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  • Increase blower size?

    I have a two story house in the atlanta area, with a split unit made by comfortmaker. I have a gas furnace in the attic (model: NTG3100) and condenser outside comfortmaker 10 (model: mac0426766). The Unit is set up in two zones, upstairs is one zone, the downstairs is the other zone. The house was built in 2002 and serviced by last summer before we bought the house in June.

    When both zones are trying to cool at the same time you can barely feel the air coming out of most of the air vents. The upstairs gets to about 85 and the downstairs to 80, and cannot cool down until the sun sets. Outside this week has been in the mid 90's. It ran the same way last year, but we made it work.

    Is there a way to put a bigger blower motor in the furnace to get more airflow? Any other suggestions?

  • #2
    Re: Increase blower size?

    You most likely will end up doing some engineering. Besides a more powerful and faster turning motor you'll want a blower wheel the same width and diameter but with more pitch and fins. If all you did was to speed up rotation with a new motor most likely your old blower wheel would be over-sped resulting in howling and maybe throbbing noise.

    Question: Do you have ducting so you could add a second air handler and make a split up system where (A) would be the basement and ground floor and (B) the second floor? If yes, you can do some really great stuff. You might be able to do some engineering where you would have too evaporator coils and T off the lines. Each coil would have it's own expansion valve or orifice. This is so the condensing unit ends up seeing the same load it does now.

    Take a look at your return grills, filters and such. Also be sure your blower does run faster for AC than heating. Close off any supply registers down near the floor which are only for heating.

    The motor and blower wheel change is the most simple, but you need to be sure you can lower the speed and air flow for heating. You'll need to run some temperature checks for heat rise and coil temps. I would first look for little simple things such as restrictions. Could you have a build up or dust-dirt in a return which needs to be cleaned?

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    • #3
      Re: Increase blower size?

      1) No. There is no way to get a bigger blower to work properly in your furnace.
      2) You dont need a bigger blower. You have a 3.5. ton a/c, and I guarantee the furnace is capable of moving 4 ton of air. If your blower is undersized, then so is your a/c unit and most likely your entire duct system. A bigger blower will do nothing by itself. Your furnace is a 100,000btu 80% builders model.

      You have other problems. Check the zone dampers to make sure they are opening. Has the filter been changed regularly? Lack of filter maintenance will cause the evaporator coil to plug up with dirt blocking off airflow into the duct system and will not allow the proper amount of refrigerant to boil off. Not changing the filter will lead to the fins on the blower wheel getting filled with dirt. If this happens, the blower will spin, but will not move any air. Check to see where the black wire from the blower motor is plugged in at.

      Andy

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      • #4
        Re: Increase blower size?

        The dampers are opening just fine, I've changed the filters regularly since I moved in a year ago. The house was five years old before I purchased it, so I don't know how well it was kept up before that. The blower is wired so it moves faster for ac, and slower for heat. Is it possible for me to open it up to see if there is any debris on the coils so they can be cleaned? I'm guessing I could get my shop vac in the unit to clean off the fins of the blower.

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        • #5
          Re: Increase blower size?

          To get access to the evaporator coil might be a little difficult. It might be best to have a pro check it out for you.

          The entire blower assembly will slide out just by removing 2 screws. You will have to unplug some wires to get it completely out, but you should be able to get a good look at the blower wheel either way.

          It sounds pretty screwed up. If each zone individually works, but the a/c wont keep up when both zones are calling, it sounds like a major design flaw in the system.

          Get a pro out to service it again and get their opinion of the system overall.

          Andy

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          • #6
            Re: Increase blower size?










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            • #7
              Re: Increase blower size?

              The Photos I just put up are of my furnace in my attic. I think I found what may be the culprit, it's a manual damper that connects the upper part of the furnace with the lower part with a 10" line. It wasn't letting any air through it, until I manually lowered it, which increased airflow out of my vents. When I first looked at it, the lever was vertical. I moved it horizontally which allowed the airflow. Which is the last photo I put up.

              Since I'm not a HVAC guy really don't understand why I have this, or what it's doing. Do I need to leave it in this mode, after about an hour or so it goes back to closed by itself without the unit shutting off. Any ideas or input would be greatly appreciated.
              Last edited by twitchymike; 06-08-2008, 05:25 PM.

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              • #8
                Re: Increase blower size?

                That looks like a bypass damper. Basically, you have a 3.5 ton a/c which requires 3.5 ton of airflow. (roughly 1400cfm) But your 2 individual zones dont require 3.5 ton each and therefore the duct systems to each zone cant, and wont be designed to handle 3.5 ton of air. Just for arguements sake lets say that your load is split up evenly. 1.75 ton per floor. With only 1 zone calling and asking for 1.75 ton of air, and the a/c needing the full 3.5 ton of airflow to function correctly, a direct bypass from the supply to the return is added to 'relieve the pressure'. With 1 zone calling, this should be open, or partially open. With both zones calling, this should be closed.

                My opinion is that zone systems like this are the biggest waste of time there is. Its not efficient at all to bypass air like that. The only way I will zone a system is by using multi-stage equipment which can fire depending on how many zones are calling.

                Hope this helps you out.
                Andy

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                • #9
                  Re: Increase blower size?

                  Thanks, that really helps and makes a lot of sense. Yeah, if I had a choice there wouldn't be a zoned unit, just two seperate units.

                  When I took the photo of the manual damper both zones were running, and the arm was all the way to the left (looks like "closed" position), and with only one zone on, it should be "open", or semi opened state. That's the way I understand it, after reading your last reply.

                  There are weights on the end of the arm that can be adjusted. I guess I need to find out where they need to be in order for it to "open" and "close" at the correct time. It was in the open position when I found it today, with both zones running.

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                  • #10
                    Re: Increase blower size?

                    What ait looks like to me is your ductwork is a cluster **** that's groasly undersized, including the cold air return. You need to have someone come in and check the air velocity at the registers for a start and make sure they take a good look at the ducwork.
                    sigpic

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                    • #11
                      Re: Increase blower size?

                      Originally posted by NHMaster3015 View Post
                      What it looks like to me is your ductwork is a cluster
                      I agree to us northerners this would be a hackjob, but I think its a pretty common installation in the south. I have a pet peeve about foil tape. It gets used on about .1% of my jobs. Even then its not the ugly stuff with the writing.

                      Originally posted by twitchymike View Post
                      Thanks, that really helps and makes a lot of sense. Yeah, if I had a choice there wouldn't be a zoned unit, just two seperate units.

                      When I took the photo of the manual damper both zones were running, and the arm was all the way to the left (looks like "closed" position), and with only one zone on, it should be "open", or semi opened state. That's the way I understand it, after reading your last reply.

                      There are weights on the end of the arm that can be adjusted. I guess I need to find out where they need to be in order for it to "open" and "close" at the correct time. It was in the open position when I found it today, with both zones running.
                      Check to make sure the shaft isnt getting hung up in the bearings.

                      If this has the adjustable weights on the end, I believe the correct term is barometric relief bypass. The weights will be adjusted to provide just enough counterweight to open partially or all the way when 1 zone is calling, and stay closed when both are wanting air.

                      Andy

                      Comment


                      • #12
                        Re: Increase blower size?

                        Originally posted by NHMaster3015 View Post
                        What ait looks like to me is your ductwork is a cluster **** that's groasly undersized, including the cold air return. You need to have someone come in and check the air velocity at the registers for a start and make sure they take a good look at the ducwork.
                        I agree, they did a s**tty job on most of the HVAC in my house. Not sure if the cold air return is the problem, there are a total of four, two for each zone(1st floor and 2nd floor, no basement). I'm an electrician though, so I could be wrong, wouldn't be the first time.

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                        • #13
                          Re: Increase blower size?

                          Originally posted by Ruudacguy View Post

                          Check to make sure the shaft isnt getting hung up in the bearings.

                          If this has the adjustable weights on the end, I believe the correct term is barometric relief bypass. The weights will be adjusted to provide just enough counterweight to open partially or all the way when 1 zone is calling, and stay closed when both are wanting air.

                          Andy
                          Thanks, I'm gonna try and get that working correctly now. I'm also going to install two electronic gable vents in my attic to try and relieve some of the stress from the unit. The second story has an attic on either side of it, which are not connected, and have their own gable vent. This area of the house gets the hottest, 85 degrees with the air going all day. Hopefully that will help.

                          Thanks for your advice.

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