Furnace filter - cost vs quality


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Old 12-17-11, 08:20 PM
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Furnace filter - cost vs quality

I hope this hasn't been talked about to death on this forum as I haven't been around here much for a while, but here goes.

Would like input on how to pick a furnace filter for a gas furnace. I have previously used a "Web" permanent washable filter until I read that these don't filter well and can lead to a lot of dirt on the A-coil.

Then I read somewhere that the best compromise was to get a MERV 8 filter from HD. This was thought by one experienced HVAC guy on a forum to be good enough to keep the coil clean, but not cost too much nor be too restrictive. I have been doing exactly this and seemed OK until changing the filter this month. After only one month, it had buckled and was very difficult to remove. I don't think anything has changed in the house which should have created a lot more dust and so caused the filter to clog up prematurely.

So now I am trying to figure out what to do next. I would rather not spend a lot of money on the pricey 3M Filtrete filters, esp since I've heard that they can be pretty restrictive when they are loaded up (we do have a couple of dogs if that is important).

I'd appreciate any advice on this.
Thanks
 
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Old 12-17-11, 10:02 PM
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If you have a conventional or mid efficiency furnace with no a/c, use fiberglass. It doesn't take much filtration to keep a blower wheel clean.

If you have a high efficiency furnace and/or cooling, use the least dense pleated filter available in your area.

Avoid anything which says "allergen reduction"

Coils and secondary heat exchangers have closely spaced fins so they can get plugged with dust.

Check the temperature difference between the supply and return; if the difference exceeds what's printed on the name plate, the filter is too restrictive.
 
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Old 12-18-11, 12:15 PM
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Thanks - that is helpful. I like the idea of having a chance to do a a little empirical research using the temperature difference. Had not heard that idea before but like it!

I do have AC - in fact a heat pump in addition to a high-efficiency gas furnace.

Here's the problem, though - the cheaper, less restrictive, filters are also mechanically flimsier it seems to me, and more likely to buckle. I suppose that could mean that I just need to change them even more often than every 4 weeks, but that seems excessive.
 
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Old 12-18-11, 12:56 PM
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I buy 3 packs of pleated filters at HD (NaturalAire by Flanders) MERV 8 I think, and they work just fine without being too restrictive.

I change them every month (though they say they can go longer), but since they only run about $8 or so...it costs me about $20 a year. I don't change them as often in the spring and summer since we don't run the system then.
 
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Old 12-18-11, 01:27 PM
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Merv 7 or 8 will be fine. Never use a fiberglass for anything
 
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Old 02-29-12, 07:28 AM
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I have allergies and asthma and so I usually get the more expensive filters with the higher ratings. I'll have to check the temperatures on the supply and return end to see if the filter is too restrictive. I never thought it would be but now I'm worried if it's putting too much stress on the blower or other parts.
 
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Old 02-29-12, 03:19 PM
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The ONLY high performance filters I recommend are the 4-5" pleated. In most homes a 1" MERV 8 is too restrictive.
 
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Old 02-29-12, 04:50 PM
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Grady,
Thanks for weighing in on this.
How would I know that a MERV 8 1" filter is too restrictive?
In other words, any other tests you recommend other than checking return and supply air temps as already suggested?
 
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Old 03-01-12, 02:14 PM
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Checking the temperatures is about the only way a homeowner can tell other than trial & error. I find I get FAR more calls traceable to an overly restrictive filter during the cooling season than the heating. The reason is generally the A/C system requires more air flow than does the heating system.
 
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Old 03-01-12, 02:47 PM
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My bias is to use cheap $1 filters UNLESS families have health issues. If that's the case, perhaps more restrictive filters are worth the money and bother.

But for most people, cheap filters are fine. With any kind of filter you need to check and see that the filter fits right and hyas adequate support so that the air goes through the filter and not around it.

Quite a few furnaces would benefit from additional support to prevent filters from collapsing or some sheet metal or plywood screwed into place to prevent air gaps around the edge of the filter.
 
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Old 03-01-12, 04:05 PM
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S/P, You're a man after my own heart. I use the cheap filters in my own equipment & after nearly 20 years, with dogs in the house, my evap coil is still clean.
 
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Old 03-01-12, 10:38 PM
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Heh, heh! My gas furnace was installed in 1962. The fan and fan compartment have never needed to be cleaned, and I've been using cheap filters since I bought the place in 1985.

The filters fit well though. I think that is important. But if fit is an issue, there are usually easy ways to fix that problem. Filters aren't rocket science.
 
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Old 03-02-12, 07:09 PM
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cheap works

we have several pets and wooden floors so the filters catch a lot. But we have found that using two cheap filters work just as good as those expensive ones. We install one as usual but are able to set a second one at an angle in the lower part of the inlet box. You would have to see if you have such an option.
 
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Old 03-03-12, 01:37 AM
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Heh, heh! My gas furnace was installed in 1962. The fan and fan compartment have never needed to be cleaned, and I've been using cheap filters since I bought the place in 1985.


Read more: http://www.doityourself.com/forum/ga...#ixzz1o2qLbgtR
Keeping a blower clean and keeping an evap coil from plugging up are two different things.
 
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Old 03-03-12, 07:13 AM
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If you don't have an evaporator coil, it's not much of an issue. Few homes in the Seattle area have central AC --- 1-2%.


The issue of properly fitting filters is going to be critical in any case.
 
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Old 03-03-12, 07:37 AM
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In 2005, I bought 30 year old townhouse and had a new Bryant 80% furnace installed. The installers clean the coil obviously and also fabricated a new set up for a 16x25x1 filter. We have 2 long hair cats and the house was loaded with dirt and also the contamination from the newly installed carpeting and white powder someone hid in the ceiling behind a smoke detector. Nice location, but owned by a slumlord that do not do anything.

I was told to use a Merv 8 filter and did. At first, the filter had to be changed in 2 weeks. I run the fan 24/7 in the heating season for comfort purposes in a 2 level with an ope stairway and set it on auto from June to October when the AC runs. For a while, I changed filters monthly, but not I really do not even have to change ever 2 months, but do just because I have it out for inspection. - No problems with my slight allergies to cats.

Last year the installer stooped bu for a free 5 year check-up. The coil was totally clean, but we also clean the 7 return grates (no filters there) every few months. From what I have seen the cheap Merv 8s from the big box work very well.
 
 

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