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  1. #1
    Join Date
    Dec 2014
    Location
    NC
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    38

    Default Air temperature from register is about 140 F

    A 10-years-old town house and the HVAC is original Lennox system.
    Air temperature from registers in third floor is about 140 F.
    Some black stains surrounding the registers as attached image.

    Do you concern this? Too hot?

    Thanks

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  2. #2
    Join Date
    Oct 2010
    Location
    MONTREAL QUEBEC-CANADA
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    1,840

    Default Re: Air temperature from register is about 140 F

    The furnace is operated by a thermostat and automatic controls, which safely keep the house at an even temperature
    I accept 120 F.

    Yes that is high but;
    What type of energy?
    What were the thermostats set at?
    What did the filters look like?
    Did you dismount a register or two to feel inside?
    Were all the registers 140.
    Did you check the returns at the plenum.
    Did you ask the home owner?

    Robert Young's Montreal Home Inspection Services Inc.
    Call (514) 489-1887 or (514) 441-3732
    Our Motto; Putting information where you need it most, "In your hands.

  3. #3
    Join Date
    Dec 2014
    Location
    NC
    Posts
    38

    Default Re: Air temperature from register is about 140 F

    Dear Robert:

    Thanks for your reply.

    Quote Originally Posted by ROBERT YOUNG View Post
    The furnace is operated by a thermostat and automatic controls, which safely keep the house at an even temperature
    I accept 120 F.

    Yes that is high but;
    What type of energy? Natural Gas
    What were the thermostats set at? 65 F
    What did the filters look like? Not bad
    Did you dismount a register or two to feel inside? what do you suggest me to feel except for hot?
    Were all the registers 140. Not all, most of register on third floor and the air handler is in attic
    Did you check the returns at the plenum. 64 F
    Did you ask the home owner?
    Planned to. Home owner was not there.


  4. #4
    Join Date
    Mar 2007
    Location
    Plano, Texas
    Posts
    4,170

    Default Re: Air temperature from register is about 140 F

    That is dirt on the ceiling which collects there because the vent damper on the register is totally closed. Closing the registers will also restrict the air flow for the heating system and raise the output temperature (but lower the energy efficiency). Open those registers and let that thing breath!
    Change the filters!

    Jim Luttrall
    www.MrInspector.net
    Plano, Texas

  5. #5
    Join Date
    Dec 2014
    Location
    NC
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    38

    Default Re: Air temperature from register is about 140 F

    Thanks. But there are open ones as well.

    Quote Originally Posted by Jim Luttrall View Post
    That is dirt on the ceiling which collects there because the vent damper on the register is totally closed. Closing the registers will also restrict the air flow for the heating system and raise the output temperature (but lower the energy efficiency). Open those registers and let that thing breath!
    Change the filters!



  6. #6
    Join Date
    Mar 2007
    Location
    Plano, Texas
    Posts
    4,170

    Default Re: Air temperature from register is about 140 F

    Quote Originally Posted by Mike Tao View Post
    Thanks. But there are open ones as well.
    Part of the dirt is from air forcing between the ceiling and the grill face due to pressures and lack of flow through the grill. Dirt will impact the ceiling and plate out on relatively cooler surfaces.
    ANY registers that are totally closed will decrease the air flow through the system and raise the temperatures.

    Jim Luttrall
    www.MrInspector.net
    Plano, Texas

  7. #7
    Join Date
    Oct 2010
    Location
    MONTREAL QUEBEC-CANADA
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    Default Re: Air temperature from register is about 140 F

    I do HVAC inspections when I can but its been some time that this has come up.
    Thanks for the exercise!

    The offset would be almost 80 degrees on the return plenum. To high.
    50 might be a high depending on the setup as well.

    Gas, in your case, or oil for that matter, would be 140 to 160 - 170+ at the plenum supply side. Depending how and were you took the temp.

    Rationally thinking, which is rare at my case ha ha ha, on the trip upstream, supply side heat loss is typical correct? Yes...

    I will say it sounds like the fan limit/ing switch needs to be corrected.
    Here is a link. Simple explanation at a simple system when you think about it.
    How the Forced-Air Furnace Works: Putting It All Together

    Hope it helps!

    Last edited by ROBERT YOUNG; 01-15-2016 at 02:48 AM. Reason: Plenum sides
    Robert Young's Montreal Home Inspection Services Inc.
    Call (514) 489-1887 or (514) 441-3732
    Our Motto; Putting information where you need it most, "In your hands.

  8. #8
    Join Date
    Feb 2008
    Location
    Caledon, Ontario
    Posts
    5,005

    Default Re: Air temperature from register is about 140 F

    1. For a ten year old unit, that should not be creating dirt accumulation at registers if the unit is tuned and function properly. More troubleshooting required beyond visual inspection and a host of speculative causes.

    2. Dirt could be the result of cheap filter. Alternatively filter could be restricting air flow due to high efficiency.

    3. Occupant activities creating dirt through dust, house situated near industrial or road ways.

    4. Candles being burned.

    5. What shape are the bearings and blower? Some older units with failing bearings, or improperly oiled (too much) can disperse oil film into air stream. However a 10 year old blower motor will likely have sealed bearings.

    6. Cracked heat exchanger?

    7. Occupants are smokers? Or not inclined to keep a clean house?

    8. Sounds as if the unit has not be regularly serviced.

    9. Yes temp differential is high, which needless to say; the unit should be serviced and or replaced due to age.

    Last edited by Raymond Wand; 01-15-2016 at 04:16 AM.

  9. #9
    Join Date
    Mar 2012
    Location
    Lansdale, PA
    Posts
    876

    Default Re: Air temperature from register is about 140 F

    That is higher than a typical allowable temperature rise for a furnace. Something may be restricting airflow.


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