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  1. #1
    Join Date
    Sep 2007
    Location
    Charleston, SC
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    4

    Default questions re: HVAC quotes

    posting here as well since these boards are low in traffic...

    We're renovating an old house and the HVAC is at the end of its life cycle, so we've gotten a couple of quotes for new everything. (2) - 2.5 ton air handlers (up and down), (2) 70k Btu gas furnaces, all new ductwork up and down, etc.

    I have a few questions regarding the quotes I've gotten, as I don't know much about the info on here and I need to know when it's better to upgrade vs take the lower-end quote. i.e. Will the differences be noticeable or negligible?

    1. SEER rating - 13 SEER vs 14 SEER & up - is the difference negligible as far as cost savings, comfort, etc?
    2. variable speed vs. multiple speed - what does this mean to me?
    3. heating stages & cooling stages - 2 vs 1 - what does this mean to me the user?
    4. dehumidification - yes or no - doesn't having AC automatically act as a dehumidifier? do i need it as an add-on?

    Also, what is the difference/advantage/disadvantage of using galvanized sheet metal ducts vs flex ducts?

    Thanks for any help or insights!

  2. #2
    Join Date
    Aug 2007
    Location
    The Great White North
    Posts
    4,045

    Default Re: questions re: HVAC quotes

    I think this link might be helpful to some of your questions :http://www.consumersearch.com/www/ho...home/furnaces/

  3. #3
    Join Date
    Aug 2007
    Location
    The Great White North
    Posts
    4,045

    Default Re: questions re: HVAC quotes

    1. SEER rating - 13 SEER vs 14 SEER & up - is the difference negligible as far as cost savings, comfort, etc?
    SEER - Seasonal Energy Efficiency Ratio, an equipment efficiency rating that measures how much energy it takes to cool the air… similar to MPG on a car, the higher the number the more efficient the unit.



    2. variable speed vs. multiple speed - what does this mean to me?
    Variable speed - the unit will start with a lower blower speed then automatically step up to a higher speed as demand for it

    Multi speed - the blower motor has the ability to deliver different speeds.
    For example …. when the furnace turns on the blower speed will be at a fixed rate that was selected and wired. It will run at this fixed speed for the duration the unit is on.
    A 3speed motor will have a selection of low, medium , high .
    A 4 speed motor will have low, medium low , medium high, high.
    These speeds are a ratio of the motor’s rated maximum RPM
    The HVAC people will determine the required CFM ( cubic feet per minute ) output from the blower by selecting the appropriate speed of the motor. The slower the blower speed the lower the CFM and the faster the blower speed the more CFM.





    3. heating stages & cooling stages - 2 vs 1 - what does this mean to me the user?
    2 stage heating – in combination with the variable speed blower and in cases a 2 stage burner.
    The heating system will start with a low blower speed and low burner setting for a period of time and if the demand is met by a determined period it will remain on low. For example…. at the beginning of the heating season when temperatures are cool but not extremely cold the demand is less to heat the home.

    When the temperatures are colder the demand is higher since it will take longer to heat the home. The furnace will start at the lower speed and burner setting , since it will take longer to meet the demand the system will automatically step up to the higher speed and burner setting to provide more heated air .

    The thought with the 2 stage heat system provides less temperature swings and greater fuel efficiency and comfort.





    4. dehumidification - yes or no - doesn't having AC automatically act as a dehumidifier? do i need it as an add-on?
    A/C will help with dehumidification if the system is sized properly.

    In the air handler is an evaporator coil that is filled with cold refrigerant. The warm inside air from the return ducts pass over this and gives up it’s heat to this coil. The air that passes over the coil leaves cooler and out to the supply vents to cool the house.
    It’s at the point when the warm air is in contact with the cold evaporator coil condensation will form … it’s the law of nature … this condensation is the humidity from the warm inside air. As it passes by the coil it will be cooler and less humid. The resulting water accumulated from the dehumidifying ( condensation ) will be drained out through a pipe or hose.

    The problem is with a system that cools too quickly is the rapid cold air coming into contact with warm humid air inside the home will allow condensation to occur in the living spaces instead and actually cause humidity problems…. it’s the law of nature.
    A simple proof of this … take something from a freezer out into the room and in short order you will see condensation appear from the rapid change.




    Also, what is the difference/advantage/disadvantage of using galvanized sheet metal ducts vs flex ducts?
    Ducting should have as few restrictions to air flow as possible, one of the reasons rigid ducting is generally used. The ribs usually found with flex ducts will have some restrictions to air flow because of its irregular inner surface compared to the relatively smooth surface of rigid ducts.


    These are just some of my thoughts on this and hopefully they make sense and are helpful.

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