I HATE that EVERY time the furnace toggles on, it turns OFF my fan and no fan for about 3 minutes. EVERY NIGHT this WAKES ME UP throughout the night.

It is so bad that I decided to turn the HEAT OFF at night so the fan reliably runs constantly. Sure, the inside temp in the house gets to 49 degrees by morning but that is more preferable to me than having the fan toggle on and off! And I HATE it when the fan turns off when I am awake as well so turning it off at night is not a complete solution.

So how can I hack my thermostat (or what can I do) to prevent it from disabling my fan while the furnace is heating? I DON'T CARE about efficiency, I know it does this to prevent from blowing cold air around, but I don't care! I also don't care about any damage it could do to my furnace (although damage is unlikely but I don't care)! I need the constant sound of the central air fan blowing around.

Please tell me how I can BLOCK or BYPASS this unwanted behavior turning off the fan constantly every time the furnace turns on.

p.s. I am not talking about the furnace blower. The fan sound I am talking about is the same whether the heat is on or off, or if the AC is on or off. This is the central air fan, and is toggled by putting my thermostat to ON for the fan.

So I am not asking to turn on my "blower" fan, I am talking about the central air fan which is used for both the heat and AC and also for neither. So when anything is on or off, this is the fan to blows air through my vents. Apparently the blower is the central air fan, thanks @ThreePhaseEel

Here is a picture of my thermostat:

enter image description here

and the motherboard of the thermostat itself (honeywell):

enter image description here

Some pictures of my furnace. Unfortunately there were no tags anywhere saying a model number unless it was in back but I could not squeeze through there to get to the back.

Also, this is a gas furnace, if that is relevant.

I also noticed when I toggle between heat on and heat off, on the thermostat, even when the thermostat is disconnected (battery inside), there is a click inside the thermostat. It seems something inside the thermostat is toggling when heat is on, maybe it is using something different to turn on the fan when the heat is on? Perhaps I can bypass this somehow?

I discovered what the clicking sound was every time the heat turns on! The clicking inside the actual thermostat was actually the little fan switch (on or auto) bouncing around in there, it seems that, as you can see in the motherboard (fan switch is on bottom right of the picture), inside the metal piece in the bottom right of the picture the CPU of the thermostat manually turns off the fan physically inside the thermostat, which caused the little platic exterior fan switch to bouce around inside causing the clicking sound. So that means that the reason why the fan turns off is because the thermostat itself physically switches off the fan inside itself whenever the heat turns on, and so I need to bypass this.

Note: Also by the way, the furnace return is actually in the kitchen. In the main part of the house (no basement). Also the furnace is in a room sealed from the garage, so it doesn't get cold in there. So the chances of a cracked heat exchanger are very slim.


By simply connecting R to G as @ThreePhaseEel suggested, now my fan is always on. So normally when the thermostat is taken off, the fan is off. But immediately upon connecting a wire between R and G, the fan turned on, even with the thermostat disconnected. I then connected the thermostat and turned up the heat. Success! The fan was NOT turned off when the heat turned on. This is going to make my life so much nicer!

p.s. update: turns out lots of people leave the fan running 24/7 especially in northern climates like Michigan, in fact HVAC people have suggested to do this, so I don't anticipate any issues from this but I do anticipate bliss, better sleep, and happiness that the fan isn't continuously shutting off.

Note: I don't care about the downvote, I didn't have any rep anyway and this will be my only question here. But I was able to solve the issue and I hope this helps someone else as well. p.s. downvote me all you like, I don't care. I will never be posting on here again anyway, so I don't care if it has 100 downvotes from 5 year olds. Feel free, my problem is solved, and downvoting me won't take that away from me! Anyway thanks for the help @ThreePhaseEel, have a great new year! Bye guys

  • What model of furnace do you have? (p.s. the central circulating fan on a forced-air system is often called a "blower") – ThreePhaseEel Jan 3 '17 at 0:23
  • I need to know what model your furnace is -- i.e. the big box in the basement with the ducts hooked up to it :P – ThreePhaseEel Jan 3 '17 at 0:27
  • Is there an easy way to just connect something inside the thermostat? – diyguy Jan 3 '17 at 0:46
  • 3
    The damage you can do to the furnace can actually be dangerous - interfering with the fan cycle during demand for heat can cause the furnace to short cycle and crack the heat exchanger. – Comintern Jan 3 '17 at 1:06
  • 1
    You may want to invest in a good carbon monoxide detector then and hope that it is loud enough to wake you up at night. – Comintern Jan 3 '17 at 1:10

Thanks to @ThreePhaseEel, I was able to solve this issue. I connected a wire between R and G, jumpering them together.

I have taken a picture. See the green horizontal wire between R and G, this is what I did to make sure the fan runs 24/7. This has indeed solved the issue. It is worth noting there is no guarantee that R and G letters are the same for your thermostat, but it was with my thermostat.

Also worth noting: A straight jumper will not allow you to turn off the fan. But this is very easy to mitigate. Just add a manual switch! Pick up a rocker or other switch from the auto parts store or hardware store for a couple bucks and install the switch as desired. This will just allow you to toggle the fan to ALWAYS ON or back to normal functionality. If it's your house you can even install a light switch into the wall as a fan toggle!

enter image description here

  • 2
    How does the homebrew switch differ from the "Auto"/"ON" switch found on many thermostats? – Harper - Reinstate Monica Jan 3 '17 at 2:17

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.