Time to change my zwave thermostat TH8320ZW1000 to Honeywell T6 Pro zwave

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Goodman ASPT Handler (Variable Speed via terminal selection) with GSX Outdoor Unit (Single stage Condenser with Electric AUX). So, not as worried about the multi stage issues. But, I want to have options if I ever upgrade the unit.

I have two units. Since Ecobee has changed so much, they no longer allow you to tie two T-stats together for schedules. So, I am having to use HE to control everything now anyhow. Would prefer to get away from wifi as Ecobee has a less than stellar record with their servers going down (usually while I am away on vacation) and I lose remote control capability as well as the ability to control with HE.

Image from Ecobee Support Website

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GoControl thermostats support 2-stage cool, and 3-stage heat. And with Hubitat, it is super easy to control when to switch from stage 1 to stage 2. Or switch to AUX in heat mode.

I’ve been using one for 2-3 years now with a 2-stage heat pump and electric AUX heat.

The 2GIG zwave thermostat is a 700-series version of the GoControl 500-series thermostat.

The only thing that the ecobee does that the GoControl cannot do is reverse staging.

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I'm late to the party, but assuming you bought the T6s, I'm curious what you think of them?

I have three T6's but I found a few issues with them after using them for a bit.

  1. Temp is in Celsius, converted to Fahrenheit. This means the F display can never show certain temperatures, like 71 F, due to rounding. 21 C rounds to 70 F and 22 C rounds to 72 F.

  2. No hysteresis setting! I have baseboard heat so it is delayed after it comes on, and continues after turned off. The default hysteresis is two degrees, I believe. My house was swinging at least two degrees either side of the setpoint, so a four degree difference in temperature overall between cycles. It was very noticeable and annoying.

I solved the hysteresis issue by using a custom virtual thermostat driver and a custom T6 controller app. I took advantage of the temp calibration feature as an attribute in the T6 driver to control the thermostat turning heat on and off, with the virtual thermostat in real control, and allowing me to use a custom hysteresis. I have to bump temp cal up until it turns off, and down until it comes on, and check every minute to keep things in sync. Settings changed on the physical T6 are synced over to the virtual thermostat.

That worked OK all last winter, but it was a bit clumsy, and when using remote temp sensors I cannot always adjust the cal enough to keep it off if it is in a colder area than the sensor. So, I took control away from the T6 entirely using a ZigBee relay module instead to control the zone valves and furnace. The thermostats sync with the virtual thermostats, so they are basically dumb interfaces now, still using a common wire to keep them mains powered.

Besides custom hysteresis, I added other features. One is showing heating by increasing the screen brightness to full, and idle with brightness to low, since these also do not show heating status on idle screen. The fact that screen brightness can be controlled through an attribute is a nice feature of the T6 driver! I also use it to turn the display off at night in the bedroom, and to turn it on bright with motion to provide a nice dim light if I get up at night.

I added the ability to use multiple remote temperature sensors. I also added using motion sensors in the rooms to activate what remote sensor to use for setpoint, so the setpoint will follow you to the room you are using. Now that I am using the relays, I now use the cal feature just to make the thermostat display the temperature of the remote sensor. The apps reverts back to the old behavior if I switch back to thermostat control.

I also added options for a pre-heater device, so I turn on the electric fireplace heat for a bit when heat is called while waiting for baseboards to heat up. I also added a fan device feature to run the fan in the bedroom to circulate heat, which uses a delay setting to wait for the heat to come up first before circulating, and a delay at off to keep circulating the heat for a bit after.

I also added a 2nd relay board to re-engage the thermostats automatically if needed, like if the hub or a board dies on a cold day. The boards are wired to just default to using physical thermostats if there is no power to the boards or they fail. I use one of the ZibBee relays to remotely switch between using thermostats or the ZibBee relay control, since the board has four relays and I only have three heating zones.

If anyone is interested in this overly complex way to run your heat and fix a few issues with the T6, I can share the driver and app code, as well as a wiring diagram and the boards I used. I spent about $50 for the two boards and some bus rails on Amazon. Both boards run off the 24V AC furnace transformer, so no external power source is needed.

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Mine definitely shows 71°F

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100% not true. I have one of my T6 thermostats set to 71F as part of its daily schedule. It displays 71 without issue. You need to set the thermostat to use Fahrenheit rather than Celsius. Set ISU 125 to Fahrenheit in the Advanced menu.

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Also, make note of the Z-Wave temperature and humidity reporting options on page 10 in the attached guide.

Honeywell T-Stats generally don't use hysteresis. They use cycles per hour. For baseboard, it should be set to 3.

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Believe the way I got around the 71°F issue in at least one of the device drivers I coded/modified was to report Celsius in half degree intervals and Fahrenheit in one degree intervals, i.e. to allow 21.5°C => 70.7°F => 71°F

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They have worked well for me; including using Alexa. When I switched to the C8 hub all of my Z-wave worked much better including my T6 Pro thermostats. Are you using the new C8 hub?

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My cycles per hour was set to 3. It is really not clear how this effects the effective hysteresis I was seeing with the large temperature swings. Even with cycles per hour, it still needs to use the heating setpoint to know if there is demand for heat or not, as it does not just cycle three times per hour blindly if there is no demand for heat. So are the cycles just timed, and the actual temperature has nothing to do with when it stops the cycle? If not, there has to be a hysteresis in the background to stop heating based on actual temp. Can anyone explain how this actually works, and why it is good thing in any way?

Also, I never saw 3 cycles per hour when using the thermostat control set to 3 cycles. I was getting long cycles that overheated to setpoint, and a long idle where it underheated to setpoint. Often less than one cycle per hour.

This seems like a dumb way to run a thermostat to me. I am using a very tight hysteresis now, and my furnace does not cycle more than once per hour in 20 degree temperatures. The inside temp is always between 68.8 and 69.4 when set to 69, as read on the external sensors. The T6 also hides this temp difference on the display. The thermostat lies and says it is at setpoint, but I noticed the temp swings and used an external temp sensor to see what the swing really was, and it was not what the display said. Display seems to always read setpoint to some extent, like if it within a couple degrees from the setpoint.

Also, it may be the Advanced Temp Report in ZWave options that allows 71 to be displayed. I had this turned off because when this is on, the temp in the driver does not match the temp on the display at all. Of course I am set to Fahrenheit.

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Yes, on the C8 for a few weeks now. I never had any issues before hub upgrade or after with the T6 driver, it has always been solid.

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Just to add, by using hysteresis instead CPH, this is the graph of my Bedroom heating.

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I tend to get just over one cycle per hour, even with the tight hysteresis. It has been in the 20s the last few days. From what I have read, it is not good to short cycle your furnace with too many cycles, and it is also more efficient to have longer cycles.

I'm sticking with hysteresis.

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This might help. Old video but explanation is good:

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Interesting, the reason for cycles per hour is to maintain uniform temperature in old houses that cool too quickly. This guy also agrees you do not want to short cycle, and that thermostat manufactures are rethinking this approach (to use fewer cycles per hour).

Despite that, I get the most uniform temp using hysteresis. The cycles per hour was not doing it with the T6 for me, it somehow gave me much larger temperature swings.

I use both a start hysteresis and a stop hysteresis. The start hysteresis is smaller since the room will continue to cool before the baseboards heat. The stop hysteresis is a bit bigger, but still small since the baseboards will continue heating after. I also can adjust these values based on each thermostat and how long it takes to recover the heat for any given zone.

Generally, my start hysteresis is .2 degrees, and the room is going back up in temp before temp drops below .5 degrees form setpoint while waiting for the heat to start flowing.

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