HVAC question

[echo4747]

i am not sure if this normal/typical with newer (2016) forced air 90+ nat gas furnaces .. here is whats happening:

1.) -furnace gets call for heat and the blower motor/fan comes on for 15-20 seconds then shuts off
2.) -inducer motor goes on , hot surface ignitor comes on, flame establishes and 20-30 seconds later circulation blower is on and heats the home
3.)- after house reaches the desired temp, flame shuts off, blower motor runs for approx 30-40 seconds and furnace is off

my question is why is the blower motor/fan turning on for 15 -20 secs as described in step 1.) ?

at my previous residence... when there was a call for heat.. inducer motor came on first

 

[bbhaag]

That's not much to go off of but it doesn't seem normal. What is the make and model of the furnace? Also are you using the proprietary thermostat that came with the unit or an aftermarket one?

A quick google search suggests that maybe a dip switch is set incorrectly. What you are describing seems to happen when either a dip switch on the furnace control board or thermostat is set to electric heat instead of natural gas. Without knowing the make and model of the unit though it's hard to say but it might give you a place to start looking.

 

[echo4747]

That's not much to go off of but it doesn't seem normal. What is the make and model of the furnace? Also are you using the proprietary thermostat that came with the unit or an aftermarket one?

A quick google search suggests that maybe a dip switch is set incorrectly. What you are describing seems to happen when either a dip switch on the furnace control board or thermostat is set to electric heat instead of natural gas. Without knowing the make and model of the unit though it's hard to say but it might give you a place to start looking.

I know the make is Comfortmaker. I'm not sure of the model ( can post this info once I get home later today)
I moved into this home this past June and replaced the existing thermostat with an ecobee wi fi unit sometime in June .. The AC seemed to work fine all summer.

 

[snoopy7548]

Some switch isn't set properly. I have a >90% gas furnace (propane, but it shouldn't make a difference) with a programmable thermostat. I have the thermostat switch set to "Gas" which I believe lets the furnace control the blower motor. The process is like this:

-Thermostat calls for heating
-Furnace turns on inducer/flame for ~1 minute to pre-heat the air or whatever
-Furnace turns on blower motor
-Once thermostat is satisfied, it stops the heating call
-Furnace turns off inducer/flame while blower motor runs for ~1 minute
-Furnace turns off blower motor

I had my old thermostat set to "Electric" which caused the thermostat to control the blower motor and turn it on as soon as it called for heating, before the furnace kicked on the inducer/flame. It seems a bit more comfortable on the "Gas" setting, since the air should be pre-heated before coming out of the vents. "Electric" would assume electric heating with instant hot air.

 

[bbhaag]

^^^Yep I agree. Either you missed a setting on the Ecobee or there is a dip switch on the furnace control board that is set incorrectly. I looked on Comfortmakers website this morning and they do provide the user manuals but unfortunately they didn't have anything in them relating to the dip switches. Hopefully you can track down a service manual for your unit if it turns out that it not the Ecobee.

 

[echo4747]

^^^Yep I agree. Either you missed a setting on the Ecobee or there is a dip switch on the furnace control board that is set incorrectly. I looked on Comfortmakers website this morning and they do provide the user manuals but unfortunately they didn't have anything in them relating to the dip switches. Hopefully you can track down a service manual for your unit if it turns out that it not the Ecobee.

Just got home and you were correct... the ecobee thermostat default setting was having the thermostat take preference over the furnace for fan control... just a simple setting to change and its working the way I'm accustomed to.

Thanks for your help steering me in the right direction

 

[bbhaag]

Just got home and you were correct... the ecobee thermostat default setting was having the thermostat take preference over the furnace for fan control... just a simple setting to change and its working the way I'm accustomed to.

Thanks for your help steering me in the right direction

You're welcome, I'm glad you were able to get to the bottom of it quickly and that the fix was simple a lot of times when it comes to HVAC it is not.
I learned a lot over the past year when we moved into out current house. I installed a Nest thinking it would be straight forward but due to the 2 stage heat pump it was not. It was actually the opposite of what you were experiencing and I had to turn control of the blower motor over to the Nest due to the heat pump.

Anyway, like I said glad you got it figured out and best of all you saved yourself the $100+ service call that an HVAC company would charge.

 

[Greenman]

Blower shouldn't come on until after the burners have warmed up.

 

[Paperdoc]

Glad you got that fixed - good info for others, too. By the way, the reason the induced-draft fan comes on first for a while before the gas and ignition system kicks on is a pre-purge phase of the sequence, commonly used in larger burning units but also in home furnaces with auto-ignition. They are designed bearing in mind the SMALL possibility that some very minor leak in the gas system might actually put some combustible gas into the furnace interior while the unit is NOT operating. This could create an explosive fuel / air mixture with disastrous consequences if the ignition system came on first! So the ID fan first exhausts all air and gas that MIGHT be inside the furnace, THEN the ignition system starts up, and as long as it is verified working, the pilot light gas is turned on. THEN, if the thermal sensor in the pilot light area verifies that it is lit, the main gas can be turned on.

It is common to have the main warm air circulation fan controlled by the temperature sensor in the furnace interior where the heat exchangers are. A thermostat often has a setting to be adjusted at installation time for what type of fuel is used in the furnace - gas, oil, electric, etc. That is for response time optimization. The time delay between igniting a fuel in the furnace and measuring a real temperature increase in the room with the thermostat depends in part on the type of fuel. The same applies to how long it takes for actual heat delivery to the room to decrease after the furnace stops burning fuel. For electric heating that's a pretty short time delay, but for oil furnaces it can be quite a bit longer. Of course, a ground source heat pump system will be very different.