On 2/6/2012 5:28 AM,
wrote:
On Feb 6, 7:29 am, wrote:
My 95.5% Gas furnace came with a fiberglass air filter
with little restriction and no filtering action.
I substituted a Filtrete allergy reduction filter and went
about my business. Been running that way for 2 years.
In my filter search today, I found a gauge that tells you when
to change the filter by monitoring negative pressure
near the blower inlet. It says it can be calibrated
for 0-.4"WC.
I did some measurements on my system.
With the filter removed and the filter door open,
I measured -0.1"WC.
I measured with my Filtrete installed and with a
lesser MERV9, I think, filter then a washable
permanent electrostatic filter.
All measured -.55"WC.
With the filter access door closed, it goes up
to -0.6"WC.
That's outside the calibration range of the filter
monitor gauge, so it got me thinking.
I don't have a fiberglass filter to compare.
I also measured some temperatures.
With indoor temperature at 65F, the air coming out
of the closest vent stabilizes at 119F. It's about
12' from the furnace and the ducts are insulated,
so it should be somewhere near the furnace output
temperature.
Looks like I'm getting60F rise across the furnace.
That's near the max claimed in the spec.
Another thing is that I don't heat part of the house.
Three registers are closed. Last time I did the experiment,
heating the whole house cost me almost 50% more in gas.
So,
I don't want to heat the whole house.
I need the better air filters.
Should I worry about overheating the furnace?
Rather than saying it's the "max claimed", I'd be
looking at it as the "max allowed".
As long as the temp rise is within the furnace spec,
which you say it is, you're not going to damage the
furnace.
Is there anything simple I can to about it?
Like turn up the blower speed?
Yes, no, maybe. It depends on the furnace. Read
the install manual and see what choices there are.
Some have at least some selection of blower speeds
for heating and cooling. Furnaces with a true variable
speed blower would have the most options which
can be set with dip switches. Then it
also depends if it's already set to the max for heating
or not.....
I do have an electronic filter that's designed to replace
the 1" paper filter. I'd have to cut it down to fit.
Looks like it has about as much material as the original
fiberglass filter, so should have lower pressure drop.
I've never seen a 1" electronic filter.
That's easily remedied.
http://www.cimatec.com/Cimatec-Air-F...creen1000.aspx
Picked it up dirt cheap at a garage sale a few years back.
Only been using it a few days, so the jury is still out.
All the electronic
filters I've seen are more like 4 or 5 inches deep and are
in their own cabinet that sits in the duct next to the
furnace.
Is that a viable alternative?
It's not clear how they compare at removing pollen.
It's hard to decide based on the vague marketing hype.
Thanks mike.
What problem are you trying to solve?
The problem I'm trying to solve is hay fever.
I built a heat recovery ventilator to solve an IAQ
problem caused by sealing up leakage.
Worked great until the pollen hit.
So, I started working on an air filter for it.
That led me to making some efficiency measurements
that side-tracked me onto the air flow in the furnace.
I made more measurements, and determined that the pressure
below the filter is pretty much independent of whatever filter
I tried. It's -.55"WC. With the filter removed, it's still
-.3"WC. That's likely the result of the flexible return pipe
they used to solve a blower noise problem with a new furnace.
It's always easier to get it right the SECOND time you do something. :-(
The airflow you
get is going to be influenced by not only the filter, but by
the duct work. You also say you've got some registers
closed off. That obviously is going to reduce airflow.
I use one of the thick pleated filters that goes into a
seperate filter cabinet. It's about 4 inches thick. By
being deeply pleated it has a lot more surface area and
hence while doing a good filtering job, it presents less
resistance than a thinner filter that would have the same
filtering capability. I think if you want good filtering and
lowest resistance, either one of those or a true electronic
one that's in it's own cabinet is the only way you're going
to get it.