Should you run A/C fan continously?

[bcwoehr]

I just had a new furnace and central a/c installed. The installer says I should run the fan 24/7, even when there is no heating or cooling going on. Is this advisable? Will it shorten the life of the fan?

[BigJon3475]

It probably is okay during heating. During cooling though it shouldn't be run 24/7 without the compressor running because it will evaporate the moisture that's condensed on the evaporator coil which you just paid to have removed for comfort from your home, the kicker is you're using more electricity to do this too. The end result will be a muggy feeling in the home during cooling season.

[tedkidd]

...or it will distribute cool air evenly and make your whole house comfortable, not just by the thermostat.

The answer is: It depends (this applies to heating too, and is usually the answer to most short questions - not just fan questions). Do have alergies and need continuous air purification? Are there uncomfortable temperature imbalances? If the house is comfortable leaving the fan on AUTO, that's probably the best place for it.

Understanding how to take advantage of your equipment to improve comfort is what you get from experimentation.

[BigJon3475]

I guess if you live in a place where the evaporator isn't below the dew point it would be okay... I don't know many areas like that but that doesn't mean they don't exist.

[superd77]

no, dont run the fan......unless its spring or fall and you want to bring in a little fresh air......i still wouldn't do it.

sounds like he dont know much about humidity

[fixitguy]

So try it and see if its more comforable. You'll know soon enough.
when in the circ mode [fan on] its usually set at a lower speed than AC or Heat so it will balance out hot cold areas..more even temp around the place.

Electricity use..if you have an ECM motor it will be very cheap to run..

try it and see is the best choice, every place/everyone likes it different...
and look at the electric bill, have to make your wallet comfortable too!!
.

[teddy bear]

What about the energy used by the fan? Regular fans use .5kw or about 12 kw per day or +$35 /mo. VS fans on low use 1/4 of this. Explain "purify the air", "bring in fresh air"?
Regards TB

[FSHS]

Making sure all is properly installed, filter maintained, & unit serviced should allow normal life of system. constantly improving the air quality,feeling air movement, & comfort is priceless.

[gary_g]

My Honeywell 8000 Series t-stat has a "circ" mode for the fan. This mode runs the fan randomly about 30% of the time. This is a good compromise if you don't want to (or don't want to pay for) running the fan 24/7.

Take care.

[dallasbill]

.......... Explain "purify the air", "bring in fresh air"?
Regards TB
Answers:

The circulating air will pass through the filter.

All houses leak unless super-sealed. The slight negative pressure caused by a running fan system will draw in outside air.

[Adnshel]

I wouldn't refer to it as the A/C fan, it is referred to as the blower. I see it like tedkidd, if you spend time in rooms that aren't comfortable (temperature and humidity same as near thermostat) I would run the fan on run. Saying that, it would be best to have a programmable t-stat and only do it during the time you use the area.

As an example, Summer - my t-stat is in hallway of a bi-level house. Living room had afternoon sun hitting it all summer. I set the stat to run the fan in the afternoon to distribute the air more evenly in the house making the living room more comfortable in the afternoon. I would not recommend running the fan continuously if you can, so that the refrigeration side of the system can remove humidity from the house. It is a case by case situation.

[BigJon3475]

Do you know how moisture and evaporator coil holds when the compressor cuts off? It's no little amount and you'll evaporate practically every bit of it back into the conditioned space. You will have paid to remove it then pay to put it right back. On top of both of those things you'll get a clammy feeling in the home. Yes there are conditions where the moisture is not as bad as say Florida but in general leaving your fan in the on position cost you more and makes you feel less comfortable.

Try it sometime... Leave your fan in the on position and record humidity levels. My previous system was, on average, always 5-10% higher in relative humidity. At the lake house I go to for vacation at times it was almost 15% higher. To compensate for that higher humidity level the t-stat always got turned down a little more, sometime through the night of course and no one ever knew who did it... Once the fan was left in auto complaints of freezing to death were heard.

[Adnshel]

In my case, getting the cooler air into the living room for a few hours in the afternoon is worth the increased humidity in the house at that time. In the evening the fan goes back to auto and humidity is remove. I look at it this way.....it is comfort cooling. If I am not comfortable, then why run the system. Nice and cool in the hallway, but about 10 degrees warmer in the living room.

[yourairman]

I have been in the HVAC industry for 20+ years and HVAC-TALK is the first place I have heard of not running the fan on in the cooling mode due to humidity issues. The KC area is very humid in the summer time with dew points in the lower 80's during the hot weeks/months. We always recommend running the fan continuously with a variable speed blower and can achieve 45-55% humidity relatively easy with a properly sized system. Someone who is opposed to running the fan continuously needs to give some factual numbers of how much water a coil has on it after shutdown that is redistributed back into the airstream. Personally myself I couldn't imagine it being more than a cup or two at best. My vote is to run the fan.

[BigJon3475]

Try 1 to 2 quarts. If you have 10° difference in room temps then you have a distribution problem or a t-stat location problem or both. I guess you could ban-aid it by running the fan all the time... If you have dual/multi speed setup the lowest stage should run along with the compressor to keep the humidity as low as possible. This will allow you to keep the thermostat setting higher and will still provide the moving air that some people like. If you want to move air around try a fan that isn't sitting in front of a coil with 2-4lbs of water on it. You'll find you can keep your thermostat setting higher and you won't be wasting the energy you just paid for by evaporating the moisture right back into the air. Yes some t-stats have continuous fan operation and they can be used effectively but you need to know if the coil is full of water to not be wasting your time and your money. If the dew point is below the temp the coil is running at fan-on position or continuous fan-on position can and probably will be fine. If you have or live in a high humidity area you can achieve better living conditions with less power if you do not re-evaporate the moisture you just paid to remove...

[yourairman]

Try 1 to 2 quarts. If you have 10° difference in room temps then you have a distribution problem or a t-stat location problem or both. I guess you could ban-aid it by running the fan all the time... If you have dual/multi speed setup the lowest stage should run along with the compressor to keep the humidity as low as possible. This will allow you to keep the thermostat setting higher and will still provide the moving air that some people like. If you want to move air around try a fan that isn't sitting in front of a coil with 2-4lbs of water on it. You'll find you can keep your thermostat setting higher and you won't be wasting the energy you just paid for by evaporating the moisture right back into the air. Yes some t-stats have continuous fan operation and they can be used effectively but you need to know if the coil is full of water to not be wasting your time and your money. If the dew point is below the temp the coil is running at fan-on position or continuous fan-on position can and probably will be fine. If you have or live in a high humidity area you can achieve better living conditions with less power if you do not re-evaporate the moisture you just paid to remove...

Where are you getting your 1 to 2 quart information from? Do you have a link that can be posted to prove these numbers?

[Adnshel]

Well, if I wanted to go to the trouble of ripping the double thickness drywall off the ceiling in my finished basement (finished when built), and run the duct work were the original installer SHOULD have run the duct work....then I wouldn't have the problem, but a hack installed the duct work and I am not going to spend the time and expense doing all that work. Instead I will run the fan for a few hours. It would take many years to pay for the errors being corrected. I like my plan better. I, like "yourairman", would like to see documentation stating your 1-2 quarts. That number sounds way too high.



Where are you getting your 1 to 2 quart information from? Do you have a link that can be posted to prove these numbers?

[BigJon3475]

http://www.cdhenergy.com/presentations/lhr_humidity_aug05.pdf




It takes 10 to 30 minutes after startup for moisture removal to begin



A typical coil holds ½ to 1 lb per ton



With constant fan, latent removal disappears below half load


More:
http://securedb.fsec.ucf.edu/pub/pub_search?term1=cooling+coils&help_select=none&query_type=keywords&results_per_page=10

First paragraph page ii:
http://www.fsec.ucf.edu/en/publications/pdf/FSEC-CR-1537-05-es.pdf

I was being conservative. The larger the system the more moisture that is retained.

[Adnshel]

okay, point taken, but that effect is not as important to my situation. I am only taking on block of time and running the fan continuously. Your report is based on running it all the time. I only run if continuously for 4 hrs. Comfort is comfort....and I do not have a humidity problem in the house to warrant special consideration.

[BigJon3475]

It's your system run it the way you want. I was just making a point...

[Adnshel]

I know you are, but you aren't taking all factors into account. All you are focusing on is humidity.

[tedkidd]

I see it like tedkidd, if you spend time in rooms that aren't comfortable (temperature and humidity same as near thermostat) I would run the fan on run. Saying that, it would be best to have a programmable t-stat and only do it during the time you use the area.



Thanks Adnshel.

Are some of us a little ocd about humidity? NO HUMIDITY! 123123123

Seriously folks, this is about comfort. That's what people are paying for. Yes, humidity is an important part, but if they don't have comfort in the rooms they want comfort, and running the fan achieves that - are some of you really saying they shouldn't run the fan?

NO HUMIDITY!123123123

And the manufacturers have routines built in to shut the fan down for 5 minutes so coils have time to drain.

NO HUMIDITY!123123123

And they have routines that delay start up so the coils get to condensing temps...

NO HUMIDITY!123123123

And the Infinity will allow you to program the fan based upon occupancy. With Zoning, you can run your fan in different areas at different times.

NO HUMIDITY!123123123

And with Infinity you can set humidity targets and the unit will adjust airflow and even go beyond cooling set temp if targets aren't being reached.

So, while I agree, NO HUMIDITY!123123123, the primary goal is comfort. Otherwise might as well shut the thing off.

[BigJon3475]

Thanks Adnshel.

Are some of us a little ocd about humidity? NO HUMIDITY! 123123123

Seriously folks, this is about comfort. That's what people are paying for. Yes, humidity is an important part, but if they don't have comfort in the rooms they want comfort, and running the fan achieves that - are some of you really saying they shouldn't run the fan?

NO HUMIDITY!123123123

And the manufacturers have routines built in to shut the fan down for 5 minutes so coils have time to drain.

NO HUMIDITY!123123123

And they have routines that delay start up so the coils get to condensing temps...

NO HUMIDITY!123123123

And the Infinity will allow you to program the fan based upon occupancy. With Zoning, you can run your fan in different areas at different times.

NO HUMIDITY!123123123

And with Infinity you can set humidity targets and the unit will adjust airflow and even go beyond cooling set temp if targets aren't being reached.

So, while I agree, NO HUMIDITY!123123123, the primary goal is comfort. Otherwise might as well shut the thing off.
No one is arguing that multistage systems are not better at removing humidity. Most people don't pay attention to humidity levels and don't understand how they influence comfort. They hear people come on a forum and give a blanket answer like keep your fan on for comfort and roll with it. His problem, in particular, isn't' fan control but distribution and/or placement of the t-stat. If you're going to recommend ban-aids to solve underlying problems then at least say so...

[BigJon3475]

Good luck to you...

[tedkidd]

His problem, in particular, isn't' fan control but distribution and/or placement of the t-stat. If you're going to recommend ban-aids to solve underlying problems then at least say so...

Some people simply like air circulation. Some have allergies and find constant air filtration makes a more pleasant environment. This is really just a discussion about the pros and cons of running a fan. Speaking of humidity, air flow removes it from your skin. Doing this continuously may allow comfort at higher temperatures.

So you accuse others of recommending "band aids" to a "problem" that has yet to be diagnosed, then conclude he has distribution and or t-stat location problems?

"cough cough."

What do you think, throat cancer? Recommend surgery?

The conclusion that someone needs to replace duct work or move their t-stat may prove accurate, not sure how that can be diagnosed from the information provided.

[BigJon3475]

Nice and cool in the hallway, but about 10 degrees warmer in the living room.
http://pics3.city-data.com/forum/images/smilies/confused.gif

[green jumper]

I dont think he's out of line, if someone says hey my house is comfortable yet this room is warmer then the others, I say lets check the air distribution. Customer says but i got no money, then I say turn the fan on.

[Carnak]

The pacific is cold, the outdoor dewpoints in the Pacific NW are on the low side.

If you live somewhere with low outdoor humidity you can run the fan all the time to even out temperatures and compensate for poor air distribution without elevating RH to a bad level.

When you run the fan all the time you need the compressor running for a good 20 minutes to get a net removal of moisture. If it runs less than that, the constant fan will dry out the coil and the small accumulation in the drain pan, in about 10 minutes time.

Depending on where you are located it can raise indoor rh by 5 to 20 points when you run the fan all the time

[Carnak]

It is an easy concept to test out in the summer in your own home, a little before noon switch the fan to 'on' and two hours later record the RH. Then switch it to Auto and record the RH after another 2 hours. Will drop. Most places prime time cooling is done for the year, but easy to try next summer

[yourairman]

Thanks Adnshel.

Are some of us a little ocd about humidity? NO HUMIDITY! 123123123

Seriously folks, this is about comfort. That's what people are paying for. Yes, humidity is an important part, but if they don't have comfort in the rooms they want comfort, and running the fan achieves that - are some of you really saying they shouldn't run the fan?

NO HUMIDITY!123123123

And the manufacturers have routines built in to shut the fan down for 5 minutes so coils have time to drain.

NO HUMIDITY!123123123

And they have routines that delay start up so the coils get to condensing temps...

NO HUMIDITY!123123123

And the Infinity will allow you to program the fan based upon occupancy. With Zoning, you can run your fan in different areas at different times.

NO HUMIDITY!123123123

And with Infinity you can set humidity targets and the unit will adjust airflow and even go beyond cooling set temp if targets aren't being reached.

So, while I agree, NO HUMIDITY!123123123, the primary goal is comfort. Otherwise might as well shut the thing off.

With all the technology being built into moisture removal, especially with variable speed fans and TXV's, You are removing so much more humidity during run times than what you could in the past. The ramping up of blower motors allowing super dehumidification takes you well below the humidity removal of systems built 20-30 years ago. Anyone can manipulate charts to get their desired results. The chart that shows humidity with fan on in the 75% range and with the fan in auto in the 55-60% range I CALL B.S. When we go out on calls that the customer's complaint of high humidity that is running the fan on continuous the last thing we would ever tell them is turn the fan to auto. The problem always stems from either a refrigerant charge problem or airflow issue. Of course the next complaint would be the newer bigger coils do not remove moisture as well as the old ones.

NO HUMIDITY 123123123!

[BigJon3475]

Yeah, Florida Solar Energy Center is making things up and outright lying to the public... You do know what an .edu is right... Your convulsions are uncalled for. I'm assuming this the level of professionalism by now though...

[yourairman]

If you think colleges or any other state funded group does not manipulate charts and results so they can prove they deserve grants you are gravely mistaken. What is not given with these results is how much fresh air is being delivered into the return, especially on commercial. If they were going to get to the specifics they would have broken down commmercial and residential seperately. To be to code commercial has to have a minimum amount of fresh air brought into the occupancy. By running the fan continuously you would automatically be introducing humidity into the conditioned space with or without a saturated coil.

[BigJon3475]

This person is in residential and I don't partake in conspiracy theories...

[yourairman]

The following is from Bulletin 2009-2 written by Donald Prather, ACCA Technical Services Specialist.

[B]COMFORT REQUIREMENTS & CODE[B]

The only code requirement relating to temperature in dwelling space is contained in the International Code Council requirement:

"dwelling units must have permanently installed heating facilities capable of maintaining a minimum room temperature of 68 deg. at a point 3 feet above the floor, and 2 feet from exterior walls, in all habitable rooms, on a day where outside air is at the design temperature."

Very few homeowners would be happy living in a home designed to meet only that minimum requirement. Obviously, the lack of formal regulation does not mean temperature control is not an important issue for HVAC contractors. Customers expect their new HVAC systems to be able to keep their homes heated and cooled evenly. When they set the thermostat, they expect to be able to walk away and forget it; knowing the house will remain at the temperature they choose. ACCA manuals provide HVAC contractors with the guidance needed to make that happen most of the time. However, some rooms in most well designed HVAC systems, for some hours, on some days, will not be able to remain at the recommended temperature difference from the central thermostat's set point.



This is where YOURAIRMAN says welcome to continuous fan.:oops:

[BigJon3475]

And you're claiming a 10 degree difference is "normal"?

[yourairman]

And for those of you who do not know what .edu means ACCA stands for air conditioning contractors of America.

[BigJon3475]

"dwelling units must have permanently installed heating facilities capable of maintaining a minimum room temperature of 68 deg. at a point 3 feet above the floor, and 2 feet from exterior walls, in all habitable rooms, on a day where outside air is at the design temperature."

On a design day at 68 deg inside the system should never cut off anyways till it cools off...

[BigJon3475]

Sizing & Selecting Equipment for
Proper Humidity Control

The likelihood of a mismatch between
equipment SHR and space SHR illustrates the
need for appropriate design analyses to ensure
that the HVAC system meets both sensible
and latent loads at full and part-load conditions.
This is absolutely critical when
outdoor air ventilation (generally, warm and
moist air) is required and/or if the HVAC system
operates with continuous fan while the
compressor cycles.
For example: Many commercial HVAC systems
operate with continuous fan, allowing the
compressor to cycle on and off based on thermostat
set points (sensible control). Hence,
under part-load conditions, continuous fan operation
with an “off” compressor increases the
evaporator temperature and could allow moisture
on the coil to evaporate and be reintroduced
into the building, raising the humidity
level in the conditioned space.https://www.acca.org/Files/?id=121

[Adnshel]

Hey guys, we see that there are multiple opinions on this subject...and that those opinions are strong. Seems like you guys are getting ticked at each other.....wouldn't it be better to drop the subject?

[BigJon3475]

Figure 6 and Table 5 compare indoor humidity
levels achieved with AUTO fan mode and fan ON
(constant) mode. Figure 6 shows measured daily
indoor humidity levels versus outdoor air humidity
levels during summer weather at a Florida field test
site (Shirey et al. 2006). For this residence, constant
supply air fan operation resulted in significantly
higher indoor humidity levels (approximately 20
gr/lb higher) compared to AUTO fan mode, in spite
of the fact that the home had a two-stage unit
operating with low fan speed during the compressor
off cycle. With a thermostat set point of 77°F, indoor
relative humidity levels were approximately 50% RH
with AUTO fan mode but rose to 60-65% RH with
constant fan operation.

Table 5 summarizes computer simulation results
showing the impacts of supply air fan operating mode
on indoor humidity levels and energy use for a
typical new house (HERS Reference) and a high
efficiency house (Henderson et al. 2007). For both
houses, continuous supply air fan mode increases
indoor humidity levels tremendously (2X to 4X
increase in hours > 60% RH). Continuous fan
operation also results in a large increase in energy use
due to increased supply air fan electrical energy use
and fan motor heat, and increased duct air leakage
(HERS Reference House only)
http://www.fsec.ucf.edu/en/publications/pdf/FSEC-PF-443-08.pdf

I don't think anyone is ticked off, at least I'm not. This is common and sometimes required to learn something... as long as it stays civil of course.