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  1. #1
    Join Date
    Jul 2009
    Posts
    8

    heat pump & auxiliary heat

    Hi, I just moved to a place that has a heat pump & auxiliary heat. I know the heat pump gets used until the outside temperature gets too cold for it to keep the inside warm, but I was wondering how the system actually knows when to start using auxiallary heat and when to stop using the heat pump heat. I assume it has temperature sensors, but i don't know if they would be located in the thermometer itself or if it is outside in the heat pump unit. All units are different, but is there a simple way to check temperature sensors to see what they are set to?

  2. #2
    Join Date
    Jun 2008
    Location
    Cincinnati, Ohio
    Posts
    2,176
    Let the machine do its work. If it is working properly, leave it alone. Have a qualified service tech come out twice a year to perform preventative maintenance on the system.

  3. #3
    Join Date
    Jun 2007
    Location
    The Twilight Zone
    Posts
    2,964
    Quote Originally Posted by anon1111 View Post
    Hi, I just moved to a place that has a heat pump & auxiliary heat. I know the heat pump gets used until the outside temperature gets too cold for it to keep the inside warm, but I was wondering how the system actually knows when to start using auxiallary heat and when to stop using the heat pump heat. I assume it has temperature sensors, but i don't know if they would be located in the thermometer itself or if it is outside in the heat pump unit. All units are different, but is there a simple way to check temperature sensors to see what they are set to?
    Depends on your thermostat and type of auxillary heating system.

    Do you have a heat pump w/gas furnace back-up or electric resistance strips in the air handler as back-up?

    Assuming your system does not have an outdoor temp sensor:

    If you have an old mercury mechanical thermostat, the house will have to lose about 2 degrees with the heat pump running before the thermostat switches to the auxillary heat.

    If you have a new digital t-stat, the stat will sense that the heat pump is losing ground, and bring on the auxillary heat (without the house dropping 2 degrees or so).

    If you have an outdoor temp sensor and a good t-stat:
    There is a programmed switchover temp from the heat pump to the furnace (gas, propane, or oil).

    Take care.

  4. #4
    Join Date
    Feb 2004
    Location
    Pacific NW
    Posts
    566
    If you live in a temperate area (such as the south or West coast, even up to Seattle) you may never need the aux heat.
    Comments below obvious do not apply to North Dakota or even St Louis.

    If it is set for the aux heat to come on at 40F (some techs set it that high) you are losing money.

    Discuss your climate area with your tech next time.
    Had my own system in Seattle was set for the aux heat to come on only when the indoor temp dropped below 64F (separate thermostat) - when after about 6-7 years noted that it NEVER came on, I physically removed the coils from my own HP to lower the resistance to airflow (small amount) and used them in another application.

    Talk it over with your tech or engineer friends.

  5. #5
    Join Date
    May 2009
    Posts
    196
    Quote Originally Posted by junkhound View Post
    If it is set for the aux heat to come on at 40F (some techs set it that high) you are losing money.
    Even on the west coast, not all HPs are sized large enough to manage a balance point below 40.

    Sure, undersizing units means higher operating costs, but guessing on sizes rather than doing it right saves the installing contractor a few hours work doing a load calc.....

  6. #6
    Join Date
    Jun 2007
    Location
    The Twilight Zone
    Posts
    2,964
    Quote Originally Posted by junkhound View Post
    Had my own system in Seattle was set for the aux heat to come on only when the indoor temp dropped below 64F (separate thermostat) - when after about 6-7 years noted that it NEVER came on, I physically removed the coils from my own HP to lower the resistance to airflow (small amount) and used them in another application.
    With the strips removed, your heat pump air handler blows frigid air during a defrost cycle.

  7. #7
    Join Date
    Jul 2009
    Posts
    8
    Thanks for the response..
    I have electric heat in the air handler and an old mercury sensor. I want to put in a new programmable thermostat to try and save some cash but I dont' want to mess up the system.

    Now I am a little concerned because I like to turn the temperature down to like 60 degrees at night and back up to 70 in the morning (during the heating season). But I wonder if that will actually "waste" money because it might kick on the auxiliary heat to get the temperature brought back up.

    Wow, too complicated...I guess I'll just have to play with the current thermostat for a season before changing it out.




    Quote Originally Posted by gary_g View Post
    Depends on your thermostat and type of auxillary heating system.

    Do you have a heat pump w/gas furnace back-up or electric resistance strips in the air handler as back-up?

    Assuming your system does not have an outdoor temp sensor:

    If you have an old mercury mechanical thermostat, the house will have to lose about 2 degrees with the heat pump running before the thermostat switches to the auxillary heat.

    If you have a new digital t-stat, the stat will sense that the heat pump is losing ground, and bring on the auxillary heat (without the house dropping 2 degrees or so).

    If you have an outdoor temp sensor and a good t-stat:
    There is a programmed switchover temp from the heat pump to the furnace (gas, propane, or oil).

    Take care.

  8. #8
    Join Date
    Jun 2007
    Location
    The Twilight Zone
    Posts
    2,964
    Quote Originally Posted by anon1111 View Post
    Thanks for the response..
    I have electric heat in the air handler and an old mercury sensor. I want to put in a new programmable thermostat to try and save some cash but I dont' want to mess up the system.

    Now I am a little concerned because I like to turn the temperature down to like 60 degrees at night and back up to 70 in the morning (during the heating season). But I wonder if that will actually "waste" money because it might kick on the auxiliary heat to get the temperature brought back up.

    Wow, too complicated...I guess I'll just have to play with the current thermostat for a season before changing it out.
    OK - we have the same system: heat pump with aux electric strip heat.

    You can't get too crazy with the setback temp with a digital programmable stat on a heat pump. I don't setback more than 3 degrees in the winter, but this depends a lot on the outdoor temps. At 45F, no problem because my heat pump has enough btu output to recover at least 5 degrees. At 32F and below, I might not setback at all.

    I think you'll be happy with a new digital stat. If you go away on vacation for a few days in the summer, you can keep the house at 80F, and be 74F when you return. You can setback in the winter as noted above.

    I have a Honeywell VisionPro 8320 touchscreen and I like it a lot. I bought it online (don't tell anyone)

    Take care.

  9. #9
    Join Date
    Jul 2009
    Posts
    8
    My lips are sealed!

    Quote Originally Posted by gary_g View Post

    I have a Honeywell VisionPro 8320 touchscreen and I like it a lot. I bought it online (don't tell anyone)

    Take care.

  10. #10
    Join Date
    Apr 2008
    Location
    Northwest Arkansas via Chicago Area via Straight Up from There on Lake Superior
    Posts
    1,411
    Quote Originally Posted by anon1111 View Post
    ...

    Now I am a little concerned because I like to turn the temperature down to like 60 degrees at night and back up to 70 in the morning (during the heating season). But I wonder if that will actually "waste" money because it might kick on the auxiliary heat to get the temperature brought back up.

    Wow, too complicated...I guess I'll just have to play with the current thermostat for a season before changing it out.
    I too have a Honeywell VisionPro IAQ tstat. It is quite complicated because the option setting has little advise. Either bone up or get a tech that has installed one to do it. One very nice point. If you get the tstat with the remote equipment Interface Module at the furnace/air handler, the 3 wires on your old tstat can be reused. Saves cost to pull new wire and possible damage to finished spaces.

    I believe that this tstat is smart enough ("adaptive intelligence") to figure out over a couple of days how long it needs to bring the temp up or down to any time period set point. Seems to me this might be gradual enough to avoid heavy electric strip use after a few days. Ask your knowledgeable tech if this is indeed true.

  11. #11
    Join Date
    Apr 2008
    Location
    Northwest Arkansas via Chicago Area via Straight Up from There on Lake Superior
    Posts
    1,411

    Question Auxialry .vs. Backup Heat

    Have possibly a stupid question. Is the term "auxiliary heat" used interchangeably with "backup heat", especially in regards to the IAQ settings?

  12. #12
    Join Date
    Jun 2007
    Location
    The Twilight Zone
    Posts
    2,964
    Jerry:

    The IAQ is the 9000 Series. I have the 8000 Series.

    Auxillary heat and back-up heat and emergency heat are pretty much the same.

    My aux/back-up/emergency heat is electric resistance strips in the air handler. For auxillary/back-up heat, these strips will be energized and work while the heat pump condenser is running. In "emergency" heat, only the electric strips are energized.

    For your dual fuel system, the furnace will be the aux/back-up/emerg heat. The furnace and heat pump will never run at the same time during a call for heat. The furnace will run, however, when the heat pump is going thru a defrost cycle to temper the cold air from the air handler.

    Take care.

  13. #13
    Join Date
    Jan 2008
    Posts
    17

    Auxillary Heat / Outdoor Tempeture Settings

    Quote Originally Posted by gary_g View Post
    Depends on your thermostat and type of auxillary heating system.

    Do you have a heat pump w/gas furnace back-up or electric resistance strips in the air handler as back-up?

    Assuming your system does not have an outdoor temp sensor:

    If you have an old mercury mechanical thermostat, the house will have to lose about 2 degrees with the heat pump running before the thermostat switches to the auxillary heat.

    If you have a new digital t-stat, the stat will sense that the heat pump is losing ground, and bring on the auxillary heat (without the house dropping 2 degrees or so).

    If you have an outdoor temp sensor and a good t-stat:
    There is a programmed switchover temp from the heat pump to the furnace (gas, propane, or oil).

    Take care.
    Gary, I have a Carrier Comfort 13 Series Heat Pump with a Honeywell Vision ProTH8000 (digital) Theromstat. I know that my unit has an outdoor temp sensor. How can I tell what temp the outdoor sensor is set at?

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