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  1. #1

    Confused

    My house is single story 1400sqft built in the mid-1960's raised on piers. The original central HVAC system was a high velocity system with electric heat and AC. The ducts are 2in diameter at the vents. There's one air return in the center of the home.

    Last Fall, one of the fan blades on the condenser unit broke and I began a long, confusing, and so far fruitless journey to getting my AC fixed.

    I'm facing many issues, including the fact that the house is located in an area that has recently been reclassified as a flood plain. The existing air handler is in a crawlspace below the 100-year flood level, so the new air handler will have to be relocated.

    But the question of the moment concerns the high velocity nature of the original unit and what can I reasonably replace it with.

    My HVAC contractor has quoted me a 2.5 ton 13 SEER split system forced air heat pump to connect into the existing duct work with the addition of one new air return vent.

    I'm worried that the 2in ducts are unsuitable for a conventional forced air system. But my contractor has not indicated that the ducts need to be replaced.

    So my question is: is this a problem? Is it possible to use a conventional air handler with the small ducts that currently exist, maybe by oversizing the system?

    Or is it necessary to redo all the ducts to work with conventional forced air. Of course, because it was originally a high velocity system, it does not have air returns in each room. So I'm thinking that maybe additional returns would be required in this scenario.

    Or should I go back with a high velocity system.

    Not sure what other information is needed. Ask away and I'll respond as best as I can. With summer coming, this thing is putting a lot of stress on me. :-)

    Thanks in advance.

  2. #2
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,095
    Only high Velocity will work on HV duct system!

    Are youo sure he isn't quoting a HV unit.
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  3. #3
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,295
    Originally posted by tomdougall
    My house is single story 1,400 sq ft built
    in the mid-1960's raised on piers.
    The original central HVAC system was a high velocity system with electric heat and AC.
    The ducts are 2 in diameter at the vents.
    There's one air return in the center of the home.

    My HVAC contractor has quoted me a 2.5 ton 13 SEER split system forced air heat pump to connect into the existing duct work with the addition of one new air return vent.

    I'm worried that the 2in ducts are unsuitable for a conventional forced air system. But my contractor has not indicated that the ducts need to be replaced.

    So my {questions are}:
    1. is this a problem?
    2. Is it possible to use a conventional air handler with the small ducts that currently exist, maybe by oversizing the system?

    3. Or is it necessary to redo all the ducts to work with conventional forced air. Of course, because it was originally a high velocity system, it does not have air returns in each room.

    4. Or should I go back with a high velocity system.
    1. Definitely
    2. Absolutely NOT possible to MIX systems
    3. Total new duct system with is needed.

    1,000 CFM for 2.5 ton unit
    requires 9 six-inch supply air ducts.

    4. It may be your only real option depending on space availability. However, based on the need to relocate the High Velocity air handler you may have to almost start from scratch on the duct work anyway.
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  4. #4
    Originally posted by beenthere
    Only high Velocity will work on HV duct system!

    Are youo sure he isn't quoting a HV unit.
    Honestly, I'm not sure of anything. This process has taken months for me to even get this quote because of going round and round with the inspector on the flood plain issue. My thought is that although I mentioned HV in Oct 05, he didn't do the quote until April 06 and he'd probably forgotten that it was an issue.

    Anyway, the part numbers he quoted me:

    Carrier Heat Pump 13 SEER, 2.5 tons R-410

    Air Handler FV4BNF002
    Outdoor unit 25HPA430A003

  5. #5
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,179
    Yupper, that ainta gonna work Will need either a Space Pak or Unico air handler. Probably could use that outdoor unit though.

  6. #6
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,095
    Also, the new HV blowers require more ouotlets then the old ones did, so they will have to add some, or you will have a noise problem.

    As baldie said that outdoor unit should be ok to use with a new HV blower.
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