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  1. #1

    Should I replace my air ducts??

    Hello everyone. I am new to this. I am looking to buy a new AC/Heater unit for my town home. The town home was built in 1979 and the ducts are on the roof exposed to the sun but are sealed. I had a guy give me a quote for a 4 ton unit but said that I should replace my ducts since I am going to a bigger unit. I have a 3 ton now.

    My question is should I replace the ones on the roof or just leave the ones I have???
    I had 2 quotes saying not to change them and 2 said to change them.

    Please help.

  2. #2
    Join Date
    Feb 2009
    Location
    Portland OR
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    Why are you putting in a bigger unit? Bigger AC is actually worse for performance, cost, comfort and humidity in 99% of homes. Does the current 3 ton not cool the home? Did anybody perform a load calculation to verify the size or did they all just guess because they have been doing this long enough? I honestly can't remember the last time I took out an AC or furnace and replaced it with a larger model.

    But to answer the original question assuming you really do need a bigger AC(which I doubt) then chances are you will need larger ductwork to accommodate the 33% more capacity and airflow.
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  3. #3
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
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    6,352
    Why are you increasing size, bigger is not always better in the hvac world. If you are going up a ton the ductwork is likely not big enough for the additional airflow. If the duct is too small you won't get 4 tons of cooling out of it, just higher power bills and a noisier system. Why in the world are the ducts on the roof? That's an awful place to put them.

  4. #4
    Jtrammel thank you for writing back. I have 3 ton now and it does not do the job. It was already here when i bought the townhome. The unit is 15 years old and does not cool. I have it tested and everything. It also does not help that I have 2 story town home and high sealing. The duct work in on the roof in a cut out the leads into the home. I have the unit tested and everything but does not push the air out as it should. You think i should re think this??

  5. #5
    skyheating it does not cool the home down at all. Heat does great. The AC it takes forever. I have 2 story place high sealing. The unit is 15 years old. Every ac guy that came out said this is a under size it. Counting the loft in the Master my unit is 1770sq ft. What do you think?

  6. #6
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
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    6,352
    Yes you should, 2 story houses are hard to evenly heat/cool with one unit especially without zoning dampers. I don't know exactly what the layout or size of the town home is but it may be best to do 2 seperate systems for up/down. Also if its a fairly small house you may want to look into the ductless minisplit systems that are ultra efficient, quiet and you can have each room controlled seperately so you could have your bedroom on while the rest of the house is off ect to save even mor on utilities. You'll also get that ugly ductwork off your roof for good. http://www.mitsubishicomfort.com/en/consumer/about-us

  7. #7
    My home is about 1700sqft

    Thank you for your time on this and all the info.

  8. #8
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    6,352
    I think something else is going on causing the existing unit not to keep up, 3 tons should be plenty big enough. The best advice I can give to have it done right is do a lot of research and have a home energy audit performed to see if there are any underlying issues. Check ou www.comfortinstitute.org www.resnet.us and www.bpi.org for mor info. I've got to get some shut eye, I'll check back tomorrow.

  9. #9
    Join Date
    Feb 2009
    Location
    Portland OR
    Posts
    1,942
    Where is your home located? What's the insulation like. What types of windows?
    It could just be that your current unit is old and not running at capacity. I know this may sound counter intuitive but a larger AC often makes the temperature difference between two floors worse, not better.
    Has anyone performed a load calculation and measured all windows, all walls, checked insulation values and confirmed the size or are they all guessing based on prior experience?
    AC does come in a 3.5 ton size too so maybe that would be better if a large unit is needed. And keep in mind an AC should run continuously on a very hot day, if it turns off and on that is bad for the unit and means its to large.
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  10. #10
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,717
    Quote Originally Posted by krinder22 View Post
    Jtrammel thank you for writing back. I have 3 ton now and it does not do the job. It was already here when i bought the townhome. The unit is 15 years old and does not cool. I have it tested and everything. It also does not help that I have 2 story town home and high sealing. The duct work in on the roof in a cut out the leads into the home. I have the unit tested and everything but does not push the air out as it should. You think i should re think this??
    It may be that the problem is the duct work is under sized. And that 3 tons is all you really need. Some service techs don't really know much about duct work. And just automatically say the unit is too small.
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  11. #11
    Join Date
    Dec 2008
    Location
    Ontario Canada
    Posts
    534
    Do you know how big the furnace is?

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