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Old 05-26-2011, 10:04 AM   #1
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re: furnace filter type


I bought a new furnace recently and I was told by my HVAC guy (who i trust) that I should use "cheapie" furnace filters during the summer as it lets in more airflow, but use the good filtrete style during the winter.

The filter I replaced that he installed was fibreglass, with a metal backing. The only fibreglass I can around here at most stores exept L**es are "Duststop" ones and I can see right through them. are they too thin? Another cheapie type I bought was at lowes, it is very thin, made of paper, "AAM dustshield". Do thin paper filters ones have considerably less airflow than a fibreglass? I want to do the right thing

please advise. I want to know if I should never use those filters for any reason. I don't like using cheap products that ruin expensive equipement
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Last edited by gramps416; 05-26-2011 at 10:12 AM.
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Old 05-26-2011, 10:52 AM   #2
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re: furnace filter type


I use a reusable that we rinse out monthly. As for the 3m Filtretes & the Ace brand of them, unless someone in the house has really bad allergies, or you have a problem with dust mites, go with something in between. Problem with the cheapies, if you have pets, or live in a area that it is dusty, you might as well run the furnace without it, or change weekly.

The Merv 6 will work. I use Merv 11's, when I need to, due to wife's allergies. The reusable that I use is rated at a Merv 6.

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Old 05-26-2011, 11:12 AM   #3
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re: furnace filter type


I just go to HD and buy the cheap pleated Merv 8 filters in a green box. I buy the 3 packs, so I can change frequently. I totally avoid the Filtrite filters.

I have minor seasonal allergies and a slight cat allergy if I touch around my eyes. We have 2 huge long hair black cats and I do not notice any allergies, so I guess they work well.

I run the fan constantly (24/7) in the heating season (for comfort) and run the fan in the auto position to get maximum dehimidification in the summer.

Dick
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Old 05-26-2011, 12:20 PM   #4
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re: furnace filter type


The more filtering being done (the less space between filter fibers), the more work it takes your furnace fan to pull air through. This causes the fan to use more power (higher bills) and can cause it to burn up more quickly. Same thing when you don't change the filters frequently - the spaces between the fibers fill up with "stuff" (dust, etc.) and block airflow, causing more work on the fan just like if you were using a higher-quality filter.

On the other hand, if you use less (or no) filtration, the fan has to do less work and runs easier, but you also let more "stuff" through that in turn coats your fan, furnace heat exchanger, and cooling coil. On the fan, more "stuff" can lead to shorter life span, just like anything that gets dirty. On the furnace HX, it probably wouldn't block airflow, but a coating of "stuff" lowers your heat exchange rate and would lead to less efficient heat transfer and overall lower heating efficiency. And on your cooling coil, it can not only block airflow (same results as a dirty filter on the fan, but also less airflow to your house), but the "stuff" on the cooling coil in a damp, cool environment fosters growth of bad things (mold, bacteria).

So it's really a toss-up as to what level of filtration to use - and very related to how clean your return air (going back to the furnace) is. In general, if you have fairly clean air, the middle-of-the-road MERV-8's (as mentioned above) are fine - the 3M Filtretes are overkill except in the most-extreme cases (old dirty houses with a lot of pet hair and "stuff" in the air).... and I hate saying that, since my dad worked for 3M for 43 years and we're very invested in them... . But the really cheap, see-through filters are letting enough "stuff" through that you risk causing eventual damage to your furnace parts.
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Old 05-26-2011, 12:33 PM   #5
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re: furnace filter type


Actually, it is an uproven fact, and in reality if the system is maintained, and spec'd properly, the filters will not affect the performance of the unit. The problems arise when homeowners do not change the filters and let them get dirty to the point that air-flow goes down, along with closing vents in rooms, which does not allow proper air-flow.
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Old 05-26-2011, 02:11 PM   #6
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re: furnace filter type


if the filtrette blocks too much airflow (extreme), removing more particles, and the cheapies, allow more airflow, but could potentially damage components, the question is along the lines of being on the other extreme, does the filter in the picture look like it would not block enough airflow?
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Old 05-26-2011, 03:02 PM   #7
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re: furnace filter type


Take it this way. If 3m filtrete filters where proved to be harmful to a/c systems, they would not be manufactured or placed on the open market. The only reason that hvac guys push for the cheaper filters that do nothing, is that it takes money out of their pocket for maintenance and yearly cleanings of the systems. If you maintain it properly, have the system checked over no more than every 24 months, you will be fine. The merv 6 will do fine.

The book for the equipment will tell you what it is rated for air flow wise, and the filters info at the website will also help you choose the best.
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Old 05-26-2011, 03:26 PM   #8
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I grew up in the shadows of 3M and remember schools being closed after accidents and most of my friends had parents that worked there. They are a great company and have made many techinical advances is many fields. I even own some stock in 3M.

They even turned a bad adhesive into "Post-It" notes by packaging, marketing and advertising. They are the leaders in their early basic abrasive products that were just plain sandpaper and they added the technical expertise to create anumber of great industrial products and used packaging and advertising to great a myriad of other DIY products on paper ot foam. They developed the adhesive tape market by offering a number of consumer-oriented products under the "Scotch" brand.

Unfortuately, not everyone has a perfect or good air flow system in the existing house and the high restriction filters are not applicable in most homes and evidenced by my 30 year old home within 10 miles of the world headquarters. I wanted to use 3M products, but they would not be appropriate for my high effiency furnace with a efficent variable speed fan.

You buy what is needed and works best and not always the "top shelf" if it is not suited for the existing situation unless you want to redo the air flow system just to use a certain product. This is especially true where most homes do not have adequate returns (capacity and location). Too often people make a decision and then try to make the product work.

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Old 05-26-2011, 03:33 PM   #9
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re: furnace filter type


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Originally Posted by gregzoll View Post
Actually, it is an uproven fact, and in reality if the system is maintained, and spec'd properly, the filters will not affect the performance of the unit.
Saying it "won't affect the performance" is not really true - it won't negatively affect the performance IF it's designed properly. Anything in the airstream affects the performance - that's a law of physics. But I think you are trying to say that the system should be designed to account for the filter. This is true - it should - and most of the time they are designed to account for a dirty filter, too. Nonetheless, if a system is designed to account for a filter (of whatever type) and "less" filter is installed, the fan won't have to do as much work and will therefore use less energy. That's just physics (fan laws).

Quote:
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The problems arise when homeowners do not change the filters and let them get dirty to the point that air-flow goes down, along with closing vents in rooms, which does not allow proper air-flow.
Sure - or, as in many cases, if the contractor who installed the system did not bother doing much design (or did it sloppily, or by a lazy rule of thumb, or did a bad job of duct installation and created bad static pressure drop situations, etc.) and the fan is undersized for the system static pressure - in which case, using "more" filter will just cause "more" problems.

As with just about any situation in HVAC, if the system is designed properly, you don't have a problem....
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Old 05-26-2011, 03:42 PM   #10
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re: furnace filter type


My unit has no problems using the 3m, because it was designed for the ability to use the Merv 6 filters. The old unit was a Octopus Gravity furnace, so accordingly duct work was figured in for proper airflow. Only place I would not use the better filters is homes that have no airflow due to improper airflow, such as those homes that attempt to feed a second or third floor from a unit in the basement. That is why the filters have the disclaimer on them to use the proper filter for your system.

Of course, humans naturally do not follow the rules is why there are so many safety's and disclaimers, because people like to sue for not following the law. If people read the instructions that come with their unit, and use the proper rated filter for their system, there is not a problem as stated before.
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Old 05-26-2011, 05:53 PM   #11
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re: furnace filter type


There are 3-4 versions of the 3M filtretes varying from Merv 8 to 11 or 12 or higher. Unfortunately they don't follow the MERV rating/advertising like everyone else but rate them in microns. The basic orange filtrete is about Merv 8 and okay for most users. The purple and more expensive ones need large adequate sized ducts which most people don't have and/or a ECM high capacity fan. The True Blue Merv 8s at HDepot is what I recommend to most of my customers. There is a Merv rating for the 3Ms but you have to dig thru their website etc to find it. Anything under Merv 8 will let enough dust thru to eventually plug your AC evaporator coil and cause it to freeze up , slug liquid refrigerant back to the compressor and damage it in my experience.

The orange filtrete or a Merv 8 True Blue is a safe bet for most people w/o having a Pro check the temp rise thru the furnace and static pressure drop etc.

http://solutions.3mcanada.ca/wps/por...ucts/AirClean/
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Old 05-26-2011, 06:19 PM   #12
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re: furnace filter type


That is why I went back to using the rinse filter, which I have found works better than the cheap, but also does not hamper the system like the higher end filters. More of a trial and error to find the best solution. Of course, regardless what filter is used, we still have to dust twice a week, due to pet dander.
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Old 05-26-2011, 06:28 PM   #13
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re: furnace filter type


I could save money by rinsing them out, but like to take the time to dry them before re-installing, so I just with the throw-aways and check them the first of the month.

Dick
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Old 05-26-2011, 06:40 PM   #14
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re: furnace filter type


Technically the ONLY way to safely know what maximum density filter to use is to have a Pro do a heat rise test on the furnace AND check the static pressure drop across the furnace. Less than 25% of the Pros probably know how to do that. I have a basic Carrier 10 yr old high efficiency furnace in a customers house (she has asthma) and am running a 5" Merv 16 pleated HEPA filter in it. Her ducts are large and she gets proper maintenance done by me once a year and there are no problems. Goes to show you that a extremely tight filter can be used if everything is sized properly and setup properly and maintained. My company sells and installs 95% of our furnaces with these Merv 10 filters x 5" and we don't have problems. They last up to 6 months and take a long time to plug up and have low static pressure drop.
http://www.lennox.com/products/indoo...-systems/HC10/
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Old 05-26-2011, 06:44 PM   #15
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re: furnace filter type


Quote:
Originally Posted by concretemasonry View Post
I could save money by rinsing them out, but like to take the time to dry them before re-installing, so I just with the throw-aways and check them the first of the month.

Dick
It only took me about 5 minutes to clean ours, and left it out for about an hour. So really it took no more time, than what it would replacing the filter if I had to run to the store to get a replacement type.

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