furnace filters

[JustinH]

A 3m filter will cause my furnace to overheat, and keep restarting. A cheap furnace filter will allow it to work properly. I stick with the green cheap ones from home depot, the 5 pack is 3 dollars. I replace every 30 days if it needs to be replaced or not.

My furnace is a new 80% efficiency Ruud unit.

 

[buickman50401]

Jumping on the MERV 8 bandwagon.

They are usually just at the "sweet spot" in the price point between cheap [censored] and the more restrictive filters.

I pick up 4 of them at Menards when they put them on sale for $2.50ish each and replace them quarterly.

There's nothing wrong with the Merv 7 or even the 4s.

I would not however run the cheapo fiberglass ones simply because they don't do a good enough job protecting the furnace itself.

 

[Nick R]

Well, our furnace doesn't seem to overheat. It never short cycles, and the airflow seems to be perfectly fine. And as I said, we use high end 3M filters in 16x25x1 size.

 

[wymi516]

My neighbors furnace would bang every time it shut off. New filter did the same thing. It was the inside walls sucking in from the restrictive filter. Changed to a low restriction filter and banging on shut off went away. I use the True Blue filters from Menards.

 

[Quest]

The overheating of the older furnace motor is partly truth, part myth.

Truth: older furnice squirrel cage blower motor are mostly 1/2hp or less, and are barely capable of keeping up to the task even w/o air filter on. Also: back in those days most of the furnace manufacturers were not aware of the use of higher filtration efficiency (particulate filtering) media but mostly just loosely spun fibreglass media), thus they can cheepen out by using spun fibreglass media and call for the day.

back a few years ago while we are still on the old, single-stage furnace, I repalced my motor with 3/4hp and changed the pully ratio (to run @about 20% higher RPM) to go with MERV 7 and higher filter and no problems with them.

Now, if you use MERV 7 or higher media in such older furnace designs, your motor may not get the sufficient cooling it needs for the windings/coils and may go south relatively quickly. But then again: that is, provided that you are still on those old, single-stage furnace that are 55% efficiency.

If you are on newer, mid (80%+) or high (92%+) efficiency variable blower motor furnace, the computer control module will actually keep track of the motor and keeping it from overheating (ref: Trane XV95 we are now using). With that in mind: you can now use mid to high efficiency 3M filter without worries.

My dad was scolded by me for playing foolish with spun fibre media back in the earlier days of single-stage furnace (I'm allergic to molds and dust in the winter, so my asthma would act up with spun fibre type which essentially does nothing but to filter dead birds from getting into the air stream).

Q.

p.s. if you are still on single-stage, pilot-light (or single stage mid-efficiency non-pilot-light but constant speed AC motor type) furnace and you want to know if you are going to overheat the motor by means of using mid to high efficiency media (compared to spun fibreglass media), just get one of those wired indoor thermometer and then stick the sensor on the motor outer casing and then run it with the media types you like (compared to no media/spun fibreglass media) and see how bad it is? If it exceeds 10C or more then it would be wise to go with a lower MERV rating one, if change is less than 10C with higher efficiency media, I'd go with the higher efficiency media and be done with it (and still sleep well at the end of the day).

 

[Cutehumor]

I have 3M filters that cost $17 a piece throughout my house. I have three filters in my home. I have a lennox a/c and gas furnace system circa 2001. the 3M filters filter out dust/allergens/mold/viruses. I think it filters everything. I have one less lung so I try to filter as much as possible so I'm breathing cleaner air.

 

[OVERKILL]

Originally Posted By: KrisZ
I'm not an HAVC guy, but I did some extensive reading when I was purchasing an AC system for my house.
What I found is that anything more than MERV 8, can cause premature furnace or AC problems. Furnace filters were never meant to clean the air inside the house, they were designed to protect furnace components.
Furnaces are designed to have a certain temp. raise across the heat exchanger, or temp. drop across the A-coil and this range is fairly narrow. If the filter is restrictive enough, it may cause the temp. raise or drop to be outside of the allowable range. This can cause all sorts of things like cracked heat exchangers, weak AC performance, furnace shutting down prematurely, or short cycling, to protect itself when the heat exchanger gets too hot.
There are furnaces with variable speed blowers that will compensate for additional air restriction, but that uses more electricity and the units are very expensive anyway, so not a lot of people have them.

In essence, if you or someone in your family needs clean air, get a proper air filtration system.


Our new furnace is multi-stage on both the fan and the heat. It moves so much air on low I'm scared to see how much it moves when it switches to high.

 

[OVERKILL]

Originally Posted By: wymi516
My neighbors furnace would bang every time it shut off. New filter did the same thing. It was the inside walls sucking in from the restrictive filter. Changed to a low restriction filter and banging on shut off went away. I use the True Blue filters from Menards.


Yes, the True Blue filters are the ones I use. Get them from Home Depot. They are inexpensive, can be purchased in a multi pack and do a much better job than the cheap fiberglass ones.

 

[dwcopple]

Originally Posted By: wymi516
I use the True Blue filters from Menards.

Me too. I have a Trion Air Bear that takes a 20x25x5 filter and when I switched to a True Blue 20x25x1 the run times dropped and the airflow greatly improved. We use Honeywell HEPA air cleaners in the bedrooms. Sleep great.

 

[bigmike]

I used 3M high efficiency filters until I started reading HVAC boards.

I now use a 24x24x5" filter instead of a 1" filter. These filters go in the return, which is my only filter location in my HVAC system.

The 5" filters can hold much greater amounts of dirt and maintain better flow.

http://youtu.be/NuCwKf7SBbI

 

[mechanicx]

I'm not very residential HVAC savvy, but high filter efficiency doesn't necessarily equal high restriction, at least if the filter is changed regularly. I need to see some evidence that 3M high efficiency filter are restrictive when not loaded. I recently started using 3M's highest efficency filter and my house has way less dust and the air seems much fresher and cleaner.

I'll even confess that I left one in for about a year

. There was still a lot of airflow coming out of the vents. And the furnace in the basement is not exactly a hot enviroment for the fan to operate in. So not being a residential HVAC guy and from what I've seen of the ones that are and considering all the nonsense I hear regarding automotive which I am familar with, I'll take it with a grain of salt. My personally opinion is it takes a lot to overheat a modern furnace fan.

 

[Quattro Pete]

Originally Posted By: bigmike
I now use a 24x24x5" filter instead of a 1" filter. These filters go in the return, which is my only filter location in my HVAC system.

Sounds interesting, but my HVAC doesn't have one large central return. Instead, I've got multiple smaller returns all around the house. Fitting each with a filter would be impractical, IMO.

 

[Virtuoso]

I use the True Blue Basic MERV 7 filter's in our 95% Heil furnace too. During the heavier heating season I have to change them every 3-4 weeks or the unit hits it's high-temperature limit during the morning house warm-up cycle.

Take the "lasts 3 months" with a grain of salt. I really didn't think the filter's looked that dirty, but my furnace guy informed me otherwise.

 

[tom slick]

My guess is if your HVAC filter is marginally sized (too small) then any extra restriction may cause a problem. If the filter is oversized then it can get plenty of flow even if the Filtrete filter is a little more restrictive.

 

[meangreen01]

Once upon a time, furnace filters were only intended to protect the furnace and A/C from excessive dust accumulation. That's pretty much all the blue fiberglass type filters do. Nowadays, with the proliferation of allergies and other respiratory ailments there are filters and other technologies that do much more.

So, it's really up to the homeowner. With as cheap as basic pleated filter are, maybe only a buck more than fiberglass, that's the cheapest filter I'd recommend using. In fact that is what I use. If you're more concerned about indoor air quality, spend more on the higher end pleated filters. Nothing wrong with 3M's, either.

Also, it's very important to check the filter regularly. Just because that filter says it's good for x number of months doesn't apply to every situation. Pull it out every so often to inspect. Hold it up to a light, you should be able to so some light through it.

 

[Drew99GT]

The Merv 8 Ace filters will bend and get sucked into the squirrel cage on my ancient furnace if I don't reinforce the sides with some thin wood sticks duct taped to the filter. Never had that problem before. Perhaps I should try some of the Merv 4 filters from Home Depot?

 

[wander2039]

We tried using the cheapy $1 filters and the dust in the house tripled. Tried using one of those cleanable filters years ago about the same till it started getting a little dirty. Restriction or not we're sticking to the regular 3M filtrete filters. You can get a 3 pack at Sams for a good price.

 

[OtisBlkR1]

Originally Posted By: wymi516
My neighbors furnace would bang every time it shut off. New filter did the same thing. It was the inside walls sucking in from the restrictive filter. Changed to a low restriction filter and banging on shut off went away. I use the True Blue filters from Menards.


I experience this with 3M. I was in Lowes and picked up a $7 3pack of something, when i got home i pulled the 3M i just replaced yesterday and held them both up to the light, obviously the 3M was thicker ect.. I put one of the economy filters in and emediately noticed better airflow and my furnace started running for shorter periods, hand over a vent and the airflow seemed increased as well. this all kinda blew me away.. when the furnace shut off no "bang"..

 

[wtd]

When I had my 80% Bryant installed four years ago, it came with a blue mesh type filter. It was not like the paper ones I used in my previous furnace. This blue filter has never really gotten dirty and looks like it is reusable. It does look pretty porus though so I don't know if it really is doing anything.

I just bang it on the side of the outside trash can to get the little bit of dust that is on it off.

Maybe I should be using a paper filter instead?

Wayne