Thermostat fan delay function

I would love to be able to make my fan turn on only after the furnace has been ignited. Right now with a normal set up the fan turns on right when the furnace turns on but the flame has not had a chance to light. With this happening it just pushes cold air for about 30-60 sec. the only work around I have found is to disconnect the G wire which allows for the fan to wait for the furnace to ignite but now I won’t be able to turn fan on independently if I want.

[Mod Edit]: Title Modified to Enhance Search Clarity.

The delay can cause flame to weaken the chamber leaking CO.

Should let the system design to do its job especially gas furnace.

I don’t think it would hurt. My gas furnace has two blowers, one just to force exhaust out the flue, and the other larger one to blow the warm air through the ducts. The delay would be for the larger blower only as the furnace control board handles the small one entirely on its own. The control board performs several safety checks (verify the flue isn’t clogged, check that the gas lights, etc) and will shut the cycle down if a problem is detected. The inducer blower keeps the exhaust moving through the furnace chamber you mentioned. This video How a Furnace Works explains it all.


Thermostat does not control fan during start sequence, it is being controlled by module/board.
once owner mods furnace, insurance will try not to pay making easier.


We’re not looking to mod the furnace; just asking to allow the furnace to control the fan instead of forcing it to come on with the call for heat.

I have captured the action of the Wyze thermostat as monitored by the power consumption in my house. The first shows the standard Wyze heat cycle (all 5 wires connected).

The second shows the Wyze heat cycle with the G wire disconnected.

The third shows the heat cycle captured three weeks ago when I had a Honeywell thermostat (and all 5 wires were connected).


This is perfect information! I had the honey as well and everything worked just as you said. This is far from being an end all but it would be nice if they could add that function in.

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Great info.

Is Wyze set on Auto Fan or Manual when G wire connected.

c wire adaptor may play a role.
try test it without the adaptor with G wire connected.

I have done with and without adapter and it is the same each way. With G wire in, I have it set to auto and it still kicks on right away. Only work around has been to disconnect G.

Both of my furnaces have five wires running from the furnace controller to the thermostats. I did not install the C wire adapters that were provided by Wyze.

I keep my systems in Auto fan mode (have never needed to run fan without the heat or the AC). The power graphs are with the system in Heat mode, Auto fan mode, no adapter to provide C.

Sounds like “fan on” command is build in into Wyze thermostat.

it is not a wish list. should file a bug ticket.

Agree with OP. Just replaced the Digital Life issued thermostat with Wyze. The first thing I noticed is no delay, which previous thermostat had, from furnace and blower. Both start at the same time.

However, I didn’t have the ac delay. Hmmmm. One for the other.

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I just got my thermostat installed and am experiencing the same problem but on the other side of the run. When my thermostat hits temp it is ending the call for heat and turning off the blower and inducer at the same time, some how making the system ignore the blower shut off delay. This is resulting in the furnace over heating and tripping the limiter, since the remaining heat is just sitting in the exchanger. I jumped R to W with no thermostat and delay works fine. Disconnect G and use thermostat, delay works fine. I am using the C adapter, but I don’t think that should have anything to do with it. There is something funky going on with how the thermostat interacts with the blower fan though.

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I would like to know when this issue is fixed also. My furnace fan comes on first then shuts down right away. It then restarts and heat finally starts working. I will try your G wire work around Chrisdanelle0414 and see if this works. If not Ill just re-install my nest thermostat and return this unit. Thanks

My new Wyze thermostat does a version of this crap too. now, the heat cycle consists of the following:

  1. Blower turns on and blows cold air
  2. Blower shuts off flame running
  3. blower comes on flame remains on to satisfy the set point

wired with C adaptor, in the wyze app I am able to independently turn the fan on.

it did not do this with 11 year old battery operated honeywell.
it would request heat, flame came on and after a period of time ~60 seconds it would start blowing hot air using the circulation fan.

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I think you are right. I am seeing the same issue. Blows cold air for a while before the heat comes on. IMHO this is a BUG, which needs to be corrected. Not a mew feature or function.

Is there anybody from Wyze Technical support or Product Management who can comment?

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There’s definitely a change needed in the firmware. My guess is that the Wyze thermostat is adding some sort of default safety program to avoid furnace over temp by turning on the fan prior to heat. However, those things typically built in to furnaces already and it’s wasting energy at best. or at worst, creating a conflict with the furnace control or triggering a fault.

Different HVAC units vary, buy my oil fired hot air furnace’s built in way of operating is:

  1. Furnace lights and gets up to temp without blower
  2. Once furnace is up to temp, blower turns on
  3. When house reaches set temp, flame shuts off.
  4. Blower continues for a short time then shuts off (less than a minute)
  5. After around a minute, the blower turns on for maybe 30 seconds to purge residual heat

Then all remains off until thermostat calls for heat and the above cycle starts over.

Having schedules, the ability to operate the fan independently, Home/away, Alexa, etc are great things. However, a thermostat shouldn’t ever add any steps to normal operations like calling for heat. Once the thermostat asks for heat or AC, it should just trigger the operation and leave the steps to the furnace/AC.


My 51 year old Carrier furnace has a delay after the gas lights before the blower fan turns on. It allows the air in the chamber to get heated up before the blower sends it through the vents. With the Wyze thermostat the blower turns on immediately when the gas lights. :frowning:


Same here. I will test with multimeter later on to see what the thermostat is doing. Was thinking of pulling a new wire and have a real c wire, but sounds like this is not the adapter causing the issue. I am going to test at furnace and see if it asks for fan and heat at the same time or what is going on. I think it should only ask for heat and the fan is literally forced to come on by the native control board. The fan on function is also available for circulation or whatever but the furnace should be allowed to handle it.

I did take the C wire off and it did not turn on the fan as was mentioned. Then the furnace control turned on the main blower once it heated up to the correct temperature. Seemed to be working fine but I decided to revert back today to my old thermostat because something just didn’t feel right.!


Thankfully I did because for some reason the Wyze thermostat was very warm to the touch which should not be the case. You can correct me if I’m wrong. Has anyone else checked if this thing gets warm?

More work needs to be done before I re-hook this up to my system. It is winter here in Wisconsin and I can’t afford to damage my system testing out a new gadget. Keep up the excellent job Wyze and feel free to reach out when you update the thermostat until then best to keep rolling with what I have. Could be a bad unit but with looking over the forum it isn’t.

Removed g wire. Heat cycles as normal. Does this thermostat implement some sort of pid control mechanism?