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  1. #1
    Join Date
    Jul 2005
    Posts
    717
    I have a one floor 1400 sq ft bungalow with a finished full basement.
    I wish to install a/c The home has a forced air oil furnace.
    The basement is VERY cool , even when there is a heat wave. The main floor can be 78 F and the basement will be a cool 64 F.
    In a heat wave,I normally will run the furnace fan on continuous low speed (sometimes with fan door off(with a filter) and this will circulate the nice cool air up to the main level and helps to lower the temp on the main level,thus bringing the lower level up.
    But if the heat wave is constant for more than 2 or 3 days this upper level gets a lot warmer.
    My question is; If a/c is installed won't this make the basement even colder?, unless of course I shut the basement registers off in the cooling season. I know in order to 'normally' cool 2 levels I will need a 2 ton unit, but by just only cooling the upper level would I just install a 1 ton unit. I don't want a 60 F basement. . Is a Zone system an option? Thanks for any input.

  2. #2
    Join Date
    May 2005
    Location
    Wilmington, NC
    Posts
    66
    Size the system for the whole house and add a zone system to controls the 2 floors seperatly. This will help to better condition the house in both heating and cooling seasons.

  3. #3
    Join Date
    Jul 2005
    Posts
    717
    Thanks for your reply Beachhvac. The problem is only in the cooling season.
    The heating season is fine as the basement area has ample supply and return outlets.
    AS the furnace does not come on in the warmer season the basement is too cool. I have looked into "zoning", but it would be much too expensive(finished basement) because of of the re-routing of ductwork plus the costs of various dampers, controls, etc.
    Any other suggestions would be much appreciated.

  4. #4
    Join Date
    May 2002
    Location
    Colorado
    Posts
    697
    Cold basements are a problem in my area. Why? Because builders won't seal the ducts properly and won't insulate them. The sealing is getting better, but they still won't insulate any of the gazillion feet of 6" metal duct that runs in the joist bays of a typical new home.

    I hope you can get to your duct work in the basement ceiling, because if you don't seal and insulate throughly your basement will keep meat fresh for six months.

    And uninsulated ducts with 55 °F air running through them are apt to sweat and drip water.

    Also, pay a few bucks and do your own load calculation by downloading HVAC-Calc. Just click on the bull's eye at the top of the screen. Remember, if you want it done right do it yourself.

    Good luck and have a great Independence Day.

  5. #5
    Join Date
    Feb 2003
    Posts
    1,996
    shutting down your basement vents sounds like the only cheap solution. Calc the load for the 1st floor only. Remember that you still have humidity down there you'll want to remove, so leave the return open down there. You can't go too small, since your furnace blower is moving air at a given CFM, requiring a minimum condenser size.

  6. #6
    Join Date
    Jul 2005
    Posts
    717
    thanks for your reply Johnsp. So i could just close the basement supplys, leave the 2 returns in the basement open, size a 1 ton unit (A- coil in plenum,with an exterior condenser)
    I figure the total cfm is approx 750-800 on medium high. There are 14 supply registers total -4x10 fed by 5" diam runs off main trunk. Because I will be shutting off the 7 registers in the basement, I probably would be best to keep the a/c air at med.high too,rather than increasing it.
    What do you think?

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