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One Thermostat To Heat With Heat Pump or Boiler?

My question is whether there is any thermostat or controller that I could connect both my Daikin Heat Pump (3MXS24JVJU) and oil fired boiler to that would choose one or the other based on outside temperature.

We have a two zone hydronic baseboard oil fired boiler that uses the standard Honeywell 24v zone valves.  The Daikin has two wall units within one zone, and a third wall unit in the second zone. (1400 sq/ft cape)

We'd like a controller that would switch, within each zone, from the heat pump at between 20 to 25 degrees F outside temperature, over to the oil fired heat when it get's below that.  If the outside temperature rises above 25 degrees F, it would switch back to the heat pump.

We already do this manually and have saved a bundle of money over strictly heating with oil.  Usually, though, by mid December, January and February, we just go with oil only.  But, here in CT, even in January, the temperature often rises above 25, and could save even more if it would automatically switch between both systems.  A true hybrid heating system.


  • Mac_7
    Mac_7 Member Posts: 14
    edited November 2013
    That could work

    Thanks for your comment.  I've looked at tying two thermostats together with an outside thermometer like that.  I'd have to have it switch between the two depending on the outside temperature.

    I've found that Daikin makes a thermostat called the ENVI that could switch off the Heat Pump at a designated outside temperature, and close an AUX switch within that thermostat.  From this I could probably have a regular thermostat that would only get power when the AUX switch closes for the oil boiler.  I'm trying to determine if that AUX connector within the ENVI simply closes at the specified outside temperature, or it it also opens and closes based on the inside temperature set.  If it does, I could just have it control the 24 volt zone valve on the oil fired boiler.

    I guess I'll be contacting Daikin for some answers on their ENVI thermostat.
  • Armadillo
    Armadillo Member Posts: 8
    Sounds like a RELAY or two would...

    I am not a heating guru but have been into electronics for ages and HAM radio yada yada...    without jumping all the way into the deep end of your "pool" it sounded like, yah, you could just switch controls based on outside temps.  It would not take much of a relay to pull it off, well, in my shop I have 5V coiled 4PDT relays... but you should be able to get THOSE for use just about any coil voltage.  It seemed to me, in reading your question, that you needed mutually-exclusive...  now I do not know what implications there are about hovering around your threshold....  I suppose you could use a timer circuit like even a 555 to make said relay stay in the state it is set to for "a while"; you would not want it short-cycling or chattering as it outside temps hovered... sorta like switch at 24F one way and BACK at 27F or whatever...  then I start thinking about old laptops or Arduinos or Raspberry Pi boards, but I have not gone that geek-road yet.  WHen you are home..there IS something to be said for the brute force method.  I'd hate to make some solution that could leave people without heat.   Good to think about what would happen if the "solution" broke.  Relays can be kinda slick that way, with no mains power they still "make" one set of contacts. if they are DT {and you have backup power for controls}.    At work we use a LOT of 1-wire technology but we do not do anything automatically WITH the data [beyond emails or alerts], though one could very easily if you can program.     Now, with relays, you can do some fun stuff too, like one set of contacts can be used to make the relay latch, and power to the latching circuit can be interrupted by another relay normally made/on...while open.. yikes.     Best hunting.     
  • Mac_7
    Mac_7 Member Posts: 14

    I have thought of cobbling something together like that.  I love tinkering with electronics, and have ever since building my first Heathkit Stereo Amp back in the mid 60's (that I still use, by the way).  But, I would prefer finding a controller/thermostat that's already designed and tested.  Also, I'd rather have one controller on each floor (zone), than two connected together with a third small box for the switching circuits between them.

    I'll be writing  an email to, or calling our local Daikin supplier first, to see what they say, and see if their new ENVI controller would work for what I want it to do.  The Daikin outside unit already has temperature sensors designed into the system.  If their unit will work, that's the route I'll take.
This discussion has been closed.