When does your Aux Heat kick on?

Discussion in 'General Discussions' started by vortrex, Dec 10, 2018.

  1. vortrex

    vortrex Member

    I have a WF7 in southeast MI in a 2250 sq ft 50 year old house. There are cathedral ceilings and a fair amount of glass. I’ve been retrofitting with new windows and better insulation, including closed cell spray foam where I can. The roof unfortunately has minimal insulation due to the home design. The Aux Heat will kick on with stat set at 70F when it’s in the mid 20F’s.

    Is this normal considering the above?

    When does your Aux Heat come on?
     
  2. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    what size 7 series?
     
  3. nc73

    nc73 Member Forum Leader

    Never. I don't have one installed.
     
  4. vortrex

    vortrex Member

    It’s the 4 ton.
     
  5. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    It depends on when you want the supplement heat coming on, meaning how big of a portion of your heat load should be carried by electric resistance heat.

    The old air source heat pumps shut off at 32F and turned on electric resistance heat only. This is supplement in the application, so the heat pump is still providing the majority of the BTUs. The IGSHPA guidelines said that geo systems should be sized for cooling and that everything needed more for heating should be supplemented with electric resistance heat.

    I try to look at providing heat pump capacity only down to 15F in your (and my) climate zone is acceptable as my own standard, covering 98% of the hours where it is above 15F. But there is no rule or code where this has to be sized.

    A lot of this I discuss with the customer, if a system uses $30 of supplement heat a year, but a larger unit would cost $3000 more, the straight payback is 100 years.

    My approach has changed with the variable speed heat pumps, since there is no penalty anymore for covering the entire peak load, and the realization that too much resistance heat will collapse the grid in the future, when they all use supplement heat at the same time.
     
  6. vortrex

    vortrex Member

    That's what the installer told me when I was concerned about the Aux Heat coming on too much, the unit is sized for cooling. The entire first floor is 4' below grade and naturally stays cool. The geo only runs for zone 2 (upstairs) in the summer and does a good job. My concern with the Aux Heat coming on was it is not good to frequently run it due to wear and cost? I don't base that on anything other than I thought it was for "emergency heat". I was paying attention last night when it was 24F outside. The Aux Heat would come on for 15 minutes at a time, maybe once every 1-1.5hrs.
     
  7. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    In Michigan, it should not sized for cooling, that way of thinking is 10-20 years old before the dual stage and variable speed units became wildly available, by people living in the south, specifically OKLAHOMA (IGSHPA). And what is the point of putting in the most efficient geo heat pump on the planet only to design it for the use of large amount of supplement resistance heat.
    I would have put in a 5 ton instead of a 4 ton, but it is very easy to come in after the fact and judge someone else work over an internet conversation, without knowing all the facts. There is no right or wrong, or any code or rule violated.
    Lets say you use $200 more a year for electricity, and the upgrade to a 5 ton would have cost you $4000 more, straight payback is 20 years. Worth the investment?
     
  8. vortrex

    vortrex Member

    It sure seems like I would save a lot more than $200 a year in electricity if the Aux Heat was not coming on so much. From looking at the stat "instant" energy data the Aux Heat is using ~11.5k watts and H9 is ~2.3k watts or roughly 5x the cost.

    As an example, Sunday was the coldest day in the past week. Low 20's during the day and down to 15F during the night. In that 24hr span it used 119KWh. Doesn't that seem excessive?
     
  9. nc73

    nc73 Member Forum Leader

    Sounds normal. Did you try unplugging the aux?
     
  10. ChrisJ

    ChrisJ Active Member Forum Leader

    I thought the aux should not come on unless the heat pump can't keep up. There must be an adjustment in the tstat to reduce the amount of aux, unless the indoor temp is loosing ground by 2 or 3 degrees.
    I think it is.

    What does H9 mean?
     
  11. nc73

    nc73 Member Forum Leader

    H9 sounds like the heat pump stage, not aux. I thought Doc said it was adjustable. I wouldn't know since I've never had heat strips. I order mine without it.
     
  12. vortrex

    vortrex Member

    I have not tried shutting off the Aux, but I will do that. I don't think it will be able to keep up, but I'll report back with the results.

    H9 is one of the higher heat stages. I just chose that because it's what it was running at the moment I looked to get the wattage. It will go up to H10 and then Aux after that.

    I think the indoor temp is losing ground too much. This is a tough house to deal with and I realize there will need to be some sacrifices. I just can't help thinking if the 5 ton would not have been better. As I mentioned, cathedral ceilings from first to 2nd floor, open floor plan, lots of glass, and very minimal insulation in the roof. I have made a lot of improvements since the geo was installed, but I still have more to go. By next winter I will have the side of the house that borders the garage spray foamed and some insulation in the garage itself. Once that is done the only thing left will be re-thinking the roof situation. I also plan on getting one of those leak tests for the ducts. I have a feeling a fair amount of heat is being lost before it makes it to the registers.
     
  13. nc73

    nc73 Member Forum Leader

    Have you measured ewt and lwt when aux is on? I'd be curious to know what the readings are.

     
  14. ChrisJ

    ChrisJ Active Member Forum Leader

    Is there a way to adjust when the aux kicks in?

    Air sealing the house and sealing the ducts will go a long way to reducing infiltration.
     
    Last edited: Dec 12, 2018
  15. vortrex

    vortrex Member

    At the start of last winter I had the installer out to do a check up and make sure everything was correct. He checked the EWT and LWT and said it was on spec. He gave me a print out with the data but unfortunately I cannot find it now! Is there any way for me to get it without Symphony or WEL?
     
  16. vortrex

    vortrex Member

    There is an Aux Lockout function of the stat, which ranges from 5F to 40F. I'm guessing that's for outdoor temp? It doesn't say, but I have no outdoor sensor anyway.
     
  17. nc73

    nc73 Member Forum Leader

    Those readings would have been for that particular time and wouldn't be valid. You can measure it yourself with a meat thermometer if you have pete's port or tape it to the incoming and outgoing pipe closest to the heat pump. I would disconnect it and see if it can keep up.

     
  18. vortrex

    vortrex Member

    OK, I will tape the thermometer to the pipes momentarily and report back. I guess the best way to shut the Aux off is the panel breaker?
     
  19. nc73

    nc73 Member Forum Leader

    That'll work
     
  20. nc73

    nc73 Member Forum Leader

    and make sure it's making contact with metal and not plastic if any.
     

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