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Thread: Insufficient air flow to all vents

  1. #1
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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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    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
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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
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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
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    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
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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
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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
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    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
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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
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    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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    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
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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.
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  13. #13
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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.

  14. #14
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    Quote Originally Posted by sammy37 View Post
    He has a package unit.
    Not good.
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  15. #15
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    wgrr: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. You are correct in the ductwork placement exactly. When I said it was not a split unit I guess I meant not zoned. It does have a/c unit outside and heater unit and evaporator connected with copper pipes like you said. My bad sorry.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. This is what I have.I will try to get the electric or gas company to do the manual J load calculation. Here is a photobucket link to my HVAC setup. I tried to make it as clear as possible so bear with me.
    http://s757.photobucket.com/albums/xx215/mcar3333/hvac/

  16. #16
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    Can anyone recommend someone to do this J load calculation in or around Springfield MO. I am afraid to have it done but I need to know what I need HVAC wise. I do not have the money to replace the HVAC unit.

  17. #17
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    That duct work design is dismal... No radius elbows, no turning vanes, round take-offs, the plenum is "T" into supply trunk, servere reduction from drop to furnace, return have jumper boxes, overall not one thing done to have even airflow without massive static losses..

    What size filter is used? What type/brand? Where is it located?

    You stated the coil was cleaned, Was it brushed cleaned? Was it chemical cleaned? Was is Hosed off? Or was it just vacuumed?

    I think that coil is the old Mini-multi-A-coil that york used that had problems with water drainage due to the design of the drain pan,, if so that is a hard coil to properly clean without removing from system and foam cleaning and spraying with hose multiple times..

    You need to look for a company that will do a proper room by room load calculation and knows the ins and outs of manual D to properly evaluate the ductwork and provide a recommendation to the duct problems,, might be better to start from scratch and reduct the home properly.. Also look for a company that is able to do static pressure testing and airflow diagnostics, they can tell you if the coil is still compacted or if it is just the shotty ductwork..

    Goodluck
    J

  18. #18
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    Advanced Response:air filter is a like a 16 x 12 or something like that disposable normal filter you buy at Lowe's or Home Depot. Yes evap core was take out and manually cleaned and looks new now. Can I install a larger blower to get airflow up to try and overcome duct problems.

  19. #19
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    Quote Originally Posted by mcar33 View Post
    Can I install a larger blower to get airflow up to try and overcome duct problems.
    No. You need the bad ductwork corrected.

    Centrifugal blowers like you have on your system are not positive displacement. You can speed up the blower wheel in an attempt to move more air; if the ducts are highly restrictive you will only increase static pressure within the duct and run the blower wheel up to its limit or worse...if you ever hear a blower wheel make a "huffing" sound while it is running, it is air actually trying to blow back through the wheel and into the return air side of the blower.

    Short answer is, again, fix the problematic areas of your ductwork and you will see improvement in air delivery to all areas of your home with your existing blower and equipment. Bad ductwork chokes the daylight out of more system performance than anything else, just about.
    Psychrometrics: the very foundation of HVAC. A comfort troubleshooter's best friend.

  20. #20
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    Quote Originally Posted by mcar33 View Post
    Advanced Response:air filter is a like a 16 x 12 or something like that disposable normal filter you buy at Lowe's or Home Depot. Yes evap core was take out and manually cleaned and looks new now. Can I install a larger blower to get airflow up to try and overcome duct problems.
    You probably already have the largest blower that can be installed in your unit now. Your duct system, I am afraid to say, is typical for SW, S central MO and AR.

    I am good friends with the Lennox rep that handles my area. I will ask him if there is a company he could recommend that is reputable in your area. He may know of one.

    There is no quick easy fix for your problem.
    Signature on hold. Trying to find a real Jefferson quote I like. Others here have bogus Jefferson quotes too.

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