[dash]

No rules of thumb.

Get yourself a Magnahelic or digital manometer,to test the ESP of the system and you'll clearly see if the "better" filter can be added or not.

Test supply and return ESP separately ,to see which side would need duct modifications to add the "better" filter.

Typically we that if the system is acceptable with a cheap filter,we can add a return duct and grille ,to reduce the return static enough to allow the better filter to be used.Here in Florida ,most ducts in the attic ,it's easy to add a ceiling return.

 

[dash]

IMHO,testing the static is a more accurate way,with fan data,to decide about adding a filter.

 

[dash]

I certainly can't argue with the math. However, let me play the devil's advocate. We have sold many thousands of pleated filters. We have over 100 contractor customers. To my knowledge my customers have never had an "air flow" problem with any of these pleated filters. Have we just been lucky or is some of this discussion like the scientists proving that a bumble bee can't fly?

On resi their system is oversized,so the reduction in sensible goes unnoticed.

If you are not the servicing contractor you'll never hear about the problems.



If they are in heat pump markets ,accumilators will save the compressors!

 

[dash]

Dash,
I will not disagree too much with your statement under these conditions:

1) New install where YOU have the data from the manufacturer on the blower and ESP.

2) new system where the indoor coil is still clean and the blower wheel is still clean,

Note that most of the time, when looking at filters, it is on a system I did not install, where I do not have the blower data with me, or SP data for the coil, where the system may have been installed a while, with a slightly dirty coil or blower (The data is now slighty wrong). Also if the ducts are not perfect at the unit, System Effect will make the blower data wrong by as much as 0.1 inches water column in residential. Using a flow hood still gives good answers even under those conditions.

I always have my flow hood with me.

But if you just installed it and have all the data, pressure drop will be as good as the flow hood.

Kevin

I recently read a little about "system effect",I understand ,or think I do,how this effect a blower,but have found nothing on air handlers and furnaces.

If you have any info please post it.

Thanks,dash

 

[dash]

Hope I can help a little here Dash.
What it boils down to in a nutshell is a fan is rated a certain way in the laboratory, inlet & discharge conditions are uniform.

In the field if the fan is not installed how it was rated in the lab it can send the fan down a phantom curve other than the rated curve that comes with the equipment.

A good example of this is when someone cuts a collar directly in the bottom of a horizontal furnace with no plenum attached to the full return opening.
Another good one is an elbow directly on top of the air handler or furnace, it is even worse if the elbow turns in the opposite direction of the fans rotation.

I will try to find some links on this subject & post them.

Thanks,I kinda get that ,but was looking for some stricter guidelines.

Check out the supply plenum/trunk on this thread,to see what I mean,I know it's a big part of his problem,just don't know how big!

http://www.hvac-talk.com/vbb/showthread.php?t=121021

 

[dash]

Response;

First;
Yes homeowners and undertrained techs and contracors add filters to systems that can.t handle them.Collectively there's a lot of equipment damage fronm this.
Variables are indeed too many, to come up with guidelines,knowledgable testing is the way to go,before installing.


Second;
You have tested them and I don't doubt your results,but it's not what we find,may be a difference in the products.
4" pleateds inside of cheap throw often are a problem.

1" ,3M filters in place of throw aways ,almost always a problem.

I agree that poor filtration ,will degrade air flow,over time.



Third;
I think the manufacturers have found ,undesized ducts ,to be a problm already.Much more education in the industry will be required.

We saw otherwise good contractors that had no idea how to corect high statis,when Infinities first came out.Many were calling the mfr. to find out what was wrong with the control,when it was undersized ducts.
Some on this and other forums advocate staying away from this product as the consumer can read the static,when it tattletales on undersized ducts or "added" filtration.

Everyone ,filter mfrs,equip. mfrs., contractors,etc., should advise the static must be tested before going with better filtration.

 

[dash]

The information I have on it is from SMACNA & some of Sam Mongers books dash.

Didn't mean to insult your intelligence with my explanation if it came across that way.
I know you know the airside well.

It certainly didn't come across that way,no problem,sorry if I made it sound that way.Thanks for the info. I'll check there.

 

[dash]

Testing static pressure may be the right approach but I afraid it is not realistic. I just don't see homeowners paying to test static to change their filter. (But, then again, maybe there is a way to package it with a "blower door" test, duct sealing, etc. as an "IAQ service.")

Unfortunately, most homeowners think static is the electricity that jumps off their fingers when they walk across carpeting and touch a door knob.

It certainly should be a part of service calls, PM's and new installs.

Fact is if everyone went by your "Manual D" none of this would be a problem.

As you said testing should be part of service calls,etc.,and that's what we do,so no big cost at all,to the homeowner.