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  1. #1
    Join Date
    Jun 2005
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    4

    Unhappy

    I have a 100 year old house Victorian with central air. The upper floor has registers but very little air flow. The first floor and the basement are very comfortable. However, the bedrooms on the second floor are very hot. The bath on the second floor is also comfortable . I have tried slightly closing that vent and some of the ones on the first floor to send more air upstairs. Should I look at some "duct booster fans" or just call for service? Thanks Mark

  2. #2
    Join Date
    Mar 2002
    Location
    Concord, CA
    Posts
    2,635
    In my experience duct boosters are of negligible benefit. For them to really push enough air they'd have to run at such a high RPM that the noise would be objectionable. But if you need just a tiny bit more airflow then a booster could do the trick.

    Typically the only way to close vents downstairs in an effective way is to close literally all of them. IF that helps it will result in a reduction of total system airflow and may result in equipment damage.

    Usually the only way to properly address a hot upstairs is to upgrade the duct going upstairs and then implement some sort of zoning. The zone system could be automated or just simple hand dampers.

    You're best bet is to find a competent tech who understands duct design and troubleshooting. Those sort of techs are rare. Good luck finding one! Most techs are trained to replace parts. And when they're especially confused then their natural conclusion is you need new equipment.

  3. #3
    Join Date
    Oct 2004
    Posts
    149
    I am having a similiar problem, but I think mine has to do with the poor ductwork in my vintage 1950 home. The HVAC tech that topped off my freon said that I probably either have a 2 speed motor incorrectly running at the lower speed (not) or my motor is going bad or the inside coil is clogged. He also said that the house I live in doesn't have particularly good ductwork by design. My question is if I can have a blower fan motor installed that will increase my air flow. It currently has a 1/4 hp 1050 RPM motor (115VAC, single phase GE 5-5/8 diameter with 1/2 diameter shaft, no separate capacitor (internal, I guess)). I assume that all I'd really need is a motor with higher RPM's, if I can get one that I can mount in the blower? Any bad side effect if I go with something like a 1625RPM 1/4 HP motor? If it matters, the motor was probably made in the early 1980's and the shaft feels "loose", but it cleaned up real good and isn't making funny noises right now.

  4. #4
    Join Date
    Mar 2002
    Location
    Concord, CA
    Posts
    2,635
    If I didn't make it clear in my reply to mwne2, his ducts are his problem as well.

    What strikes me most zzyzzz is that the tech "thinks" the speed may be low? Why didn't he just check?!

    Fan law states that to increase a fan from 1075 RPM to 1625 RPM when you started with 1/4 HP means you'd end up with a .86 HP motor. Since typical HP fractions run either 3/4 or 1.0 you'd have to find a 1 HP 1626 RPM 115 VAC motor. Good luck! I tried for exactly that once. I couldn't find it. Although since most motors draw less than their rating because of restricted ducts you might get away with a 3/4 HP motor at the increased speed. I think I saw a 1625 RPM 3/4 HP motor once. But it's a gamble worth hundreds of dollars potentially wasted. Most contractors wouldn't even consider the idea. If you had started with a 1/5 HP motor and you'd sign a waiver saying you understand it may go south, I'd actually try it. I've always wanted to see how loud a furnace would scream if the wheel spun at 1625 RPM.

    Obviously the correct answer to the problem is correcting the ducts. When that can't be done then sometimes we can alter the ducts that are accessible and then compensate for the rest with an oversized blower in a new furnace.



  5. #5
    Join Date
    Oct 2004
    Posts
    149
    Originally posted by Irascible
    What strikes me most zzyzzz is that the tech "thinks" the speed may be low? Why didn't he just check?!

    I've always wanted to see how loud a furnace would scream if the wheel spun at 1625 RPM.

    When that can't be done then sometimes we can alter the ducts that are accessible and then compensate for the rest with an oversized blower in a new furnace.
    The tech is a neighbor who put in the compressor in 1996. He's a semi-retired HVAC tech who fixes a lot of stuff in the neighborhood. He is very busy and I was lucky to have him come over on a really hot day for a limited amount of time. It was already past 8PM and it's not like he was going to do everything when there were other people in the neighborhood who have more serious HVAC problems. He looked at the blower motor and said that it was very dirty and suggested cleaning the motor and blower (and oiling the motor, if possible). He said to check to see if the blower motor was running at the right speed and said that even if it is, as dirty as it was the dirt may have gotten in the bearings and slowed the motor down a bit. He also told me how to clean the inside coil in case it's clogged. I know the vent system is not great. The line farthest away from the furnace is at least 3-4X longer than any other and also run with that flex duct which also slows down the air flow. I'm more than overqualified to do my own electrical stuff, so I was able to confirm that I have power to the right coils on the motor for high speed, I was questioning if I could even put in a slightly faster motor (OK, maybe not 1675, but something in between 1050 and 1675 or get a 1675 RPM motor that has a bunch of speeds and pick one I like for A/C and one I like for heating). I live someplace that has high humidity so I can't speed it up too much for the A/C.

  6. #6
    Join Date
    Oct 2002
    Posts
    6
    I plan on installing a/c into my old victorian (about 125 years old)I have just purchased this house and doubt that the ducts on the second floor can handle the necessary flow. this may require putting an additional unit on three and ducting down. All somewhat pricy. good luck with your task.

  7. #7
    Join Date
    Jan 2004
    Posts
    108
    Top floors in older houses are hot because of little or no insulation between the hot attic and the ceiling. If you add insulation, the top floor will get a lot cooler.

  8. #8
    Join Date
    Oct 2004
    Posts
    149
    When I bought the house there was no insulation in the "attic" (if you could call it that, it's a flat roof). It's been stuffed with as much insulation as can be put in it. Not sure how that would help with A/C much though, since heat rises.

  9. #9
    Join Date
    Mar 2002
    Location
    Concord, CA
    Posts
    2,635
    It's just not practical zz. Take a look at the motors at Grainger.com. The 1075 RPM motor is the standard. There's a smattering of 1625 RPM motors. And in between are a few one-offs for special situations. You'll have to search the ends of the Earth to find something like you want. And in the unlikely event that you do it's going to cost an arm and a leg.

    OEMs address airflow by changing the blower wheel diameter and width. Other than VS motors, they ALL use 1075 RPM motors - a five ton or a two ton, it's still 1075.

  10. #10
    Join Date
    Oct 2004
    Posts
    149
    Originally posted by Irascible
    It's just not practical zz. Take a look at the motors at Grainger.com. The 1075 RPM motor is the standard. There's a smattering of 1625 RPM motors. And in between are a few one-offs for special situations. You'll have to search the ends of the Earth to find something like you want. And in the unlikely event that you do it's going to cost an arm and a leg.

    OEMs address airflow by changing the blower wheel diameter and width. Other than VS motors, they ALL use 1075 RPM motors - a five ton or a two ton, it's still 1075.
    I've been looking and so far what you said seems to be about right. Anyway, the multiple speed motors only give one speed, which I assume is the highest. Any reason why they don't say what the other speeds are?

  11. #11
    Join Date
    Jun 2005
    Posts
    4
    ok so it looks like I have 10-12" square ducts to the 2nd floor. Should I have them "resleeved" down to the furnace area? Its a straight shot. I guess smaller like a 6 or 8" duct with in the original.Would that speed up the flow? Thanks for the help

  12. #12
    Join Date
    Mar 2002
    Location
    Concord, CA
    Posts
    2,635
    zz,

    Run of the mill multi-speed motors only list their top speed because they're not truly multi-speed. They are actually multi-horsepower. At all of the so called speeds the motor is trying to go the full rated speed whatever that is. But at the slower so called speeds the motor bogs down more because the slower speed is actually less horsepower. Only variable speed motors are truly multi-speed. So again you're going to have to trust me when I say that a higher speed motor is simply not practical. Try the booster fan if you wish or upgrade the ducts or upgrade the furnace blower (new furnace).

    mw,

    You might increase velocity with smaller ducts but you'd have less volume overall. You need bigger ducts or a bigger blower or you can try the booster fan idea. Though the boosters I've seen are round so you'd end up having to do sheet metal transitions. In the end the best option is always bigger ducts.

  13. #13
    Join Date
    Jun 2005
    Posts
    4
    ok so don't resleeve,but somhow increase the flow, So bigger blower?

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