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  1. #1
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    Jul 2004
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    Insufficient air flow to all vents

    I have a 4 ton a/c unit with 1600 cfm blower on a house that is 10 years old. It is not a split a/c system. I bought the house used. It blows cold but does not have enough air flow. I have 23 vents in house with a walkout basement that is finished, size of house 3200 SF. I close the basement vents in the summer and open the upstairs vents. It has always had low airflow, had a/c tech come and check and removed a/c evaporator and cleaned fins still has low air flow. It has low airflow to all vents not just certain ones. He checked inlets and they were all good. A/c runs all day without cycling during summer days with temps above 87 deg t-stat usually set on 75 deg temp upstairs stays 2-3 deg higher than t-stat so it does not cycle off. He told me I needed 100 cfm per vent so I need a 2300 cfm blower. Can I install a larger blower to get the needed air flow without messing up the a/c balance or whatever it's called. I do not have the funds to replaced the heating and a/c system. Does anyone know reputable HVAC tech in or around Springfield Missouri.

  2. #2
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    Jan 2004
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    PA
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    Must be a real real big bathroom that you need 100 CFM to it.

    You need a better tech. One that can actually measure air flow in CFM, and check static pressure of the duct system. Good chance your duct system is undersized.

    Your return system may be undersized enough, that it is only allowing your blower to move 1200 CFM.
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  3. #3
    Join Date
    Feb 2010
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    The midwest.
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    Quote Originally Posted by mcar33 View Post
    I have a 4 ton a/c unit with 1600 cfm blower on a house that is 10 years old. It is not a split a/c system. I bought the house used. It blows cold but does not have enough air flow. I have 23 vents in house with a walkout basement that is finished, size of house 3200 SF. I close the basement vents in the summer and open the upstairs vents. It has always had low airflow, had a/c tech come and check and removed a/c evaporator and cleaned fins still has low air flow. It has low airflow to all vents not just certain ones. He checked inlets and they were all good. A/c runs all day without cycling during summer days with temps above 87 deg t-stat usually set on 75 deg temp upstairs stays 2-3 deg higher than t-stat so it does not cycle off. He told me I needed 100 cfm per vent so I need a 2300 cfm blower. Can I install a larger blower to get the needed air flow without messing up the a/c balance or whatever it's called. I do not have the funds to replaced the heating and a/c system. Does anyone know reputable HVAC tech in or around Springfield Missouri.
    I was going to say it might be a plugged coil. You have had that cleaned.
    Are the filters clean? Is there enough return air openings? Are the dampers open? CFM per register/supply varies. If your home is a two story or a ranch and you're counting the basement supplies, then when you "balance" the airflow to the season, all 23 won't be (totally) open.

  4. #4
    Join Date
    Dec 2003
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    south NJ shore area
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    How many return air grills and what size are they? What size is the supply duct and return duct? How long is the supply duct and return air duct? What size are the feed lines to the register boots? Help us Help you
    GOOD WORK IS NOT CHEAP! AND CHEAP WORK IS NOT GOOD!

    IF YOU THINK A GOOD HVAC COMPANY IS EXPENSIVE. THEN YOU SHOULD TRY A BAD ONE.

  5. #5
    Join Date
    Jul 2004
    Location
    spfld mo
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    Thread Starter
    Beenthere:I need someone local who can do what you say measure cfm and static pressure or whatever. I do not know who to call there are so many in phone book. A/c tech did not measure any airflow just went by rating on unit.

    Todd S 2: Filter are clean. As far as return opening tech took a kleenex and held up in front or each of the returns, 1 main level, 1 dedroom main level, 1 basement and the kleenex would move up against the vent grate when it was held within 1/2 to 1 inch of opening did not seem to have much flow or suction. If it was a return problem would not air flow increase when I take the ft of the furnace unit, it opens up the blower area and takes the return or intake side totally out of picture. When all of the vent downstairs closed air flow still really low upstairs.

    Hvac-learning: I will measure the things you want the best I can. I can access and measure main trunk and off shoots in unfinished area of basement and inlet or return stuff.

  6. #6
    Join Date
    Aug 2002
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    Office and warehouse in both Crystal River & New Port Richey ,FL
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    Coils can be impacted(dirty inbetween the fins,inside the fin pack),what was done to clean the coil? Was it removed for cleaning?

  7. #7
    Join Date
    Dec 2003
    Location
    south NJ shore area
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    mcar33 3Returns with a 4 ton very ???????able most 4 ton drive units on the heater should be ducted by either a bottom return or bottom and side or both sides just something to look at check in the install book to see what will apply. what size return goes up stairs? maybe just 2 wall plates just my thought with out any pics.
    GOOD WORK IS NOT CHEAP! AND CHEAP WORK IS NOT GOOD!

    IF YOU THINK A GOOD HVAC COMPANY IS EXPENSIVE. THEN YOU SHOULD TRY A BAD ONE.

  8. #8
    Join Date
    Jul 2004
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    spfld mo
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    Thread Starter
    dash: coil was taken out and set in floor and cleaned. Visually inspected after it looked like new when done.

    hvac-learning: If you would like I can send you some pics of duct work and inlets if you would like? If I can figure out how to send them to you. I can try to post to this thread but I do not know if I can. As far as return on unit itself, if you stand in front on unit with the unit on the left and the return is on the right. The unit and the return together form a U-shape with the inlet to unit at bottom. I would say the return would be a side return. The access panel is on the ft of the unit. I remove it to access filter. It comes in at bottom on the rh of the unit goes through the filter then get blown by blower up into furnace heater things and then into the evaporator coil.

  9. #9
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
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    A dirty coil got air from the blower. The blower wheel blades, if not cleaned, will reduce air flow. Cleaning a coil is only half the job. Cleaning the blower wheel blades is the other half.

    Beyond that, what is your ductwork made of..flexible, sheet metal, or duct board?
    Psychrometrics: the very foundation of HVAC. A comfort troubleshooter's best friend.

  10. #10
    Join Date
    Jul 2004
    Location
    spfld mo
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    Thread Starter
    shophound: I replaced the blower wheel last year due to it came loose from blower motor and ruined the bushing on it So I know it is clean. I replaced it with the exact same blade assembly. At that time I asked about buying a larger blower blade and they said it would mess up my a/c balance or whatever.

  11. #11
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    Aug 2003
    Location
    Fort Worth, TX
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    This then brings the focus back to your ductwork. Post some pictures of it if you wish and I know it will draw some choice commentary from the pros that gather here.
    Psychrometrics: the very foundation of HVAC. A comfort troubleshooter's best friend.

  12. #12
    Join Date
    Jul 2004
    Location
    NW Arkansas
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    Quote Originally Posted by mcar33 View Post
    I have a 4 ton a/c unit with 1600 cfm blower on a house that is 10 years old. It is not a split a/c system. I bought the house used. It blows cold but does not have enough air flow. I have 23 vents in house with a walkout basement that is finished, size of house 3200 SF. I close the basement vents in the summer and open the upstairs vents. It has always had low airflow, had a/c tech come and check and removed a/c evaporator and cleaned fins still has low air flow. It has low airflow to all vents not just certain ones. He checked inlets and they were all good. A/c runs all day without cycling during summer days with temps above 87 deg t-stat usually set on 75 deg temp upstairs stays 2-3 deg higher than t-stat so it does not cycle off. He told me I needed 100 cfm per vent so I need a 2300 cfm blower. Can I install a larger blower to get the needed air flow without messing up the a/c balance or whatever it's called. I do not have the funds to replaced the heating and a/c system. Does anyone know reputable HVAC tech in or around Springfield Missouri.
    I am having a hard time wrapping my head around exactly what kind of unit you have. You state it is not a split system but when describing the coil cleaning you said the tech pulled it out and set it on the floor. I am familiar with the area and know most cooling systems are split system with a unit outside connected by a copper line set to the indoor air handler/heater with a cooling coil on top or underneath. The other possibility is a package unit that contains everything needed to cool and heat the house. The package unit is connected to the houses ductwork outside at the unit.

    Is the house one story with a finished basement. are the vent openings coming out of the ceiling in the basement and out of the floor on the main floor. If so I imagine the ductwork is in between the floor. This never works out very well in a house this size.

    Unless your home is super tight and super insulated a 4 ton unit will not cool 3200 sq/ft in this area. I also suspect the blower is not moving enough air to supply your duct system.

    Call some companies and ask for a tech that can do a manual J load calculation on your home. Be sure you tell them you are willing to pay for it. Better yet, see if the electric or gas utility company will do it. Most of the time it is free. I assume this is a gas fired heater. Once you have this load calculation you will know what you need to correct your problem. It will tell you room by room how much cooling and heating is needed and how many CFM of air are required for each room to achieve it.

    Many times around this area I have run in to the exact complaint you are expressing here. The problem is builders of spec or even custom homes want the absolute lowest price from the heating and cooling companies for the install. As long as it passes code, blows warm air in the Winter, cool air in the Summer and it gets them through the one year warranty period they are happy.

    Good luck. Wish I was a little closer I would take a look see at it myself.
    Signature on hold. Trying to find a real Jefferson quote I like. Others here have bogus Jefferson quotes too.

  13. #13
    Join Date
    Feb 2007
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    Las Vegas,NV
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    Quote Originally Posted by hvac-learning View Post
    mcar33 3Returns with a 4 ton very ???????able most 4 ton drive units on the heater should be ducted by either a bottom return or bottom and side or both sides just something to look at check in the install book to see what will apply. what size return goes up stairs? maybe just 2 wall plates just my thought with out any pics.
    He has a package unit.

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