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Brain Teaser: What makes a Network Room's internal doorknob hot?

Yep, it sounds silly, like maybe it's a joke?  But it's really something I'm trying to discover.

A couple of my 250+ network rooms have internal doorknobs that are noticeably warmer than expected.

The air conditioning is working perfectly inside the room and also out in the hall.

Anyone inside the network rooms comments about the brushed-aluminum-looking doorknobs being warm.  Not hot, but warmer than expected when you're in a cooled room.

The rooms are good sized--12'x16' or bigger, with 14' ceilings.  There's not a lot of network equipment or other electronics in them--maybe six Cisco 2960XR's in network racks in the middle of the room, a few wall-mounted intercom and electronic security boxes, and that's it.

This particular building has eight network rooms, only two of which have warm doorknobs.

The building is a cancer treatment center and clinic that's only eight years old.  I jokingly asked our Radiologists and Physicists whether loose neutrons might be a cause; they were thoughtful, then smiled and shared that the treatment rooms are encased in six to twelve feet of concrete on all sides, with thick concrete neutron baffles for their halls, and thick lead doors isolating them.  They didn't think their equipment would be a possible source of the heat.

There are motion sensors over each internal door.  Could some form of infrared motion detection emit enough radiation that a door handle might become just slightly warmer than the surrounding air?

But other doors have the same detectors, and don't have warm doorknobs.

I've not measured the temp on the handles--yet.  ;^)  But the air temp is probably 68F around them, and they are probably 85F or warmer, at a guess.

Apparently I need a way for NPM to measure and track and report on doorknob temperatures.  Maybe I should relabel this for a Halloween story . . .


  • is it only the doorknobs inside the room and not outside of the door as well ?

    I would suspect that either a exhaust fan is blowing on them or there is heat being conducted to it somehow.

    Heat is transferred either via conduction, radiation, or convection.  So either something touching it, something near it is hot, or something below it is hot. 

  • It's only the internal side of the door which has a warm doorknob.

    You're absolutely correct as far as I can see--there must be a source of heat pointing at that metal, but I can't discover it.

    I also believe the outside doorknob should have at least a slightly warmer feel, since it should conduct the heat through the metal of the knobs from inside to outside.  It's a mystery so far, but I'll update this once I find the cause.  IF I find the cause.

  • I found that once on our campus.  It turned out that the electronic lock portion of the door knob was pulling current and warming the knob.  Many of our campus doors have fob locks attached to them.  Fob the door, and the solenoid either locks or unlocks the door.  But keep that current up and the whole thing warms up.  I don't know if that might apply to your doors.

  • Ahh, electromagnets.  You have a coil with current running through it.  That is effectively a heating element.

  • Exactly right.  In our case this was only a couple of doors that were drawing more current than others.  Too much current.  They needed repairs.  I have an electronics background so I was able to understand what was going on and alert our facilities team to the issue and they were able to repair the part so it wasn't pulling so much current and heating the latch like it was.

  • Usually result of MAG Locks... and now that I read ^Up^ I see that you've been helped.

  • A couple of questions/points:

    1. I guess a simple environmental sensor is out of the question? You want to 'geek' this solution up?

    2. What is the actual door made out of?

    3. And does the door get warm as well?

    4. If it does you may have some type of loose current mistakenly being run into that door. Forgive me, I am not an electrician. I use these terms loosely.

  • I brought my Infra Red thermometer to the site and checked eight network rooms' internal door handles' temperature.  Six of eight were noticeably hot.  The warmest was over 83F.  I've got the electrician looking into it now.


  • Someone is probably playing a well thought-out prank haha. Just Kidding, but that would be pretty funny

  • So what did the electrician say?