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rileyafterall

Oversized Furnace - can we still use it?

RileyAfterAll
9 years ago

We've got a 70k btu Amana Furnace AMH950703BXAD installed for our 800 sq ft upstairs. It's two stage and apparently has 4 fan speeds.

Right now it gets uncomfortably hot when it comes on but I'd like to know if there's a good remedy - for example simply setting it on the low speed (I'm not sure what speed it's on now).

I've gotten conflicting info from contractors. Some say they can just dial it down while others say we need to replace it if we want things right.

Thanks!

Comments (7)

  • mike_home
    9 years ago

    What thermostat do you currently have? If you have a true 2-stage furnace, and it is set up correctly with the furnace, then the furnace should operate in the low stage most of the time.

    Did any of the contractors bring this up? The other option is to up the furnace so that it only operates in the low stage. This is done with settings inside the furnace.

  • tigerdunes
    9 years ago

    Have dealer disengage the high stage of your furnace. You will never need it.

    IMO

  • RileyAfterAll
    Original Author
    9 years ago

    Thanks so much for the help. I've got an Ecobee Smart Si. The air is pretty hot and blows quite hard. It heats up too fast and is uncomfortable. Should it ever blow on a lower speed? It only seems to be one speed.

    How do I know if it's a "true" 2-stage furnace? Here are the specs: http://www.amana-hac.com/portals/1/pdf/ss/ss-amh95.pdf
    From the specs:
    ⢠Two-stage gas valve with technology that
    allows installer to activate the two-stage
    valve with the flip of a dipswitch
    ⢠Self-adjusting feature automatically
    adjusts to high- or low-stage operation
    based on outside temperature without
    an outdoor temperature sensor

    One contractor said the entire job was crap and everything needed to be redone. The other two said we could just have it operate on the lowest setting - I thought they meant fan speed but I guess now they were referring to low stage. But one of those two said we should swap it out for a variable speed instead of mess with it. That it'd be worth the money up front because it would pay for itself in a few years with the energy savings. Good advice?

    Would there be a difference between the 70k on low stage only, a 45k two stage or a variable for our purposes? What would you guys do?

    Here is a link that might be useful: AMH95 Gas Furnace

  • mike_home
    9 years ago

    The furnace has a 2-stage gas valve. That's what make it a 2-stage furnace. The statement about automatically adjusting to outside temperatures without an outside temperature is marketing hype in my opinion.

    The gas valve works with the fan speeds. Low stage means both low gas valve opening and low fan speed.

    The Ecobee thermostat can control both the high and low stages if it has been wired for 2-stage operation.

    The fact that you don't hear a difference in speeds suggests the furnace is not set up correctly. I think your best option is to have the furnace set to run in low stage only. the furnace is rated at 95% efficiency. Getting a variable speed furnace is not going to save you money and will never pay for itself. This advice was given by someone who wants to sell you a new furnace.

    If the installation was done poorly, then find a contractor who you trust and have him fix it and limit it to the low stage.

  • RileyAfterAll
    Original Author
    9 years ago

    Thanks Mike, that was all super helpful info. Despite getting 3 other bids, I'm not entirely comfortable with any of them. And these were the highest rated HVAC contractors in my area.

  • tigerdunes
    9 years ago

    Dealer should decommission high stage and at same time check the air speed of blower and adjust lower if indicated.. What do you do if anything about AC?

    My suggestion is only a fix for an obviously oversized furnace. Worth a try. To get things right though, you need a properly sized furnace for such a small living space.

    Dealer who recommended this size furnace did you a terrible disservice.

    IMO
    Good Luck

  • sktn77a
    9 years ago

    Agree with the above posts to set the furnace on the first stage only. However, DO NOT let anyone indiscriminately lower the airflow rate without checking the temperature differential. Airflow rate is set by measuring the temperature differential across the heat exchanger, not by airflow coming out of the vents or temperature of the air coming out of the vents (the fact that the air coming out of the vent is uncomfortably hot suggests it's already set too low). Lowering the airflow increases the temperature differential and, if too high, can damage the heat exchanger. Ask your contractor about these issues and if they don't understand or try to blow you off, move on to the next contractor.