furnace filter - in/out - cold/hot

I've had this on again off again mental debate concerning our furnace filter. It's the usual 20x25, and I get the upgraded pleated version, vs the plain fiberglass version.
However, in my mind, the pleated version restricts the air flow more so than the fiberglass - nature of the beast.
SO - when it gets really hot in the summer, or below zero in the winter - I temporarily pull the air filter out for max air flow...
Now, not sure why exactly.... thinking of pushing more "treated air" into the ducts & house. BUT - does it make any sense ?
Since the air stream is going faster across the heat exchanger (winter), or the A/C A-coil (summer) maybe the air outflow is higher but the temperature is not at the max.... I'll have to take a test run with my IR kitchen therm and point at the duct vent.
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But, the pleats make the apparent cross-sectional area of the filter approx 2x the 20 x 25 so even if the resistance per square inch of the pleated filter is 2x the resistance of the fibreglass filter, the overall resistance is the same. But, the pleated filters do get clogged faster because they filter better, so you do have to change them out more often. But, they reverse flow rinse in a laundry tub pretty easily and can be reused after they dry out.
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wrote:

Exactly. There is a pressure drop spec for the various filters that show how much resistance they create. Any filter is a compromise between how fine a particle it can catch and the resistance to airflow it presents. The better filters have deep pleats to increase surface area while keeping resistance reasonable.
I would not be removing it to try to improve performance. With it in, you probably get a little less airflow, but it's at a higher temperature. With them out, you get a little more airflow, but the air is slightly lower temp. It's not going to make any material difference in energy usage that makes it worth doing. Plus they are there for a reason. Is saving $2 a year worth clogging up the coils, getting the blower covered with dirt?
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Your right. Don't want to get dust and grime in heat exchanger though. Sometimes increasing flow will cause dust in vents to get moving. I told my furnace installer I wanted bigger filter size, and the goof put in a 16X20 . I turned it into a 20X 25 myself. Same thinking. The electrostatic helps take out that very fine grime that's hard to clean.
Greg
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On Wed, 23 Jan 2013 22:28:39 -0600, "ps56k"

The makers of HVAC units spend millions of dollars over decades engineering filters systems for your units so you figure you can just take them out and improve performance?
Your perception is entirely wrong. Too much air flow can impede performance rather then enhance it. You can also clog up your coils making for costly repairs. Your conclusion is correct, the temperature will not be the same.
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Running without a filter will allow dust to clog the AC coil, resulting in even less air flow. So, by trying to be smarter than the designers, you're making things worse. As Ed comments, expensively so. I've also seen blower fans clogged badly. I've had to take furnaces apart, and clean the blower fans. No fun at all. I'd run with a filter all the time, for sure.
Christopher A. Young Learn more about Jesus www.lds.org .
The makers of HVAC units spend millions of dollars over decades engineering filters systems for your units so you figure you can just take them out and improve performance?
Your perception is entirely wrong. Too much air flow can impede performance rather then enhance it. You can also clog up your coils making for costly repairs. Your conclusion is correct, the temperature will not be the same.
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They engineer HVAC units to reduce their shipping weight and size you can carry them down the stairs into the basement.
If they really designed residential systems for efficiency, they'd have a much larger filter surface area than they presently do, and they'd have a duct system that allows you to bypass the AC coils during the heating and air-circulation seasons (ie - the time of year when you just have the fan running - no heat or AC).

That's a function of the fan speed and blower size. Generally the more air you can push per unit time, the more efficient you can make the system (increased ability to transfer heat from the exchanger or to the AC coil).
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They have those. They are called filter units, available in a wide variety of designs. They go in the return right before the furnace. It doesn't make sense to design a real filter into the furnace when customer A wants an electrostatic one and customer B wants a media type. Plus, it would make the furnace 5" larger. With a seperate unit, it can be located as the installer desires, not necessarily making the furnace itself taller or wider.
and they'd

What exactly is that going to save in the grand scheme of things? Instead of a simple flow through design, you'd have sharp bends, at least to fit it into a reasonable space. The AC coils obviously don't present such a flow restriction that they are a problem. And the blower runs at a much lower speed in heating mode than in AC mode, greatly reducing the pressure drop across the coils...

That I agree with.
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But too much is no good either. You need balance and there are curves on the optimum residence time needed for heat transfer to take place. Very slow air movement gains a bit temperature change, but at the expense of proper circulation.
In any case, dust bunnies, pet hair, pollen can build up on evaporator coils and make the unit pretty useless.
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Slow air movement results in LESS heat transfer because the air leaving is at a higher temperature and less heat is extracted from the combustion gases. The more airflow, the more heat that will be extracted, the more heat you will get out for the same energy put in. But it's a diminishing return, moving more air doesn't come for free, and there are other considerations.
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wrote:

yeah, like feeling drafty
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On Thu, 24 Jan 2013 10:31:00 -0800 (PST), " snipped-for-privacy@optonline.net"

Unless we put numbers on this, it is all meaningless. How slow is slow? How much heat potential can be absorbed, etc, etc. Absorbing the maximum heat is also useless unless you have the air flow to properly distribute it where needed.
The manufacturer spent tons of money engineering these things so their settings are a damned good starting point.
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Running without a filter will do a bunch of bad things, clogging your system with dust. I think that is a very poor idea, and should not be done.
Christopher A. Young Learn more about Jesus www.lds.org .
I've had this on again off again mental debate concerning our furnace filter. It's the usual 20x25, and I get the upgraded pleated version, vs the plain fiberglass version.
However, in my mind, the pleated version restricts the air flow more so than the fiberglass - nature of the beast.
SO - when it gets really hot in the summer, or below zero in the winter - I temporarily pull the air filter out for max air flow...
Now, not sure why exactly.... thinking of pushing more "treated air" into the ducts & house. BUT - does it make any sense ?
Since the air stream is going faster across the heat exchanger (winter), or the A/C A-coil (summer) maybe the air outflow is higher but the temperature is not at the max.... I'll have to take a test run with my IR kitchen therm and point at the duct vent.
--
/ _/ _/ _/ _/ _/ _/ _/ _/ _/ _/ _/ _/ _/ _/ _/ _/ _/ _/ _/
No Good Deed -
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hey Mormon - you may like to be on top, but everyone else on the Internet uses BOTTOM posted messages to follow the thread of discussion...
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ps56k wrote:

Hmm, Very funny! For one, blower speed is different between cooling and heating mode. System is designed to work with filter. Air flow should be certain amount with filter installed and your job is to replace it regularly depending on your situation. My filter is 16x25x5 and every 4 month I put in new one(MERV 12 ones(
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tnx for the comments..... interesting tidbits... I put the filter back into place....
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I recall putting a stainless thermometer into the forced exaust gas pipe to measure temperature. That will tell how much heat is extracted. I also put in a water level vacuum gauge after the filter.
Greg
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