Using 'fan only' on central a/c to filter pollen


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Old 05-14-18, 05:41 AM
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Using 'fan only' on central a/c to filter pollen

I have a system that basically looks like the pic below.

Using the Nest thermostat (or probably any thermostat) I can just run the fan. When I do so, I've been told that it will cycle the interior air through the handler in the attic (where the disposable filter is) and therefore filter the air for pollen (and other particles). Half my family has bad seasonal allergies, so if running the fan really does it, I want to give it a try (at the expense of my electric bill...).

However, when I run the fan only, I don't hear any noise (though I admit I haven't gone to the attic to see if anything is actually happening). Normally, when the whole system is on, I can hear both the attic and outdoor units.

I also don't feel much, if any, air coming from the vents, and certainly nothing like when the full a/c system is running.

Thoughts?

Thanks!

 
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Old 05-14-18, 07:43 AM
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If you can't feel the air moving, then the fan isn't on.


It may depend on on what generation thermostat you have, and how many physical wires you have going to the fan, and the controller board.

About 5 eyars ago I switched to a thermostat that suported "fan-auto / fan-on"; however, the "fan on" function didn't actually work; that required an updated controller board and an additional control wire to the furnace.

A "basic" heat/ac setup is probably setup so that "fan on" is triggered if heat/ac are running.
Enabling it as a circulation fan may be as simple as reading the manual and setting a jumper on the board; but it might be a bit more work, i.e. find the part numbers, find the manual, buy a control board and perhaps run some new control wire(s) .
 
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Old 05-14-18, 08:20 AM
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If your unit is also a gas furnace.... FAN ON may be a slower speed than in A/C mode.

I can tell you that your system running in FAN ON mode will do little to nothing to reduce pollen and allergens. You would need special filters that most air handling systems can't use. Pollen is too small for most filters to even stop.
 
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Old 05-14-18, 09:34 AM
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Your furnace filter isn’t intended to be a whole house air cleaner. It’s there to protect the equipment only. If you want a whole house filter, it’s possible, but it needs to be included into the equipment design and needs special filters.
I hope your not using thick, pleated filters (like 3M).
Running the indoor blower constantly during cooling season can raise indoor humidity.
 
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Old 05-14-18, 11:10 AM
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If you or anyone in your family is allergic to pollen, dust, and other air borne stuff I would have an HVAC company install an electronic air cleaner. They are great at removing pollen and dust. I had one installed with my system and everyone in my family can breathe easier. Once installed they need to be cleaned every 2-3 months, depending on the number of occupants in your home including any animals. I clean mine in the dish washer on a short cycle. And contrary to a statement made by someone else, running the indoor blower constantly during the cooling season has no effect on the humidity and will not raise the humidity. BY the way, my indoor fan has run for 20+ years, 24/7. stopping only when my wife wanted to air out the house with no problems ever.
 
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Old 05-14-18, 11:56 AM
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Actually it can raise humidity, that’s a well known fact. The moisture on the evaporator can reevaporate into the air stream going back into the space.
Electronic air cleaners are being outsold by 4” and 5” media filters. Less maintenance and not that much difference in filtering ability.
 
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Old 05-14-18, 06:01 PM
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In order for an electronic air cleaner to be able to lower the pollen level.... it's going to need to be cleaned every other week in the pollen season.

Electronic air cleaners are very effective but they MUST be routinely serviced. There is no forgetting about them.
 
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Old 05-15-18, 07:35 AM
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Originally Posted by roughneck77
Electronic air cleaners are being outsold by 4 and 5 media filters. Less maintenance and not that much difference in filtering ability.
Originally Posted by roughneck77
I hope your not using thick, pleated filters (like 3M).
.

So are thick filters a problem or a solution??
 
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Old 05-15-18, 08:15 AM
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The 1” 3M pleated filters are horrible for airflow. Depending on the setup they can reduce airflow and cause problems.
The 4” and 5” media filters are great. Plenty of airflow and long life.
 
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Old 05-16-18, 07:33 AM
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So these thick expensive media filters are all marketing BS and won't keep your house cleaner or catch the pollen they claim to?

And the thin "fine" filters just load up quick, reduce system efficiency & overheat your furnace?
 
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Old 05-16-18, 07:42 AM
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The 4” and 5” filters do exactly as they say they do, and are highly recommended for proper airflow.
The 1” pleated filters, especially the 3M filters with the flashy wrappers in the store that tell you all the dangerous things they filter out, can cause equipment malfunction. 3M doesn’t even use MERV ratings on their products. Those filters have been nicknamed furnace killers.
 
 

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