proper location of filter

[charles2]

Is there any advantage or disadvantage to having the return air filter at the end of the return plenum rather than at the beginning of the return plenum? In particular, I'm asking whether one location is more efficient than the other in terms of filtration and maximizing air flow.

[charliebear]

I'm not a pro, but I would think the closer the filter is to the unit, the better results you will get, since there is less distance for the air to travel after it has been filtered. (since the returns could be dusty or have air leaks, etc)

[mrlighturfire]

I always prefer at the furnace for a filter to me it seems more efficient like in a return drop boot that comes off the furnace they return air drop boot is popular in MN cause most furnaces are in the basement here. Plus if you put it at other end you gonna make sure it is picking up all the return in the duct from the house other wise it does no good if you know what I mean. That is my opinion.

[mobileguy]

Filters go in the return air plenum at the furnace. Why filter the air than have it travel another 10' once again picking up dust and who knows what else!

What does your furnace installation manual say?

If your looking to maximize air flow, look at what you are using to filter rather than where its done

[charles2]

Filters go in the return air plenum at the furnace. Why filter the air than have it travel another 10' once again picking up dust and who knows what else!

If the ducts are sealed, how does it pick up dust in the ducts? Looks like both options are equally good. Hopefully a pro will chime in at some point and confirm that.

[RyanHughes]

If the ducts are sealed, how does it pick up dust in the ducts? Looks like both options are equally good. Hopefully a pro will chime in at some point and confirm that.

You'd be surprised at what some ductwork looks like on the inside. Dust is sucked into the ductwork at the returns from the home itself. Filters don't necessary stop all dust. Please correct me if I'm wrong. :eek:

[dash]

Return ducy leaks can be an issue.

That aside the size of the filter is limited at the plenum/eqipment,when they are at they grilles,they can b larger and more efficient,since the air will move slower the larger filters.Also less restriction to air flow.

[charles2]

So basically you agree that either choice is fine?

[dash]

I prefer filters at the grilles ,for the lower restrictin to air flow ,if designed larger.

[RoBoTeq]

Less static pressure to contend with when the filter is located right at the blower housing.

Also, a filter grill of the same size as a filter in a rack at the furnace will have about 40% more restriction due to the actual free area of the grill.

If you are going to have a grill located remotely from the air handling unit (furnace) it should be significantly larger to accomodate added ducting static pressure as well as free area restrictions of grill. Also, the ducting between the filter and the blower compartment "MUST" be 100% sealed, and that includes all connections and even screw holes.

[dash]

Less static pressure to contend with when the filter is located right at the blower housing.

RESPONSE:At the furnace is typically smaller ,lso more restriction,no brainer!

Also, a filter grill of the same size as a filter in a rack at the furnace will have about 40% more restriction due to the actual free area of the grill.

RESPONSE:You'll still have a grille ,so it's the same restriction ,no brainer.A non-filter grille ,plus a filter at the furnace is the same restriction,other than style/model differences,as a filter grille.

If you are going to have a grill located remotely from the air handling unit (furnace) it should be significantly larger to accomodate added ducting static pressure as well as free area restrictions of grill. Also, the ducting between the filter and the blower compartment "MUST" be 100% sealed, and that includes all connections and even screw holes.

RESPONSE:Yes the sealing of the return duct is more important with filter grilles.

The total restriction/static of the return system will be no different with a filter of the same size at the grille or at the furnace,no need to be larger if at the filter,although it can be which is a way to reduce the static,whereas you have limited filter size at the furnace!

NO Brainer Again!

Is this my Christmas Present???

[smokin68]

Easier to change out in a filter grill and keeps the ductwork cleaner, so my preference.

[dash]

Easier to change out in a filter grill and keeps the ductwork cleaner, so my preference.

No comments on robo's opinion??

[smokin68]

No comments on robo's opinion??


You guys are way above me when argueing airflow, so I stay out...

[dash]

Care to guess who is correct??

[deejoe]

Easier to change out in a filter grill and keeps the ductwork cleaner, so my preference.
************************************************** *****

On most typical forced air duct systems there could be numerous return grilles placed thru out the home. Having filters in each of these grilles would be a waste of time and money to replace them,whereas having a properly sized filter right at the furnace would make it so much easier and less costly to replace.

[DanW13]

I just finished installing a electronic air filter on my furnace yesterday, and after installing the air cleaner I taped all the joints around the return air ducting, ever joint and screw hole that I could see and after doing so I could feel the difference in air circulation immediately, not to mention I also noticed a difference in the running of my furnace as well. If you have ever taken apart a return air duct you would simply be amazed by the amount of dust in the ducting, I was !!!! I vacuumed the return duct as far back as I could before putting everything back togeather when cleaning the ducting I had approximately a good 1/4" of caked dust on the bottom side of the duct work, But in saying that I have to tell you that my duct work is about 25yrs old most everything is only 2 maybe 3 piece sections of heavy gauge sheet metal. I will let you know how the Electronic air cleaner fairs in about a month or so.

[mobileguy]

Sorry I'm not pro enough for you.....

Give me a call when you find a perfectly sealed duct. Maybe a pro can come and do a test for the proper seal, maybe get them to install the filter rack for you while they're there.

[charles2]

I meant no disrespect. Thanks for your input, and Happy Holidays.:)

[Dave-B]

Properly sealed ductwork is very important no matter where the filter is located. The duct leakage test is an important step in commisioning any new system. Most of my systems include an air purifier, so it will be at the furnace location.
Yes, I am always amazed at the amount of dust I find in some old system's ductwork.

[drsmith012]

I have a 28x30x2" MERV 11 filter at my air handler and the cheapest blue filters I can get for the grills. The grill filters are there to catch the big stuff and help keep the ducts clean and to make that expensive behemoth of a air filter last longer.

[WANDERSON41]

If it's a new install with new duct work, I would use filter return grills.( keeps the new duct from getting dirty in the future). If using existing duct that has already built up dust,I would just change it at the furnace.

[dash]

I have a 28x30x2" MERV 11 filter at my air handler and the cheapest blue filters I can get for the grills. The grill filters are there to catch the big stuff and help keep the ducts clean and to make that expensive behemoth of a air filter last longer.

Doubling up on filters is fine,IF the Resistance of the filters was taken into account in the duct design(Man. D).

Addings additional filters ,or better filters,isn't a good idea ,without testing first.

[drsmith012]

I would like to have a bigger grill upstairs but with the cheapest least restrictive filter I can buy there is not much additional restriction when compared to an empty grill (tested with a manometer). My returns are very short and dump into approx 28x30" return plenum. The face velocity for the merv 11 at 1300 CFM is 222Ft/min, Which is off the charts, low side, of every filter manufactuer who publishes their initial resistance, but the system normally runs at 900 CFM. I have a manometer on the merve 11 but it also gets the heatexchager too. 8 months on the filter and the coil is still 60-70% of the pressure drop of .22" on low. Haven't been on high yet this year.

[dash]

I would like to have a bigger grill upstairs but with the cheapest least restrictive filter I can buy there is not much additional restriction when compared to an empty grill (tested with a manometer). My returns are very short and dump into approx 28x30" return plenum. The face velocity for the merv 11 at 1300 CFM is 222Ft/min, Which is off the charts, low side, of every filter manufactuer who publishes their initial resistance, but the system normally runs at 900 CFM. I have a manometer on the merve 11 but it also gets the heatexchager too. 8 months on the filter and the coil is still 60-70% of the pressure drop of .22" on low. Haven't been on high yet this year.


Heat Exchanger is already fiqured in the specs.

Where are you testing the static,ever test the total supply and return??

[dash]

Properly sealed ductwork is very important no matter where the filter is located. The duct leakage test is an important step in commisioning any new system. Most of my systems include an air purifier, so it will be at the furnace location.
Yes, I am always amazed at the amount of dust I find in some old system's ductwork.


As Robo indicated,filter grilles cause more static in the return duct ,so it is more important as return duct leakage,if any will be increased with the higher static due to filter grilles versus one in the furnace.

[drsmith012]

Heat Exchanger is already fiqured in the specs.

Where are you testing the static,ever test the total supply and return??

I have the manometer attached to the return plenum and the air handler so I only measure drop across the filter and coil.

I have not measured total supply pressure. Would this be better?

[gevans]

Several pros and cons to this arguement. My personal favorite is a mixture of both: a whole house filter at the air handler or furnace, and separate filter grills (with the cheap blue filters).
Filter grilles do indeed provide more restriction than a filter at the AH, due to the grille itself. But you can size them properly to overcome that.
Filters at the grilles are far more likely to be changed by the consumer, especially if the AH is hard to reach (attic, crawlspace, or just "out of sight, out of mind")
Filters at the grilles will INCREASE any return air leakage, especially when the filters are high MERV or dirty. This will also increase dust and dirt in the system.
A properly installed whole house filter, at the AH, will catch virtually ALL the dirt and dust, extending the life and efficiency of your equipment.
But, those whole house filters can be pricey. Once or twice a year ain't too bad.
I use both in my house, and I currently recommend a whole house filter with EVERY installation.

[charles2]

Filter grilles do indeed provide more restriction than a filter at the AH, due to the grille itself.

Ducted returns have grilles regardless of whether they contain filters. So that's no basis for a decision.

[geodude]

It has been my experiance that when filters are in grilles AND in the airhandling equipment, The grilles are typicaly not sized for the extra friction penalty. And on systems where both are installed together,( filter grille and at the furnace) the home owner either forgot about the one in the air handler ( out of site out of mind?!) or did not know it even existed! Especially if they bought the house from the person who had the double filters installed. We reccomend filters at the airhandling equipment and on our installs we put in 4 or 5 inch pleated filters and size them as big as we can fit into the duct!

[russtown]

filter location is a homeowers choice. if the duct is sealed properly and sized properly sized the only thing left is static drop across the filter. filter grills need to be larger if you plan to use pleated filter merv 10+. with 4" and 5" filter most have .2" drop or more, you may need 2 filter racks in parallel not series to over come the drop. a filter should be designed to have no more that 20% of your systems static.

[dash]

I have the manometer attached to the return plenum and the air handler so I only measure drop across the filter and coil.

I have not measured total supply pressure. Would this be better?

At te inlet and outet of the furnace or air handler for the total external,and yes that will tell much more.