{"id":152,"date":"2011-08-17T21:22:11","date_gmt":"2011-08-17T21:22:11","guid":{"rendered":"http:\/\/bathursthandyman.ca\/?p=152"},"modified":"2011-08-17T21:22:11","modified_gmt":"2011-08-17T21:22:11","slug":"which-furnace-filter-is-right-for-you-are-washable-filters-the-most-environmentally-consious-choice","status":"publish","type":"post","link":"https:\/\/buildingology.com\/?p=152","title":{"rendered":"Which Furnace Filter is right for you? Are washable filters the most environmentally consious choice?"},"content":{"rendered":"

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You may ask yourself, do I have the technical know how to determine what is best for my HVAC system?\u00a0 The answer is a definite yes, it is not difficult, but will take a little bit of reading to understand how the system works.<\/p>\n

Why you should care<\/h1>\n

Forced air HVAC systems require a cartridge \u201cmedia\u201d style furnace filter for my furnace.\u00a0 We know what they look like.\u00a0 The packaging usually says \u201c16x25x1 or 20x25x1.\u201d\u00a0 When you go to the big box store, there are so many furnace filter types and it is easy to get little overwhelmed from what seems should be a really simple choice. \u00a0To complicate matters, HVAC experts can\u2019t agree on what is the best method of filtration as there is a wide difference of opinion.\u00a0 I think this is attributed to the fact that a \u201cone size fits all\u201d solution does not really exist.\u00a0 Who cares honestly? Well you should, the type of filter can affect the life of your furnace, your health, and the energy efficiency of your system as a whole.\u00a0 It is possible that your 95% efficient furnace with a variable speed ECM motor can consume the same amount of natural gas as a 92% furnace because of poor airflow or using the wrong filter.\u00a0 It\u2019s a bold statement. \u00a0\u00a0More often than not, the most expensive disposable filters are not necessarily the best choice for the average homeowner\u2019s furnace. \u00a0\u00a0The analogy I would use is filling your car with 92 octane gasoline, when the car manufacture specifies 87 in the owners manual.\u00a0 Despite that many people feel 92 octane is cleaner and therefore better for their car is a misconception which is still debated to this day the same as furnace filter quality.<\/p>\n

Who is going to cough first from poor air quality, you or your HVAC system components?<\/h1>\n

Indoor air quality needs for a person is not necessarily the same as the HVAC system component needs.\u00a0 Those two different needs are far too often blurred as the same requirement.\u00a0 Furnace components are expensive to replace.\u00a0\u00a0 They can and sometimes do fail prematurely by getting dust trapped in the blower, heat exchanger or air-conditioning coils.\u00a0 This is especially the case with ECM variable speed motors in 95% efficient furnaces, as they are prone to failure if it is running at full speed for weeks at a time.\u00a0 This is far longer than a variable speed is designed to run. You can be surely kicking yourself for not spending only a little bit of time once in your life to learn about filters and $5 t every three months on the proper filter for your system, so listen good.<\/p>\n

At first, I found it hard to find good information because there are a lot of useless marketing out there about your HVAC systems requirements.\u00a0 It is easy to get confused from what should be a simple choice to buy their product.\u00a0 As mentioned before, the requirement for a furnace\/air-conditioning\u00a0 filter to function properly is not necessarily the same as the requirements that a human has to feel comfortable.\u00a0 What I mean by this, is your filter can be doing it\u2019s job properly, but you may be sneezing from pet dander.\u00a0 Obviously in that scenario, you don\u2019t have a good enough filter.\u00a0 Or in a different scenario, possibly your furnace model can be sensitive to particulate matter and running too often with high static pressure, and you are a rough and tough human being affected by the extra particulate matter in the air, and you don\u2019t feel the difference.\u00a0 Just know that your requirements are not necessary the same as the furnace\u2019s.<\/p>\n

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Particulate matter types<\/h1>\n

Here is a small example of different particle sizes of common household particles if you are susceptible to certain airborne irritants.<\/p>\n

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A word on manufacturer\u2019s rating systems<\/h1>\n

There are different methods of comparing the ability of how effective filters to do their job on the packaging literature, but I will just focus on the two most common ones you may run into.<\/p>\n

MERV<\/h2>\n

which was developed by ASHRAE<\/a>\u00a0 (ASHRAE 52.1, 52.2).\u00a0 Most filters use this method to describe their products filter efficiency effectiveness.\u00a0 Basically the higher the number, the higher the effectiveness for the cartridge (filter) to filter out smaller particles.\u00a0 This numerical system is the method required for filters in LEED buildings to measure particulate matter during construction and renovations when particulate matter is higher than when the building is occupied.<\/p>\n

Particle sizes measured are 0.3-10 microns, and broken down into subcategories for effectiveness at different particle sizes. of 0.3 to 1 micron, 1 to 3 microns, and 3 to 10 microns.<\/p>\n

3M Filtrete\u2019s system (MPR)<\/h2>\n

\u00a0The only reason why 3M Filtrete system is mentioned at all is because \u201cfiltrete\u201d, easily the most readily available premium and arguably the most recognizable filter brand.\u00a0 Filtrete uses a \u201cmicroparticle performance rating\u201d system (MPR).\u00a0 This system only applies to 3M\u2019s filters.\u00a0 The packaging states that 0.3 \u2013 1 micron diameter particles is what it uses for its rating.\u00a0 Filters range from a rating of 300-2200.\u00a0 This MPR is mixed with a lot of marketing lingo in the explanation and not very descriptive on how it arrived at its numbers and what they really mean.\u00a0 The numbers appear to be arbitrary and I don\u2019t think they really have much relevance to your purchase without a comparison to other well known rating systems.\u00a0 Good luck trying to find a MERV rating for Filtrete, you wont find it anywhere on 3M\u2019s product literature, but from what I know, the most common one they sell (1000 MRP).\u00a0 Information I have gathered estimates these filters at around MERV 11 \u2013 12.<\/p>\n

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Furnace filters: filtering vs. airflow<\/h1>\n

When my new furnace was installed, I was pretty much convinced that washable filters were the way to go in comparison with filters that you throw away.\u00a0 It should be a no brainer, you don’t throw away washable products contributing to the landfill, and it should save you money by not having to pay for disposable filters.\u00a0 After some closer inspection and some research, washable filters work great in theory, but might not actually be the best choice for a furnace filter for every HVAC system for a number of different reasons.\u00a0 If your airflow is not very restrictive, you wont filter much (really cheap fibreglass $1 filters), but if you filter to much, then you will have no airflow, and poor system performance.\u00a0 The key to understanding this principle is knowing that there must be a balance between filtering and airflow.\u00a0 Before a choice is made, it is important to understand how filters impact your system and where the balance lies.<\/p>\n

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The more airflow you have, the better your system will run<\/h2>\n

Lets pretend for a moment, that you want to filter out as many particles as possible, so you decide to use a filter with dense material usually having a higher MERV rating.\u00a0 This obviously a great way to filter as many particles as possible, but it comes at a high price.\u00a0 Literally.\u00a0 You see, the filter itself is an obstruction in your HVAC system.\u00a0 It is literally placed in the centre of the duct, a duct that has flowing air.\u00a0 In the above example the air could be passing through the duct at 2 meters per second (before it hits the filter).\u00a0 After the air passes through the filter, the airspeed is slightly decreased.\u00a0 It could now be 1.9 meters per second or even more.\u00a0 The light blue arrows shows the reduction in volume of air that passes through the duct every second.\u00a0 After the air passes through the filter, the blower fan in the furnace engages and moves more air (dark blue) to compensate for any loss in volume passing through the system when heat is required.\u00a0 The lower the airflow, the longer that motor has to work.<\/p>\n

Other factors that play a role in how hard the blower works include the condition of your ducts including undersized ducts, poor fittings length of ducting.\u00a0 It is very common to have a return duct that was knocked loose during a renovation, that is now inside your wall.\u00a0\u00a0 Air-conditioning requires larger diameter ducting than your heating system requires.\u00a0 Therefore your duct size should be dictated by air-conditioning needs.\u00a0 This means that many people may have ducts that are too small if their house was constructed before air-conditioning became widespread in the 1950s and 1960s. Very often, in older homes, return ducts were not installed at all. \u00a0All of these factors play a role in the air pressure difference between the supply and the return air ducts.<\/p>\n

If this is at all confusing, that’s fine, you can hire an HVAC technician to figure out if you have an issue with your ducts.\u00a0 Ask them to perform a test called a “static pressure drop” to determine the amount of resistance in your system between the supply and return. \u00a0\u00a0 By knowing the resistance you currently have in the system, how know how much resistance you can afford (using\u00a0 a more restrictive filter).\u00a0 This static pressure value attained from this test is used in a chart that is usually located in the instruction manual of your particular furnace, and that chart dictates what your pressure losses are.\u00a0 This is not a DIY test or even for a handyman.\u00a0 Special equipment is required to perform it unless you happen to be an expert in fluid dynamics.\u00a0 If your HVAC technician does not know how to perform this test, find a new HVAC company.\u00a0 This stuff is literally HVAC 101, and you would be surprised at some of the hacks out there.\u00a0\u00a0 Side note, never have your furnace installed from a company that does not service equipment as well.\u00a0 You will save yourself a load of trouble in the future. Trust me.<\/p>\n

Your restrictive filters can cause higher utility bills and increase your carbon consumption, and ruin your furnace components.<\/h2>\n

If your filter is more restrictive, it can have a huge impact on your energy consumption, and will hurt your over HVAC system efficiency.\u00a0 Your system will react to your restrictive filter. \u00a0 In heating mode, your system will turn on more often, burning more fuel than if it was less restricted and your 95% variable speed ECM motor is now running at full speed.\u00a0 Not only are you burning up more energy now, but if your components are running at full speed all of the time, when they were designed to run at full speed some of the time.\u00a0 This increased duty-cycle, reduces the life of your your motor.\u00a0 It is not uncommon for these components to fail in less than 10 years in these type of conditions.\u00a0 Some motors are designed to run longer, but most dont.\u00a0 It is also common practice for alot of companies to replace the whole motor rather than just one component.\u00a0 Expect to pay $1500 to $2000 for that repair.<\/p>\n

Why is that room so hot in the summer? (or cold in the winter)<\/h2>\n

\u00a0If some of your rooms in your house always too hot, (or too cold in the winter), using a restrictive filter will impede the volume of\u00a0 air to reaching those spaces at all in the amount you need.\u00a0 This is especially the case in the summer due to the higher requirements for airflow.\u00a0 Try swapping your filter to one with good airflow to see if it makes a difference in comfort level.\u00a0 You will have to wait a day or two before you will notice a difference.\u00a0 This alone can make a difference in temperature and airflow for some spaces.<\/p>\n

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Furnace filters compared<\/h1>\n

Okay, lets look at some examples of what is available in the market today with their advantages and disadvantages.<\/p>\n

\u00a0Fibreglass filters.\u00a0 MERV 1 to 4.\u00a0\u00a0 $1.25 to $3.00<\/h2>\n

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This category is the least expensive filters you can buy.\u00a0\u00a0\u00a0 The filter on the right was purchased at Canadian Tire.\u00a0 All big box stores sell similar filters to the one on the right.\u00a0 I have seen some brands that use blue fibreglass instead of white.\u00a0 \"\"<\/a>I found that all of these filters are not very dense at all.\u00a0 You can see the couch right through them in the picture above, and they would be on the lower end of the MERV scale.\u00a0 Besides having a lower density, the filter on the right of the picture is missing one key component that should be a deal breaker for any purchase.\u00a0 It is missing the metal cage support on the back side of the filter (see picture on right).\u00a0 All other types of filters have support in one way or another.\u00a0 Basically the purpose of it, is to prevent the filter from being sucked into the fan if it is blowing at high speed.\u00a0 The filter on the left is a “Dafco Aerostar”\u00a0 was purchased at a local HVAC supply store for $2.25 a piece.\u00a0 I could not find the higher density fibreglass with support at any of five of Ontario’s major hardware\/building supply box stores.\u00a0 Lets take a look at how this filter performs when installed.<\/p>\n

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The airflow through these filters is excellent due to having holes that are wide in diamter in comparison to other filters.\u00a0 As you can see from the picture, the low density does not impede airflow that much and does not encourage a static pressure drop.\u00a0 Fibreglass is able to trap only larger particles as it (green circles), but those particles are not only trapped on the front surface layer, but throughout the full 1″ thickness of the filter.\u00a0 Being trapped in different layers encourages good airflow.\u00a0 Some filters are better at filtration than fibreglass, but they are very thin, and get clogged up more easily because it does not use the full 1″ thickness.\u00a0 This good airflow reduces noise during operation.<\/p>\n

Verdict:\u00a0<\/strong><\/em> Controversial even between HVAC professionals as they cannot agree if it is the best all around, instead I will focus on its advantages and disadvantages. A good quality fibreglass is the excellent for airflow, and average for your furnace’s long term health, causing little strain to the components, while covering them with slightly more dust.\u00a0 Poor for filtering.\u00a0 Good noise control.\u00a0 Very poor indoor air quality, and poor in the environmentally conscious department due to it being disposable, but not a too intensive manufacturing process.<\/p>\n

Washable Filters \/ Reusable Filters.\u00a0 MERV ~4.\u00a0 $25-$65<\/h2>\n

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Though reusable filters seem at first glance to be the most environmentally friendly filters, they have their caveats and may not be most environmentally conscious product available today for filtering. The picture on the left is a polyester washable filter that is dirty. The picture on the right is the same filter just cleaned.\u00a0 There are still some dirty areas because you can’t be “too rough” when cleaning or the membrane will break.\u00a0 Some areas of the washable filter inevitably become difficult to clean, and this comes with the territory with owning this type of polyester filter, that it’s filtering effectiveness is reduced over time.<\/p>\n

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One of the biggest problems with it’s filtering ability, is that the thickness of the filter is not really 1″ thick.\u00a0 There is a thin membrane in the centre.\u00a0 This membrane is in a narrow plane.\u00a0 The issue with this type of filter, is that one plane is the only line of defense for filtering, while other products utilize the whole 1″ thickness to capture particles while maintaining airflow.\u00a0 Once the particle makes it past the plane, comes through the other side without a second layer of filtering resulting in poor filtering performance.\u00a0 No other filter has such a thin membrane.\u00a0\u00a0 It makes sense if you think about it. When you clean a surface, the dirt has to be able to be washed away, and that cant be done if there were multiple layers.\u00a0 It’s like trying to clean the dirt out of a couch or mattress.\u00a0 You can really only clean the surface layer.\u00a0 If you had multiple filter layers, the dirt would get lodged inside, and would not be able to come out.\u00a0 My example at the top, even with only one layer still had some dirt leftover that I could not remove (without breaking it).\u00a0 If it were possible to clean multiple layers, the manufacture would have put in several layers.\u00a0 In the future maybe some manufacturers will invent a method to disassemble a filter with multiple layers in the future so each layer could be individually be cleaned resulting in better MERV ratings and less turbulence, by making the holes slightly bigger.\u00a0 Hey that’s a good idea.\u00a0 Patent pending!. \u00a0 I find it highly doubtful for any washable filter to have a rating above MERV 4.\u00a0\u00a0 Due to your filters clogging up on only one layer, your standard 3 month replacement schedule may be much shorter.<\/p>\n

The other major issue with this filter is with airflow is poor.\u00a0 If you have a filter that uses the whole 1″ thickness, and there is an obstruction caused by dirt, the air has a chance to move around that dirt (like an air passing over and under and airplane wing).\u00a0 But when you only have one surface area with no depth, and it is blocked, the air is forced to move through that restricted dirty area.\u00a0 Your static pressure difference just hit a wall, and now you are making your furnace fan work much harder than it should, burning up more fuel and using more electricity to heat or cool your home at the designed temperature.\u00a0 Another side effect is the air passing through the filter will be very loud as the air tries harder and harder to move through obstructed air.\u00a0 If you have a bedroom or an office next to your furnace room, you will notice the loud\u00a0 “whistling” sound, I guarantee it. \u00a0 In addition a lot of the coatings degrade over time, meaning your filter is not “lifetime”, and this is especially the case if your filter is made of foam rather than polyester.\u00a0 If you have a UV light in your HVAC system, it will degrade your washable filter much faster.\u00a0 Do you still think this is the most environmentally conscious choice?.\u00a0 It is a hard question to answer definitvely without doing energy modelling and a life cycle analysis, but my gut feeling tells me it is one of the worst performers of the lot.<\/p>\n

Verdict:\u00a0 <\/strong><\/em>There is <\/em>a consensus between HVAC technicians on this filter.\u00a0 They find them poor performers all around.\u00a0 \u00a0 Very poor for airflow, poor for your furnace’s long term health.\u00a0 Poor at filtering,\u00a0 Very poor in the indoor air quality. Poor noise control (it can get loud while running the A\/C on full) \u00a0 Average in in environmentally conscious category due being washable, but increased environmental impacts on reducing system components.<\/p>\n

<\/strong><\/em>Medium quality cotton, paper or polyester.\u00a0 Merv 6-8.\u00a0 $5 to $8<\/h2>\n

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The filter on the left is a “Garrison” MERV 8 filter from Canadian Tire, and the filter on the right is an “AAF Dust Shield”\u00a0 MERV 6 filter from Lowes.\u00a0 These filters are priced as the middle of the road solution.\u00a0 Both filters are pleated giving a larger surface area than a flat filter like the fibreglass and the washable.\u00a0 The larger surface area can trap more particles and contribute to the filters being louder during use.\u00a0 Lets take a closer look at the performance.<\/p>\n

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The pleated filters don’t have a wide plane as the fibreglass (they don’t use the whole 1″ thickness), but are thicker than washable filters.\u00a0 They do a much better job at filtering than a MERV 4 filter, and can block some mould spores.\u00a0 There is an improvement in indoor air quality, but MERV 6 – 8 filter still let through allergens along with most other smaller particles.\u00a0 It is not an ideal solution if indoor air quality is at the top of your list.\u00a0 This filter is a little restrictive with airflow, but not too bad.<\/p>\n

Verdict:\u00a0<\/strong><\/em>\u00a0 Airflow is average.\u00a0 Filtering quality is average.\u00a0 Indoor air quality is average. Poor noise control due to it’s pleated shape (this is almost unavoidable). \u00a0 Average in in environmentally conscious category due to having one of the best effects for system components on the long term, but of course it is disposable.<\/p>\n

Filtrete or other MERV 11 to MERV 12. $15 to $30<\/h2>\n

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Filtrete’s media is very “fluffy” like stuffing in a stuffed animal.\u00a0 In addition to being pleated, it is easy to see how particles can get caught is material that is more “fluffy”, and this filter’s effective thickness is better than the mid range filters, though not the full 1″.\u00a0\u00a0 Due to these filters very often being electrostatic, the MERV rating is exadurated to a higher number.\u00a0 This is falsehood (which I will explain later), and you should watch out for it.\u00a0 Lets look at a close up of the filter in place.<\/p>\n

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There is no question that a large amount of particles are blocked by the filtrate filter having smaller holes.\u00a0 There are many small holes that are tightly woven together similar to a high thread count with fabrics, the amount of drag (turbulence), or static pressure drop is even worse than the washable filter.\u00a0\u00a0 In fact, the affect on airflow is so drastic that\u00a0 HVAC technicians who care know not to recommend these filters inside their customer’s furnaces unless<\/em> they intentionally oversized the motor.\u00a0 This is common practice only for those who need this extra filtration whose are very sensitive to Indoor Air Quality.\u00a0 If you really want this type of filter, you can sit down with your HVAC technician, he can find out if your furnace was oversized (which happens relatively often).\u00a0 If it is oversized, then you may be in luck.\u00a0 Like the washable filter, this filter will reduce the life of your system components by making the fan work harder to move conditioned air into the spaces you need, and subsequently, it can hinder your furnace or A\/C’s ability to heat or cool a room.\u00a0 If you are set on using a filter like this one, spend the money for an HVAC technician service call and ask him to perform the “static pressure drop” test to know if it is possible to use one in your current configuration.\u00a0 This filter will be really loud when installed.<\/p>\n

Verdict:\u00a0<\/strong><\/em>\u00a0 Airflow is very poor.\u00a0 Filtering quality is excellent.\u00a0 Excellent. Very poor noise control. \u00a0 Very Poor in in environmentally conscious category due to more material waste and detrimental effects to system components over the long term.<\/p>\n

Alternatives:\u00a0 4″ thick MERV 8 to 12 filters $25 to $40<\/h2>\n

Most furnaces have a standard 1″ thick slot to fit a filter.\u00a0 It is possible to get better performance from the previous categories by using a 4″ filter, but an HVAC technician has to be able to expand your slot (playing around with sheet metal), which is no easy task, and has to provide a motor that will be able to pull air through a very thick filter.\u00a0 Don’t be surprised if you have to replace your motor with one that can pull air through this.\u00a0 The filtering performance is very similar to a Filtrete 1″ filter.<\/p>\n

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The one major advantage this setup has over the 1″ high MERV, is that airflow is better.\u00a0 In the above diagram, wherever there is dirt blocking the path of air, the sheer volume of the filter allows the air to take a different path, and its flow is less hindered.<\/p>\n

Alternatives:\u00a0 Permanent filter.<\/h2>\n

I’m not going to say it’s overkill, but I will not go into too much detail about this filter type as other system components need to be modified.\u00a0 This is a very expensive solution. \u00a0 Ask your HVAC tech if it’s for your needs.<\/p>\n

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Filter Comparison Chart<\/h1>\n
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Legend: Excellent, Good, Average, Poor, Very Poor.\u00a0 Metrics are based on an unmodified, unchecked system and are the opinion of the author.<\/figcaption><\/figure>\n

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There is a best time of year to change your filters<\/h1>\n

Since air conditioners need more airflow than furnaces, you may want to consider possibly using a different filter during the summer months with higher airflow, than in the winter.\u00a0 This is especially important if your climate gets hot enough that your air conditioner runs continuously for days at a time.\u00a0 In Toronto, Ontario this happens frequently in the summer.\u00a0 Since airflow is more crucial in the summer, it is important to know which months your air-conditioner runs at full speed.\u00a0 There is an easy way to figure this out.\u00a0 By using this tool<\/a>, you can find our your local climate’s “Cooling Degree Days<\/a>” or CDD.\u00a0 This is basically the measure of cooling your climate requires for proper indoor comfort levels. \u00a0\u00a0 All you have to do is input your location (for an example lets use Toronto, On), and look at the “Base Year” column under “CDD” (2006 as an example).\u00a0 You will notice that the reading is zero in months where the air conditioner is not used such as Jan, Feb, Nov, Dec.\u00a0 You can change from Fahrenheit to Celsius if you wish.\u00a0 I will. \u00a0\u00a0 In the example, Toronto requires 120 degree days for June,\u00a0 240\u00a0 for July and 195 for August.\u00a0 There is cooling in other months but it is not a significant amount 50 or less. \u00a0 I am approximating the number, but if you have to cool your house more than 4 degrees Celsius per day, you should have high airflow.\u00a0 4 degrees x 30 days= 120 CDD.\u00a0 I think that is a good number for\u00a0 your cut off\u00a0 point.\u00a0 For Toronto, I only need three months of high airflow which coincides with the lifetime of one disposable furnace filter.\u00a0 So that means on June 1 and Sept 1, the filters should be replaced.\u00a0 If you climate is different and cool for more or less than three months, you may want to adjust your times slightly.<\/p>\n

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\u00a0Conclusion and final thoughts<\/h1>\n

It is quite amazing, that a simple decision about choosing a furnace filter can take seconds to make, but it is really a type of purchase that requires quite a bit of thought that cannot be conducted in aisle 4 of your local building centre.\u00a0 Before making an educated guess on which filter is best for you, weigh the importance of\u00a0 Long term furnace motor health, Airflow, Filtering, Indoor air quality, and Environmental impacts by using the provided chart. I guarantee you that your needs will not be the same as your neighbour, or the person in the closest city.<\/p>\n

Just a few bits of extra information:\u00a0 Dirty filters are more efficient at filtering than clean ones, as they can trap smaller particles, until airflow is reduced by too much, and that is why you have to replace them every three months.\u00a0 It is not uncommon for filters to be very dirty in a much shorter time, it just depends on your environment.\u00a0 Electrostatic filters can arguably increase effectiveness of the filter, but not the MERV rating.\u00a0 It does not make sense that the MERV value should increased with electrostatics because the MERV scale has only to do with density which is about the ability to prevent particles of certain sizes from passing through a barrier and nothing<\/span> about the ability trap more particles through electrostatics.\u00a0 Personally, I think anything higher than a MERV 12 for homes is overkill if indoor air quality is important for you unless your doctor says so.\u00a0 Do you need a duct cleaning service, ever? NO!.\u00a0 It surprisingly does not have a large an impact on the system as you may think. The particles that are trapped in the ducts are trapped<\/em>.\u00a0 Remember that new particles from the outside comes through all the time. A total waste of money.<\/p>\n

What filter is in my HVAC system?<\/h1>\n

There is one bedroom in my house that is always a little too hot during the summer, and\u00a0 I don’t want that room to be even hotter than it is currently.\u00a0 I suspect that a duct was disconnected inside the floor in an inaccessible spot before I lived in the house (i can feel a cold spot).\u00a0 The goal here is trying to maximize airflow, so I am using the supported\u00a0 MERV ~4 fibreglass filter I got from the local HVAC supply store. \u00a0 This of course is slightly lower than ASHRAE’s minimum recommended filter<\/a> MERV 6 for the summer season. During the other three seasons of the year when airflow is not as critical, I use a MERV 8 filter because I think that is the most environmentally friendly and economical choice in the long run.<\/p>\n

\"Buildingology<\/a><\/p>\n