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  1. #1
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    90% colemans motor ramping up & down?

    Large property had furnaces replaced. 40+ year old bldgs. 60 & 80,000 btu furnacws installed. Installers say fix is to remove high speed wire to programed motor to hopefully correct problem. They insist static pressure test not necessary. All are coleman 90+ furnaces. help.

  2. #2
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  3. #3
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    They probably don't know how to measure it, or already know that its too high.

    What reason do they give.
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  4. #4
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    something about a paper blocking test that rules out it being a static pressure problem.

  5. #5
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    Other than tenants complaining of the fan noise, what problems with the system should I be concerned with?

  6. #6
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    When ductwork is insufficient, the ECM type motors try to make up for the ductwork by working too hard, and they have a high failure rate in those situations.

    This would be the only 60 year old building design that I had ever heard of where the ductwork was sufficient or proper by ACCA standards.

    If I were you, I would bring in a company that is capable of doing a load calculation and a survey of the needed ductwork, so you know what the real story is.
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  7. #7
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    Like most mechanical products, there are design parameters within which the product must be operated. In the case of ECM motors, they too are designed with maximum values. If your system exceeds the maximum value for the motor, the motor will ramp up to max, then ramp back down, repeating the process ad infinitum. If your installing company is, for whatever reason, failing to deliver the information needed to determine the cause of the problem, then it's time to get a second, educated opinion. Did the original company do a load and duct analysis of each system before installing the new furnaces? I have a friend who had a new home built in an over 55 development. Seems the installing company had two furnaces sizes for the homes. The smaller furnace for the basic home the large for the homes with the optional breakfast area 10x12 room on the back of the home. Alas, a load analysis reveals that even the smaller furnace is too big for any of the homes, as well the AC systems. So just because they've put in a bunch of furnaces, certainly doesn't absolve them of their responsibility to do a load and duct analysis in each and every unit.

  8. #8
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    Quote Originally Posted by kevin rosewicz View Post
    something about a paper blocking test that rules out it being a static pressure problem.
    Paper is not a way to check if static pressure is a problem.
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  9. #9
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    no load or duct analysis was done on the units prior to installing. My thoughts were that they oversized the systems. Duct work is all enclosed. If so, systems should be replaced with properly sized systems? They claim it a system issue and they are working with the factory to resolve it. They have not been paid for work yet. Last units to be installed tues-wed next week. How might this affect ac system? Heat exchangers. Motor life? They are expensive.

  10. #10
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    Load analysis is the basis for all the calculations. Well, actually, a blower door test to check the rate of air exchange per hour in each home is the proper way to begin the process. Then tighten up the home against excessive air exfiltration/infiltration, then do a load analysis. Once the analysis is accurately completed, the company can then measure the ducts, observe the supply outlets and predict whether the proposed furnaces are going to perform as anticipated, including the blower within the furnace.

    Variable speed motors, ECM constant torque are all permanent magnet DC motors that use a fraction of the watts of an AC motor. However, that's only when the resistance to airflow is relatively low. By low, I'm speaking of .5 Inches of Water Column or less. Up to .8 IWC could be tolerated and is about the 'break even' point for energy use. Anything above that will result in higher energy costs and potentially premature failure of the motors. This is not a lesson you'd like to learn 2 or 3 years down the calendar. If you're already having blower problems, you need some assurance that the units are properly sized for the homes. Again, that mandates a load analysis at the very least. if the installing company can't do that (oh my, what's new?) then find a company that can and hire them to do an analysis on few of the homes. If it's discovered that the furnaces are properly sized, then you've got documentation to take to the manufacturer as evidence of an equipment problem. But if you find the units are oversized, then you'll need to have a conservation with the installing company.

    You may want to consult with a building inspector, mechanical engineer or other knowledgeable entity about the building codes in your state. It may well be that a load analysis is required and if so, you've got the installing company in violation of state building codes and that leaves them without a leg to stand on if things turn out to be not properly sized.

    As stated before, testing of the duct static pressure will reveal whether there's a problem with the ducts and that also should be accomplished. But that alone won't determine if the issue lays with the furnace size (they do come with different blowers in many instances but it's up to the installing company to specify which blower they want for the furnace) or with the duct system.

    This sounds like it could get to be a can of worms. I'd move to find a company to do a load analysis very quickly (like the next business day) before money changes hands.

  11. #11
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    Thank you for your time and expertise, it is greatly appreciated.

  12. #12
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    That's load analysis AND duct analysis.
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  13. #13
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    Nov 2005
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    Kansas
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    Quote Originally Posted by kevin rosewicz View Post
    Large property had furnaces replaced. 40+ year old bldgs. 60 & 80,000 btu furnacws installed. Installers say fix is to remove high speed wire to programed motor to hopefully correct problem. They insist static pressure test not necessary. All are coleman 90+ furnaces. help.
    I have to agree with the installers. I need to know furnace model. In Kansas City furnaces are normally oversized as the blower motor capacity for AC dictates the sizing of a furnace.
    York/Coleman smallest furnace with ECM is 60k and comes from the factory set on high speed, which is actually set way too high. This furnace needs 900CFM in heating mode and not the 1200CFM as it is probably set at. The ECM motor will try to pull that amount of air, which causes the motors to rump up and down, which is a bad thing. Once the speed is set correctly, the static pressures should be in the normal range.
    The ductwork is probably not ideal, but in general the sizes in Kansas City fulfill minimum requirements and only restrict size of AC.

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