Help...! "Fan On" Switch on New Furnace...

[Zip]

I have a new Rheem RGLS 80%, 75,000 BTU furnace.

While using the Fan On switch... when the desired temp is reached, the fan continues to run until the room temp drops to the point at which heat is again called for, and then the fan shuts off momentarily, and the sound of the draft inducer begins, followed by the burners, and then the fan finally starts again.

Is this normal?

My old furnaces without draft inducers never shut off the fan during the heat cycles.

Thank You All.....!

[BigDog91]

This is normal. Almost all of the manufactures that I work with shut off the blower if it is in the "FAN ON" mode at the start of a heat call. Nothing to worry about.

[keeplearnin]

DO you want the fan to run continuously?

[Zip]

It certaintly defeats the purpose of the switch.

I wish there was a way to keep the fan running.

I like to use the Fan-On early morning when I am calling for about a 6 degree temp change.
With a cold house, the frequency of the heat cycles is increased.

Zip

[HVAC Teacher]

Normal on some units.

[2old2rock]

The blower control is working normally. However, it should not be cycling at all when you're recovering 6 degrees. Sounds like it may be hitting hi limit. I would ask the installer to check it out.
In most situations, fan on is wasting electricity.

[keeplearnin]

The only thing that is happening is that you have the fan in the on position on the t-stat, yes I know you Know that however when the t-stat calls for heat the fan control board overrides the t-stat switch and controls your fan at a different speed. You don,t really need to circulate air when not calling for heat. That's your choice the controls are set up to make sure your furnace works correctly despite your best efforts. Stop over thinking your t-stat and let the machine do what it,s supposed to do.

[Zip]

The blower control is working normally. However, it should not be cycling at all when you're recovering 6 degrees. Sounds like it may be hitting hi limit. I would ask the installer to check it out.
In most situations, fan on is wasting electricity.


It's not cycling during the 6* increase in temp. It's cycles after the desired temp has been reached and room temp is on it's way down.


My whole idea was to leave it on Fan-On for about 2 hours in the early morning to avoid the frequent start up of the fan motor.

Thanks...

[Tech23]

I have a new Rheem RGLS 80%, 75,000 BTU furnace.

While using the Fan On switch... when the desired temp is reached, the fan continues to run until the room temp drops to the point at which heat is again called for, and then the fan shuts off momentarily, and the sound of the draft inducer begins, followed by the burners, and then the fan finally starts again.

Is this normal?

My old furnaces without draft inducers never shut off the fan during the heat cycles.

Thank You All.....!

Yes it is normal, the furnace uses a different fan speed for "fan on" then what it uses for it's heating cycle. So if the fan is running when there is a call for heat, it must shut the blower down, let the furnace light and then it can switch and use the other speed for the heat cycle. Then when the temp is reached and the funace cycles down, if the fan is in the on position at the stat it will switch again back to the speed that it uses for "fan on".

[garya505]

Some newer furnaces have a separate setting for continuous (Fan ON) speed with more than one selection. Mine has 5. Don't know about the RGLS though.

[heaterman]

Normal for that unit.

[garya505]

Normal for that unit.

So there is no setting for the continuous fan speed on the RGLS? I noticed the RGPR has 2 choices but can't find the manual for for RGLS.

On all the furnaces I have seen with only one speed, it might be the lo-heat or hi-heat blower speed. Usually only the VS furnaces have a really low speed option.

[seuadr]

It certaintly defeats the purpose of the switch.



does that 30 seconds or so really cut into your day that bad?:toetap:

[garya505]

does that 30 seconds or so really cut into your day that bad?:toetap:

Ah sorry, I thought the OP was complaining about the speed. No, just the time when it's off due to the furnace starting up. Mine does that too, it's no big deal.

[commerce48]

Yes it is normal, the furnace uses a different fan speed for "fan on" then what it uses for it's heating cycle. So if the fan is running when there is a call for heat, it must shut the blower down, let the furnace light and then it can switch and use the other speed for the heat cycle. Then when the temp is reached and the funace cycles down, if the fan is in the on position at the stat it will switch again back to the speed that it uses for "fan on".

There is no reason that a variable speed fan cannot go from one speed to another without shutting down first. There is another reason, and while somewhat obscure, appears to be for safety while the gas ignites. I've never understood this for modern furnaces because the combustion chamber is completely sealed off from the circulating blower (absent a heat exchanger crack).

[Zip]

does that 30 seconds or so really cut into your day that bad?:toetap:

Hi Again All,

First of all... Thanks for your replies.

Just a bit of explanation:

My whole idea of running on Fan-On for the first couple of hours on cold mornings, is to eliminate the frequent cycling of the fan motor itself during the heat cycles. I'm told that continuous operation of the blower motor is easier on the motor, and a bit easier on my electric bill due to the higher electrical demand used at motor start up.
The noise factor is also very important too. I'm in a condo with my furnace just off my kitchen in a laundry room. The frequent cycling drives me nut's.

Anyway..., I guess I'm stuck with Auto, and just put up with the cycling.

Zip

[big sky hvac]

Hi Again All,

First of all... Thanks for your replies.

Just a bit of explanation:

My whole idea of running on Fan-On for the first couple of hours on cold mornings, is to eliminate the frequent cycling of the fan motor itself during the heat cycles. I'm told that continuous operation of the blower motor is easier on the motor, and a bit easier on my electric bill due to the higher electrical demand used at motor start up.
The noise factor is also very important too. I'm in a condo with my furnace just off my kitchen in a laundry room. The frequent cycling drives me nut's.

Anyway..., I guess I'm stuck with Auto, and just put up with the cycling.

Zip

I'm confused. What "frequent cycling" are you talking about? If you have a setback of 6*F, the furnace should run until the demand is satisfied. If it's cycling during the recovery from setback, there's something wrong with your system. If the furnace is cycling on and off after recovery, then the thermostat is short cycling. You might consider changing the Cycles Per Hour(cph) on the thermostat to 3 or lower. This would give longer run times and fewer run times per hour. You may have a bad thermostat as well.

[Tech23]

There is no reason that a variable speed fan cannot go from one speed to another without shutting down first. There is another reason, and while somewhat obscure, appears to be for safety while the gas ignites. I've never understood this for modern furnaces because the combustion chamber is completely sealed off from the circulating blower (absent a heat exchanger crack).

I agree a variable speed does not have to switch from one motor speed to another like a standard motor does and the furnace this person has installed has a standard motor in it.

It is not for safety as far as the lighting of the furnace is concerned, but the motor needs to shut down to switch speeds or it could damage a standard motor. Also this allows for the exchanger to warm up a little before the fan starts blowing across it.

Remember this person is asking about the furnace installed in their house and it does not have a variable speed motor in it.

[commerce48]

No big deal is a personal matter. For me, I'm a light sleeper and any change in noise levels wakes me up. I figured I could alleviate that by selecting fan on, but no - turning all the way off and then on again 30 seconds or so later is just as sleep disturbing.

[Zip]

I'm confused. What "frequent cycling" are you talking about? If you have a setback of 6*F, the furnace should run until the demand is satisfied. ( It does...) If it's cycling during the recovery from setback, there's something wrong with your system. (It's Not...)If the furnace is cycling on and off after recovery, then the thermostat is short cycling. You might consider changing the Cycles Per Hour(cph) on the thermostat to 3 or lower. This would give longer run times and fewer run times per hour. You may have a bad thermostat as well.

No, No, No....

On cold morning (Chicago 4 degrees outside)
I have turned down the temp night before to 65.
In the morning I kick it up to 72 (+ 7*)
The house is cold soaked.
Then I get frequent cycling which is normal in the morning when I kick it up to 72*

I would prefer Fan On, for the first couple of hours in the morning to avoid the frequent cycling of the Fan motor!

Zip

[Twilly]

does that 30 seconds or so really cut into your day that bad?:toetap:


Twilly says that is definitely a bummer and has caused blindness in laboratory animals.

[Twilly]

It certaintly defeats the purpose of the switch.

I wish there was a way to keep the fan running.

I like to use the Fan-On early morning when I am calling for about a 6 degree temp change.
With a cold house, the frequency of the heat cycles is increased.

Zip

There is a way and Twilly has done it but it is not recommended as the Rheem wants the blower off during the heat up cycle.

[Zip]

There is a way and Twilly has done it but it is not recommended as the Rheem wants the blower off during the heat up cycle.


Love to hear how.....?

[Twilly]

Twilly can't tell you due to site rules, however a local company should be able to figure it out....involves standard relays. Are you an engineer as Twilly performed this for an engineer that Twilly installed a Rheem for that wanted to run constant blower and never have it shut off.

[garya505]

No, No, No....

On cold morning (Chicago 4 degrees outside)
I have turned down the temp night before to 65.
In the morning I kick it up to 72 (+ 7*)
The house is cold soaked.
Then I get frequent cycling which is normal in the morning when I kick it up to 72*

I would prefer Fan On, for the first couple of hours in the morning to avoid the frequent cycling of the Fan motor!

Zip

There's something wrong with your thermostat or your furnace. The furnace should run continuously during the setback recovery from 65F to 72F.

[commerce48]

I agree a variable speed does not have to switch from one motor speed to another like a standard motor does and the furnace this person has installed has a standard motor in it.

It is not for safety as far as the lighting of the furnace is concerned, but the motor needs to shut down to switch speeds or it could damage a standard motor. Also this allows for the exchanger to warm up a little before the fan starts blowing across it.

Remember this person is asking about the furnace installed in their house and it does not have a variable speed motor in it.

Perhaps not. But no furnace with a variable speed motor does it differently that I've been able to find. Can you tell me a brand/model that does continue with the blower on through a fire-up sequence without first shutting it off?

[Tech23]

Perhaps not. But no furnace with a variable speed motor does it differently that I've been able to find. Can you tell me a brand/model that does continue with the blower on through a fire-up sequence without first shutting it off?

No, as I did not say they did...I said they did not have to as the motor is desigend to ramp up and down. As opposed to a standard PSC motor that is not designed to switch speeds on the fly.

Again, the main reason for shutting down is to allow the exchanger to warm up.

[egads]

While there may be legitimate reasons for one to want to have the fan on continuously, I don't think Zip's reason is. Folks do a lot of wacky things because "someone" told them it was a good idea.

[commerce48]

Also this allows for the exchanger to warm up a little before the fan starts blowing across it.


Again, the main reason for shutting down is to allow the exchanger to warm up.

I did miss the earlier quote, but I would not have taken that as a primary technical reason for this behavior. Are you serious?

[Tech23]

I did miss the earlier quote, but I would not have taken that as a primary technical reason for this behavior. Are you serious?

Yes, a lot of older furnaces used a fan and limit control that would allow the exchanger to heat up to a certain degree and then kick on the blower.

Also, you cannot energize more than one speed on a psc motor at the same time or it will burn out or short out the motor...so a short shut down of the motor to allow it to de-energize one speed and energize the other needs to be done.

[fearlessfurnace]

The noise of the blower kicking on and off bothers a lot of people. there is no real reason not to have an option for the fan to run 24-7 in heat speed in the winter and 24-7 in cool speed in the summer. the manufactures just do not do it. IMO

[fearlessfurnace]

for that matter what exactly happens to a standard motor switching speeds that does not happen spooling up and down from a normal cycle?

[fearlessfurnace]

i have taken out some old two stage furnaces that had a two speed belt blower and a two speed fan and limit. those old motors must have been 30-40-50 years old.

[Tech23]

for that matter what exactly happens to a standard motor switching speeds that does not happen spooling up and down from a normal cycle?

The difference is while "spooling down" as you put it, the speed of the motor has already been de-energized. The motor does not have to stop spinning in order to start speeding back up, but one speed must be de-energized before another speed can be energized.

[fearlessfurnace]

The difference is while "spooling down" as you put it, the speed of the motor has already been de-energized. The motor does not have to stop spinning in order to start speeding back up, but one speed must be de-energized before another speed can be energized.

OK but the fan relay is going to de-energize low as it energizes high. it just a double pole relay only one pole is hot at a time.

[commerce48]

Yes, a lot of older furnaces used a fan and limit control that would allow the exchanger to heat up to a certain degree and then kick on the blower.

Also, you cannot energize more than one speed on a psc motor at the same time or it will burn out or short out the motor...so a short shut down of the motor to allow it to de-energize one speed and energize the other needs to be done.

So I am asking why current furnaces cannot keep the blower motor on, and you are discussing older furnaces and PSC blowers. Scratching head.

One reason could be heating up the exchanger first so the homeowner doesn't get hit with a blast of cold air. I know you haven't said it yet, but this one is irrelevant as well as the blower was already blowing cold air by homeowner choice.

[Tech23]

So I am asking why current furnaces cannot keep the blower motor on, and you are discussing older furnaces and PSC blowers. Scratching head.

One reason could be heating up the exchanger first so the homeowner doesn't get hit with a blast of cold air. I know you haven't said it yet, but this one is irrelevant as well as the blower was already blowing cold air by homeowner choice.


The OP has a current model furnace.
The OP's current model furnace has a PSC motor in it.
The psc motor in the OP's furnace uses a different speed for fan on, than what it does for heat, so it must shut down long enough to de-energize one speed and energize another speed.

[commerce48]

The OP has a current model furnace.
The OP's current model furnace has a PSC motor in it.
The psc motor in the OP's furnace uses a different speed for fan on, than what it does for heat, so it must shut down long enough to de-energize one speed and energize another speed.

So your answer is that you don't know why this happens in every furnace, not just older furnaces, not just furnaces with PSC blowers, and not just the OP's furnace?

As far as the OP's furnace, how do you know it is calling for a different speed?

[fearlessfurnace]

the BPD furnaces "G" blower is heat speed and the thing shuts down the blower for the purge ignitor warm-up and 45 seconds of burner for no reason I can figure. even if you are changing fan speeds seems like the split second as the relay shifts would be enough

[fearlessfurnace]

the two stage funaces do not all have a long pause as they shift from low heat blower to high heat blower

[Tech23]

So your answer is that you don't know why this happens in every furnace, not just older furnaces, not just furnaces with PSC blowers, and not just the OP's furnace?

As far as the OP's furnace, how do you know it is calling for a different speed?

I am far from being a know it all... I know how the furnaces work, however I cannot answer the WHY they were designed to work that way since I did not manufacture them, you will have to take that up with the manufacturers.




As far as the OP's furnace, how do you know it is calling for a different speed?

Because I read the OP and seen the words..."When I use the FAN ON..." Meaning the OP has the fan turned on at the stat. And since the company I work for has been installing the OP's brand of furnace since 1983, I know that the OP's furnace has a separate terminal on the control board marked, "FAN" and one for "Heat" and one for "Cool". I also know that the factory sends the furnace out with High speed on "Cool", med speed on "Heat" and low speed on "Fan" in that particular model.

I also know that when the fan is turned on at the stat it will power the "Fan" terminal on the board which will power that speed, which from the factory is "Low" and I also know that if there is a call from the stat for heat or cool, even if the fan is turned on...the control board will override the "Fan" terminal, de-energize that speed and power either the heat speed or the cool speed....thus causing a brief shut down and restart of the motor.

Even though I know how they work, that doesn't mean I can answer why they were designed to work that way.

[beenthere]

Even though I know how they work, that doesn't mean I can answer why they were designed to work that way.

A factory rep told me that they did that so that the heat exchanger would have time to warm up in heat mode and not have a condensation issue. And so that the evap cool in cool mode could get colder faster, so that it would begin to remove moisture faster.

[Tech23]

A factory rep told me that they did that so that the heat exchanger would have time to warm up in heat mode and not have a condensation issue. And so that the evap cool in cool mode could get colder faster, so that it would begin to remove moisture faster.

Thanks beenthere...that makes alot of sense!:yes: