Check Air Filters to Extend Your HVAC System

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Subject: Air Filter furnace

Actually a restriction is not so bad on the blower as it is on the heat exchanger. Less airflow means the heat exchanger heats up more then it should because lack of airflow means its transfers heat more slowly.
What people really should do is find out what the furnace maker recommends for a filter. Your going to get differing opinions on what is acceptable but its all a give and take. More filtration means a bit less air flow. This is compounded as the filter gets dirtier. So looking at the filter rating of a new filter only means that number will increase. My advice is if you use the more restrictive filters then change them more frequently.
Otherwise you risk over heating your heat exchanger. That's a new furnace and more costly then a blower motor.


Subject: The problem is that without

The problem is that without air pressure monitoring you don't know when a filter becomes too restrictive because of particle buildup. Most HVAC contractors I have talken to do not like the high efficiency filters since folks leave them in too long and restrict air flow. The sweet spot for filters is a MERV 10 equivalent or in Filtrete terms, the 1000 or 1200 filter. I was using Filtrete 1600 filters on my new furnace changing them every 90 days. After 8 years the fan motor failed and the likely cause was the filter. Keep in mind that any filter as it collects collects debris, naturally becomes more restrictive and the more efficient the filter, the more restrictive it gets as it does its job. I've since gone to using MERV 10 rated filters and notice no difference in the interior cleanliness of my furnace blower. My son just got a new furnace and the contractor installed a large filter holder that accommodates a 4 inch deep filter. He explained that those thicker filters present more surface area to collect debris yet due to their depth provide much more airflow and are less restrictive. A typical 1 inch depth filter has to be woven much more densely to provide higher particle capture than a thicker 4 inch filter. I think the thing we have to remember is that 90 day filter changes may be too long, dependent on the dust factors in your home and how high the efficiency rating is of your filter. For some this may be as often as monthly. Keep in mind that good airflow not only protects your furnace components, but it reduces your energy cots for heating and cooling.


Subject: Filters

Using thick heavier higher Merv rating filters will destroy you blower, heat exchanger, compressor, and exhaust induced fan! That heavy filter will allow dust and air around it into the furnace anyways as blower cannot pull enough air thru it! (High static pressure destroys systems) duh

Lou Ziolczyk

Subject: HVAC Filters

The statement that a dirty air filter makes the blower motor work harder is misleading. The amperage drawn by the motor is a result of the work it does, i.e. move air. A clean filter allows the blower motor to run at maximum efficiency because more air moves. A higher rated filter will catch more dirt and reduce the flow of air. The reduced air flow will cause the fan motor to move less air and therefore have a lighter load. If the filter is alowed to get too dirty, the components down the line will suffer because of insufficient air flow and the motor will have to run longer to achieve the disired temperature.
So what the repairmen are saying is a more expensive filter will catch more dirt and keep the fan motor running longer. True if you let the filter get too dirty. Cheaper air filters let more dirt through the fan, motor, ductwork, etc get dust and dirt buildup. This will eventually require service to clean and remove the dirt and dust buildup.
In my industrial experience, 20+ years, put in the best grade filters you can reasonably afford and change them at the recommended intervals or sooner if needed.
This will keep the proper amount of air moving and help keep the ductwork, fan blades, etc cleaner.
I've also found that the electrostatic filters catch a lot more dirt and dust than the non-electrostatic filters. I've used 3M Filtrete 1000 but now run either a 1500 or 1900, depending on which I can find at the store. Since I have 6 cats I want the best filter I can afford to help clean the air.
That's my 2 cents worth, but it's the truth, not conjecture.

Sofia Jacobsen

Subject: Air Duck Cleaning!!!

This is something that I have wanted done since the day we moved in and guess what I have been told??
That it's not needed in a new house but why all the dust??

Don S


I use a re cleanable filter based on static/magnetism, Closest I can describe it. I used it in my old system that I replaced last year. The old system was 20 years old. The filter still works perfectly, Paid about 60 bucks back then. Wash it out monthly with ammonia Then flush with water

holly van hest


My experience is this: my Lennox HVHC system is over 22 years old. I've replaced the blower moter once when I couldn't afford the recall and upgrade even at 1/2 price (wish I had but too late now). I've used the GM filtrets for years, and had my system maintained prof. for 19 yrs. The hvac tech used the middle of road filter but since I discoverd the 1500-1900 filtrets, I've experimented w/when I change them. Just did my 2 mo. change tonite. Used to wait for 6 months to let tech do it (yikes) and now I do it my self. with four pets and all of us wlong hair, a 4 story carpetd townhouse - the filters get very dirty w/in 2.5 months, so i may go to 1'x a month just to keep the system running for as long as I can. I know i'm on borrowed time but still - 22.5 years isn't a bad track record - most other unit owners have replace dhteir entire system due to neglecting them.



Everything mechanical is a matter of tolerance. Too little filtration makes downstream motors, blades, etc. clog and lose life. Too much filtration restricts airflow and causes less efficient work to be done by down stream components. You should check a new filter weekly in your house to see (measure/characterize) how time frame it takes till it needs replacing. Repeat this test until confident. (More data points = more confidence) Take into account other factors when deciding level of filtration: allergies, age of equipment, clean/dirty environment, season, cost, time, etc.
How much can the system tolerates with the least impact to life is the question you are trying to answer. Like everything, every situation is unique and require a bit of work.

Mechanical Engineer



Here is what 3M says about their Filtrete filters that I use. Ideally there would be a spec for maximum pressure drop across the filter in a system and a way to monitor it.

If you use a Filtrete filter for longer than three months, it may begin to restrict airflow or cause your heating/cooling system to malfunction. It also could restrict airflow in some higher-efficiency air conditioning systems. When in doubt, change the filter more frequently.



With respect, careful who you listen to Ann, Linda & James, as you may have been misinformed. My former HVAC people once told me nearly the same thing. I ran this past my best friend, a environmental engineer, who holds a mid level government security clearance, that said essentially what this article said with respect to filters. My friend's info was also recently reconfirmed by a HVAC professional that provided a bid to replace my entire HVAC system. Two final items of note for the record: 1.) I was unable to use the aforementioned HVAC professional's bid, as it was a bit too high. 2.) The same HVAC professional was also a engineer, with a degree in mechanical engineering from Purdue.



Actually as long as you change your filter on a regular basis the pleated filters are great. And actually keep alot of debris from getting into your blower motor. Debris that can cause damage over time, and cost you more money in repairs. Keeping your air clean also keeps your system clean and prolongs it's life.



We had to replace our blower motor twice and stopped using the allergin filters to save the motor. So far we have not had a problem with the pleated filters that are about $5 apiece, so that is what we use now. An A/C service in Dallas told me to use the cheaper filters and spray the intake side lightly with End Dust. I find that to be very effective



I agree, the more expensive filter is far the best. Cheap ones will work, but still do less even when replaced frequently. Yes, HVAC may work harder and need more maintenance, but that is worth the cleaner air.

I always want the best quality of everything, especially food. Cheap food costs a lot more for doctors and drugs they prescribe.

Eddie Cameron

Subject: Not that simple

It's just more maintenance cost, it's breaking your unit. If you reduce the air flow too much you can freeze the evaporator coil which stops your house from cooling and can cause overflow water coming over the drain pan. Also it can burn out your blower motor from making it draw more amps than its designed to do.



My HVAC repairman stated the same thing that Ann did in her email IF you have an older unit and you don't have allegeries. The pleated ones make your system work too hard and can burn out the unit.

James Burke


My furnace repair said that 3M Allergen filters are the worst for placing extra load on the blower motor. They really advise against "high efficiency" and "allergy" filters because of damage on the blower motor due to impeded air flow. However, if you need to use one of them for health, then they say to always change them EVERY 30 days no matter what. That way you don't have as bad a drag on the blower motor. Beyond 30 days those filters are clogged even though they don't look "dirty".



I totally disagree. My HVAC repairman said to use the cheapest filter available. The pleated style cost more and make your unit work harder and wear it out faster. They place quite a strain on the unit. Change your filter every 4 to 6 weeks and get your duct work cleaned when necessary.

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I second the original question (still unanswered). Speaking as someone who logged in today to try to find an attorney, I see this category as one that's exactly what I have my Angie's List membership for:

1. It's important that I find a good one
2. I'm not an expert enough to know myself who is a good one
3. The industry is full of advertisements and misinformation
4. I wish I knew what experiences other people have had

I don't care about lawns--I planted mine in clover and don't have to mow it. When I do need to mow I use a rotary Fiskars mower, which is great--or a scythe. That's right--a scythe (the European type, which is smaller, and it's very good exercise). Gas-powered mowers, chemical fertilizers and weed killers--all nasty stuff that gets into everyone's air, soil, and water. I'm sure my neighbor doesn't like my wildflowers, semi-wild pockets of fruit bushes, and unmown areas and yes, dandelions (I have 10 acres) but that's too bad. It's better habitat for wildlife, especially the pollinators on which our food supply depends. I think this obsession with the Great American Lawn is a waste of time and resources. Plant some food instead.

I'm not sure Angie et. al. want you to have a complete answer to this question. By re-subscribing at the Indiana State Fair in 2012, I think I paid $20.00 per year for a multi- year subscription. Maybe even less. At the other extreme--and I hope my memory isn't faulty about this--I think the price, for my area, for ONE year was an outrageous $70.00. And they debited me automatically without warning. I had to opt out of that automatic charge. I like Angie's List, but if some of the companies they monitor behaved the way they do in this respect, they'd be on some sort of Pages of Unhappiness. I'll be interested to see if this comment gets published or censored out of existence.

That's very difficult to answer without seeing the house. As one poster said, the prep is the most important part. On newer homes that don't have a lot of peeling paint, the prep can be very minimal even as low as a couple or a few hundred dollars for the prep labor.

On a 100 year old home with 12 coats of peeling paint on it, then the prep costs can be very high and can easily exceed 50% of the job's labor cost.

A 2100 sq ft two story home could easily cost $1000 just for the labor to prep for the paint job. That number could climb too. Throw in lots of caullking  or window glazing, and you could be talking a couple or a few hundred dollars more for labor.

Painting that home with one coat of paint and a different color on the trim could run roughly $1000 or more just for labor. Add a second coat  and that could cost close to another $1000 for labor.

For paint, you may need 20 gallons of paint. You can pay from $30-$70 for a gallon of good quality exterior paint. The manufacturer of the paint should be specified in any painting contract. Otherwise, the contractor could bid at a Sherwin-Williams $60 per gallon paint and then paint the house with $35 Valspar and pocket the difference. $25 dollars per gallon times 20 gallons? That's a pretty penny too.

That was the long answer to your question. The short answer is $2000 to $4000 and up, depending upon the amount of prep, the number of coats, the amount of trim, and the paint used.