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  • Blocking part of Air Intake

    My brother has covered my parents' air intake with aluminum foil to the extent that only 25% of air can get into the central air natural gas furnace. The reason is because my mother doesn't like the few minutes of cold air blowing on her in the morning before the house heats up. It's a new furnace and it is a 4 ton Goodman unit. The A/C man put it on low speed for the winter so it would not blow out so hard, but my mother is not satisfied. So my brother who is an electrical engineer says that it will not hurt the motor, but it will increase the heat and decrease the amount of air coming out, and this has seemed to please my mother. But can't this hurt the motor. I think my brother is crazy. He says he is making it easier on the motor because the air is less dense. Is he right?

  • #2
    Re: Blocking part of Air Intake

    Originally posted by AliciaT View Post
    My brother has covered my parents' air intake with aluminum foil to the extent that only 25% of air can get into the central air natural gas furnace. The reason is because my mother doesn't like the few minutes of cold air blowing on her in the morning before the house heats up. It's a new furnace and it is a 4 ton Goodman unit. The A/C man put it on low speed for the winter so it would not blow out so hard, but my mother is not satisfied. So my brother who is an electrical engineer says that it will not hurt the motor, but it will increase the heat and decrease the amount of air coming out, and this has seemed to please my mother. But can't this hurt the motor. I think my brother is crazy. He says he is making it easier on the motor because the air is less dense. Is he right?

    Let Brother know he needs to stick to electrical work...It is too easy to restrict the airflow to the point that you trip the high limit.

    Might I suggest adjusting registers or installing different grills to change the throw patterns to keep mom out of the drafts.

    When Mom is not looking remove the foil but don't tell her, I bet she will not notice

    Okie
    Last edited by OkieBill; 01-22-2009, 08:44 PM.

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    • #3
      Re: Blocking part of Air Intake

      Your brother is right in that it will not hurt the motor as the current draw in the motor will decrease due to the decrease in torque because the blower wheel has less air to grab. You will destroy the heat exchanger which will cost a lot more than a motor! The heat exchangers in today's furnaces are designed to have a certain amount of air blowing across them to remove the heat generated by the flame and combustion gasses. Most duct systems are just barley designed large enough to meet this air flow requirement. There is a over temperature limit switch built into your furnace to shut off the flame if the furnace gets too hot. The limit switches are a safety devices designed for one time or short term overheating caused by problems like a burned out blower motor or plugged filter. The temperature ratings on limit controls are higher than the design temperature ratings for continuous use on heat exchangers. By blocking off that much return air your supply air is hotter than normal so your mother is comfortable but every time the furnace fires up the metal in the heat exchanger is expanding further than was it designed to and will result in thermal stress cracks. A crack in the heat exchanger may result in the flame rolling out or carbon monoxide entering the living space. Every furnace has the acceptable temperature rise listed in the name plate information. It may say something like temperature rise 35-55 degrees. This means that the temperature of the air leaving the plenum taken just beyond the direct sight of the heat exchanger, must be between 35 and 55 degrees higher than the temperature taken at the return air entering the furnace. Your mother will not be happy when the furnace fails and may blame the manufacturer for building a poor product. Tell her to run her thermostat a couple degrees higher than she normally does and she may find the house more comfortable but get rid of that tin foil before she wrecks her new furnace.
      sigpichttp://woodburyfurnace.comhttp://www.heatpumpmn.com/

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