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  1. #1
    Join Date
    Mar 2005
    Posts
    11
    Recently I replaced a 30 year old Lennox belt drive furnace with a Carrier Infinity. The good news is that my gas bills are lower. The bad news is that while the Infinity on low speed is as quiet as my old Lennox, on high speed the infinity wakes me up out of a sound sleep. Fortunately it only goes to high speed when we have a very cold day with high wind.

    So I suggest that the only way to achieve the same low noise as the best of 30 years ago is to get a quiet two-speed system and size the total heat loss to the low speed output of the furnace. Is this progress?

  2. #2
    Join Date
    Feb 2003
    Location
    Huntsville,AL
    Posts
    4,125
    you sleep in the day?

    search here for ideas as to how to cut down the noise -- are the ducts isolated from the air handler?
    is the air handler vibrating?

    get some white noise --

    I used to awaken when the gas burner fired up just after converting from oil to gas in 1958!
    harvest rainwater,make SHADE,R75/50/30= roof/wall/floor, use HVAC mastic,caulk all wall seams!

  3. #3
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,274

    Sound Sleep ?

    Originally posted by nielso
    ..., on high speed the infinity wakes me up out of a sound sleep. Fortunately it only goes to high speed when we have a very cold day with high wind.

    So I suggest that the only way to achieve the same low noise as the best of 30 years ago is to get a quiet two-speed system and size the total heat loss to the low speed output of the furnace. Is this progress?
    More Thorough Analysis shows:

    Progress would be to Sleep DEEPLY
    after having a glass of fine wine

    and the leave "Sound sleep" to others.
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  4. #4
    Join Date
    Feb 2003
    Location
    S.W. PA
    Posts
    3,298
    how loud is it and what kind of noise?
    have you had the installing company back to look it over?

  5. #5
    Join Date
    Mar 2002
    Location
    Richmond, Virginia
    Posts
    4,264
    Something that has always puzzled me. Why would anyone switch their allegiance to a new product when their original one gave them 30 years of satisfactory service?

    Maybe a great salesman. If I bought a Ford that lasted 300,00 miles with very few problems, why would I switch to Chevy?

    I know this doesn't help, but I've always found it curious.

    As for your Infinity system, has the installing contractor been back out to make adjustments? Your system is of a complicated design and needs to be addressed by an expert.
    There is nothing more frightful than ignorance in action....Mark Twain

  6. #6
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Your Infinity is not the problem.


    It is either oversized,running on high only in the most extreme weather,or the ducts are too small,or both.

    Any variable speed furnace fan,will "try" to deliver the correct cfms, with more success and noise,then your old furnace with a standard motor.

    With the proper duct system ,noise would not be objectionable on high,but it will be quieter on low.

  7. #7
    Join Date
    Mar 2004
    Posts
    1,042
    Older furnaces were frequently rated for higher temperature rise than modern ones, too. Since it was permissible to put so much heat in a smaller volume of air, weak airflow wasn't such a problem. But a new furnace, properly set up, will probably have to more more air. If properly configured, you'd get the same noise from a new furnace with a PSC motor- that's just how much airflow is required. All that variable speed does is give the furnace the smarts to insist on moving enough air to stay within its rated specs, even if your ductwork isn't up to snuff for that much airflow. Whooooosh!

    If you replaced your furnace with an otherwise identical one, just one size larger, and ran it only on low, the airflow and noise would be about the same as running the current one on high. Regardless of the cause, it's almost certainly the case that your system is trying to push more air through your ductwork than the ductwork can really handle.

  8. #8
    Join Date
    Mar 2004
    Posts
    1,042
    [double posting deleted]

  9. #9
    Join Date
    Mar 2005
    Posts
    11
    First, the reason I switched from Lennox to Carrier is that all the dealers within 100 miles have switched--there is no Lennox dealer anywhere near.

    Second, I believe the air noise is in the fan/heat exchanger, not in my old ductwork. Although the old belt drive furnace is gone, I remember the blower cylinder being huge, something like 12" in diameter by 15" wide. The new blower looks tiny in comparison. The old heat exchanger was also much larger. Therefore, to move the same cfm, the velocity in the old system was much lower.

    It is true that the old Lennox had a higher temperature rise, but it was as specified by Lennox. The air coming out of the outlets felt good and warm. The air out of the new system seems barely warm at all. I believe Carrier (and presumably other manufacturers) have increased the velocity just to get the good advertising of 90+ percent efficiency, and not with maximum comfort in mind.

    I got a good installation, with no rattles or metallic noise. It is just the air rushing through the heat exchanger that I hear. What is "acceptable" noise is a personal thing, and I consider acceptable the system on low speed. I believe manufactures of forced air equipment have largely given the luxury market away to radiant heat systems by ignoring the air motion noise issue.

  10. #10
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,935
    Post pics of your duct work.

    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  11. #11
    Join Date
    Aug 2002
    Posts
    1,647
    One question I have is what size was your previos unit? Btu wise input/output? Do you have the model # to your old unit?

    What size is the new infinity unit? What is the model #?

    Was there a load calculation done?

    Older units had a higher allowable temp rise than a newer unit has, this requires a new unit to move more airflow than the older unit.. Also many old units did not move even the required amount but only what the ductwork allowed..

    Your new infinity has a Variable speed blower that will ramp up the rpms to move the required cfm needed for the equipments proper operation.. On a undersized duct system this will have the velocity of the air so high that it will be noisy..

    Either the unit is oversized or the ductwork is undersized for the unit installed..

    J

  12. #12
    Join Date
    Mar 2004
    Posts
    1,042
    Interesting. I have a 58CVA070, and if I command full-blast fan output, the furnace is still very quiet, even to stand right next to the unit. I get tons of duct noise in the house, though, because 1200 CFM in my ductwork is about 1.0"Hg, and the ECM has to ramp up to the RPM limit to get there. For that matter, it can really only get to about 1150, because my ductwork just wasn't built to accomodate that much airflow. Thankfully, I don't actually need that much airflow in my application, so it's not really a problem. I just am impressed that the thing can be so quiet even when with the system under a worst-case scenario.

    Then again, you're talking about a condensing unit. Maybe the secondary HX makes the difference? Also then again, the old furnace having a huge blower wheel still doesn't tell the whole story of CFM. It probably turned pretty slowly, so it's still likely that it was moving less air than the new unit. The velocity in the new furnace is almost certainly higher, though.

    Do you per chance know what the static pressure is in the ducts when the system is running on high heat?

  13. #13
    Join Date
    Mar 2002
    Location
    Richmond, Virginia
    Posts
    4,264
    Since you ungraded your furnace, did you also upgrade your air filter? Have you started using more efficient, more restrictive filters? Anything that creates a restriction in the air flow, be it undersized duct, over-sized equipment, duct fittings that are too narrow or otherwise choke the air, or a brand new 3M micro pleat air filter will cause the VS motor to ramp up. Try to think about anything else that is different other than the equipment.
    There is nothing more frightful than ignorance in action....Mark Twain

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