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Default is it always better to use a thicker filter in furnace?


"bq340" wrote in message
...
Smitty Two wrote:

The part I'm having trouble with is the completely unjustified and
unsubstantiated claim that doubling surface area doubles (or improves by any
factor) air flow, given the same cross-sectional area of duct.


Sounds like you are envisioning a fiberglass filter, not the fan-fold paper
ones.

If you have a fan-fold one that has 1" thick folds then we will arbitrarily
say it has 2000 tiny holes in it (although it really has more, obviously).
Now if we make the pleats 2" thick we now have twice as many holes in it,
allowing twice as much air to pass thru it.

The outside dimensions stay the same, but the thickness of the filter paper
pleats (surface area) is doubled.


That's was going to be my analogy also.


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"DerbyDad03" wrote in message
...
On Oct 23, 3:52 pm, dpb wrote:
Erma1ina wrote:
Bob F wrote:
"dpb" wrote in ...
james wrote:
My furnace was installed with a 16x20x1 pleated filter.


It looks like there is enough space to fit a 16x20x2 filter. This should
last
longer and reduce air resistance.


Is there any reason not to?
How can doubling the thickness _reduce_ resistance?
It doubles the surface area.


Keeping the CROSS SECTIONAL area (duct size) constant while increasing
the area (what you've called "SURFACE AREA")of filter material in
contact with the fluid (i.e., AIR) moving through the duct increases the
air resistance (in this case, the VISCOUS drag). QED


There ya' go...right. I was concentrating on the areas knowing at best
it could stay same.

--- Hide quoted text -

- Show quoted text -


I was the one that brought up the issue of loading.

Would you agree or disagree that spreading the same amount of dust
over twice the surface area would "improve" the air flow over time -
by that I mean it would flatten the "degradation of air flow" curve
over the life of the filter. Not an actual increase in air flow, but a
stronger flow for a longer time due to less restriction.

That's a legitimate question on my part - I'm not trying to convince
you of anything, 'cuz i I don't know the answer. It just seems (to me)
that the system ought to act that way.

************************************************** *******8

It would do that, and lessen the drop across the brand new filter also.

If you look at the "holes per area" analogy, there are twice as many holes for
air to flow through, and twice as many holes to collect the same amount of dust,
so they plug more slowly.


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"Bob F" wrote in message
news

"DerbyDad03" wrote in message
...
On Oct 23, 3:52 pm, dpb wrote:
Erma1ina wrote:
Bob F wrote:
"dpb" wrote in ...
james wrote:
My furnace was installed with a 16x20x1 pleated filter.


It looks like there is enough space to fit a 16x20x2 filter. This should
last
longer and reduce air resistance.


Is there any reason not to?
How can doubling the thickness _reduce_ resistance?
It doubles the surface area.


Keeping the CROSS SECTIONAL area (duct size) constant while increasing
the area (what you've called "SURFACE AREA")of filter material in
contact with the fluid (i.e., AIR) moving through the duct increases the
air resistance (in this case, the VISCOUS drag). QED


There ya' go...right. I was concentrating on the areas knowing at best
it could stay same.

--- Hide quoted text -

- Show quoted text -


I was the one that brought up the issue of loading.

Would you agree or disagree that spreading the same amount of dust
over twice the surface area would "improve" the air flow over time -
by that I mean it would flatten the "degradation of air flow" curve
over the life of the filter. Not an actual increase in air flow, but a
stronger flow for a longer time due to less restriction.

That's a legitimate question on my part - I'm not trying to convince
you of anything, 'cuz i I don't know the answer. It just seems (to me)
that the system ought to act that way.

************************************************** *******8

It would do that, and lessen the drop across the brand new filter also.

If you look at the "holes per area" analogy, there are twice as many holes for
air to flow through, and twice as many holes to collect the same amount of
dust, so they plug more slowly.



Why else would they pleat filters?


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In article ,
bq340 wrote:

Smitty Two wrote:

The part I'm having trouble with is the completely unjustified and
unsubstantiated claim that doubling surface area doubles (or improves by
any factor) air flow, given the same cross-sectional area of duct.


Sounds like you are envisioning a fiberglass filter, not the fan-fold
paper ones.


Well, if you really believe that's what I'm envisioning, then you
haven't followed this thread very closely.


If you have a fan-fold one that has 1" thick folds then we will
arbitrarily say it has 2000 tiny holes in it (although it really has
more, obviously). Now if we make the pleats 2" thick we now have twice
as many holes in it, allowing twice as much air to pass thru it.


Snake oil. Those holes are placed at a steeper angle to the direction of
flow, reducing the effective size of each hole. And there's a lot more
"not hole" material in the path of the air, too, creating additional
friction.


The outside dimensions stay the same, but the thickness of the filter
paper pleats (surface area) is doubled.

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In article ,
"Bob F" wrote:



Why else would they pleat filters?


To make them intrinsically stronger, and functionally stronger by
placing filter material at an angle to the force of the moving air.


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Smitty Two wrote:
In article ,
(Dave Martindale) wrote:

Smitty Two writes:

/\/\/\/\ -- that's a 1" thick pleated filter
I can't do it with my keyboard, but extend those pleats to 2" and
decrease the angle so each 2" pleat is just as wide as a 1" pleat, and
you've got twice the surface area.
Yeah, that part I get. Reducing the resistance is the part I don't.

The filter resistance per CFM per unit area remains the same, but you
now have twice the area of filter for the air to pass through. So the
CFM per unit area is reduced to half, and that reduces the pressure
drop.

A single 2" thick pleated filter is almost equivalent to two 1" thick
pleated filters in parallel (side by side, so half the air goes through
each).

Dave


I think your statements here are awkwardly worded, and I believe you
could do a little better. But maybe I just need to read it a few more
times. Given your pedigree on AHR, I'm going to mull these ideas over a
bit more and see whether I can follow your reasoning. So far, you're the
only one on the other side of the fence who's gone as far as to actually
present a credible argument.


a credible argument

Smitty Two,

I didn't see a response to my question on loading (pasted below).

What are your thoughts on that?

*** Begin Included Text ***

I was the one that brought up the issue of loading.

Would you agree or disagree that spreading the same amount of dust
over twice the surface area would "improve" the air flow over time -
by that I mean it would flatten the "degradation of air flow" curve
over the life of the filter. Not an actual increase in air flow, but a
stronger flow for a longer time due to less restriction.

That's a legitimate question on my part - I'm not trying to convince
you of anything, 'cuz i I don't know the answer. It just seems (to me)
that the system ought to act that way.

*** End Included Text ***
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Default is it always better to use a thicker filter in furnace?

DerbyDad03 wrote:
....
I didn't see a response to my question on loading (pasted below).

What are your thoughts on that?

....

I did make a response where I mentioned someone else had brought it
up...it's valid within the context of longevity.

On the other argument, despite the argument there's an additional flow
volume, there's also the same proportional flow restriction -- that is,
as well as doubling the hole area, the structural area is also doubled.

--
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On Oct 24, 4:27*am, Smitty Two wrote:
In article ,
*"Bob F" wrote:



Why else would they pleat filters?


To make them intrinsically stronger, and functionally stronger by
placing filter material at an angle to the force of the moving air.


They make them pleated so there is MORE surface area. That allows a
denser filter which traps smaller particles while still maintaining an
acceptable pressure drop. As another benefit, it allows the filter
to collect more dirt while still maintaining a reasonable pressure
drop.

I don;t see how anyone could not recognize that more filter area
translates into less resistance and less pressure drop. Imagine
breathing through a length of 2" plastic pipe with a sheet of dense
filter material fastened straight across in the middle. The filter
is dense enough to make it difficult to draw air. Now imaging a
filter of the same material, shaped like a cone and instead of being
just a 2" circle, it;s an extended cone, like an exagerated coffee
filter, stretching 3 inches within the pipe. Which would you rather
breathe through?
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On Fri, 24 Oct 2008 00:07:54 -0700, "Bob F"
wrote Re is it always better to use a thicker filter in furnace?:


"Caesar Romano" wrote in message


I don't think so, unless you rig the filters in parallel.


Parallel. Exactly. The thicker filter is like two thinner ones side-by-side.


No, a thicker filter is like to thinner ones in series, one behind the
other.


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On Oct 24, 4:22*am, Smitty Two wrote:
In article ,

*bq340 wrote:
Smitty Two wrote:


The part I'm having trouble with is the completely unjustified and
unsubstantiated claim that doubling surface area doubles (or improves by
any factor) air flow, given the same cross-sectional area of duct.


Sounds like you are envisioning a fiberglass filter, not the fan-fold
paper ones.


Well, if you really believe that's what I'm envisioning, then you
haven't followed this thread very closely.



If you have a fan-fold one that has 1" thick folds then we will
arbitrarily say it has 2000 tiny holes in it (although it really *has
more, obviously). Now if we make the pleats 2" thick we now have twice
as many holes in it, allowing twice as much air to pass thru it.


Snake oil. Those holes are placed at a steeper angle to the direction of
flow, reducing the effective size of each hole. And there's a lot more
"not hole" material in the path of the air, too, creating additional
friction.



Good grief. Let's say the holes are randomly oriented, which is
obviously a lot closer to how a real filter of the type under
discussion is going to behave. So now we have twice as many randomly
oriented holes in the 2" pleated filter as in the 1" pleated filter.
Which one is going to have less pressure drop across it and allow air
to flow through easier?







The outside dimensions stay the same, but the thickness of the filter
paper pleats (surface area) is doubled.- Hide quoted text -


- Show quoted text -


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Caesar Romano wrote:
On Fri, 24 Oct 2008 00:07:54 -0700, "Bob F"
wrote Re is it always better to use a thicker filter in furnace?:


"Caesar Romano" wrote in message


I don't think so, unless you rig the filters in parallel.


Parallel. Exactly. The thicker filter is like two thinner ones
side-by-side.


No, a thicker filter is like to thinner ones in series, one behind the
other.


Incorrect when the thickness is achieved by larger pleats. The actual
filter *material* is the same. Bigger pleats in a thicker filter
"container" means more area and less resistance.


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"Rick Brandt" wrote in message
...
Caesar Romano wrote:
On Fri, 24 Oct 2008 00:07:54 -0700, "Bob F"
wrote Re is it always better to use a thicker filter in furnace?:


"Caesar Romano" wrote in message


I don't think so, unless you rig the filters in parallel.

Parallel. Exactly. The thicker filter is like two thinner ones
side-by-side.


No, a thicker filter is like to thinner ones in series, one behind the
other.


Incorrect when the thickness is achieved by larger pleats. The actual filter
*material* is the same. Bigger pleats in a thicker filter "container" means
more area and less resistance.


That's it.


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wrote in message
...
On Oct 24, 4:22 am, Smitty Two wrote:
In article ,

bq340 wrote:
Smitty Two wrote:


The part I'm having trouble with is the completely unjustified and
unsubstantiated claim that doubling surface area doubles (or improves by
any factor) air flow, given the same cross-sectional area of duct.


Sounds like you are envisioning a fiberglass filter, not the fan-fold
paper ones.


Well, if you really believe that's what I'm envisioning, then you
haven't followed this thread very closely.



If you have a fan-fold one that has 1" thick folds then we will
arbitrarily say it has 2000 tiny holes in it (although it really has
more, obviously). Now if we make the pleats 2" thick we now have twice
as many holes in it, allowing twice as much air to pass thru it.


Snake oil. Those holes are placed at a steeper angle to the direction of
flow, reducing the effective size of each hole. And there's a lot more
"not hole" material in the path of the air, too, creating additional
friction.



Good grief. Let's say the holes are randomly oriented, which is
obviously a lot closer to how a real filter of the type under
discussion is going to behave. So now we have twice as many randomly
oriented holes in the 2" pleated filter as in the 1" pleated filter.
Which one is going to have less pressure drop across it and allow air
to flow through easier?

************************************************** *************8

It's not like the air can't make a turn. In fact, it probably makes several
going through a good filter. One turn a little harder isn't going to make much
difference.


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wrote in message
...
On Oct 24, 4:27 am, Smitty Two wrote:
In article ,
"Bob F" wrote:



Why else would they pleat filters?


To make them intrinsically stronger, and functionally stronger by
placing filter material at an angle to the force of the moving air.


They make them pleated so there is MORE surface area. That allows a
denser filter which traps smaller particles while still maintaining an
acceptable pressure drop. As another benefit, it allows the filter
to collect more dirt while still maintaining a reasonable pressure
drop.

I don;t see how anyone could not recognize that more filter area
translates into less resistance and less pressure drop. Imagine
breathing through a length of 2" plastic pipe with a sheet of dense
filter material fastened straight across in the middle. The filter
is dense enough to make it difficult to draw air. Now imaging a
filter of the same material, shaped like a cone and instead of being
just a 2" circle, it;s an extended cone, like an exagerated coffee
filter, stretching 3 inches within the pipe. Which would you rather
breathe through?

************************************************** ************

Or, imagine the cone is as long as the tube. Say - 6 feet. There'd be a very
large surface area to the filter. Just like pleats give (But with a little more
blockage do to the edge area blocking the flow. Obviously, if you put in too
many pleats, the air won't be able to get to them.





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"Bob F" wrote in message
. ..

wrote in message
...
On Oct 24, 4:27 am, Smitty Two wrote:
In article ,
"Bob F" wrote:



Why else would they pleat filters?


To make them intrinsically stronger, and functionally stronger by
placing filter material at an angle to the force of the moving air.


They make them pleated so there is MORE surface area. That allows a
denser filter which traps smaller particles while still maintaining an
acceptable pressure drop. As another benefit, it allows the filter
to collect more dirt while still maintaining a reasonable pressure
drop.

I don;t see how anyone could not recognize that more filter area
translates into less resistance and less pressure drop. Imagine
breathing through a length of 2" plastic pipe with a sheet of dense
filter material fastened straight across in the middle. The filter
is dense enough to make it difficult to draw air. Now imaging a
filter of the same material, shaped like a cone and instead of being
just a 2" circle, it;s an extended cone, like an exagerated coffee
filter, stretching 3 inches within the pipe. Which would you rather
breathe through?

************************************************** ************

Or, imagine the cone is as long as the tube. Say - 6 feet. There'd be a very
large surface area to the filter. Just like pleats give (But with a little
more blockage do to the edge area blocking the flow. Obviously, if you put in
too many pleats, the air won't be able to get to them.



But longer pleats don't block more air flow. The edge area is the same. But they
do increase the surface area.


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Bob F wrote:
"Rick Brandt" wrote in message

....
Incorrect when the thickness is achieved by larger pleats. The actual filter
*material* is the same. Bigger pleats in a thicker filter "container" means
more area and less resistance.


That's it.


There's double the additional structural material too...I'm still not
convinced the dP goes down at all, it just may not go up much...

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On Oct 22, 11:33*am, "james" wrote:
My furnace was installed with a 16x20x1 pleated filter.

It looks like there is enough space to fit a 16x20x2 filter. This should
last longer and reduce air resistance.

Is there any reason not to?


It is impossible to say from the information provided. The type of
material the design etc all make differences. The most important
factor is to make sure the filter meets the specifications given for
your furnace.

Personally I believe far too much worry is made about filters. You
need to meet the specifications for the furnace to protect it, but you
should not really expect some sort of real change in air quality in
your home because you use this or that air filter. Most of the
advertising related to air filters or all kinds are all fluff. They
don't provide any evidence that the products advertised add anything
to the quality of life in the home where they are used.
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