Omnistat 2 Compatability

[ano]

I'm in the market for a new HVAC system, which is gas heat and AC. The AC end is much more important because I live in AZ. My 100% requirement is that it be controlled with my Omni Pro II.

I've read through many other posts, and lots of comments that this system or that system won't work with a OmniStat 2, but what I can't find a list of what HVAC units can be controlled via a OmniStat 2 or maybe an other means. Before I purchase it, how can I tell if it will work?

I'd also possibly like to look at a zoned system with maybe three zones. If I go that route, how does that work? Does the OmniStat 2 connect to the zone controller and the zone controller to the HVAC?

I haven't gotten any estimates yet, buy my guess is that those giving me the estimate will have no idea how to answer these questions, so I thought I would start here first.

Anyone have any success stories?

 

[Acromion]

I have a fair bit of experience with the Omnistat 2 so I'll give this a try. The Omnistat 2 is a very flexible thermostat. It will support 2 stages of cooling and has options for controlling a heat pump. That should be adequate for most any HVAC system you would purchase. The RC-2000 also has humidify and dehumidify outputs as well so I can't see any reason that it wouldn't do everything you need.

As for zoning - the proper method is as you have said: a zone controller to control the HVAC system and the thermostats just connect to the zone controller. The RC-2000 can act as a zone controller (discrete outputs for heat and cool mode) for these systems. From the perspective of your HVAC installer they can just treat the Omnistat 2 as any old thermostat. If they give you any trouble it is because the Omnistat 2 has LOTS of terminals and programming options and it might be confusing for them. A simple solution is to get them to install whatever thermostat they want and then change it out afterward.

My current project involves a single RC-2000 and 13 RC-80 thermostats (not all installed yet but I have them and most of the wire is ran). The RC-2000 controls a forced air furnace, a boiler, A/C unit, humidifier and HRV unit. The 13 RC-80 thermostats each control 1 zone of floor heat from the boiler. I can't think of many configurations that the RC-2000 couldn't handle.

 

[ano]

Thanks for the info. What I worry about is I'm sure I'm going to get the company line that "this HVAC only works with our special thermostats and you need to buy both" whether that is true or not. While I think 2-speed units will work with the Omnistat 2, I might be wrong but I don't think it will work with variable speed units.

 

[Acromion]

I'm not sure how the HVAC company will treat it but I didn't have any trouble with mine. As far as the two stage/variable speed issue goes you should be fine. To my knowledge there are no variable speed thermostats. The variable speed options are typically for the fan in the furnace so that you can slow it down to do dehumidify (which the rc-2000 supports) and so that it runs at different speeds based on which stage of heating/cooling you are in. Also, with the variable speed blower you can jumper inside the unit to choose different blower speeds to match the needs of the install. That said the thermostat has no knowledge or control of the fan speed (other than the dehumidify mentioned above).

To put this another way:
The thermostat simply dictates which stage (1/2/Emergency) of heat or which stage of cooling (1/2) and the possibility of needing to dehumidify and then the furnace with variable speed blower responds to those requests based on how it is jumpered inside.

Of course I may be wrong on some point but that is my experience.

 

[ano]

Thanks. That is good news. I'm trying to educate myself before they come out.

 

[tmbrown97]

It's also helpful to get the exact models of the air handler they propose to install so you can research the hookups. As said above, *most* are really standard and common - but some of the new high-end stuff does require their special controllers.

 

[rsw686]

I had no problem installing the RC-2000 on a Carrier heat pump with variable speed blower. As long as you have the normal 6 wires, hot (red), common (black), fan (green), compressor (yellow), reverse (orange), auxiliary (white), it will just work. The variable fan speed is set on the HVAC board. Where you can't use the thermostat is when the HVAC unit requires a communicating thermostat like the Carrier Infinity system. These only use 4 wires, hot, common, data a, data b. Although HAI has a Carrier/Bryant serial port mode, where you can connect the HAI OmniPro to the Carrier Serial Access Module.