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  1. #1
    Join Date
    Sep 2010
    Location
    Pittsburgh , PA
    Posts
    7

    Confused Emergency heat relay?

    This is not for DIY work or pricing, I just want to know more about the emergency heat relay in a heat pump application. We came across it in class, and i'm not too sure on it's function. Could someone enlighten me?


    I remember that it locked out something, and that it bypassed something else. Any help would be very nice.

  2. #2
    Join Date
    Dec 2008
    Location
    Ontario Canada
    Posts
    546
    Emergency heat can be wired and controlled any number of ways, it just depends on the installer, the application and the equipment.

    Generally its purpose is to disable the outdoor unit and run the back-up heat source in the event of a heat pump failure. This lets the home owner see a problem, switch over to EM, then not kill the equipment and still have heat until the service tech arrives.

    Every technician has his own opinion as to how emergency heat should be wired, but that is the general concept behind an emergency heat relay

  3. #3
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,179
    I can't remember the last time I saw an emergency heat relay used. Probably the last time I saw outdoor thermostats used. They cost money to install. Without outdoor stats to bypass, don't need an emergency heat relay. Putting the stat on em heat setting eliminates energizing the compressor and sends call for heat straight to the strips. All of them, just like backup.

  4. #4
    Join Date
    Dec 2008
    Location
    Ontario Canada
    Posts
    546
    Quote Originally Posted by BaldLoonie View Post
    I can't remember the last time I saw an emergency heat relay used. Probably the last time I saw outdoor thermostats used. They cost money to install. Without outdoor stats to bypass, don't need an emergency heat relay. Putting the stat on em heat setting eliminates energizing the compressor and sends call for heat straight to the strips. All of them, just like backup.
    definately a thing of the past like you said, a lot of old heat pumps out there though that still need service!

  5. #5
    Join Date
    Jul 2006
    Posts
    1,091
    I've never seen this emergency heat you speak of. I just thought it was a tstat function.

  6. #6
    Join Date
    Dec 2008
    Location
    Ontario Canada
    Posts
    546
    Quote Originally Posted by rickboggs View Post
    I've never seen this emergency heat you speak of. I just thought it was a tstat function.
    the switch itself is a T-stat function, but depending on the system, i wouldent be suprised to see the switch activate an external relay

    the origional posters question was in regards to a wiring diagram seen in trade school, there must have been a relay on there somewhere called out as "Emergency Heat Relay", if one was there, that is how I would expect to see it work.

    Now days you are correct, most emergency heat switching is done %100 by the stat, no relays, no outdoor thermostats

  7. #7
    Join Date
    Jul 2006
    Posts
    1,091
    I live in the deep south and when it comes to dual fuel and outdoor tstat, there's just a lot I haven't seen.

  8. #8
    Join Date
    Oct 2004
    Location
    Central WA
    Posts
    1,534
    Many older heat pump setups and still many mobile home installs have an outdoor thermostat that will limit the auxillary heat strips based on outdoor temp. An emergency heat relay will bypass this control and allow the auxillary heat to come on regardless of outdoor temp.

    Most installs now don't use this outdoor control, and if auxillary heat limiting is used at all it is often done with a digital thermostat (Vision Pro 8000, etc) with an outdoor sensor.

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