Thermostat kicks on fan briefly before heat

It would already help if there were a configuration setting allowing us to tell the thermostat to not use the G-wire if the furnace in use is intelligent enough to manage its own fan cycle while heating.

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Thanks @WyzeGwendolyn… In my past life, my company made thermostats for Trane, Vivint, ADT, etc. I would be happy to chat with your PM/Eng team to pass along my observations and suggestions. Love the T-Stat, but there are a couple things I would tweak.

My issue with the Stat forcing the fan on is that there is COLD air blowing for a few minutes prior to the Gas elements heating up. That’s the reason the Stat doesn’t kick on the Fan for Gas Heat systems.

Feel free to have the team reach out. Thanks!

PS: Excited about the Door Bell Cam too!!

Thank you for the feedback. First of all, don’t worry. Blower fan operation will NOT impact your furnace life. I can explain the reason and our approach to improving the experience. We send the signal to the fan for blowing air and furnace to start the heat simultaneously when we see the heating load (call for heating). However, some control board, in your case, has its own device level logic to overwrite our command. It will check the inducer fan, ignitor temperature, valve pressure, etc to determine when to turn on the main blower fan. As a result, at the beginning when the hot plate is not hot enough, it will turn off the fan because the condition is not satisfied. The traditional thermostat does not have the layer of its logic so it is simply controlled by the control board, that’s why you don’t experience it. In our next firmware update, We will add a 30s delay for the fan to turn on during heating. Thank you.


Thank so much @Chuan :slight_smile: Do you expect this update to be ready for release within days or within weeks?

Also, there are many people anxiously awaiting the release where the differential temperature setting will no longer be hidden in the settings. Would you know when we can expect this to happen?

Thanks! :slight_smile:

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@Chuan, thank you for this. I want to add that I really like this stat. I have 2 actually running into a Honeywell minizone on my system. There’s a few things to address but overall, to me, in an early access / pre-order scenario it’s been great. We’ll wait for the adjustments and enhancements as they hit your release plan.

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About that firmware update…

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I see your logic but doesn’t it seem wasteful for thousands of blowers across the country to start needlessly? Wouldn’t it be better to disable this feature for systems that can’t use it? Would save a lot of electricity.

Not all furnaces turn off the blower if it is being called by the thermostat, and running the blower while the heat exchanger is heating up can and does cause damage to the heat exchanger. The higher efficiency gas furnaces will condense the exhaust while still in the ends of the primary heat exchanger tubes instead of the secondary heat exchanger, which can cause rusting to occur. This has been broken for over 2 months now - what’s the holdup with getting this fixed?

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I’m sorry, but in this case you’re wrong. First of all, not all furnaces will “override” what you are doing, I doubt many will. On a forced air furnace, even one without AC, the fan can be controlled independently of the heat if the green fan wire is hooked up and the thermostat has a fan switch. Sending a fan signal will overide the furnaces normal behavior in many cases, not the other way around. The furnace manufacturer is the expert on their furnace and has designed the controls, sensors and sequence of events for a reason.

A smart thermostat can do many things to improve economy by setting schedules, allowing remote access, etc, but messing with the standard heat operation is problem and shouldn’t be done. Once the thermostat calls for heat, it should do one thing and one thing only, and that’s call for heat like any old dumb thermostat. As evident by the mountain of thermostat threads in the forum, there is a huge variety of furnace models and brands ranging from new and fancy to decades old. Since Wyze can’t possibly know how how adding a fan signal in addition to simply calling for heat will effect every furnace, it shouldn’t be done, period. That includes adding a 30 second delay as you have proposed. Just have the thermostat call for heat and leave it alone and up to the furnace after that.

Features such as fan cycle and coast to cool are nice OPTIONAL features. In fact I use the Fan cycle feature myself to help move air around from our wood pellet stove, but leave the furnace operation to the furnace when it calls for heat.

Fixing this issue of your thermostat sending a fan signal when calling for heat needs to be a top priority and done asap.


There certainly seems a slowdown from Wyze these days, I guess they are struggling with the pace and number of products they are rolling out. We are still getting a number of updates for the cams, but the vacuum and thermostat have certainly stalled. What are the thoughts on pulling the G, seemed like it was unwise for someone with a combined AC and gas furnace system?

You want G if you are going to be using the AC. If you have your thermostat in Heat only mode and you do not have a heatpump, you can pull the G wire temporarily until wyze releases a fix, just make sure you don’t try to use the AC or your inside coil will ice up.

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Right, ok well being in AZ it could be coming on any day now so not worth the risk!

Thanks for confirming.

Exactly the issue I’ve been thinking about too. Not even an update regarding potential updates that I’ve seen for the thermostat lol

Looks like firmware 1.1.2 released today 3/10/2021. States they added a 15 second delay to the fan starting. I haven’t updated yet, and likely won’t for at least several days to see what other issues may have been introduced. …But 15 seconds wasn’t really the ‘fix’ for HE gas furnaces. But perhaps it will help.

I just upgraded one of mine (I’m running 2) and so far everything looks to be in order. Actually the temperature preferences and home , away and sleep setting seem fixed where they actually apply to the schedule rather than having to set them independently. Agree the wait 15 isn’t great, but it’s much better than a blast of cold air in the middle of the night!

15 seconds is not nearly enough. When the call for heat comes, it takes my heater between 35 and 40 seconds to ignite. It then takes another 30 to 40 seconds for the fan to start running, Even if the 15 second delay would start counting at the time that the ignition occurs (which I doubt it does), it would still turn on the fan long before my heater would with the G wire disconnected (as I’ve had it run since I connected the Thermostat).

@Chuan I’m not sure what units Wyze uses to test Thermostat development, but there really needs to be an option to not use the G wire at all to be a valid replacement for “old company” thermostats. Either that, or something like an option to choose the delay. Maybe in increments of 15 seconds up to 120 seconds or more, or something like that.


This is a good idea. We will start to plan the option for the user to define the delay. The short time of 15s is more for safety measure, we have to balance the risk of overheating caused by long delay

I envision it could be something like an On/Off switch, and the On state allows for a slider to be used to set the delay. Out of the box, to mimic current behavior it would be set to On with 15 seconds. But we have the possibility to slide it as allowed. Or turn it Off if not needed.

I’ll be happy to test if you need people. Once this is in I won’t have to mess with the G-wire anymore (I had to connect it last week to have the A/C run, but this week the cold is brutal again so I disconnected it :slight_smile: )

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Could you please explain what safety issues you’re talking about? Every plain old thermostat on earth just calls for heat without doing anything additional with the fan. In fact a really plain thermostat just has two wires that connect when heat is called for with a simple switch.

By adding any fan signal with a heat call, it could be argued that Wyze is causing a potential safety issue by changing the designed function of the furnace.

You shouldn’t have any fan signal at all, just leave it to the furnace.


There is no risk of overheating a gas furnace with no G wire connected, because the furnace has a limit switch that would cut out power to the gas valve if the fan didn’t kick on. Look at how other thermostats do it - they don’t try to control the fan at all when gas is selected as a heat source. The only furnace that needs the thermostat to control the fan during heat is an electric heater with resistive coils.

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