Lennox Air Handler watt inconsistency
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  1. #1
    Join Date
    Oct 2012
    Posts
    6

    Lennox Air Handler watt inconsistency

    I have a Lennox Air Handler (CBX32MV i think) with electric heat. No heat pump attached at the moment. When I had it installed new a few years ago, the installer determined I needed 12.5 kWh electric heat for my house.

    My power meter was recently updated to one of the smart meters. With it I can now look over the Internet at the wattage being used at any given minute, hour, or day

    Using the smart meter's website, I've observed that when my furnace runs, it only shows around 8,600 watts being used. In the very first minute it turns on however, it shows a wattage of around 12,500, but then drops off in the next minute to the 8,600 where it stays. I thought this was odd as I had a 12.5 kWh furnace, and expected to see the wattage stay around 12,500. I called the company that installed it and had them come check whether everything was working properly.

    The tech took the panel off and used his ammeter and determined that all three elements were drawing power. I don't remember the exact amps, but something like 40, 25, and 18 ( it's been a year since he checked, so I don't remember the exact values). He told me that likely what was happening is the furnace determines the airflow and will only turn on the elements it needs to.

    He however couldn't explain why the power meter showed 8,600 watts being with all three elements working when it should be 12.5 kWh? It seemed to me that the 8,600 I was seeing would indicate only two of the elements were working (plus a few watts for other house items, which is usually around 200 watts without furnace running). When he checked the elements with the ammeter showing all three working fine, the cover was off, but when we would look at the power meter, the cover would be on. His other explanation was that it's possible the elements were rated at 12.5 kWh at a different voltage then the furnace is currently using, which could cause the difference in the wattage.

    So my question is, is this normal behavior for my furnace? Even though it's rated for 12.5 kWh, would it be normal to see ~8.6 kWh being used on my power meter, or is there an issue with my furnace and I'm not getting full heat out of it? Even after running for 30 minutes, it will still be drawing around 8,600 watts.

    Thanks in advance.

  2. #2
    Join Date
    Apr 2012
    Location
    winnipeg
    Posts
    1,330
    you have an issue.....
    it was working.... played with it.... now its broke.... whats the going hourly rate for HVAC repair

  3. #3
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,579
    Good chance you have a low air flow issue.

    Posting model number of air handler and strip heater package would tell us more about your air handler.

    40 amps at 240 volts is only 9600 watts.
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    How many times must one fix something before it is fixed?

  4. #4
    Join Date
    May 2008
    Location
    Central Fla.
    Posts
    311
    That Particular A/H needs to be configured for multiple heat stages , I am assuming that is what you have since this is a variable speed unit. W1 is first stage, W2 is 2nd stage and so on. If the stages don't get a call they won't come on. Not sure if they would all come on to give you a warmer startup air temp or not(since you don't have a pump with it) and then cycle back down and search for what stages it is calling for.Need to have a "senoir" tech go out and check it.Not all that familiar with this unit.

  5. #5
    Join Date
    May 2008
    Location
    Missouri
    Posts
    3,409
    Seemingly stupid question, but does this unit heat your home? If it does so, then what is the problem? If your home heats fine using 8600 watts, then great! If you use additional wattage, then the bill may increase along with the higher usage?

  6. #6
    Join Date
    Oct 2012
    Posts
    6
    The particular unit I have is CBX32MV-024/030, and heat strip is ECB29-12.5. As I mentioned earlier, there is no heat pump, so I use it for only electric heat.

    Here's more that I've noticed after looking at it more closely today. When running, it draws the 8,600 watts as before. However, when I temporarily take the front panel off it, the fan slows down, and the wattage goes up to 12,500. It will stay at this point indefinitely. I tried adjusting the fan speeds between the highest and lowest speeds using the jumpers, and it would have the same effect (8,600 watts with cover on, 12.5 with it off). So I'm guessing this must be related to an air pressure switch?

    With the cover off, there is noticeably warmer air coming from the vents.

    I guess the main reason I'm concerned the furnace isn't operating correctly is it seems to take awhile for the house to warm. Obviously under normal use only two of the three elements are working. Is that normal and efficient, or is something still not right and I would be better off if all elements worked to heat the house? I do know my ducts and return air are on the small side, so is the furnace not getting enough intake air flow to work properly, which is why it heats better with the cover temporarily off?

  7. #7
    Join Date
    May 2006
    Location
    Austin, Texas
    Posts
    278
    Sounds like airflow is low(restrictive airflow) causing limit switch to keep a strip off when door is in place. Maybe as simple as replacing filter. Or may need duct modifications

  8. #8
    Join Date
    Oct 2012
    Posts
    6
    Quote Originally Posted by rglasgow View Post
    Sounds like airflow is low(restrictive airflow) causing limit switch to keep a strip off when door is in place. Maybe as simple as replacing filter. Or may need duct modifications
    The filter is new and replaced regularly. Looking at my return air grill, it is 14"x14" with a 12" duct that's about 20' from the furnace.

  9. #9
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    6,207
    That's too small, it's probably overheating due to insufficient duct and causing one if the elements to shut down. Need to fix the ductwork, adding another return would probably help.

  10. #10
    Join Date
    May 2008
    Location
    Missouri
    Posts
    3,409
    Are you using the highly restrictive pleated 1" filters? If so, throw them away and get a simple air filter (non-pleated).

  11. #11
    Join Date
    Mar 2011
    Location
    Galveston Texas
    Posts
    530
    as Jtrammel stated your R/A is too small and not letting enough air flow over the heat strip and causing the limit to trip one set of elements off. That's why when your tech came out and checked the amp draw of the system all of them were working because the door was off and allowed enough air to move over the strips. Have your ductwork inspected and properly sized. once this is done you'll see an improvement of the system

  12. #12
    Join Date
    Oct 2012
    Posts
    6
    Thanks everyone for the help. I've come to the conclusion the return air duct is causing this and needs to be fixed. It's the only logical thing it could be, and explains why the furnace seems to work properly and more efficiently with the front panel off.

    I've got a tech coming out next week to take a look and hopefully get it fixed.

  13. #13
    Join Date
    Oct 2012
    Posts
    6
    A quick follow up. Had the return air vent replaced with a larger 16" vent and 20"x20" grill. The furnace is now working properly. The wattage is reading correctly, and the house heats up much quicker now. The airflow is also quieter, although still not silent (probably due to small supply ducts as well).

    Anyways, thanks to all that helped me figure this out.

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