Turns out my BIG furnace filters are unnecessary?

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Question for the group:
I moved into a house with a 1990s Lennox whisper heat furnace. The installed filter is the 4" thick kind, not the usual 1" kind. So I've been paying 30 bucks every six months for new filters.
However, I dug up the technical furnace manual on the net. Turns out, it is specced for the 1" washable filters.
Would I be safe rigging up the furnace to run 1" filters?
I was contemplating welding in a little bracket to do so. The smaller filters, even the nice ones, are so much cheaper even with the more frequent changes.
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On 8/21/2010 1:49 PM, Bryan Scholtes wrote:

Why are you changing it every 6 months, is it clogged up?
TDD
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wrote:

I am following the recco on the filter.
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Let me get this straight, you want to redesign the filter system to go to a 1 inch pleated filter that has a higher static pressure (resistance to air flow) to save $10.00 a year?? It will cost you at least twice that much in higher utility bills to make that change. BTW... just because it says that the 1 inch filter is good "up to" 3 months, doesn't mean it so..... like the insurance commercials where they say you could save "up to" $500 on your car insurance. Don't believe it. The 1 inch filters need to be replaced *EVERY MONTH* (about 10 hours of actual run time)
You must either be a landlord, or an EE... neither of which has a clue about how HVAC systems are designed to work, or why they work that way.
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Wow, what a HELPFUL post. This tells me EVERYTHING I need to know and isn't flamebait at all. You really have me pegged. How are you so prescient?
I can't WAIT for your next post.
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Wow, what a HELPFUL post. This tells me EVERYTHING I need to know and isn't flamebait at all. You really have me pegged. How are you so prescient?
I can't WAIT for your next post.
-------------------------------
yup, another EE trying to re-invent the wheel.
The 4 inch pleated filter was installed because of lower airflow restriction(static pressure), it exceeds factory spec, and you only have to replace it twice a year. If it isn't broke, don't *fix* it. As far as the dirt and dust in the 55 year old ducts, get them cleaned or replaced. They don't last forever.
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Steve wrote: snip

In which discipline is YOUR advanced degree?
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Journeyman machinist, retired Coast Guard engineer, major in mechanical engineering, minor in environmental science, and master HVAC tech.
next ??
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wrote:

    Got milk ?
--
Click here every day to feed an animal that needs you today !!!
www.theanimalrescuesite.com/
  Click to see the full signature.
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you spelt it wrong..... its milf :-)
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On 8/21/2010 2:40 PM, Bryan Scholtes wrote:

Some people change the oil in their vehicle unnecessarily. Fleet operators actually test their oil to see if it really needs changing. Get yourself a Filter Minder, there are several different devices on the market to let you know when it's time to change your filter. Here are a few links to examples:
http://www.filterminder.com/hvac.asp
http://www.nordicpure.com/pages/store_item_detail.asp?item_id 3
TDD
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wrote:

That is a nifty idea. Cheap too. In my situation it would definitely pay for itself within a year.
Do you have any thoughts on why my system was installed with the big 4" pleated filter? is that a factor of overall CFM, pressure, fan size, etc? I am also concerned that a pleated filter had been installed when the tech manual didn't call for it.
If it helps, I had to open a return air duct this week, and it was filthy inside. Granted it probably hadn't been opened since it was built in 1955, but there was a think cohesive layer of dust on the bottom of the horizontal cold air return duct.
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That is probably the whole reason for the 4" media filter right there. The system had too high of a TESP and they used a better filter to help compensate for it rather than fix the ductwork issues that caused it in the first place. TESP is total external static pressure, AKA how restrictive the return and supply duct systems are to airflow. The TESP has to be within a certain range specified by the equipment manufacturer. Too low and the blower motor overloads and burns out as the torque required to turn a centrifugal blower varies directly with the airflow through it. It can also cause the primary heat exchanger to run too cool and cause condensation in it thus rusting it out. In cooling mode too much airflow can make the condensate fly off the evaporator instead of draining to the pan thus wetting the inside of the supply duct where it re-evaporates and raises the humidity in the house and also drains out and causes water damage. Too high pressure and the airflow drops causing the blower motor to overheat from lack of airflow, and causing the heat exchanger to overheat and crack. In cooling mode the coil runs too cold and can freeze and the reduced temperature lowers the suction pressure and causes the compressor to pump less thus reducing the cooling capacity of the system.
As you can see if the 4" filter was the easiest way to make the system work within the specified limits I would keep using it. It is either that or have extra returns and supplies added as necessary and have the existing ductwork cleaned to lower the TESP enough that the 1" filter will work.
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Common sense...doesn't exist. It is what you believe others should know, based on your years of experience. Its a myth. Nobody learns anything without asking questions and doing stuff, and that includes everybody here.
What is an EE?
I cant help but feel sorry for people who are territorial about their profession. There is nothing an HVAC tech can do that I couldn't do without the proper knowledge and equipment. You've admitted it yourself: it's a series of calculations and some book knowledge. It's basic mechanical engineering with maybe a touch of fluid dynamics. And there are those who insult people who haven't learned it yet and are stupid enough to wonder about it.
The only difference between home electrical and home HVAC, is that there aren't a bunch of DIY books on the subject. And someday that will change. Just like with all the other trades, people will hire a pro only when the job is too much to bite off. And they'll have the knowledge to properly tackle the jobs safely. No longer will we have to suffer $75 service calls just to get browbeaten.
For those who helped me, thanks! You've confirmed that my project is best left untackled. And I will get a pro to help balance the system before I finish the basement.
For those with disdain for the DIY'er... You might be better served by specializing in fixing amateur jobs. Because all your secret knowledge is being gradually pried open. There will be a day when people won't have to take abuse from guys because they happen to bend sheet metal and run calculations for a living.
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Common sense tells you that if you hit your hand with a hammer, its going to hurt, or if you stick a fork in an electrical outlet, its going to knock the crap out of them. We have a lot of Darwin Award nominees that come in here that haven't figured that out yet.

Electrical Engineer

The ones who get insulted are the ones who won't listen to good advice and council, and get nasty because they get told what they don't want to hear. We get a lot of that in here because the folks asking the questions are trying to do things that are inherently dangerous, without the proper tools, and will put themselves, their familys, as well as their home at risk.

They can't print the books fast enough to keep up with new technologies. $75 only gets a tech there, and basic diagnosis. Repairs are extra. Unfortunately, you can bring your broken air conditioner to our shop, so we have to bring our shop to you in the form of a service truck.

indeed. To a point that there are only a handfull of techs are trained on them. 2 of the systems I worked on today have serial controlled, variable frequency, inverter drive heat pumps and modulating gas furnaces..... and these are residential systems. You can now add "electronics tech", and "computer tech" to the long list of vocations that are encompassed by the HVAC trade.
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wrote:

unit and up to 4 indoor units with occupancy sensors?
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You would be better served by a conventional ducted system, and the installed cost would be about the same.
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How so?
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Do a little homework on warranties, pricing, and problems. My wholesale cost for a 3 ton, 4 cassette Mitsubishi mini-split heat pump is considerably higher than a 15 SEER conventional system including ductwork. Just because it looks good on paper, doesn't mean that its going to be better, or last longer, or cost less less to install. Then there is a small problem of technologies... the higher tech the system is, the fewer choices your going to have for finding a tech that is actually qualified on it, and knows what he is doing with it. OTOH, if you got more dollars than sense...
I'm not saying don't go with the mini-split, I'm just saying that you better have a tech that has had the training, and understands the digitaly controlled, variable frequency inverter drives that are used on them.
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But you didn't take issue with is statement that the installed cost would be about the same.

I'm only trying to clarify the issues. I have a choice between adding a (single) mini-split unit and extending one of my air handlers. The air handler is actually in the area I want to add (an attic), but the mini-splits look quite attractive, for many reasons.
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