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  1. #1

    ruud gas furnace and ac

    I have a split level ranch 2000 sq foot total. The gas furnace is 30 years old. I am looking at Ruud for both furnace (80%, 2 stage)and ac. The registers are near the floor for most of the house, especially upstairs. Here are my questions:

    1. I don't understand the difference between variable speed motor and multiple speed motor for the furnace and also the upflow and downflow furnaces. Presently I have a vertical downflow unit.

    2. I was given an estimate with a 5 ton coil and 4 ton furnace (need to move 4.5 - 5 ton air total, 3.5 above). Is it possible to do mismatch components like this? Someone said the coil might freeze, is this correct? Would it still be under warranty?

    3. Any websites I can read up some pertinent info on?
    I hope you guys can give me some valuable input on these matters.

    Thanx
    Just a single gal looking to make informed choices

  2. #2
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    67,722
    Variable speed blower. Has its CFM of air flow set by jumper/dip switches. It then speeds up to move that set amount of air even if your ducts are slightly undersized.(key phrase slightly)

    Multispeed, is a 3 or 4 speed motor. The installer sets it to a speed tap, and it spins at X RPM, weather or not that is enough to move the desired amount of air.

    Many brands use a larger rated indoor coil then the rating of the outdoor unit.
    And the furnace blower is rated at its max air flow ability.

    Upflow means it blows the air up, and downflow means it blows down.

    The question is. Did they do a load calc to see what size you need, or are they just guessing.

    What size is your current A/C, and furnace. And did it heat and cool the house ok, excluding maybe uneven temps vetween teh first and second floor.
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  3. #3
    Join Date
    Mar 2008
    Location
    Central Maryland
    Posts
    246
    Quote Originally Posted by householder View Post
    I have a split level ranch 2000 sq foot total. The gas furnace is 30 years old. I am looking at Ruud for both furnace (80%, 2 stage)and ac. The registers are near the floor for most of the house, especially upstairs. Here are my questions:

    1. I don't understand the difference between variable speed motor and multiple speed motor for the furnace and also the upflow and downflow furnaces. Presently I have a vertical downflow unit.

    2. I was given an estimate with a 5 ton coil and 4 ton furnace (need to move 4.5 - 5 ton air total, 3.5 above). Is it possible to do mismatch components like this? Someone said the coil might freeze, is this correct? Would it still be under warranty?

    3. Any websites I can read up some pertinent info on?
    I hope you guys can give me some valuable input on these matters.

    Thanx
    Just a single gal looking to make informed choices
    Upflow or downflow is how the configuration is set up, usually dictated by the space the builders had to work with and where the duct work ended up. Some manufacturers make an air handler that can be configured in two or three of up, down, or sideways, some make different models for each, etc.

    Most change-out spec the same type since they usually re-use existing ductwork. This is one area you don't need to sweat as a homeowner, let the installer pick what installs easiest. Just ask them how hard it will be to access the air filter for easy changing.

    Furnaces are not usually rated in Tons, Heat Pumps are as are A/C's. Nonetheless they are the same idea, a measure of heat delivered or removed over time.

    Variable speed air handlers also have the benefit they can run on very low speed/low power and continuously circulate air in the house. This helps lessen hot spots/cold spots and keep a more even temp in the house.

    I don't understand why a 2000 sq ft needs 4 tons of cooling. Do you live in equatorial Africa, have screens for walls, or is your HVAC pro a member of the Tool Time "more power" "Bigger is better" club? An oversized A/C will work deliver less comfort, dehumidify poorly, and not last as long as a properly sized unit.

    On top of that, putting a larger coil on it makes it even less likely to dehumidify well. If you live in an arid zone, though, it may not matter.

    -HF

  4. #4

    thanks and more questions

    Hello,
    Thank you for the two replies I received.
    So, I am understanding that variable speed is better than multi-speed for the blower as it will evenly heat and cool the house and also be more efficient.

    I have no ac in my house right now. I live on Long Island, NY where the weather is muggy and hot in summer. I am not an ac person and therefore do not plan to use my ac all the time, but it is still good to have it on very hot days. If my present furnace is 100,000 BTU then is the 5 ton coil and the 4 ton condenser too much for my split 2000 sq feet ranch? if yes what would you guys recommend?

    Correction: I understand I have vertical upflow furnace and not a vertical downflow as I mentioned in my earlier message
    thanx again

  5. #5
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,722
    A load calc to find out what size you really need. Oversized A/Cs don't do good at removing moisture from the house.
    Oversized furnaces tend to use cost more to heat the house.


    Your current furnace is probably 20 to 40% bigger then you need.
    And 4 tons may also be more then you need, considering it doesn't get that hot in your area, but has high humidity.

    Call other companies, and ask if they do load cacls. If not don't ask them for a quote.
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  6. #6
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    VS blowers can help to even out room temps. They are not a cure all for bad duct systems.
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  7. #7

    thanx again

    I am going to look at the load calculation. It resonates with me. I have 2 contractors who have so far said the duct work in my house is inadequate for a/c. So what is a better option price wise and efficiency wise?

    1. Run the a/c thro the attic and drop a few ducts into the downstairs? I was told a 3 ton unit would be sufficient for it?

    2. Put a 3 ton unit off the furnace downstairs and hope it will cool and remove some moisture upstairs too?

    3. Any other options you can suggest?

  8. #8
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    Your best option may be to install teh A/C in teh attic.
    If there is no way to increse teh duct work of the heating system. Which is often the case of split levels.
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  9. #9
    Join Date
    Jan 2008
    Posts
    85
    Get a load calc done. I don't see how anyone can truly say your ducts aren't sized for A/C without educated guessing at this point.

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