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Old 10-24-13, 11:07 AM   #27
gspike
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A makeup air controller may be an cheap easy mechanical switch to preform the same task.

commonly used in commercial hvac setups its a adjustable temp and humidity switch that is usualy used to open a damper(but could control a fan) connecting outside air to the return of hvac. Sometimes used to allow air into a tight building for combustion(or generally make up for building air losses), sometimes just to improve HVAC eficiency. The idea is that sometimes outside air is more temperate than the return, so why not use it and save some btus?

Its been a while since i looked at one, but if i recall the cheap ones only did hot or cold settings on but not both. Some did comparative temp reads of outside and return air temps, and some had a single rheostat setpoint and some may output 24VAC for HVAC dampers and controls. But as i recall the cheap ones cost about fifty bucks wholesale.

Just remembered its called an economizer when used to temper with outside air, did a quick search and could not find the cheap mechanical ones, only the expensive microelectronic.

Google the air-2 controller to get a general idea. Its sort of a retail evolution of the thing.

Last edited by gspike; 10-24-13 at 11:57 AM..
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