Furnace Blower Fan on 100% of the time - Good or Bad or it depends?

I was at a dinner party last night and two guests described how their HVAC reps told them to run their furnace blowers 100% of the time.  The HVAC reps reasons for the recommendation, as relayed by the dinner guests, were:
1. continuous running reduces the wear and tear on the blower motor that cycling on and off causes, thereby avoiding an earlier motor replacement
2. circulating the air around the home provides better balanced temperatures throughout the home and, 
3. continuous air flow would provide cleaner air due to the continuous filtering.

We live in northern Michigan and are a heating dominate climate.  I am curious to hear from the HVAC professionals about what they recommend to their clients and why.  At the moment I don't buy the above arguments and feel those customers end up paying more in energy costs for little benefit.  However I do understand there is no disputing tastes when talking about perceived comfort.  Also if anyone knows of a good source or any research done on this issue I would like to see a more in depth analysis (if its out there).

[NOTE: Neither home has an ERV, HRV, or other mechanical ventilation other than intermittent bath and kitchen fans.  Both are natural gas, forced air furnaces.]

Any discussion on this subject?
Thanks,
TJ

Tags: HVAC, IAQ, energy, motors

Views: 132133

Replies to This Discussion

We find a common reason for a large number of households with high electric baseload use to be air handler fan switch on the t-stat set to "on"
Attachments:


Allison A. Bailes III said:
Great topic for discussion here, TJ. The answer is that you should NOT leave the fan in the ON position. It will cost a lot more in electricity, as Michael Blasnik said. If the house has unbalanced duct leakage, it will also cost extra in heating and cooling because of the added air leakage.

Yes, having an HVAC system that runs longer has benefits, but you want to achieve that by having a properly sized system and, if you can afford it, a variable speed blower with an ECM. As has been mentioned by others, running the fan in the cooling season in a humid climate will increase the humidity in the house because it will evaporate moisture from the coil and drain pan.

If you want cleaner air, filtration is the last step you take, so your point number 3 isn't valid either. First you get bad stuff out of the house and seal the air leaks and duct leakage so you don't bring more bad stuff in.

Boy, I think I found this discussion just in time.
I had my HVAC guy out yesterday, since I have a slightly bad odor (which smells like a metallic, burning of something). Three days ago I heard the blower go on, made a real high pitching noise, shut down and then came back up normally. Since then I have had this smell, even had my neighbor come over to confirm. She said it smelled kinda like the burning covering over a wire. Service guy came over, the same people who installed this furnace which is a Trane XV-90 HE.
He could not smell anything...so I called my neighbor back over and again we both smelled it, especially when it hit the second stage, but this guy was still couldn't smell anything. I AM GETTING TO THE PART ABOUT THE FAN, BUT HOPING SOMEONE HERE CAN HELP ME WITH MY ORIGINAL PROBLEM. I have a down-draft furnace, meaning the blower is behind the board and no way to look at it unless you remove everything including cutting into the PVC to get to the blower. So, does anyone know how I can take a look at this motor without ripping out it's guts? I will never buy a Trane again...problems since day one.
So getting back to the fan. This guy told me to leave it running 24/7 because not only will it keep the air circulating around my small ranch house, but when it calls for heat it will take less energy for the blower to kick in, meaning less wear and tear on motor, blower or anything else. So let me throw in my 2 cents. I have worked with electronics for over 35 years in television. With any product, there is a Mean Time Before Failure, meaning if you keep turning something on and off with a switch i.e your TV, eventually that switch will no longer work and it might even take out a few components with it.
So, if keeping the fan on 24/7 will reduce the wear and tear on the blower/motor it kinda makes sense to keep it on, unless of course your furnace is very old and it cost a lot more to run the fan then it's your decision...but to me, this makes a lot of sense.
Now, can anyone help me wth my first problem, I sure would appreciate any input
Thanks

It sounds like a mouse, I've removed dozens from the blades of furnace blowers. If you have to cut the flue to remove the fan that's a poor install. The blower assembly is actually easy to remove, take the control board off and tie it out of the way, then find the 2 screws in the flange of the housing, remove them and slide the whole assembly out. It sounds like the tech didn't want to cut the flue, so he couldn't smell anything.

The other problem it might be is a plugged condensate drain. This would cause condensate to back up into the combustion fan which will cause the furnace to shut down. You can check this by removing the drain line at the bottom of the hx.

Bruce,

I would have a different company send a technician. From your description, the furnace will have to make way to look at the blower. Is the smell just in the furnace area, or is it throughout the house? Might make a difference, you could look at the draft assist fan first.

I also refer to my post earlier about failure of blowers in many furnaces I operated. I disagree with the weight you are giving the "Mean Time Before Failure" in this situation.
Since your furnace is a down or counterflow, you should be able to remove the filter (located in the return duct above the furnace?) and look down at the blower motor. All counterflow furnaces, regardless of manufacturer, are a pain to get into to see the blower motor. Yor XV furnace has a Variable speed motor and they use a lot less electricity when they run (not Start- that is a small amount) than a regular PSC motor. The motor will also change speed to provide better comfort as the furnace operates at first and 2nd stage heat. It will also remove more humidity in the summer and increase the efficiency of the A/C as well.
Did the service person remove the baffle and inspect the motor? I have found that the filter can be sucked out of the rack (if not changed often) and can lay on top of the motor causing higher than normal heat rise.
As to the odor. Diagnosing without an exam is malpractice if you are a DR. If you are unsure about the installing company, call someone else. The high pitch noise sound like something rubbing in or on the fan. I would look at the motor. You may have to cut the flue pipes to do this and reseal them with rubber hub connectors (use the clamps)
Sorry you are having a problem with the Trane furnace. The main issue may be the furnace or maybe how it was installed. I sell them and have had few problems with them. Trane (our distributor) has been very supportive if there has been a problem. Look at trane.com and you should be able to send them an email with your problem. The area distributor will have people on staff who can help you. Send me an email if you need more help. lewis_htg_clg@sbcglobal.net and I will get you what I can


John Nicholas said:
Bruce,

I would have a different company send a technician. From your description, the furnace will have to make way to look at the blower. Is the smell just in the furnace area, or is it throughout the house? Might make a difference, you could look at the draft assist fan first.

I also refer to my post earlier about failure of blowers in many furnaces I operated. I disagree with the weight you are giving the "Mean Time Before Failure" in this situation.

Thanks for the quick reply John
I picked this company because they were the people who installed it. When I first got this Trane, the DC fan was making this rattle type noise and sounded like it had water in it. 1st guy came out and just replaced it, 2 weeks later a different guy came out replaced the fan again...2 weeks later the third person, an elderly gentlemen who said he had very little experience working with Tranes, heard the noise, saw the problem, which was a hose that should have been lowered or raised, can't remember, but cut off some of that hose, installed a new fan and haven't had a problem with it since. When I heard it yesterday, it was not as quiet as when it was last fixed, sounded like the bearings were going, but this guy said it was normal. This service call cost me $109...just to come here, yep, that's not a typo. I told him I wanted them to send someone out for a second opinion since me and my next door neighbor could smell it, but he couldn't and when he walked in he told me he had a stuffed up nose. If they do not send someone out next week, I will dispute the charges on my charge card. And to add, since he could not smell anything, he did not remove the intake grill on the wall and look inside...he really didn't do anything.

So yes, I have had concerns about this company since the installation. The smell is throughout the house but if you smell the vents, they don't have that smell I described. I do not have a lot of knowledge in the furnace dept, so when you say draft assist fan, is that the DC motor fan that's mounted in the front and has been replaced 3 times?

The reason of keeping the fan on kinda made sense to me which is why I threw it out there. I figured if the blower was always on, when it called for heat it would take less energy then going from a cold start. I will read your earlier post and sure you're probably right.

I truly appreciate your response, thanks.


Steven Lewis said:
Since your furnace is a down or counterflow, you should be able to remove the filter (located in the return duct above the furnace?) and look down at the blower motor. All counterflow furnaces, regardless of manufacturer, are a pain to get into to see the blower motor. Yor XV furnace has a Variable speed motor and they use a lot less electricity when they run (not Start- that is a small amount) than a regular PSC motor. The motor will also change speed to provide better comfort as the furnace operates at first and 2nd stage heat. It will also remove more humidity in the summer and increase the efficiency of the A/C as well.
Did the service person remove the baffle and inspect the motor? I have found that the filter can be sucked out of the rack (if not changed often) and can lay on top of the motor causing higher than normal heat rise.
As to the odor. Diagnosing without an exam is malpractice if you are a DR. If you are unsure about the installing company, call someone else. The high pitch noise sound like something rubbing in or on the fan. I would look at the motor. You may have to cut the flue pipes to do this and reseal them with rubber hub connectors (use the clamps)
Sorry you are having a problem with the Trane furnace. The main issue may be the furnace or maybe how it was installed. I sell them and have had few problems with them. Trane (our distributor) has been very supportive if there has been a problem. Look at trane.com and you should be able to send them an email with your problem. The area distributor will have people on staff who can help you. Send me an email if you need more help. lewis_htg_clg@sbcglobal.net and I will get you what I can

Thanks Steven, he did not remove the return and look down at anything. I will do that. Since I am paying him $109 just to show up, I figured I would let him work for it...but pretty sure I got nothing in return. He did not remove the baffle or look at the motor. Since he could not smell anything, and we could, I'm pretty sure he had no idea what to do. I check and change filters every month or two.

Here is another question I am sure you can answer. I was always told, I believe I even called Trane on this one, but was told never to put in a filter higher then a Merv 8. This person that came here yesterday told me I could put a higher one, actually the highest Filtrete has to offer and the furnace since it is an HE will adjust itself for the proper airflow, your input on this would certainly be appreciated.

Also thanks for your help, I appreciate any and every bit of advice I can receive on this furnace. I admit, I am pretty much clueless when it comes to furnaces, but if you ever need a TV station built, give me a call. :)
The higher the MERV # the more restrictive the filter is to airflow. You need to balance filtration with performance/airflow. You need to know the static pressure in the supply and return duct and then add in the furnace and evap coil pressure drops. The total static pressure is then applied to the airflow chart in the installation packet with the furnace. As the static pressure goes up the delivered airflow goes down. ECM fans will deliver better airflow against resistance but will only do so to a certain extent. When you add in the resistance of a high efficiency filter you can eceed the temp rise of the furnace. Have someone take the static pressures or you can take the temp rise. Find out the airflow settings your furnace is set to. Should be dip switch settings on the control board then look at the temp rise for that aiflow and you can get an idea of your true airflow.

To low temp rise and moisture can form in the main heat exchanger and cause premature failure. To high temp rise causes more rapid cycling of the burner limit switch that can impact operating costs and cause premature failure of the ignitor, limits and heat exchanger.

HE is for high efficiency VS is for variable speed. There are two variable speed fans the main blower that we are discussing and the variable speed inducer motor. That is the small motor assembly that starts when there is a call for heat from the thermostat. The installation instructions should have a sequence of operation listed in them so you can look at them for your information as to proper operation.

if the contractor didnt leave them with you, I can get you a copy. need the model and serial no's


Steven Lewis said:
The higher the MERV # the more restrictive the filter is to airflow. You need to balance filtration with performance/airflow. You need to know the static pressure in the supply and return duct and then add in the furnace and evap coil pressure drops. The total static pressure is then applied to the airflow chart in the installation packet with the furnace. As the static pressure goes up the delivered airflow goes down. ECM fans will deliver better airflow against resistance but will only do so to a certain extent. When you add in the resistance of a high efficiency filter you can eceed the temp rise of the furnace. Have someone take the static pressures or you can take the temp rise. Find out the airflow settings your furnace is set to. Should be dip switch settings on the control board then look at the temp rise for that aiflow and you can get an idea of your true airflow.

To low temp rise and moisture can form in the main heat exchanger and cause premature failure. To high temp rise causes more rapid cycling of the burner limit switch that can impact operating costs and cause premature failure of the ignitor, limits and heat exchanger.

HE is for high efficiency VS is for variable speed. There are two variable speed fans the main blower that we are discussing and the variable speed inducer motor. That is the small motor assembly that starts when there is a call for heat from the thermostat. The installation instructions should have a sequence of operation listed in them so you can look at them for your information as to proper operation.

if the contractor didnt leave them with you, I can get you a copy. need the model and serial no's

The contractor left me nothing but a bill and a headache.
What you just explained about the the MERV is exactly what the Trane Rep told me, almost exactly word for word.
So now I am thinking this guy who came out is pretty clueless about all he told me and the work he performed.
Is this VS motor that you are talking about, is that the DC motor that is mounted on the front, that has been replaced 3 times? If not, what does that DC motor do? If not, please don't tell me this VS motor is also behind the guts of the furnace, meaning behind the circuit board?
Either you or John suggested checking the baffle, can you tell me where this is located? I am having my next door neighbor come over today and he used to be in the HVAC business years ago. When I asked him about the baffle, he had no idea what I was talking about (he has been out of the business at least 15 years) and asked me to ask you where
this is located and what it's function is?
The house yesterday was not as bad, I could smell it a little, but not as bad as the past few days. Had girlfriend over last night for dinner and she is very sensitive to odors. About 8pm she came out of one of the rooms, I am on the phone with my neighbor who had smelled it too, the furnace kicked in, GF said she could smell something, I could start smelling it too. I can only say it's an oily, metallic odor that you can almost taste and once you breath it in, it stays with you meaning I got into my car and could still smell it, my neighbor went home and she could still smell it. It eventually goes away and all is well, even when the furnace is running again. I think my next step is to get a priest over here and perform and exorcism on this furnace.
I can't tell you how much I appreciate your input and sticking with me on this. I truly owe you a big thanks.


Bruce Gold said:


Steven Lewis said:
The higher the MERV # the more restrictive the filter is to airflow. You need to balance filtration with performance/airflow. You need to know the static pressure in the supply and return duct and then add in the furnace and evap coil pressure drops. The total static pressure is then applied to the airflow chart in the installation packet with the furnace. As the static pressure goes up the delivered airflow goes down. ECM fans will deliver better airflow against resistance but will only do so to a certain extent. When you add in the resistance of a high efficiency filter you can eceed the temp rise of the furnace. Have someone take the static pressures or you can take the temp rise. Find out the airflow settings your furnace is set to. Should be dip switch settings on the control board then look at the temp rise for that aiflow and you can get an idea of your true airflow.

To low temp rise and moisture can form in the main heat exchanger and cause premature failure. To high temp rise causes more rapid cycling of the burner limit switch that can impact operating costs and cause premature failure of the ignitor, limits and heat exchanger.

HE is for high efficiency VS is for variable speed. There are two variable speed fans the main blower that we are discussing and the variable speed inducer motor. That is the small motor assembly that starts when there is a call for heat from the thermostat. The installation instructions should have a sequence of operation listed in them so you can look at them for your information as to proper operation.

if the contractor didnt leave them with you, I can get you a copy. need the model and serial no's

The contractor left me nothing but a bill and a headache.
What you just explained about the the MERV is exactly what the Trane Rep told me, almost exactly word for word.
So now I am thinking this guy who came out is pretty clueless about all he told me and the work he performed.
Is this VS motor that you are talking about, is that the DC motor that is mounted on the front, that has been replaced 3 times? If not, what does that DC motor do? If not, please don't tell me this VS motor is also behind the guts of the furnace, meaning behind the circuit board?
Either you or John suggested checking the baffle, can you tell me where this is located? I am having my next door neighbor come over today and he used to be in the HVAC business years ago. When I asked him about the baffle, he had no idea what I was talking about (he has been out of the business at least 15 years) and asked me to ask you where
this is located and what it's function is?
The house yesterday was not as bad, I could smell it a little, but not as bad as the past few days. Had girlfriend over last night for dinner and she is very sensitive to odors. About 8pm she came out of one of the rooms, I am on the phone with my neighbor who had smelled it too, the furnace kicked in, GF said she could smell something, I could start smelling it too. I can only say it's an oily, metallic odor that you can almost taste and once you breath it in, it stays with you meaning I got into my car and could still smell it, my neighbor went home and she could still smell it. It eventually goes away and all is well, even when the furnace is running again. I think my next step is to get a priest over here and perform and exorcism on this furnace.
I can't tell you how much I appreciate your input and sticking with me on this. I truly owe you a big thanks.

One last question. Is it normal to have a slight gas smell where the furnace and water heater are located? The HVAC guy said this was normal? I have had this smell for years, basically since they installed the furnace. I live in a ranch home with a crawl space. The furnace and hot water tank are located in a utility closet. I ask this because 1. I don't want to blow up my house or myself 2. Where I read on the internet, it basically tells me you should not have any gas smell and something isn't vented properly. Your opinion please.

Thanks
Bruce,

If you smell a slight gas smell like this and it persists, call the gas company. It could be a lot of things. They will come check. This is not about venting! This is safety.

The small DC motor in front everything you are referring to is what I called the draft assisted fan. It is not VS. It comes on to improve the draft of the furnace at the beginning of the cycle, before the chimney has had time to warm up. This is primarily an efficiency measure. The older 60 AFUE furnaces do not have them and are atmospherically vented, like a hot water heater. A furnace with this type of fan is at least 78 AFUE.
Quite an increase.

The VS motor Steven is referring to is your blower motor.


John Nicholas said:
Bruce,

If you smell a slight gas smell like this and it persists, call the gas company. It could be a lot of things. They will come check. This is not about venting! This is safety.

The small DC motor in front everything you are referring to is what I called the draft assisted fan. It is not VS. It comes on to improve the draft of the furnace at the beginning of the cycle, before the chimney has had time to warm up. This is primarily an efficiency measure. The older 60 AFUE furnaces do not have them and are atmospherically vented, like a hot water heater. A furnace with this type of fan is at least 78 AFUE.
Quite an increase.

The VS motor Steven is referring to is your blower motor.

Thanks John, I agree about the gas. It is always there, never really leaves the furnace area but I rather be safe then blown to shreds.
I opened up the intake vent, took a look down to see the blower and all I could see was the blower was covered and a molex connector. This problem with the original smell will probably kill me mentally and if I were to design a down or counterflow furnace, I would make sure there would be an access area on the side. From an engineering point of view, this is a very poorly designed furnace, especially if you have to cut through the duct work and remove basically everything in order to see, test a motor...etc.
Thanks for the info on the motor. From what I am gathering this VS motor does a lot of work a long with the blower. I am starting to think that this metallic oil smell I have may be some kind of sealed bearing that may be going bad, but of course, how do you check without ripping out the whole unit? Yep, back to that poorly design of this type of furnace.

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