Don't want to lose my omnistat2's. Can u help? Newbie to forum FYI

[Legomylego]

I have a Omnipro IIe, HAI switches, and security cameras. My house is 5 years old. I have been having trouble controlling my geothermal unit with these stats. I have a 2 zone system hooked to a 3 stage heat/2 stage cool geothermal unit. Part of the problem is the zone controller they installed is only designed for a 2stage heat system. my new HVAC guy says he can put in the correct zone controller (Honeywell) but he will need to use Honeywell thermostats to control this. I would like to keep my omnistats, but he says they won't work with his controller, and he also asked his regional Honeywell rep.

 

[ano]

If they are talking about the Honeywell HZ432K 3-stage heat/2-stage cool zone controller, it works fine with OmniStat2's. 
Now you do realize, for a 2 stage thermostat to control a 3 stage furnace, the zone controller needs to do a few tricks, like control stage 3 with a timer, eg. after stage 2 runs for X minutes, then activate stage 3.  You may have to experiment with the control setup to see what works best for you, but in any case, the Honeywell is pretty flexible but YOU need to learn it. DON'T rely upon some AC guy to set it the way that works best for YOU.   Since compressors don't usually run 3 stages, its most likely just a fan that goes higher or lower in response to he third stage signal, or stage 3 might be "emergency heat" which is electric heat, which you may want to be careful using as your electric bill will skyrocket.

 

[Legomylego]

Thanks for the quick reply. I have not seen the details of which controller they want to use, but the HZ432K looks appropriate. I am all electric, so the third stage heat is exactly as you describe- emergency heat through an electric element. Yes, my winter bills have been BAD. I think my current zone controller defaults to emergency heat instead of using my second stage.

When I program the two omnistats, do I set both to traditional 3h/2c settings?

If they insist on using Honeywell stats, I may buy them locally at a big box, have them install the Honeywell stats, verify settings, and then try to swap out with my omnistats. That way, I can return them if omnistats work just as well.

Thanks!

 

[ano]

Hi
 
First, I've never seen an Honeywell thermostat that was special and didn't fit any HVAC unit. They are all standard stuff.
 
Second, on the stages and zones, you need to realize the connections are not just "standard" where every installer will do it the same, and it will be what YOU want.  Its NOT just connect stage 1 from thermostat to stage 1 of controller, etc.  A zone controller CAN base the stage on the number of thermostats calling. For example, maybe if one zone is calling for AC then the zone controller uses stage one. If two thermostats need AC, then the zone controller uses stage 2 AC.  In this case, the thermostat zone 2 has nothing whatsoever to do with the zone 2 of the AC.  How could one thermostat KNOW how hot it is in another part of your house? It can't.  A zone controller can also switch stages based on a timer.
 
Some of this takes some trial and error and its what YOU want. The installer will be long gone so he probably doesn't care much how it works.  I would highly recommend that you read the manual for the zone controller, learn what it can do, and set it the way YOU want. There is NOT a standard way of doing this. ONE stage thermostats can work fine with a 3 stage HVAC unit if its set up correectly, because the zone controller has the smarts. The OmniStat2 is pretty smart but it has NO idea what is happening at another OmniStat2, but the zone controller DOES.
 
I happen to live in an area with many houses over 10,000 sq. ft. yet the HVAC guys from the area had little knowledge of how a zone controller actually works. Zone controllers are NOT that complex, and if an installer doesn't know if a OmniStat2 will work with it, this also tells me he knows very little about zone controllers in general. Yours might be the first one they have installed.

 

[tmbrown97]

Good info Ano...  I had my HVAC replaced last year and talked to a dozen installers first - every one of them wanted to install the Honeywell zone controls; and I told every one of them that I wanted to keep my existing system.  That said, the Honeywell zone controller is much more robust in flexibility especially when multi-stage systems are in play.  I'm still a little torn - I love my RCS system because I know what's going on with the control board from any tstat - but it's not as powerful as a Honeywell zone controller.
 
Something I specifically wanted to chime in on - anyone who has those emergency heat strips (typical in heat pump installs) should really have a good understanding of how they work.   I was lucky - when I moved into a rental when I was pretty young, I called the local utility who had a database showing the type of heat, water heater, etc - and warned me about heat pumps and how they work.  Many people think they're saving energy by setting their thermostats back to like 60 degrees when they're not around or at night - then bump it up to 70 when they're home.  The problem is, if there's more than a 2-degree difference (with heat pumps at least - I'm not sure about geothermal) then they kick on the electric heat - 10,000 watts in my last one.  Running that to "catch up" costs WAY more than just leaving the house at 70-degrees 24/7. 
 
I know some thermostats have predictive cycles to figure out the most cost effective way to catch up and know when to start heating up in order to make their cycle times - but that's getting more complex than I've ever bothered with.