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  1. #1
    Join Date
    May 2013
    Location
    georgia
    Posts
    16

    Variable speed 90% gas furnace?

    I installed the v.s. 90% high efficiency gas furnace and a friend said that it works better with a thermostat with a built in humidity control. Or with a humidistat... I'm not very clear. Can someone explain? Surely appreciate it.

  2. #2
    Join Date
    Apr 2003
    Location
    Maple Grove, MN
    Posts
    1,247
    Most of the newer furnaces that have variable speed motors have the ability to run in "de-humidify" mode, with the right thermostat. When in this mode, the fan will spin slower. When the fan spins slower, the air is allowed to be in contact with the cold evaporator longer, which allows it to ring more moisture out of the air.

  3. #3
    Join Date
    Aug 2012
    Location
    willowick ,oh
    Posts
    261
    He may be referring to operating a humidifier from a thermostat with a option that monitors humidity in the house, and brings the fan on with a call for humiditiy. The honeywell prestige has this function. I set one up for a guy that used a wood burner alot, to bring moisture back in the house.The honeywell true steam setup. Worked awesome.

  4. #4
    Join Date
    Apr 2003
    Location
    Maple Grove, MN
    Posts
    1,247
    You are right, johnnyb. I was only thinking of the ability to de-humidify. To clarify, in order for the unit to de-humidify, the air conditioner will have to turn on, in addition to the fan slowing down.

    To have it add humidity, you will need to have a humidifier that is hooked up to the furnace.

  5. #5
    Join Date
    May 2013
    Location
    georgia
    Posts
    16
    Quote Originally Posted by ammoniadog View Post
    Most of the newer furnaces that have variable speed motors have the ability to run in "de-humidify" mode, with the right thermostat. When in this mode, the fan will spin slower. When the fan spins slower, the air is allowed to be in contact with the cold evaporator longer, which allows it to ring more moisture out of the air.
    you said," with the right thermostat"... which type of thermostat would that be?
    Could you give me a few out there that has dehumidification built in?
    thanks

  6. #6
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    33,918
    Vision Pro IAQ, Prestige IAQ, many of the high end Emerson, Aprilaire 8910...

  7. #7
    Join Date
    Apr 2003
    Location
    Maple Grove, MN
    Posts
    1,247
    Many high end furnaces can aso use what is known as a "communicating" thermostat. If your system can use one of those, that will give you the best control, along with some extra diagnostic features. This special communicating thermostat needs to come from the same company that made your furnace (Carrier, Trane, Lennox, etc). What kind of furnace did you get?

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