auxiliary heat vs. emergency heat

decadentFebruary 13, 2012


I have a Bryan Evoltion Control heat pump system. My house runs entirely on electric power. Recently with the advent of higher charges we've decided to lower the thermostat setting at night, going from 70-62. We've noticed in the morning that the auxiliary heat kicks on.

What's the difference between auxiliary heat and emergency heat? The Evolution System has both. Does auxiliary heat expend more energy as the emergeny heat setting? Am I spending more $ in setting back my thermostat at night just to have the system work harder to reach the desired temp?

I live outside Philadelphia where the winter has been mild to say the least but any savings I can obtain would help.

Thanks in advance, Bill.

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According to the guide emergency and auxillary heat are the same thing. The heat strips are coming on due to the large temperature set back.

Large temperature set backs don't work well with heat pumps. You may not be savings any money, and possibly using more electricity. Keep the set back at 3 - 4 degrees.

Here is a link that might be useful: Bryant Evolution Guide

    Bookmark   February 13, 2012 at 8:38PM
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The difference between auxiliary and emergency is only that the compressor (heat pump) is locked-out from running in emergency mode. The heat strips run the same either way.

Auxiliary, the heat strips activate to supplement the heat pump's output when it can't keep up with the load. The compressor continues to run and the heat strips activate via a 2nd circuit in the thermostat if the indoor temp drops (generally) more than 2F below the setpoint ... or if the setpoint is manually raised more than 2F above the current room temp.

Emergency mode is activated manually via a switch on the thermostat and is intended for use if the compressor fails and there's no source of heat other than the heat strips. Emergency can also be used in extreme weather conditions such as snow or ice storms in which the outdoor unit remains iced-over for an extended period.

There are setback thermostats specifically for heat pumps that "learn" how fast the temp drops during setback and how fast it rises during recovery, and then start the recovery period *before* the target time, ramping the temp up slowly so as to avoid triggering the auxiliary. In some cases the auxiliary may still trigger at the target time if the full recovery temp hasn't been reached ... but it'll run for a shorter time.

There are also optional outdoor temp sensors (available for most systems) that work with an electronic thermostat to fully lock-out the auxiliary until the outdoor temp drops to a specific (adjustable) temperature. If the outdoor temp is above the lock-out point, then the auxiliary will *never* run no matter how far-off the setpoint is from the actual room temp. Note that the emergency setting still will run the heat strips, and they'll also run during defrost cycles as per the usual.

    Bookmark   February 13, 2012 at 9:08PM
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The Evolution stat has adaptive recovery which should start the warm up with enough time to avoid going into aux heat. I believe it works best with an outdoor sensor but it isn't perfect either way.

The outdoor sensor may help and otherwise you should reduce your setback. I personally don't agree with a specific temperature limit for setbacks but going into aux heat is a sign you setback too much.

    Bookmark   February 14, 2012 at 7:57AM
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There is false economy with too large setbacks whether auxiliary is energized or locked out.


    Bookmark   February 14, 2012 at 8:06AM
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"There is false economy with too large setbacks whether auxiliary is energized or locked out."

Kindergarten physics dictates that if not using expensive auxiliary heat, the larger the set back, the lower the cost. That is, unless you are taking into consideration something other than pure heating costs, like frozen pipes.

    Bookmark   February 14, 2012 at 3:00PM
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If your thermostat has adaptive recovery, it has to be turned on, usually via a 'settings' function.

    Bookmark   February 14, 2012 at 3:27PM
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Thank you for all the replies and the information provided. To recap:

* auxiliary heat is basically the same as emergency heat in regards to the amount of energy expended;
* my setback may be too large and needs to be shortened;
* an adaptive recovery setting may solve the problem if my thermostat is equipped with it;

In regards to the lockout temp setting, does the Bryant Evolution system come equipped with that? I have all the manuals and do not see anything in regards to a lock-out temp that prevents the auxiliary heat from coming on until the temp drops below that setting. Is that something that needs to be bought separately I presume?

Thanks again for all your answers and advice as they are much appreciated, Bill.

    Bookmark   February 14, 2012 at 7:08PM
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You have to go into the service menu to set the lockout temperature. You can enter the service menus by holding the advanced button down for 10 seconds. The lockout setting is under the furnace set up section. The contractor should have set this during the initial installation.

Here is the link to the manual. Be careful not to change other settings.

Here is a link that might be useful: Bryant Evolution controller manual

    Bookmark   February 14, 2012 at 7:37PM
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Thanks for the link, that manual I do not have. Is there a suggested temp to which the lockout should be set? Thanks again Mike, Bill.

    Bookmark   February 14, 2012 at 8:56PM
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Upon further inspection there is not a FURNACE(I have no furnace as I am all electric) option under the SETUP menu. Here is the setup menu:




That's the only spot I could find a HEAT LOCKOUT. It seems the contractor/installer did not set this as he should have. Is the ELECTRIC HEAT LOCKOUT what I want? What's a good temp to set it? Are there any other settings I should check to make sure the contractor/installer set them right?

Thanks again for the help, Bill

    Bookmark   February 14, 2012 at 9:12PM
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My mistake, I forgot you don't have a furnace. I don't have a heat pump so I am going by what I am reading in the manual.

In the set up menu you should have heat pump listed. You should see the electric heat lock out (page 9 of the manual. The default is no lock out. You can set a temperature. I think 35-40 degrees is a good range, but I will let the heat pump experts comment on this. For most items the default value is fine. You should not need to change anything else.

Note this version of the manual is old. You may have a newer version of the controller so you may be some differences.

    Bookmark   February 14, 2012 at 10:14PM
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35-40 would seem high to me considering this is a higher efficiency system. I would be picking something around 28f, but it depends on your comfort level.

It looks like 'smart recovery' is defaulted to ON. Your unit should start 90 minutes before the setback completes.

    Bookmark   February 15, 2012 at 4:30PM
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So, to clarify, if I set my lockout to 28f, it won't matter how much of a setback I choose because auxiliary heat will not activate unless outside temp dips below 28f? Am I correct in saying that? Thanks weedmeister and all, Bill.

    Bookmark   February 15, 2012 at 6:45PM
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I would not go any lower than 28 because if the heat pump failed and the temp is below the freezing set temp long enough you could have frozen pipes.

    Bookmark   February 15, 2012 at 7:21PM
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Decadent... did you have any luck in modifying this lockout setting? My setting is 35F and I too only have 1 fuel: electric. My issue (as posted at link below) is too many defrost cycles which might be bringing down efficiency more than just running emergency/aux heat. Did you find a secondary lockout setting which could turn the heat pump off at a certain temp and rely only on electric auxiliary heat?

Here is a link that might be useful: Link to reference post

    Bookmark   December 26, 2012 at 3:23PM
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I have a problem for my heating system. It stays at Aux Heat On all the time regardless on how I increase my temperature.

    Bookmark   January 27, 2013 at 11:40AM
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Hello all, I know this is an old post but it talks about my issue. I am changing out an old York Heatpump Thermostat that was installed in 2000 when the unit was new. I am changing over to a Honeywell RTH6350 digital unit. I know the white wire on the old unit is for the heat strip/ auxiliary heat but it has a tan wire run to a 2nd R terminal and I'm wondering if that is for the Emergency heat which has to be manually switched on. The new unit has terminals for both and if I knew for sure that the tan was the emergency heat I could hook the new unit up.Any help would be greatly appreciated

    Bookmark   January 1, 2015 at 8:30PM
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While I can't be 100% positive in your situation, my educated guess would be that, like on my system, the tan wire is probably the 24 VAC common wire, i.e. the "other side" of the 24VAC transformer. The white wire completely controls the heater strip. When the thermostat decides that aux heat is needed, it turns on the heater strips (white wire = 24 VAC) while the compressor stays on (Yellow wire = 24 VAC). The "emergency heat" switch simply turns off the compressor (removes 24 VAC from the yellow "compressor on/off" wire) and turns on the heater strips (applies 24 VAC to the white wire). You can easily verify your situation with a voltmeter.

    Bookmark   March 1, 2015 at 10:08PM
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