18 at 0:41
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As @spehro-pefhany pointed out, the main difference of hair dryer from other heat sources is high air flow. So you need an unobstructed way for air to escape, or risk overheating the dryer.

But this requirement creates another problem - hot air will escape quickly when dryer is off, so you will have high temperature fluctuations and constant switching of the dryer on/off.

One simple way to improve this setup is using lightweight shutter (flap) on the exit hole, similar to dryer/duct covers.

Also, make sure the intake opening for dryer is located at the bottom and exhaust (with shutter) is at the top. This will prevent hot air escaping through the dryer when it is off.

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