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Optimal Furnace Fan Speed?

Chris Homeowner
Chris Homeowner Member Posts: 1
in THE MAIN WALL
The 120v 1/8 HP 1050rpm fan motor died on the Armstrong G65-105D furnace in one of my apartments. The tech used a "universal" motor that sounded too slow when he first tried it, because it was wired to "low". He rewired to one of the "medium" speeds, providing 1/4 HP. He said the RPMs always stay at 1075, but I don't understand how this works.
The tenant said it feels ok, but I've never lived in the apartment so I can't comment on airflow. They have complained about the fuel costs.

The motor has 5 choices of speeds, and I think the tech chose the correct one, but I'm trying to understand it better. I know I don't want top speed, but might opt for a little higher speed since the airflow isn't great to the 2nd floor, and to extract maximum heat.

How do you know the best speed/setting?
How does the relationship between HP & RPM work?

Comments

  • Weezbo
    Weezbo Member Posts: 6,232
    interesting....

    have any of you heard of any recent fires bought about by variable speed blower fans with out some finer control on the furnace burner ? it has crossed my path a while ago,just checking.... I have done a bit of forced air.. dialing the speeds up and down on the furnace has a few variables to it. so ,it may be best that you try hvac.com there you may get a lively debate or two on this subject and someone who will come over and balance the system....
  • Jeff Lawrence_24
    Jeff Lawrence_24 Member Posts: 593
    It's not fan speed

    It's actually the temp rise across the heating section.

    Most furnastys have on the rating plate the temp rise in degrees. The fan speed needs to be adjusted up or down to have the delta T fall within these guidelines.

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